Charge and critical density of strange quark matter

合集下载

PhysRevLett.110.012301

Charge separation relative to the reaction plane in Pb-Pb collisions at ﬃﬃﬃﬃﬃﬃﬃﬃﬃs NN p ¼2:76TeVB.Abelev et al.*(ALICE Collaboration)(Received 5July 2012;published 2January 2013)Measurements of charge-dependent azimuthal correlations with the ALICE detector at the LHC arereported for Pb-Pb collisions at ﬃﬃﬃﬃﬃﬃﬃﬃs NN p ¼2:76TeV .Two-and three-particle charge-dependent azimuthal correlations in the pseudorapidity range j j <0:8are presented as a function of the collision centrality,particle separation in pseudorapidity,and transverse momentum.A clear signal compatible with a charge-dependent separation relative to the reaction plane is observed,which shows little or no collision energy dependence when compared to measurements at RHIC energies.This provides a new insight for under-standing the nature of the charge-dependent azimuthal correlations observed at RHIC and LHC energies.DOI:10.1103/PhysRevLett.110.012301PACS numbers:25.75.Ld,11.30.Er,11.30.Qc,12.38.AwThe possibility to observe parity violation in the strong interaction using relativistic heavy-ion collisions has been discussed for many years [1–3].In quantum chromody-namics (QCD),this symmetry violation originates in the interaction between quarks and topologically nontrivial gluonic ﬁelds,instantons,and sphalerons [4].This interac-tion,which is characterized by the topological charge [5],breaks the balance between the number of quarks with different chirality,resulting in a violation of the P and CP symmetry.In [6,7],it was suggested that in the vicinity of the deconﬁnement phase transition,and under the inﬂu-ence of the strong magnetic ﬁeld generated by the colliding nuclei,the quark spin alignment along the direction of the angular momentum (i.e.the direction of the magnetic ﬁeld)and the imbalance of the left-and right-handed quarks,generates an electromagnetic current.The experimental search of these effects has intensiﬁed recently,following the realization that the consequent quark fragmentation into charged hadrons results in a charge separation along the direction of the magnetic ﬁeld,and perpendicular to the reaction plane (the plane of symmetry of a collision deﬁned by the impact parameter vector and the beam direction).This phenomenon is called the chiral magnetic effect (CME).Because of ﬂuctuations in the sign of the topologi-cal charge,the resulting charge separation averaged over many collisions is zero.This makes the observation of the CME possible only via P -even observables,expressed in terms of two-particle and multiparticle correlations.The previous measurement of charge separation by the STAR Collaboration [8]is consistent with the qualitative expec-tations for the CME and has triggered an intense discussion [9–13].A signiﬁcant source of uncertainty in the theoretical consideration of the CME is related to the expected center-of-mass energy dependence.In [7],the authors argued that the uncertainty in making any quantitative prediction relies on the time integration over which the magnetic ﬁeld develops and decays.As long as a decon-ﬁned state of matter is formed in a heavy-ion collision,the magnitude of the effect should either not change or should decrease with increasing energy [7].In addition,in [12]it is also suggested that there should be no energy depen-dence between the top RHIC and the LHC energies,based on arguments related to the universality of the underlying physical process,without however explicitly quantifying what the contribution of the different values and time evolution of the magnetic ﬁeld for different energies will be.On the other hand,in [13]it is argued that the CME should strongly decrease at higher energies,because the magnetic ﬁeld decays more rapidly.Such spread in the theoretical expectations makes it important to measure the charge-dependent azimuthal correlations at the LHC,where the collision energy is an order of magnitude higher compared to the RHIC.In this Letter we report the measurement of charge-dependent azimuthal correlations at midrapidity in Pb-Pb collisions at the center-of-mass energy per nucleon pair ﬃﬃﬃﬃﬃﬃﬃﬃs NN p ¼2:76TeV by the ALICE Collaboration at the LHC.Azimuthal correlations among particles produced in a heavy-ion collision provide a powerful tool for the experi-mental study of particle production with respect to the reaction plane.They are usually quantiﬁed by the aniso-tropic ﬂow coefﬁcients,v n ,in a Fourier decomposition [14].Local violation of parity symmetry may result in the additional P -odd sinus terms [3,8,15]:dNd’ $1þ2X n ½v n; cos ðn Á’ Þþa n; sin ðn Á’ Þ ;(1)where Á’ ¼’ ÀÉRP is the azimuthal angle ’ of the charged particle of type relative to the reaction plane*Full author list given at the end of the article.Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0License .Further distri-bution of this work must maintain attribution to the author(s)and the published article’s title,journal citation,and DOI.angle,ÉRP.The leading order coefﬁcient a1; reﬂects the magnitude while the higher orders(a n; for n>1)describe the speciﬁc shape in azimuth of the effects from local parity violation.We thus employ a multiparticle correlator [15]that probes the magnitude of the a1coefﬁcient,and at the same time suppresses the background correlations unrelated to the reaction plane:h cosð’ þ’ À2ÉRPÞi¼h cosÁ’ cosÁ’ iÀh sinÁ’ sinÁ’ i:(2) The indices and refer to the charge of the particles.The brackets denote an average over the particle pairs within the event as well as an average over the analyzed events.In practice,the reaction plane angle is not known and is esti-mated by constructing the event plane using azimuthal par-ticle distributions.In Eq.(2),the terms h cosÁ’ cosÁ’ i and h sinÁ’ sinÁ’ i quantify the correlations in-and out-of plane,respectively.The latter is sensitive to the charge correlations resulting from the CME:h sinÁ’ sinÁ’ i$ h a1; a1; i.The construction of the correlator in Eq.(2)as the difference between these two contributions suppresses correlations not related to the reaction plane orientation (nonﬂow).The contribution from the CME to the correla-tions of pairs of particles with same and opposite charge is expected to be similar in magnitude and opposite in sign. This expectation could be further modiﬁed by the medium created in a heavy-ion collision,that may result in the dilution of the correlations between particles with opposite sign[6,7].In order to evaluate each of the two terms in Eq.(2),we also measure the two-particle correlator:h cosð’ À’ Þi¼h cosÁ’ cosÁ’ iþh sinÁ’ sinÁ’ i;(3) which in contrast to the correlator in Eq.(2)is independent of the reaction plane angle and susceptible to the large P-even background contributions.The combination of these correlators provides access to both components, h cosÁ’ cosÁ’ i and h sinÁ’ cosÁ’ i,which is impor-tant for detailed comparisons with model calculations.It should be pointed out that both correlators of Eq.(2) and Eq.(3)could be affected by background sources.In [10],it is argued that the effect of momentum conservation inﬂuences in a similar way the pairs of particles with opposite and same charge,and could result in a potentially signiﬁcant correction to both h cosð’ þ’ À2ÉRPÞi and h cosð’ À’ Þi.Also in[10],it was suggested that local charge conservation effects may be responsible for a sig-niﬁcant part of the observed charge dependence of the correlator h cosð’ þ’ À2ÉRPÞi.Recent calculations [16]suggest that the correlator in Eq.(2)may have a negative(i.e.out-of-plane),charge-independent,dipole ﬂow contribution originating fromﬂuctuations in the initial energy density of a heavy-ion collision.A description of the ALICE detector and its perform-ance can be found in[17,18].For this analysis,the follow-ing detector subsystems were used:the time projection chamber(TPC)[19],the silicon pixel detector(SPD), two forward scintillator arrays(VZERO),and two zero degree calorimeters(ZDC)[17].We analyzed a sample of about13Â106minimum-bias trigger events of Pb-Pb collisions atﬃﬃﬃﬃﬃﬃﬃﬃs NNp¼2:76TeV collected with the ALICE detector.The standard ALICE ofﬂine event selection criteria[20]were applied,including a collision vertex cut ofÆ7cm along the beam axis.The collision centrality is estimated from the amplitude mea-sured by the VZERO detectors[17].The data sample is divided into centrality classes which span0%-70%of the hadronic interaction cross section,with the0%-5%class corresponding to the most central(i.e.smaller impact pa-rameter)collisions.Charged particles reconstructed by the TPC are accepted for analysis within j j<0:8and0:2< p T<5:0GeV=c.A set of requirements described in[20] were applied in order to ensure the quality of the tracks but also to reduce the contamination from secondary particles. To evaluate the systematic uncertainties in the analysis, events recorded with two different magneticﬁeld polarities were analyzed leading to an uncertainty that is less than7% for all centrality classes.The cut on the collision vertex was varied fromÆ7cm toÆ10cm from the nominal collision point,with steps of1cm,contributing a maximum of5%to the total uncertainty.A bias due to the centrality determina-tion was studied by using multiplicities measured by the TPC or the SPD,rather than the VZERO,and was found to be less than10%.Contamination due to secondary tracks that do not originate from the collision vertex was reduced by requiring that the distance of closest approach between tracks and the primary vertex is less than2cm.The effect of secondary tracks on the measurement was estimated by varying the cut from2to4cm in steps of0.5cm and was calculated to be below15%.Effects due to nonuniform acceptance of the TPC were estimated to be below2%and are corrected for in the analysis.A signiﬁcant contribution to the systematic error is coming from the uncertainty in the v2measurement,which is used as an estimate of the reaction plane resolution.The v2 estimate is obtained from the2-and4-particle cumulant analyses[20],which are affected in different ways by non-ﬂow effects andﬂowﬂuctuations.For this analysis,v2was taken as the average of the two values,with half of the difference between v2f2g and v2f4g being attributed as the systematic uncertainty.The values of this uncertainty range from9%for the20%–30%centrality to18%(24%)for the 50%–60%(60%–70%)centrality class.The differences in the results from the four independent analysis methods (described below)were also considered as part of the system-atic uncertainty and were estimated to be3%for the 20%–30%and the50%–60%centrality bins and47%for the most peripheral centrality class.The contributions from all effects were added in quadrature to calculate the totalsystematic uncertainty.For the correlation between pairs of particles with the same charge it varies from 19%(28%)for the 20%–30%(50%–60%)centrality up to 55%for the 60%–70%centrality class.The correlations between oppo-site charged particles for 0%–60%centrality and for the same charge pairs for 0%–20%centrality are compatible with zero with a systematic error below 5:5Â10À5.Figure 1(a)presents the centrality dependence of the three-particle correlator,deﬁned in Eq.(2).The correla-tions of the same charge pairs for the positive-positive and negative-negative combinations are found to be consistent within statistical uncertainties and are combined into one set of points,labeled same .The difference between the correlations of pairs with same and opposite charge indi-cates a charge dependence with respect to the reaction plane,as may be expected for the CME.To test the bias from the reaction plane reconstruction,four independent analyses were performed.The ﬁrst analysis uses a cumu-lant technique [21],whereas for the three other analyses the orientation of the collision symmetry plane is estimated from the azimuthal distribution of charged particles in the TPC,and hits in the forward VZERO and ZDC detectors [22].There is a very good agreement between the results obtained with the event plane estimated from different detectors covering a wide range in pseudorapidity.This allows us to conclude that background sources due to corre-lations not related to the orientation of the reaction plane are negligible,with perhaps the exception of the peripheral collisions for the pairs of particles with opposite charge.Figure 1(b)shows the centrality dependence of the two-particle correlator h cos ð’ À’ Þi ,as deﬁned in Eq.(3),which helps to constrain experimentally the P -even back-ground correlations.The statistical uncertainty is smaller than the symbol size.The two-particle correlations for the same and opposite charge combinations are always posi-tive and exhibit qualitatively similar centrality depen-dence,while the magnitude of the correlation is smaller for the same charged pairs.Our two-particle correlation results differ from those reported by the STARCollaboration for Au-Au collisions at ﬃﬃﬃﬃﬃﬃﬃﬃs NN p ¼200GeV [8]for which negative correlations are observed for the same charged pairs.Figure 1(c)shows the h cosÁ’ cosÁ’ i and h sinÁ’ sinÁ’ i terms separately.For pairs of particles of the same charge,we observe that the h sinÁ’ sinÁ’ i correlations are larger than the h cosÁ’ cosÁ’ i ones.On the other hand,for pairs of opposite charge,the two terms are very close except for the most peripheral collisions.Further interpretation of the results presented in Fig.1(c)in terms of in-and out-of-plane correlations is complicated due to the signiﬁcant nonﬂow contribution in h cos ð’ À’ Þi .Figure 2presents the three-particle correlator h cos ð’ þ’ À2ÉRP Þi as a function of the collision centrality com-pared to model calculations and results for RHIC energies.The statistical uncertainties are represented by the errorbars.The shaded area around the points indicates the systematic uncertainty based on the different sources described above.Also shown in Fig.2are STAR results [8].The small difference between the LHC and the RHIC data indicates little or no energy dependence for the three-particle correlator when changing from the collisionenergy of ﬃﬃﬃﬃﬃﬃﬃﬃs NN p ¼0:2TeV to 2.76TeV .In Fig.2,the ALICE data are compared to the expectations from the HIJING model [23].The HIJING results for the three-particle correlations are divided by the experimentally〉)R P Ψ - 2βϕ + αϕ c o s (〈-0.50.5-3〉)βϕ-αϕ c o s (〈00.0020.0040.006centrality, %0.0020.003FIG.1(color online).(a)Centrality dependence of the correla-tor deﬁned in Eq.(2)measured with the cumulant method and from correlations with the reaction plane estimated using the TPC,the ZDC,and the VZERO detectors.Only statistical errors are shown.The points are displaced slightly in the horizontal direction for visibility.(b)Centrality dependence of the two-particle corre-lator deﬁned in Eq.(3)compared to the STAR data [8].The width of the solid red lines indicates the systematic uncertainty of the ALICE measurement.(c)Decomposition of the correlators into h cosÁ’ cosÁ’ i and h sinÁ’ sinÁ’ i terms.The ALICE results in (b)and (c)are obtained with the cumulant method.measured value of v 2(i.e.h cos ð’ þ’ À2’c Þi =v 2f 2g )as reported in [20]due to the absence of collective azimuthal anisotropy in this model.Since the points do not exhibit any signiﬁcant difference between the correlations of pairs with same and opposite charge,they were averaged in the ﬁgure.The correlations from HIJING show a signiﬁcant increase in the magnitude for very peripheral collisions.This can be attributed to correlations not related to the reaction plane orientation,in particular,from jets [8].The results from ALICE in Fig.2show a strong corre-lation for pairs with the same charge and simultaneously a very weak correlation for the pairs of opposite charge.This difference in the correlation magnitude depending on the charge combination could be interpreted as ‘‘quenching’’of the charge correlations for the case when one of the particles is emitted toward the center of the dense medium created in a heavy-ion collision [6,7].An alternative ex-planation can be provided by a recent suggestion [16]that the value of the charge-independent version of the corre-lator deﬁned in Eq.(2)is dominated by directed ﬂow ﬂuctuations.The sign and the magnitude of these ﬂuctua-tions based on a hydrodynamical model calculation for RHIC energies [16]appear to be very close to the mea-surement.Our results for charge-independent correlations are given by the shaded band in Fig.2.The thick solid line in Fig.2shows a prediction [13]for the same sign correlations due to the CME at LHC ener-gies.The model makes no prediction for the absolute magnitude of the effect and can only describe the energy dependence by taking into account the duration and time evolution of the magnetic ﬁeld.It predicts a decrease of correlations by about a factor of 5from RHIC to LHC,which would signiﬁcantly underestimate the observed magnitude of the same sign correlations seen at the LHC.At the same time in [7,12],it was suggested that the CME might have the same magnitude at the LHC and at RHIC energies.Figure 3shows the dependence of the three-particle correlator on the transverse momentum difference,j p T ; Àp T ; j ,the average transverse momentum,ðp T ; þp T ; Þ=2,and the pseudorapidity separation,j À j ,of the pair for the 30%-40%centrality range.The pairs of opposite charge do not show any signiﬁcant dependence on the pseudorapidity difference,while there is a dependencecentrality, %〉)R P Ψ - 2βϕ + αϕ c o s (〈-0.6-0.4-0.200.20.40.6-3FIG.2(color online).The centrality dependence of the three-particle correlator deﬁned in Eq.(2).The circles indicate the ALICE results obtained from the cumulant analysis.The stars show the STAR data from [8].The triangles represent the three-particle correlations [h cos ð’ þ’ À2’c Þi ]from HIJING [23]corrected for the experimentally measured v 2f 2g [20].Points are displaced horizontally for visibility.A model prediction for the same sign correlations incorporating the chiral magnetic effect for LHC energies [13]is shown by the solid line.The shaded band represents the centrality dependence of the charge-independent correlations.)| (GeV/c T,β - p T,α|p 〉)R P Ψ - 2βϕ + αϕc o s (〈-0.4-0.20.2-3))/2 (GeV/c T,β + p T,α(p |βη - αη = |η∆FIG.3(color online).The three-particle correlator deﬁned in Eq.(2)as a function of (a)the transverse momentum difference,j p T ; Àp T ; j ,(b)the average transverse momentum,ðp T ; þp T ; Þ=2,and (c)the rapidity separation,j À j ,of the charged particle pair of same (closed symbols)and opposite (open symbols)sign.on j p T ; Àp T ; j (stronger)and ðp T ; þp T ; Þ=2(weaker).The correlations for pairs of particles of the same charge show no strong dependence on the p T difference,allowing one to exclude any type of short range correlations (e.g.quantum statistics correlations)as the main source of the effect.In addition,it is seen that the magnitude of the same charge correlations increases with increasing average p T of the pair.This observation is in contradiction to the initial expectations from theory [7]that the effect should originate from low p T particles.The dependence of the correlations on the j À j indicates a width of one unit in pseudor-apidity,beyond which the value of h cos ð’ þ’ À2ÉRP Þi is close to zero up to Á %1:5.Similar results were reported also at RHIC energies [8].At the moment there are no quantitative model calculations of the charge-dependent differential correlations.In summary,we have measured the charge-dependentazimuthal correlations in Pb-Pb collisions at ﬃﬃﬃﬃﬃﬃﬃﬃs NN p ¼2:76TeV at the LHC using the ALICE detector.Both two-and three-particle correlations are reported.A clear signal compatible with a charge-dependent separation rela-tive to the reaction plane is observed.However,our results are not described by the only available quantitative model prediction of the CME for the LHC energy.The lack of realistic model calculations for the centrality and pair differential dependencies based on models incorporating CME and possible background contributions does not allow us to make a ﬁrm conclusion regarding the nature of the charge-dependent correlations originally observed at RHIC and now established at the LHC.The observation of a small collision energy dependence of the three-particle correlation and the simultaneous signiﬁcant change in the two-particle correlations between top RHIC and LHC energies put stringent constraints on models built to interpret such correlations.Analyses of higher harmonic correlations are planned and may yield a better understanding of the com-plex charge-dependent correlations seen at LHC energies.The ALICE Collaboration would like to thank all its engi-neers and technicians for their invaluable contributions to the construction of the experiment and the CERN accelerator teams for the outstanding performance of the LHC complex.The ALICE Collaboration acknowledges the following fund-ing agencies for their support in building and running the ALICE detector:Calouste Gulbenkian Foundation from Lisbon and Swiss Fonds Kidagan,Armenia;ConselhoNacional de Desenvolvimento Cientı´ﬁco e Tecnolo ´gico (CNPq),Financiadora de Estudos e Projetos (FINEP),Fundac ¸a˜o de Amparo a `Pesquisa do Estado de Sa ˜o Paulo (FAPESP);National Natural Science Foundation of China (NSFC),the Chinese Ministry of Education (CMOE),and the Ministry of Science and Technology of China (MSTC);Ministry of Education and Youth of the Czech Republic;Danish Natural Science Research Council,the Carlsberg Foundation,and the Danish National Research Foundation;The European Research Council under the EuropeanCommunity’s Seventh Framework Programme;Helsinki Institute of Physics and the Academy of Finland;French CNRS-IN2P3,the ‘‘Region Pays de Loire,’’‘‘Region Alsace,’’‘‘Region Auvergne,’’and CEA,France;German BMBF and the Helmholtz Association;General Secretariat for Research and Technology,Ministry of Development,Greece;Hungarian OTKA and National Ofﬁce for Research and Technology (NKTH);Department of Atomic Energy and Department of Science and Technology of the Government of India;Istituto Nazionale di Fisica Nucleare (INFN)of Italy;MEXT Grant-in-Aid for Specially Promoted Research,Japan;Joint Institute for Nuclear Research,Dubna;National Research Foundation of Korea (NRF);CONACYT,DGAPA,Me´xico,ALFA-EC,and the HELEN Program (High-Energy Physics Latin-American–European Network);Stichting voor Fundamenteel Onderzoek der Materie (FOM)and the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO),Netherlands;Research Council of Norway (NFR);Polish Ministry of Science and Higher Education;National Authority forScientiﬁc Research-NASR (Autoritatea Nat ¸ionala˘pentru Cercetare S ¸tiint¸iﬁca ˘-ANCS);Federal Agency of Science of the Ministry of Education and Science of Russian Federation,International Science and Technology Center,Russian Academy of Sciences,Russian Federal Agency of Atomic Energy,Russian Federal Agency for Science and Innovations and CERN-INTAS;Ministry of Education of Slovakia;Department of Science and Technology,South Africa;CIEMAT,EELA,Ministerio de Educacio´n y Ciencia of Spain,Xunta de Galicia (Consellerı´a de Educacio ´n),CEADEN,Cubaenergı´a,Cuba,and IAEA (International Atomic Energy Agency);Swedish Research Council (VR)and Knut &Alice Wallenberg Foundation (KAW);Ukraine Ministry of Education and Science;United Kingdom Science and Technology Facilities Council (STFC);the United States Department of Energy,the United States National Science Foundation,the State of Texas,and the State ofOhio.[1]T.D.Lee,Phys.Rev.D 8,1226(1973);T.D.Lee andG.C.Wick,Phys.Rev.D 9,2291(1974).[2]P.D.Morley and I.A.Schmidt,Z.Phys.C 26,627(1985).[3] D.Kharzeev,R.D.Pisarski,and M.H.G.Tytgat,Phys.Rev.Lett.81,512(1998);D.Kharzeev and R.D.Pisarski,Phys.Rev.D 61,111901(2000).[4]T.Scha¨fer and E.V .Shuryak,Rev.Mod.Phys.70,323(1998).[5]S.S.Chern and J.Simons,Ann.Math.99,48(1974).[6] D.Kharzeev,Phys.Lett.B 633,260(2006);K.Fukushima, D.E.Kharzeev,and H.J.Warringa,Phys.Rev.D 78,074033(2008).[7] D.Kharzeev,L.D.McLerran,and H.J.Warringa,Nucl.Phys.A803,227(2008).[8] B.I.Abelev et al.(STAR Collaboration),Phys.Rev.Lett.103,251601(2009); B.I.Abelev et al.(STAR Collaboration),Phys.Rev.C 81,54908(2010).[9] B.Mu¨ller and A.Scha¨fer,Phys.Rev.C82,057902(2010).[10]S.Schlichting and S.Pratt,Phys.Rev.C83,014913(2011);S.Pratt,S.Schlichting,and S.Gavin,Phys.Rev.C84,024909(2011).[11] A.Bzdak,V.Koch,and J.Liao,Phys.Rev.C81,031901(2010);A.Bzdak,V.Koch,and J.Liao,Phys.Rev.C83, 014905(2011).[12] A.R.Zhitnitsky,Nucl.Phys.A853,135(2011);A.R.Zhitnitsky,Nucl.Phys.A886,17(2012).[13]V.D.Toneev and V.V oronyuk,arXiv:1012.1508.[14]S.V oloshin and Y.Zhang,Z.Phys.C70,665(1996);A.M.Poskanzer and S.A.V oloshin,Phys.Rev.C58,1671 (1998).[15]S.A.V oloshin,Phys.Rev.C70,057901(2004).[16] D.Teaney and L.Yan,Phys.Rev.C83,064904(2011).[17]K.Aamodt et al.(ALICE Collaboration),JINST3,S08002(2008).[18]K.Aamodt et al.(ALICE Collaboration),J.Phys.G30,1517(2004);K.Aamodt et al.(ALICE Collaboration), J.Phys.G32,1295(2006).[19]J.Alme et al.(ALICE Collaboration),Nucl.Instrum.Methods Phys.Res.,Sect.A622,316(2010).[20]K.Aamodt et al.(ALICE Collaboration),Phys.Rev.Lett.105,252302(2010).[21] A.Bilandzic,R.Snellings,and S.V oloshin,Phys.Rev.C83,044913(2011).[22]S.V oloshin, A.M.Poskanzer,and R.Snellings,inRelativistic Heavy Ion Physics,Landolt-Bornstein V ol.1 (Springer-Verlag,Berlin,2010),pp.554.[23]M.Gyulassy and X.N.Wang,mun.83,307(1994);X.N.Wang and M.Gyulassy,Phys.Rev.D44,3501(1991).B.Abelev,1J.Adam,2D.Adamova´,3A.M.Adare,4M.M.Aggarwal,5G.Aglieri Rinella,6A.G.Agocs,7 A.Agostinelli,8S.Aguilar Salazar,9Z.Ahammed,10N.Ahmad,11A.Ahmad Masoodi,11S.A.Ahn,12S.U.Ahn,13A.Akindinov,14D.Aleksandrov,15B.Alessandro,16R.Alfaro Molina,9A.Alici,17,18A.Alkin,19E.Almara´z Avin˜a,9J.Alme,20T.Alt,21V.Altini,22S.Altinpinar,23I.Altsybeev,24C.Andrei,25A.Andronic,26V.Anguelov,27J.Anielski,28C.Anson,29T.Anticˇic´,30F.Antinori,31P.Antonioli,17L.Aphecetche,32H.Appelsha¨user,33N.Arbor,34S.Arcelli,8A.Arend,33N.Armesto,35R.Arnaldi,16T.Aronsson,4I.C.Arsene,26 M.Arslandok,33A.Asryan,24A.Augustinus,6R.Averbeck,26T.C.Awes,36J.A¨ysto¨,37M.D.Azmi,11M.Bach,21A.Badala`,38Y.W.Baek,39,13R.Bailhache,33R.Bala,16R.Baldini Ferroli,18A.Baldisseri,40A.Baldit,39F.Baltasar Dos Santos Pedrosa,6J.Ba´n,41R.C.Baral,42R.Barbera,43F.Barile,22G.G.Barnafo¨ldi,7L.S.Barnby,44V.Barret,39J.Bartke,45M.Basile,8N.Bastid,39S.Basu,10B.Bathen,28G.Batigne,32B.Batyunya,46C.Baumann,33I.G.Bearden,47H.Beck,33I.Belikov,48F.Bellini,8R.Bellwied,49E.Belmont-Moreno,9G.Bencedi,7S.Beole,50I.Berceanu,25A.Bercuci,25Y.Berdnikov,51D.Berenyi,7 A.A.E.Bergognon,32D.Berzano,16L.Betev,6A.Bhasin,52A.K.Bhati,5J.Bhom,53L.Bianchi,50N.Bianchi,54 C.Bianchin,55J.Bielcˇı´k,2J.Bielcˇı´kova´,3A.Bilandzic,56,47S.Bjelogrlic,57F.Blanco,58F.Blanco,49D.Blau,15C.Blume,33M.Boccioli,6N.Bock,29S.Bo¨ttger,59A.Bogdanov,60H.Bøggild,47M.Bogolyubsky,61L.Boldizsa´r,7M.Bombara,62J.Book,33H.Borel,40A.Borissov,63S.Bose,64F.Bossu´,50M.Botje,56B.Boyer,65E.Braidot,66P.Braun-Munzinger,26M.Bregant,32T.Breitner,59T.A.Browning,67M.Broz,68R.Brun,6E.Bruna,50,16G.E.Bruno,22D.Budnikov,69H.Buesching,33S.Bufalino,50,16K.Bugaiev,19O.Busch,27 Z.Buthelezi,70D.Caballero Orduna,4D.Caffarri,55X.Cai,71H.Caines,4E.Calvo Villar,72P.Camerini,73 V.Canoa Roman,74G.Cara Romeo,17W.Carena,6F.Carena,6N.Carlin Filho,75F.Carminati,6A.Casanova Dı´az,54J.Castillo Castellanos,40J.F.Castillo Hernandez,26E.A.R.Casula,76V.Catanescu,25 C.Cavicchioli,6C.Ceballos Sanchez,77J.Cepila,2P.Cerello,16B.Chang,37,78S.Chapeland,6J.L.Charvet,40S.Chattopadhyay,10S.Chattopadhyay,64I.Chawla,5M.Cherney,79C.Cheshkov,6,80B.Cheynis,80V.Chibante Barroso,6D.D.Chinellato,81P.Chochula,6M.Chojnacki,57S.Choudhury,10P.Christakoglou,56 C.H.Christensen,47P.Christiansen,82T.Chujo,53S.U.Chung,83C.Cicalo,84L.Cifarelli,8,6,18F.Cindolo,17J.Cleymans,70F.Coccetti,18F.Colamaria,22D.Colella,22G.Conesa Balbastre,34Z.Conesa del Valle,6 P.Constantin,27G.Contin,73J.G.Contreras,74T.M.Cormier,63Y.Corrales Morales,50P.Cortese,85I.Corte´s Maldonado,86M.R.Cosentino,66F.Costa,6M.E.Cotallo,58E.Crescio,74P.Crochet,39E.Cruz Alaniz,9E.Cuautle,87L.Cunqueiro,54A.Dainese,55,31H.H.Dalsgaard,47A.Danu,88D.Das,64K.Das,64I.Das,65S.Dash,89A.Dash,81S.De,10G.O.V.de Barros,75A.De Caro,90,18G.de Cataldo,91J.de Cuveland,21A.De Falco,76D.De Gruttola,90H.Delagrange,32A.Deloff,92V.Demanov,69N.De Marco,16E.De´nes,7 S.De Pasquale,90A.Deppman,75G.D.Erasmo,22R.de Rooij,57M.A.Diaz Corchero,58D.Di Bari,22T.Dietel,28C.Di Giglio,22S.Di Liberto,93A.Di Mauro,6P.Di Nezza,54R.Divia`,6Ø.Djuvsland,23A.Dobrin,63,82T.Dobrowolski,92I.Domı´nguez,87B.Do¨nigus,26O.Dordic,94O.Driga,32A.K.Dubey,10A.Dubla,57L.Ducroux,80P.Dupieux,39M.R.Dutta Majumdar,10A.K.Dutta Majumdar,64D.Elia,91D.Emschermann,28。

AP化学单词

Part 1foundation chemistry 基础化学Chapter 1acid酸apparatus仪器，装置aqueous solution水溶液arrangement of electrons电子排列assumption假设atom原子（化学变化中的最小粒子）atomic mass原子量atomic number原子序数atomic radius原子半径atomic structure原子结构be composed of由……组成bombardment撞击boundary界限cathode rays阴极射线cathode-ray oscilloscope (C.R.O)阴极电子示波器ceramic陶器制品charge-clouds电子云charge-to-mass ratio(e/m)质荷比（质谱分析时样品质量的测量以质量与其离子电荷之比表示）chemical behaviour化学行为chemical property化学性质（物质在化学变化中表现出来的性质）clockwise 顺时针方向的compound化合物（由不同元素组成的纯净物）configuration构型copper铜correspond to相似corrosive腐蚀d-block elements d 区元素deflect使偏向，使转向derive from源于deuterium氘diffuse mixture扩散混合物distance effect距离效应distil蒸馏distinguish区别distribution分布doubly charged(2+) ion正二价离子dye染料effect of electric current in solutions电流在溶液里的影响electrical charge电荷electrical field电场electrically neutral atom电中性原子electricity电electrolysis电解electron电子（负电荷粒子，电量等于4.77×10-10绝对静电单位）electron shielding电子屏蔽element元素（具有相同核电荷数即荷内质子数的一类原子的总称）emission spectrum发射光谱（根据发射光源和激发能量方式所产生的特征电磁波谱）energy level能态，能级（稳态能量，有相同主量数的电子壳层）fertiliser肥料first ionisation energy一级电离能fluorescent screen荧光屏fluoride 氟化物fuel燃料fundamental substance基础物质fuzzy模糊的galaxy星系，银河gas气体gaseous state气态gravity重力GroupⅠ第一族Heisenberg’s uncertainty principle海森堡测不准原理hydrofluoric acid氢氟酸identical同一的，相等的in terms of根据，在……方面innermost最内的，最深的interaction相互作用internal structure内部结构interpret解释investigate研究,调查ionisation energy电离能（从原子或分子中移走一个电子至无穷远处所需的能量，以电子伏特eV 表示）ionise电离isotope同位素（原子里具有相同的质子数和不同的中子数的同一元素的原子互称同位素）J.J. Thomson’s e/m experiment汤姆森质何比实验Latin拉丁lepton轻粒子liquid液体magnet磁铁magnetic field 磁场Maltese Cross马耳他十字marble大理石mass number质量数matter物质metal foil 金箔meteorite陨星microbe微生物，细菌Millikan’s ‘oil-drop’ ecperiment密立根油滴实验model-building模型建筑mole摩尔（表示一个系统的物质的量的单位，该系统中所包含的基本单元数与12g碳12即12C的原子数目相等,每摩尔物质含有阿佛加德罗常数个微粒）molecule分子（保持物质的化学性质的最小粒子）narrow beam狭窄的光线negative electrode（cathode）阴极negligible 可以忽略的neutron中子nitrate硝酸盐noble gas稀有气体normal pressures常压nuclear charge（原子）核电荷nuclear model for atoms原子核模型nuclear reaction核反应nucleus （pl.nuclei）核Orbital轨道paraffin wax石蜡particle微粒，粒子Pauli exclusion principle保里不相容原理（每个原子轨道至多只能容纳两个电子；而且，这两个电子自旋方向必须相反）Periodic Table周期表physical property物理性质（物质不需要发生化学变化就表现出来的性质，如颜色、状态、气味、熔沸点、密度等）plastics塑料plum-pudding李子布丁positive charge正电荷（带有质子的物质，用丝绸摩擦玻璃棒，在棒上会产生正电荷）positive electrode(anode)阳极positively charged particle(ion)离子potential difference电位prediction预言principal quantum number主量子数（标示轨道电子的波函数，包括轨道角动量和自旋量子数，电子的能级和距原子核的平均距离主要取决于主量子数）probe探测，探究protium氕proton质子quantum （pl. quanta）量子（一个电子转移到原子的下一层轨道时发出的有限辐射能单位）quantum mechanics量子力学Quantum Theory量子理论quark夸克（组成基本粒子的更小的粒子）radioactive source放射源repel排斥repulsion斥力respectively 分别地rung梯级scattering effect散射作用Schr?dinger equation薛定谔（波动）方程（一偏微分方程，描述基本粒子波动性）scintillation火花shell电子壳层shielding effect屏蔽效应simpler substance单质（指由同种元素组成的纯净物）solid固体sphere球spin自旋stable state稳态sub-atomic particle原子内的粒子subset子集，小团体successive ionisation energy逐级电离能symbol符号symmetry对称the lowest-energy orbitals最低能量轨道transition elements过渡元素tritium氚X-ray X 射线α-particlesα粒子，即alpha-particle（带有两个质子和中子的粒子，即氦原子核，对物质的穿透力较强，流速约为光速的1/10）α-ray α 射线β-particlesβ粒子β-ray β 射线γ-patticlesγ粒子γ-rayγ 射线Chapter 2abbreviation缩写absorption吸收abundance丰度accelerate加速alloy合金alter改变atmospheric pressure大气压Avogadro’s constant阿佛加德罗常数（12g12C 含有的原子数，约为6.02×1023）azide叠氮化物balance chemical equation配平化学方程式balance ionic equation配平离子方程式benzene苯blast furnace高炉bromide溴化物bulk体积burette滴定管butane丁烷carbon dioxide二氧化碳carbon monoxide一氧化碳carbonate 碳酸盐collide with冲突combustion analysis燃烧分析concentration浓度conical flask锥形瓶convert转化covalent bonds共价键（原子间通过共用电子对形成的化学键）decimal place小数位deposit沉淀物detonator炸药dioxide二氧化物dissolve溶解dropwise逐滴地electric current电流empirical formulae 实验式，经验式（只表示化合物中原子间最简单比例关系，非分子式，而为成分式）end-point终点enthalpy焓（热力学状态函数，单位质量的热含量，恒压下系统改变状态时增加的热含量等于内能与体系体积与压力乘积之和）equation方程式ethanoic acid 乙酸filament灯丝formula （pl. formulae）化学式（用元素符号来表示物质组成的式子）granule颗粒Group Ⅰ- the alkali metal 第一族,碱金属Group Ⅱ-the alkaline earth metal 第二族,碱土金属Group Ⅲ-第三族Group Ⅳ-Carbonic Group碳族Group Ⅴ-Nitric Group氮族Group Ⅵ-Oxygenic Group氧族Group Ⅶ, the halogens第七主族，卤族hexane己烷horizontal axis横坐标hydrocarbon碳氢化合物，烃hydrochloric acid盐酸hydrogen peroxide过氧化氢hydroxide氢氧化物hypothesis假设indicator指示剂inspect检查，查看iodide碘化物ionic compound离子型化合物（电负性相差大的两种元素相互作用，发生电子转移，变为正、负离子，正、负离子结合形成离子型化合物）iron oxide氧化铁low pressure低压mass spectrometer 质谱仪methane甲烷mixture混合物（由两种或多种物质混合而成的，这些物质相互间没有发生反应，混合物里各物质都保持原来的性质）molar mass摩尔质量（1摩尔物质的质量）molarity摩尔浓度，也叫物质的量浓度（以1升即1立方分米溶液里含有多少摩溶质来表示溶液组成的物理量）molecular formulae分子式（根据元素分析和分子量表示的化学式）monoxide一氧化物negative ion (＝anion)阴离子neutralise中和nitric acid硝酸non-metal非金属octane辛烷organic compound有机化合物oxidation state氧化态oxide氧化物peroxide过氧化物phosphate磷酸盐pipette移液管positive ion (＝cation)阳离子precipitation reaction 沉淀反应reactant反应物reaction反应reagent试剂，反应物redox reaction氧化还原反应relative atomic mass 相对原子质量（以碳12原子的质量的1/12约1.66×10－27kg作为标准，其他原子的质量跟它比较所得的值）relative formula mass相对式量relative isotopic mass 相对同位素质量relative molecular mass相对分子质量（化学式中各原子的相对原子质量的总和）room temperature室温singly charged 单核stoichiometric ratio化学计量比stoichiometry化学计量法sulphate 硫酸盐sulphide硫化物sulphite亚硫酸盐sulphuric acid硫酸temperature温度thermite铝热剂，灼热剂titration滴定法（将已知浓度的标准溶液加到被测溶液中，直到反应完成，借以测定其浓度）vaporize汽化vertical axis纵坐标vice versa反之亦然volume体积weld焊接Chapter 3adjacent molecule相邻的分子amide酰胺(含-CONH2基)ammonia氨atmosphere 大气层atomic orbital原子轨道attractive force吸引力biochemical compound生化化合物boiling point沸点bond angle键角(与同一原子连接的两个键之间的角度)bond enthalpybond length键长(分子中两个原子核间的平衡距离)bonding pair 成键电子对brine盐水brittle脆的building-block(=monomer unit)单体(聚合物中最简单的重复结构单元)catalyst催化剂（能改变反应速度而它本身的组成和质量在反应前后保持不变的物质）chemical bonding化学键（分子或晶体中，原子或离子之间直接的、主要的和强烈的相互作用称为化学键）chemical bonding and structure化学键及结构chloride 氯化物cleavage裂开condense浓缩conduct electricity导电covalent compound共价化合物crystal晶体crystal lattice晶格crystal plane晶体平面crystalline solid晶状固体cyclohexane环己胺dative covalent bond=coordinate bond配位键decomposition离解density密度dipole-dipole force取向力dot-and-cross diagram电子式,点叉式double bond双键double helix双螺旋ductile 可塑性,易变形的,可延展的electric dipole电偶极子（一对相距极近，符号相反、数值相等的电荷所形成的体系）electrical insulator电绝缘体electrical transformer变压器electronegativity电负性（原子或基团吸引并持留价电子的能力）electron-pair电子对electron-pair repulsion theory电子对互斥理论（是利用中心原子周??子的排斥理??盍?的分子及滕子(去除金?部分)的形?）electrostatic attraction静电吸引（引力）emerald翡翠enthalpy change of vaporization蒸发焓ethane乙烷ethanol乙醇，又叫酒精evaporation蒸发fabric布,fibre纤维fibrous纤维状的formation of ions离子的形成gaseous state气态gemstone宝石graphite石墨haemoglobin血红蛋白hard硬的high-density poly(ethene)高密度聚乙烯hydrated ion水合离子（与水结合而成，如H3O ＋）hydrogen bond氢键(氢键是由于与电负性极强的元素如氟、氧等相结合的氢原子和另一分子中电负性极强的原子间所产生的引力而形成)insoluble不溶instantaneous dipole-induced dipoleforces诱导力intermediate character两性intermolecular force分子间作用力(又称van der Waals’ force 范德华力)interval间隙ionic bonding离子键（由原子得失电子后，生成的正负离子之间，靠静电作用而形成的化学键）ionic crystal离子晶体（离子间通过离子键结合而成的晶体）ionic lattice离子晶格jewellery珠宝kinetic theory of matter物质运动论(所有物质的分子处于恒动状态)liquid state液态lone-pairs孤对电子low-density poly(ethene)低密度聚乙烯LP-LP repulsion> LP-BP repulsion> BP-BP repulsion孤电子对―故电子对斥力>孤电子对―成键电子对斥力>成键电子对―成键电子对斥力lubricant润滑剂magnetise磁化malleable有延展性的melting point熔点metal complex金属络合物（由金属离子与电子给予体结合而成）metallic bonding金属键(通过自由运动的价电子将金属原子连结起来的键)metallic element金属元素mineral矿物质mobile electron流动电子molecular orbital分子轨道molten熔化non-contuctor非导体non-linear molecule非直线分子non-metallic element非金属元素non-polar molecule非极性分子non-stick properties不黏性nylon尼龙,聚酰胺纤维octahedron八面体oppositely charged electron电性相反的电极oppositely charged ion电性相反的离子outer-shell electron外层电子oxonium ion(=hydronium ion) 水合氢离子polar molecule极性分子polarisation of ions离子极化（在阴阳离子自身电场作用下，产生诱导偶极，而导致离子的极化，即离子的正负电荷重心不再重合，电子云发生变形，致使物质在结构和性质上发生相应的变化）polarized极化poly聚乙烯poly(ester) chain聚酯链polychlorinated biphenyls (PCBs)多氯联（二）苯polymer聚合物,高分子polymer chain聚合物链protein蛋白质quartz石英relative bond strength相对键能repulsion斥力ruby红宝石sapphire蓝宝石semi-precious stone亚宝石single bond单键slippery光滑sodium chloride 氯化钠solid state固态solubility溶解度（物质在溶剂中达到饱和时的溶解程度）soluble可溶sparingly soluble难溶sublimation升华(固体不经液态直接转变为气态) sublime升华(固体不经液态直接转变为气态) sucrose蔗糖surface tension表面张力(由于表面层下面的分子与表面层下面的分子间的分子吸引,液体表面收缩成最小表面的趋向)symmetrical distribution对称分布tensile strength抗拉强度tetrahedral molecule四面体分子tetrahedron四面体the δ+ and δ-chargesδ+ 和δ-电荷three-dimensional arrangement三维排列triangular pyramidal molecule三角锥形分子trichloromethane三氯甲烷trigonal planar molecule 三角锥形分子triple bond三键unit cell晶胞vapour pressure(蒸汽压)viscosity黏度(流体流动阻力的表示,为液体中黏合力和内聚力的综合效果)volatility挥发性washing-up liquidwater is peculiar水是特殊的weapon武器δbondδ键δorbitalδ轨道π bondπ键π orbitalπ轨道Chapter 4 and 5antacid tablet解酸的药片atomic radii(＝atomic radius) 原子半径barium meal钡餐Blocks of elements in the Periodic Table周期表中元素的分区brick red砖红色bricklaying砌砖，泥水业brilliant whitish flame明亮的白色火焰bubble 泡camera lenses照相机镜头cement水泥chalk白垩chemical species化学物种clay黏土，泥土cliff悬崖cloudy white precipitate浑浊的白色沉淀covalent radius共价半径covered with a layer of its oxide覆盖一层氧化物薄膜crucible坩埚crumble粉碎d-block d区diatomic molecule双原子分子dilute稀释disulphur dichloride 二氯化二硫dolomite白云石electronegative带负电的，负电性的electropositive带正电的，正电性的evolution（气体）散出exothermic reaction放热反应f-block f区filtration过滤firework焰火flare照明弹good conductivity of heat and electricity良好的导电导热性gypsum石膏hydrogencarbonate碳酸氢盐incendiary bomb燃烧弹indigestion remedy消化不良的治疗lanthanide and actinide elements镧系和锕系元素（周期表中，ⅧB族有32种元素，包括钪、钇、镧和锕，其中镧这一格代表15种镧系元素[Z=51~71]，锕这一格代表15种锕系元素[Z=89~103]）Law of Octaves八行周期律（当元素按原子量增加的顺序排列成以八个为一组时，则上下每组对应元素有相似的性质）Law of Triadslime石灰lime water石灰（水溶液）limelight灰光灯limestone石灰石liquid phase液相magnesium ribbon镁条marine invertebrate海里的无脊椎动物Mendeleev’s periodic table门捷列夫周期表（按原子序数递增顺序排列成行，并将元素性质相同者置于各行之下，由此形成18列，各列元素的化合价按正规顺序变化）metal hydride金属氢化物metallic radius金属半径molten slag熔渣monatomic ion一价离子mortar灰浆negative oxidation state负化合价opaque 不透，不传导oxidation氧化oxidation number (abbreviated ox. no.)氧化数（某元素一个原子的荷电数，这种荷电数由假设把每个键中的电子指定给电负性更大的原子而求得）oxidation state氧化态oxidising agent氧化剂（得到电子的物质）p-block p区periodic patterns周期律periodicity周期性photographic flash bulb感光photosynthesis光合作用pitchblende沥青铀矿plaster石膏plaster of Pairs熟石膏positive oxidation state正化合价quicklime生石灰reactivity活动性reciprocal倒数redox system氧化还原体系reducing agent还原剂（逝去电子的物质）reduction还原refractory material难熔物质rotary kiln回转窑（炉）saturated solution饱和溶液s-block s区scum 浮垢sedimentary rock沉积岩siemens per metre (S m-1)西门子/米（西门子是电导实用单位，亦称姆欧，欧姆的倒数）single atom单原子slaked lime石灰（固）solid phase固相suspension悬浮液the outmost electrons最外层电子the rising parts of the curve曲线的上升部分the trend is uneven趋势是不规则的thermal decomposition热（分）解toxic有毒的tracer bullet示踪子弹trough曲线上的最小值valency化合价vapour phase气相vigorous剧烈的Chapter 6a cream precipitate米黄色沉淀aerosol propellant气溶胶喷射剂ammonia solution氨水anomalous properties异常的性质antiseptic抗菌剂，防腐剂apparent透明的bacteria细菌bleach漂白bromine is a dark red liquid giving off a dense red vapour溴是深红色液体，会挥发浓的红色溴蒸气capture an electron捕获一个电子CFCS(chlorofluorocarbons)含氯氟烃chlorine is greenish yellow gas氯是黄绿色气体contamination污染covalent diatomic molecule共价双原子分子cyclohexane环己烷dichloromethane二氯甲烷displacement reaction置换反应（由一种单质跟一种化合物起反应,生成另一种单质和另一种化合物的反应：1.非金属取代―电负性强者取代弱者；2.金属取代―金属性强者取代弱者）disproportionation reaction歧化反应（又叫自身氧化还原反应，在歧化反应中同一种元素的一部分原子[或离子]被氧化,另一部分原子[或离子]被还原）electron affinity电子亲合势（原子保持其离子电荷的亲合势）fire extinguisher 灭火器flammable 易燃的fluoride controversyfluorine is pale yellow gas氟是淡黄绿色气体foaming agent 起泡剂germicide 杀菌剂halate次卤酸根离子halide卤化物halogen卤族元素，简称卤素hydrated halide ion水合卤素离子inert惰性的iodine in alcohol碘酒iodine is a shiny, grey-black crystalline solid which sublimes to a purple vapour碘是有光泽的灰黑色晶体，会升华变成紫色碘蒸气liver damage肝脏损伤Lubricant 滑润剂non-flammable 不易燃的organic solvent有机溶剂organo-chlorine 有机氯ozone layer臭氧层poisonous有毒的PTFE (polytetrafluoroethene)聚四氟乙烯PVC聚氯乙烯refrigerant 制冷剂solvent 溶剂thyroid problem甲状腺问题volatility挥发性water purification水质净化waterproof clothing防水布Chapter 14reaction rates反应速率acidity 酸性，酸度adsorb吸附aldehyde乙醛at normal temperatures and pressures在常温常压下basicity 碱度；碱性Bung塞camphor 樟脑catalytic converter催化转化器celluloid 赛璐珞(明胶)chemical analysis化学分析chemical kinetics化学动力学colorimeter色度计colour intensity色度concentration of reactants反应物浓度constant random motion永恒的无规则运动desorb解吸entropy熵（热力学状态函数，用于量度系统无序度，等于吸收之热与吸热时绝对温度之商）esterification酯化exhaust gases排放气体factors that affect the rate of a reaction影响反应速率的因素gas syringe气体注射器glass delivery tube玻璃导管heterogeneous catalysis多相催化（催化剂与反应物处于不同相如在固体和流体相界面间发生催化作用）homogeneous catalysis均相催化（催化剂与反应物在同相中反应）intensity of the radiation 照射的强度inverted, water-filled burette倒置的装满水的量管latitude纬度low-energy collisions低能量碰撞nitrocellulose 硝化纤维素nitroglycerine 硝化甘油oxyacetylene torch 氧乙炔火炬peroxyacetyl nitrate(PAN)硝酸过氧化乙酰ppb 十亿分之一（10－10）ppm 百万分之一（10－6）pressure sensor压力感受器rate determining step决定反应速率的步骤removal去除Ribena scanning probe microscopy(SPM)扫描显微探针sealed container密闭容器self-sustainedspectrophotometer 分光光度计(根据样品对可见光分解为单色光后的透（反）射能量与波长的函数关系，可准确分析色度或比较两种波长的发光强度)surface area表面积temperature sensor 温感器（能对温度变化作出反应）the asymmetric shape of the curve曲线的不对称形状the Boltzemann distribution玻耳兹曼分布（处于热平衡的气体中具有不同能级的分子数的几率）the collision theory of reactivity碰撞理论（化学反应速率等于反应物分子间的碰撞数乘以有效碰撞因子）Timer计时器Chapter 15equilibra 平衡base碱closed system封闭系统constancy of macroscopic propertiescotton wool脱脂棉dynamic equilibrium动态平衡（在一定条件下德可逆反应里，正反应和逆反应德速率相等，反应混合物中各组成成分德含量保持不变）fertility肥(沃)度forwards direction正方向irreversible one-way reaction不可逆单向反应keep the pressure constant保持恒压Le Chatelier’s principle勒沙特列原理（如果改变影响平衡的一个条件如浓度、压强或温度等，平衡就向能够减弱这种改变的方向移动）macroscopic propertiesnail varnish remover洗甲油Ostwald process奥斯特瓦尔德法（制硝酸，采用高温铂网催化剂，将氨氧化为氧化氮，经水吸收成硝酸）porous iron多孔的铁reaction vessel反应容器reverse direction反方向reversible reaction可逆反应。

Two-Dimensional Gas of Massless Dirac Fermions in Graphene

Two-Dimensional Gas of Massless Dirac Fermions in Graphene K.S. Novoselov1, A.K. Geim1, S.V. Morozov2, D. Jiang1, M.I. Katsnelson3, I.V. Grigorieva1, S.V. Dubonos2, A.A. Firsov21Manchester Centre for Mesoscience and Nanotechnology, University of Manchester, Manchester, M13 9PL, UK2Institute for Microelectronics Technology, 142432, Chernogolovka, Russia3Institute for Molecules and Materials, Radboud University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, the NetherlandsElectronic properties of materials are commonly described by quasiparticles that behave as nonrelativistic electrons with a finite mass and obey the Schrödinger equation. Here we report a condensed matter system where electron transport is essentially governed by the Dirac equation and charge carriers mimic relativistic particles with zero mass and an effective “speed of light” c∗ ≈106m/s. Our studies of graphene – a single atomic layer of carbon – have revealed a variety of unusual phenomena characteristic of two-dimensional (2D) Dirac fermions. In particular, we have observed that a) the integer quantum Hall effect in graphene is anomalous in that it occurs at halfinteger filling factors; b) graphene’s conductivity never falls below a minimum value corresponding to the conductance quantum e2/h, even when carrier concentrations tend to zero; c) the cyclotron mass mc of massless carriers with energy E in graphene is described by equation E =mcc∗2; and d) Shubnikov-de Haas oscillations in graphene exhibit a phase shift of π due to Berry’s phase.Graphene is a monolayer of carbon atoms packed into a dense honeycomb crystal structure that can be viewed as either an individual atomic plane extracted from graphite or unrolled single-wall carbon nanotubes or as a giant flat fullerene molecule. This material was not studied experimentally before and, until recently [1,2], presumed not to exist. To obtain graphene samples, we used the original procedures described in [1], which involve micromechanical cleavage of graphite followed by identification and selection of monolayers using a combination of optical, scanning-electron and atomic-force microscopies. The selected graphene films were further processed into multi-terminal devices such as the one shown in Fig. 1, following standard microfabrication procedures [2]. Despite being only one atom thick and unprotected from the environment, our graphene devices remain stable under ambient conditions and exhibit high mobility of charge carriers. Below we focus on the physics of “ideal” (single-layer) graphene which has a different electronic structure and exhibits properties qualitatively different from those characteristic of either ultra-thin graphite films (which are semimetals and whose material properties were studied recently [2-5]) or even of our other devices consisting of just two layers of graphene (see further). Figure 1 shows the electric field effect [2-4] in graphene. Its conductivity σ increases linearly with increasing gate voltage Vg for both polarities and the Hall effect changes its sign at Vg ≈0. This behaviour shows that substantial concentrations of electrons (holes) are induced by positive (negative) gate voltages. Away from the transition region Vg ≈0, Hall coefficient RH = 1/ne varies as 1/Vg where n is the concentration of electrons or holes and e the electron charge. The linear dependence 1/RH ∝Vg yields n =α·Vg with α ≈7.3·1010cm-2/V, in agreement with the theoretical estimate n/Vg ≈7.2·1010cm-2/V for the surface charge density induced by the field effect (see Fig. 1’s caption). The agreement indicates that all the induced carriers are mobile and there are no trapped charges in graphene. From the linear dependence σ(Vg) we found carrier mobilities µ =σ/ne, whichreached up to 5,000 cm2/Vs for both electrons and holes, were independent of temperature T between 10 and 100K and probably still limited by defects in parent graphite. To characterise graphene further, we studied Shubnikov-de Haas oscillations (SdHO). Figure 2 shows examples of these oscillations for different magnetic fields B, gate voltages and temperatures. Unlike ultra-thin graphite [2], graphene exhibits only one set of SdHO for both electrons and holes. By using standard fan diagrams [2,3], we have determined the fundamental SdHO frequency BF for various Vg. The resulting dependence of BF as a function of n is plotted in Fig. 3a. Both carriers exhibit the same linear dependence BF = β·n with β ≈1.04·10-15 T·m2 (±2%). Theoretically, for any 2D system β is defined only by its degeneracy f so that BF =φ0n/f, where φ0 =4.14·10-15 T·m2 is the flux quantum. Comparison with the experiment yields f =4, in agreement with the double-spin and double-valley degeneracy expected for graphene [6,7] (cf. caption of Fig. 2). Note however an anomalous feature of SdHO in graphene, which is their phase. In contrast to conventional metals, graphene’s longitudinal resistance ρxx(B) exhibits maxima rather than minima at integer values of the Landau filling factor ν (Fig. 2a). Fig. 3b emphasizes this fact by comparing the phase of SdHO in graphene with that in a thin graphite film [2]. The origin of the “odd” phase is explained below. Another unusual feature of 2D transport in graphene clearly reveals itself in the T-dependence of SdHO (Fig. 2b). Indeed, with increasing T the oscillations at high Vg (high n) decay more rapidly. One can see that the last oscillation (Vg ≈100V) becomes practically invisible already at 80K whereas the first one (Vg <10V) clearly survives at 140K and, in fact, remains notable even at room temperature. To quantify this behaviour we measured the T-dependence of SdHO’s amplitude at various gate voltages and magnetic fields. The results could be fitted accurately (Fig. 3c) by the standard expression T/sinh(2π2kBTmc/heB), which yielded mc varying between ≈ 0.02 and 0.07m0 (m0 is the free electron mass). Changes in mc are well described by a square-root dependence mc ∝n1/2 (Fig. 3d). To explain the observed behaviour of mc, we refer to the semiclassical expressions BF = (h/2πe)S(E) and mc =(h2/2π)∂S(E)/∂E where S(E) =πk2 is the area in k-space of the orbits at the Fermi energy E(k) [8]. Combining these expressions with the experimentally-found dependences mc ∝n1/2 and BF =(h/4e)n it is straightforward to show that S must be proportional to E2 which yields E ∝k. Hence, the data in Fig. 3 unambiguously prove the linear dispersion E =hkc∗ for both electrons and holes with a common origin at E =0 [6,7]. Furthermore, the above equations also imply mc =E/c∗2 =(h2n/4πc∗2)1/2 and the best fit to our data yields c∗ ≈1⋅106 m/s, in agreement with band structure calculations [6,7]. The employed semiclassical model is fully justified by a recent theory for graphene [9], which shows that SdHO’s amplitude can indeed be described by the above expression T/sinh(2π2kBTmc/heB) with mc =E/c∗2. Note that, even though the linear spectrum of fermions in graphene (Fig. 3e) implies zero rest mass, their cyclotron mass is not zero. The unusual response of massless fermions to magnetic field is highlighted further by their behaviour in the high-field limit where SdHO evolve into the quantum Hall effect (QHE). Figure 4 shows Hall conductivity σxy of graphene plotted as a function of electron and hole concentrations in a constant field B. Pronounced QHE plateaux are clearly seen but, surprisingly, they do not occur in the expected sequence σxy =(4e2/h)N where N is integer. On the contrary, the plateaux correspond to half-integer ν so that the first plateau occurs at 2e2/h and the sequence is (4e2/h)(N + ½). Note that the transition from the lowest hole (ν =–½) to lowest electron (ν =+½) Landau level (LL) in graphene requires the same number of carriers (∆n =4B/φ0 ≈1.2·1012cm-2) as the transition between other nearest levels (cf. distances between minima in ρxx). This results in a ladder of equidistant steps in σxy which are not interrupted when passing through zero. To emphasize this highly unusual behaviour, Fig. 4 also shows σxy for a graphite film consisting of only two graphene layers where the sequence of plateaux returns to normal and the first plateau is at 4e2/h, as in the conventional QHE. We attribute this qualitative transition between graphene and its two-layer counterpart to the fact that fermions in the latter exhibit a finite mass near n ≈0 (as found experimentally; to be published elsewhere) and can no longer be described as massless Dirac particles. 2The half-integer QHE in graphene has recently been suggested by two theory groups [10,11], stimulated by our work on thin graphite films [2] but unaware of the present experiment. The effect is single-particle and intimately related to subtle properties of massless Dirac fermions, in particular, to the existence of both electron- and hole-like Landau states at exactly zero energy [912]. The latter can be viewed as a direct consequence of the Atiyah-Singer index theorem that plays an important role in quantum field theory and the theory of superstrings [13,14]. For the case of 2D massless Dirac fermions, the theorem guarantees the existence of Landau states at E=0 by relating the difference in the number of such states with opposite chiralities to the total flux through the system (note that magnetic field can also be inhomogeneous). To explain the half-integer QHE qualitatively, we invoke the formal expression [9-12] for the energy of massless relativistic fermions in quantized fields, EN =[2ehc∗2B(N +½ ±½)]1/2. In QED, sign ± describes two spins whereas in the case of graphene it refers to “pseudospins”. The latter have nothing to do with the real spin but are “built in” the Dirac-like spectrum of graphene, and their origin can be traced to the presence of two carbon sublattices. The above formula shows that the lowest LL (N =0) appears at E =0 (in agreement with the index theorem) and accommodates fermions with only one (minus) projection of the pseudospin. All other levels N ≥1 are occupied by fermions with both (±) pseudospins. This implies that for N =0 the degeneracy is half of that for any other N. Alternatively, one can say that all LL have the same “compound” degeneracy but zeroenergy LL is shared equally by electrons and holes. As a result the first Hall plateau occurs at half the normal filling and, oddly, both ν = –½ and +½ correspond to the same LL (N =0). All other levels have normal degeneracy 4B/φ0 and, therefore, remain shifted by the same ½ from the standard sequence. This explains the QHE at ν =N + ½ and, at the same time, the “odd” phase of SdHO (minima in ρxx correspond to plateaux in ρxy and, hence, occur at half-integer ν; see Figs. 2&3), in agreement with theory [9-12]. Note however that from another perspective the phase shift can be viewed as the direct manifestation of Berry’s phase acquired by Dirac fermions moving in magnetic field [15,16]. Finally, we return to zero-field behaviour and discuss another feature related to graphene’s relativistic-like spectrum. The spectrum implies vanishing concentrations of both carriers near the Dirac point E =0 (Fig. 3e), which suggests that low-T resistivity of the zero-gap semiconductor should diverge at Vg ≈0. However, neither of our devices showed such behaviour. On the contrary, in the transition region between holes and electrons graphene’s conductivity never falls below a well-defined value, practically independent of T between 4 and 100K. Fig. 1c plots values of the maximum resistivity ρmax(B =0) found in 15 different devices, which within an experimental error of ≈15% all exhibit ρmax ≈6.5kΩ, independent of their mobility that varies by a factor of 10. Given the quadruple degeneracy f, it is obvious to associate ρmax with h/fe2 =6.45kΩ where h/e2 is the resistance quantum. We emphasize that it is the resistivity (or conductivity) rather than resistance (or conductance), which is quantized in graphene (i.e., resistance R measured experimentally was not quantized but scaled in the usual manner as R =ρL/w with changing length L and width w of our devices). Thus, the effect is completely different from the conductance quantization observed previously in quantum transport experiments. However surprising, the minimum conductivity is an intrinsic property of electronic systems described by the Dirac equation [17-20]. It is due to the fact that, in the presence of disorder, localization effects in such systems are strongly suppressed and emerge only at exponentially large length scales. Assuming the absence of localization, the observed minimum conductivity can be explained qualitatively by invoking Mott’s argument [21] that mean-free-path l of charge carriers in a metal can never be shorter that their wavelength λF. Then, σ =neµ can be re-written as σ = (e2/h)kFl and, hence, σ cannot be smaller than ≈e2/h per each type of carriers. This argument is known to have failed for 2D systems with a parabolic spectrum where disorder leads to localization and eventually to insulating behaviour [17,18]. For the case of 2D Dirac fermions, no localization is expected [17-20] and, accordingly, Mott’s argument can be used. Although there is a broad theoretical consensus [18-23,10,11] that a 2D gas of Dirac fermions should exhibit a minimum 3conductivity of about e2/h, this quantization was not expected to be accurate and most theories suggest a value of ≈e2/πh, in disagreement with the experiment. In conclusion, graphene exhibits electronic properties distinctive for a 2D gas of particles described by the Dirac rather than Schrödinger equation. This 2D system is not only interesting in itself but also allows one to access – in a condensed matter experiment – the subtle and rich physics of quantum electrodynamics [24-27] and provides a bench-top setting for studies of phenomena relevant to cosmology and astrophysics [27,28].1. Novoselov, K.S. et al. PNAS 102, 10451 (2005). 2. Novoselov, K.S. et al. Science 306, 666 (2004); cond-mat/0505319. 3. Zhang, Y., Small, J.P., Amori, M.E.S. & Kim, P. Phys. Rev. Lett. 94, 176803 (2005). 4. Berger, C. et al. J. Phys. Chem. B, 108, 19912 (2004). 5. Bunch, J.S., Yaish, Y., Brink, M., Bolotin, K. & McEuen, P.L. Nanoletters 5, 287 (2005). 6. Dresselhaus, M.S. & Dresselhaus, G. Adv. Phys. 51, 1 (2002). 7. Brandt, N.B., Chudinov, S.M. & Ponomarev, Y.G. Semimetals 1: Graphite and Its Compounds (North-Holland, Amsterdam, 1988). 8. Vonsovsky, S.V. and Katsnelson, M.I. Quantum Solid State Physics (Springer, New York, 1989). 9. Gusynin, V.P. & Sharapov, S.G. Phys. Rev. B 71, 125124 (2005). 10. Gusynin, V.P. & Sharapov, S.G. cond-mat/0506575. 11. Peres, N.M.R., Guinea, F. & Castro Neto, A.H. cond-mat/0506709. 12. Zheng, Y. & Ando, T. Phys. Rev. B 65, 245420 (2002). 13. Kaku, M. Introduction to Superstrings (Springer, New York, 1988). 14. Nakahara, M. Geometry, Topology and Physics (IOP Publishing, Bristol, 1990). 15. Mikitik, G. P. & Sharlai, Yu.V. Phys. Rev. Lett. 82, 2147 (1999). 16. Luk’yanchuk, I.A. & Kopelevich, Y. Phys. Rev. Lett. 93, 166402 (2004). 17. Abrahams, E., Anderson, P.W., Licciardello, D.C. & Ramakrishnan, T.V. Phys. Rev. Lett. 42, 673 (1979). 18. Fradkin, E. Phys. Rev. B 33, 3263 (1986). 19. Lee, P.A. Phys. Rev. Lett. 71, 1887 (1993). 20. Ziegler, K. Phys. Rev. Lett. 80, 3113 (1998). 21. Mott, N.F. & Davis, E.A. Electron Processes in Non-Crystalline Materials (Clarendon Press, Oxford, 1979). 22. Morita, Y. & Hatsugai, Y. Phys. Rev. Lett. 79, 3728 (1997). 23. Nersesyan, A.A., Tsvelik, A.M. & Wenger, F. Phys. Rev. Lett. 72, 2628 (1997). 24. Rose, M.E. Relativistic Electron Theory (John Wiley, New York, 1961). 25. Berestetskii, V.B., Lifshitz, E.M. & Pitaevskii, L.P. Relativistic Quantum Theory (Pergamon Press, Oxford, 1971). 26. Lai, D. Rev. Mod. Phys. 73, 629 (2001). 27. Fradkin, E. Field Theories of Condensed Matter Systems (Westview Press, Oxford, 1997). 28. Volovik, G.E. The Universe in a Helium Droplet (Clarendon Press, Oxford, 2003).Acknowledgements This research was supported by the EPSRC (UK). We are most grateful to L. Glazman, V. Falko, S. Sharapov and A. Castro Netto for helpful discussions. K.S.N. was supported by Leverhulme Trust. S.V.M., S.V.D. and A.A.F. acknowledge support from the Russian Academy of Science and INTAS.43µ (m2/Vs)0.8c4P0.4 22 σ (1/kΩ)10K0 0 1/RH(T/kΩ) 1 2ρmax (h/4e2)1-5010 Vg (V) 50 -10ab 0 -100-500 Vg (V)50100Figure 1. Electric field effect in graphene. a, Scanning electron microscope image of one of our experimental devices (width of the central wire is 0.2µm). False colours are chosen to match real colours as seen in an optical microscope for larger areas of the same materials. Changes in graphene’s conductivity σ (main panel) and Hall coefficient RH (b) as a function of gate voltage Vg. σ and RH were measured in magnetic fields B =0 and 2T, respectively. The induced carrier concentrations n are described by [2] n/Vg =ε0ε/te where ε0 and ε are permittivities of free space and SiO2, respectively, and t ≈300 nm is the thickness of SiO2 on top of the Si wafer used as a substrate. RH = 1/ne is inverted to emphasize the linear dependence n ∝Vg. 1/RH diverges at small n because the Hall effect changes its sign around Vg =0 indicating a transition between electrons and holes. Note that the transition region (RH ≈ 0) was often shifted from zero Vg due to chemical doping [2] but annealing of our devices in vacuum normally allowed us to eliminate the shift. The extrapolation of the linear slopes σ(Vg) for electrons and holes results in their intersection at a value of σ indistinguishable from zero. c, Maximum values of resistivity ρ =1/σ (circles) exhibited by devices with different mobilites µ (left y-axis). The histogram (orange background) shows the number P of devices exhibiting ρmax within 10% intervals around the average value of ≈h/4e2. Several of the devices shown were made from 2 or 3 layers of graphene indicating that the quantized minimum conductivity is a robust effect and does not require “ideal” graphene.ρxx (kΩ)0.60 aVg = -60V4B (T)810K12∆σxx (1/kΩ)0.4 1ν=4 140K 80K B =12T0 b 0 25 50 Vg (V) 7520K100Figure 2. Quantum oscillations in graphene. SdHO at constant gate voltage Vg as a function of magnetic field B (a) and at constant B as a function of Vg (b). Because µ does not change much with Vg, the constant-B measurements (at a constant ωcτ =µB) were found more informative. Panel b illustrates that SdHO in graphene are more sensitive to T at high carrier concentrations. The ∆σxx-curves were obtained by subtracting a smooth (nearly linear) increase in σ with increasing Vg and are shifted for clarity. SdHO periodicity ∆Vg in a constant B is determined by the density of states at each Landau level (α∆Vg = fB/φ0) which for the observed periodicity of ≈15.8V at B =12T yields a quadruple degeneracy. Arrows in a indicate integer ν (e.g., ν =4 corresponds to 10.9T) as found from SdHO frequency BF ≈43.5T. Note the absence of any significant contribution of universal conductance fluctuations (see also Fig. 1) and weak localization magnetoresistance, which are normally intrinsic for 2D materials with so high resistivity.75 BF (T) 500.2 0.11/B (1/T)b5 10 N 1/2025 a 0 0.061dmc /m00.04∆0.02 0c0 0 T (K) 150n =0e-6-3036Figure 3. Dirac fermions of graphene. a, Dependence of BF on carrier concentration n (positive n correspond to electrons; negative to holes). b, Examples of fan diagrams used in our analysis [2] to find BF. N is the number associated with different minima of oscillations. Lower and upper curves are for graphene (sample of Fig. 2a) and a 5-nm-thick film of graphite with a similar value of BF, respectively. Note that the curves extrapolate to different origins; namely, to N = ½ and 0. In graphene, curves for all n extrapolate to N = ½ (cf. [2]). This indicates a phase shift of π with respect to the conventional Landau quantization in metals. The shift is due to Berry’s phase [9,15]. c, Examples of the behaviour of SdHO amplitude ∆ (symbols) as a function of T for mc ≈0.069 and 0.023m0; solid curves are best fits. d, Cyclotron mass mc of electrons and holes as a function of their concentration. Symbols are experimental data, solid curves the best fit to theory. e, Electronic spectrum of graphene, as inferred experimentally and in agreement with theory. This is the spectrum of a zero-gap 2D semiconductor that describes massless Dirac fermions with c∗ 300 times less than the speed of light.n (1012 cm-2)σxy (4e2/h)4 3 2 -2 1 -1 -2 -3 2 44Kn7/ 5/ 3/ 1/2 2 2 210 ρxx (kΩ)-4σxy (4e2/h)0-1/2 -3/2 -5/2514T0-7/2 -4 -2 0 2 4 n (1012 cm-2)Figure 4. Quantum Hall effect for massless Dirac fermions. Hall conductivity σxy and longitudinal resistivity ρxx of graphene as a function of their concentration at B =14T. σxy =(4e2/h)ν is calculated from the measured dependences of ρxy(Vg) and ρxx(Vg) as σxy = ρxy/(ρxy + ρxx)2. The behaviour of 1/ρxy is similar but exhibits a discontinuity at Vg ≈0, which is avoided by plotting σxy. Inset: σxy in “two-layer graphene” where the quantization sequence is normal and occurs at integer ν. The latter shows that the half-integer QHE is exclusive to “ideal” graphene.。

第2章夸克与轻子 (2)

第二章夸克与轻子Quarks and leptons2.1 粒子园The particle zoo学习目标Learning objectives：我们怎样发现新粒子？能否预言新粒子？什么是奇异粒子？大纲参考：3.1.1￣太空入侵者宇宙射线是由包括太阳在内的恒星发射而在宇宙空间传播的高能粒子。

如果宇宙射线粒子进入地球大气层，就会产生寿命短暂的新粒子和反粒子以及光子。

所以，就有“太空入侵者”这种戏称。

发现宇宙射线之初，大多数物理学家都认为这种射线不是来自太空，而是来自地球本身的放射性物质。

当时物理学家兼业余气球旅行者维克托·赫斯（Victor Hess）就发现，在5000m高空处宇宙射线的离子效应要比地面显著得多，从而证明这种理论无法成立。

经过进一步研究，表明大多数宇宙射线都是高速运动的质子或较小原子核。

这类粒子与大气中气体原子发生碰撞，产生粒子和反粒子簇射，数量之大在地面都能探测到。

通过云室和其他探测仪，人类发现了寿命短暂的新粒子与其反粒子。

μ介子（muon）或“重电子”（符号μ）。

这是一种带负电的粒子，静止质量是电子的200多倍。

π介子（pion）。

这可以是一种带正电的粒子（π＋）、带负电的粒子（π－）或中性不带电粒子（π0），静止质量大于μ介子但小于质子。

K介子（kaon）。

这可以是一种带正电的粒子（K＋）、带负电的粒子（K－）或中性不带电粒子（K0），静止质量大于π介子但小于质子。

科学探索How Science Works不同寻常的预言An unusual prediction在发现上述三种粒子之前，日本物理学家汤川秀树（Hideki Yukawa）就预言，核子间的强核力存在交换粒子。

他认为交换粒子的作用范围不超过10－15m，并推断其质量在电子与质子之间。

由于这种离子的质量介于电子与质子之间，所以汤川就将这种粒子称为“介子”（mesons）。

一年后，卡尔·安德森拍摄的云室照片显示一条异常轨迹可能就是这类粒子所产生。

CP-Violating Phases in the MSSM

dgq /e
∼
αs π
mqmg˜|A∗ + m4f˜
µ tan β|
sin γ
(1)
For up-type quarks, take tan β → cot β. Here
γ is the argument of the oﬀ-diagonal element of the squark mass matrix, γ = arg(A∗ + µ tan β).
For typical values of the masses, mg˜ = mf˜ = |A∗ + µ tan β| = 100 GeV, the requirement that
the quark EDM contribution to the neutron EDM satisfy the experimental bound[4] of |dn| < 1.1 × 10−25e cm implies that the phase γ be very small, sin γ <∼ 0.001. However, this bound can be considerably relaxed by making the squarks heav-
af
=
g′4 128π
(YL2 + YR2)
m2f (mf˜2 + mB2
− m2f )2 ,
(2)
and the p-wave suppression is evident, as af ∼ m2f . Here YL(YR) is the left(right) sfermion hypercharge. In the presence of CP -violation and

PhysicalReviewFocus-CosPA物理评论的焦点cospa

DepartmentsPhysical Review Focus Edited by David Ehrenstein, Editor, Physical Review Focus, APS.Copyright 2009, The American Physical Society. Below are introductions to recent stories from Phys. Rev. Focus; see / to read the complete stories.Physical Review Focus, Vol. 24, Story 11, 21 September 2009THE OVERLAP OF TWO PHOTONSPhysicists routinely use a movable mir-ror to measure the timing of laser pulses that are only femtoseconds (10-15 sec-onds) long, and now they have extended the technique to pairs of photons. A team reporting in the 18 September Physi-cal Review Letters studied “entangled” photons, which are created in pairs and maintain a quantum connection with their mates. Such photon pairs may be useful for quantum computers and cryp-tography, and this new technique could complement others aimed at revealing their properties. (Kevin A. O’Donnell and Alfred B. U’Ren, Phys. Rev. Lett. 103, 123602.)Physical Review Focus, Vol. 24, Story 12, 2 October 2009BEAD’S RECOIL UNDER LIGHT PRESSURE Radiation pressure – the force light exerts on matter – is so slight that it’s usually evident only in the atomic world or in the vacuum of space. Now a pair of studies published in the 27 February Physical Review Letters and the October Physical Review E suggests that a com-mon laser-and-microscope technique is sensitive enough to measure the recoil felt by a micron-sized silica bead emit-ting light from its surface. Researchers used lasers to trap a bead and measure the forces acting on it, while simultane-ously recording the light generated by molecules coating the bead’s surface. They report that the forces acting on the bead were correlated with the intensity of emitted light, as would be expected if emitted photons were nudging a beadback and forth like the exhaust from tinythrusters. (Satish Rao et al., Phys. Rev.Lett. 102, 087401.)Physical Review Focus, Vol. 24, Story13, 2 October 2009STONES FROM STICKSNatural diamonds are forged in the hightemperatures and crushing pressures ofthe earth’s interior. But to make na-noscale diamond crystals, researchershave used their own tricks, includingrecipes involving carbon nanotubes.Now a team explains at the atomic levelhow nanotubes can convert to diamonds.Their computational studies in the Oc-tober Physical Review B show that it ispossible for carbon atoms from adjacentwalls of multi-walled nanotubes to bondto each other to form both the cubic andhexagonal structures of diamond. Whilesuch nano-carat diamonds won’t appearat the jeweler’s anytime soon, research-ers think that their strength and hardnessmay make them useful components ofnanoscale machines. (Andre R. Muniz etal., Phys. Rev. B80, 144105.)Physical Review Focus, Vol. 24, Story14, 12 October 2009PHOTONIC THERMOSThe pure vacuum of a thermos is not thebest possible insulator for keeping yoursoup warm. Last year a team found theo-retically that a structure known as a pho-tonic crystal could block heat flow evenmore effectively than vacuum. In theOctober Physical Review B they presenta complete theory explaining the phe-nomenon and reveal that the structure’sinsulating ability is surprisingly indepen-dent of its structural details. Their worksuggests that photonic crystals, whichhave promising applications in com-munications and computing, might oneday be used for their thermal properties,perhaps in devices that turn the sun’sheat into usable energy. (Wah Tung Lauet al., Phys. Rev. B80, 155135.)Physical Review Focus, Vol. 24, Story15, 16 October 2009SO CLOSE, YET SO FARObservations of cosmic microwaves from380,000 years after the big bang havebeen essential to modern cosmology, butcosmic neutrinos should carry informa-tion on the state of the universe whenit was less than a second old. In the 23October Physical Review Letters, a teampoints out a curious and hithertoignored fact about these relic neutrinos:because of their masses, they travelmore slowly than light does and actuallyoriginate from a much nearer region ofthe universe than the cosmic microwaves.Although detecting cosmic neutrinos isstill a long way off (if it’s possible at all),the work clarifies the type of informationthat, in theory at least, could be gleanedfrom relic neutrinos. (S. Dodelson and M.Vesterinen, Phys. Rev. Lett. 103, 171301.)Physical Review Focus, Vol. 24, Story16, 26 October 2009STORAGE RING DUST-UPHigh-energy physicists have finallypinpointed their dust problem. Insidemulti-million dollar storage rings,high-speed trains of electrons are oftenderailed by micron-sized specks of dust.Now a team has shown that dust grainsarise from sparks inside a Japanese stor-30AAPPS Bulletin December 2009, Vol. 19, No. 6Research Newsage ring, as they report in an upcoming paper in Physical Review Special Topics – Accelerators and Beams (PRST-AB), a free, online journal. The team also serendipitously caught on video oneof the tiny grains being swept along in the electron beam – the particle phys-ics equivalent of a criminal caught by a security camera. The feat opens the possibility for further characterization of the dust. (Y. Tanimoto et al., Phys. Rev. ST Accel. Beams12, 110702.)Physical Review Focus, Vol. 24, Story 17, 30 October 2009 MOLECULAR CURRENTS European researchers have measured the electrical conductance between a single pair of precisely oriented C60 molecules. In the 13 November Physical Review Letters they describe picking up one molecule on the tip of an ultrafine scanning-tunneling-microscope probe and monitoring the current when it is positioned over another C60 molecule. Understanding and controlling electric current between neighboring molecules will be important if electronic circuits are to be built using individual mol-ecules.（Guillaume Schull et al., Phys. Rev. Lett.103, 206803.）Physical Review Focus, Vol. 24, Story 18, 9 November 2009 GETTING THE SMALL PICTURE A new technology could provide nano-meter-resolution, 3-D images of small semiconducting structures or proteins in-side cells, according to a proposal in the 20 November Physical Review Letters. The system would construct images by examining how light scatters off of the sample and a nearby metal nanoparticle positioned with an atomic force micro-scope. The nanoparticle solves a crucial problem faced by an earlier design and may allow the technique to become a practical way of imaging small objects without cutting into them. (Alexander A. Govyadinov et al., Phys. Rev. Lett.103, 213901.)Physical Review Focus, Vol. 24, Story19, 13 November 2009RIPPLES ON A CELLDetailed new observations of wavesrippling across the surfaces of livingcells may give researchers new insightinto how such waves are formed. A teampublishing in the 20 November PhysicalReview Letters used a sensitive micros-copy technique to track surface ripplespropagating backward from the edgesof human skin cells that have the abilityto move into the region of a wound. Theresults suggest that elements of the cell’smovement machinery are responsiblefor the waves. (Chien-Hong Chen et al.,Phys. Rev. Lett., to be published.)Physical Review Focus, Vol. 24, Story20, 20 November 2009QUARKS INFLUENCED BYTHEIR NEIGHBORHOODThe internal structure of a proton orneutron is not completely fixed – experi-ments going back decades suggest thatthe particles are slightly different wheninside a nucleus. Now results in the13 November Physical Review Lettersshow that the effect is not dependent onthe mass or on the density of the entirenucleus, as some theories have predict-ed. Instead, neutrons and protons appearto change according to their immedi-ate neighborhood within the nucleus.(J. Seely et al., Phys. Rev. Lett. 103,202301.)Physical Review Focus, Vol. 24, Story21, 2 December 2009HANGING DROPLETS FEELMORE FRICTIONAccording to high school textbooks,the force needed to slide a box acrossthe floor increases with its weight. Butfor a liquid drop on a solid surface, thatisn’t always true, reports a team in the11 December Physical Review Letters.They measured the force needed to pusha millimeter-sized droplet and found thata droplet hanging upside down from thesurface required more force to get mov-ing than a droplet resting on top of thesurface. The result could help research-ers identify which forces are responsiblefor pinning liquid droplets to differentsurfaces. (R. Tadmor et al., Phys. Rev.Lett. to be published.)Physical Review Focus, Vol. 24, Story22, 8 December 2009QUARK COLORS UNBOUNDIn the minds of theorists, quarks come ina rainbow of different colors. Althoughexperiments clearly indicate that thereare just three types of “charge” (color)for quarks interacting through the strongnuclear force, calculations become muchsimpler when the number of colorsis very large. Computer simulationsdescribed in the 5 December PhysicalReview Letters strengthen the case thatmulti-color theories provide roughlythe same predictions as the three-colortheory. The paper also shows that oneclass of these models derived fromstring theory makes predictions thatclosely match the results computed insimulations using the three-color theory.(Marco Panero, Phys. Rev. Lett. 103,232001.)AAPPS Bulletin December 2009, Vol. 19, No. 631。

附录内容

参考资料For reference《高二物理》（AS Physics）（高中物理课程大纲A）常用数据Useful data for AS Physics (Specification A)数据Data高二物理公式AS formulae粒子物理Particle physics基本粒子Fundamental particles夸克性质Properties of quarks电荷重子数奇异数－eμr反粒子：e＋，，μ＋，，r＋，几何方程Geometrical equations弧长=rθ圆周长=2πr圆面积=πr2圆柱体表面积=2πh圆柱体体积=πr2h球体表面积=4πr2球体体积=πr3光子和能级Photos and energy levels 光子能量E=hf=光电效应hf=ф＋E Kmax能级hf=E1－E2德布罗意波长λ=电学Electricity电流和电压I=V=R=电动势є=є=IR＋Ir串联电阻R= R1＋R2＋R3＋……并联电阻电阻率ρ=功率P=VI=IR2=交流电I rms=V rms=力学Mechanics 力矩力矩=Fd速率和加速度v=a=运动方程v=u＋ats=v2=u2＋as力F=ma功、能量和功率W=FscosθEk=mv2ΔE p=mgΔhP=P=Fv机器功效= 有效输出功率/输入总功率材料Materials密度ρ=胡克定律F=kΔL杨氏模量=弹性应力/弹性应变=存储能量E=波Waves波速c=fλ周期T=条纹间距w=衍射光栅dsinθ=nλ物质的折射率s1n s=两种不同物质的折射率分别为n1、n2，折射定律n1sinθ1=n1sinθ2临界角如果n 1＞n2，则术语表Glossaryacceleration: change of velocity per unit time.加速度：单位时间内速率的变化量。

acceleration of free fall: acceleration of an object acted on only by the force of gravity.自由落体加速度：一个物体只受重力作用情况下所具有的加速度.accuracy: a measurement that is obtained, using accurately- calibrated instruments correctly, is said to be accurate.精确性：正确使用准确标定仪器得到的测量结果具有准确性。

超弦理论与量子引力

超弦理论与量子引力（作者卢杲研究员英国伦敦技术物理研究院）第一章量子引力理论§宇宙存在三级量子恒星、中子星、黑洞、宇宙奇点四者之间存在体积、能量、质量、密度方面的巨大差异，可以断定它们是由三种不同量级的量子组成，恒星由原子组成，中子星由粒子（中子）组成，黑洞由引力子组成，宇宙奇点由奇子组成。

从宇宙奇点看，引力子、粒子、原子都有一种泡沫结构，我们对其中的原子泡沫已很熟悉，从中子星向黑洞、宇宙奇点反推上去，粒子、引力子的内部还是很空旷的。

由于目前的科技水平所限，我们无法在人工实验室中分离出电子、光子、夸克、引力子的亚结构，但却可以利用宇宙天体这一天然实验场，用大量的原子或粒子或引力子构成的天体来研究物质的亚结构。

当恒星塌缩成中子星，既可知中子是原子的构成材料之一，这是我们已知的。

当中子星塌缩成黑洞，既可知引力子是中子等粒子的构成材料之一，黑洞是纯引力天体，是纯引力子的世界，当吞噬了宇宙大部分物质的宇宙黑洞塌缩成宇宙奇点时，既可知奇子是引力子的结构材料之一，黑洞奇点和宇宙奇点在能量、质量、密度、温度方面存在极大差异，且黑洞奇点产生向内的力，宇宙奇点产生的是巨大的向外爆发的力，所以，引力子和奇子不可能属于同一级量子。

构成宇宙万物的原子之内是很空旷的，原子核的直径约为原子直径的十万分之一，相当于标准足球场中心的一粒大豆，电子相当于足球场外围的几粒沙子，请大家切记原子与质子的大小之比，这种真实差距将凸显传统原子模型的致命缺陷（这种对比实验最好到足球场去做，图中的原子与原子核大小之比已严重失真）。

当个太阳质量的恒星死亡后，被自身引力压缩成直径10公里的中子星，这时星体的主要成分是中子，如果该中子星不断吸引空间物质，当达到一定质量时，会被自身引力压缩成极小的黑洞，这说明与中子同类的粒子之内也是很空旷的，在黑洞中任何粒子都被压缩成更小的量子――引力子。

黑洞里有什么起码有它自己，大量的引力子。

恒星的平均密度是1gcm－3，当恒星塌缩成白矮星，其平均密度是107gcm－3，由电子的简并压力和引力相平衡。

Cosmic Rays and Particle Physics

a rXiv:as tr o-ph/11331v118Jan21Symposium on Fundamental Issues in Elementary Matter (2000)000–000Fundamental Issues in Elementary Matter Bad Honnef,Germany September 25–29,2000Cosmic Rays and Particle Physics Karl-Heinz Kampert Universit¨a t Karlsruhe (TH),Institut f¨u r Experimentelle Kernphysik Forschungszentrum Karlsruhe,Institut f¨u r Kernphysik P.O.B.3640,D-76021Karlsruhe,Germany Abstract.The study of high energy cosmic rays is a diversiﬁed ﬁeld of observational and phenomenological physics addressing questions ranging from shock acceleration of charged particles in various astrophysical objects,via transport properties through galactic and extragalactic space,to questions of dark matter,and even to those of particle physics beyond the Standard Model including processes taking place in the earliest moments of our Universe.After decades of mostly independent evolution of nuclear-,particle-and high energy cosmic ray physics we ﬁnd ourselves entering a symbiotic era of these ﬁelds of research.Some examples of interrelations will be given from the perspective of modern Particle-Astrophysics and new major experiments will brieﬂy be sketched.1.Introduction Cosmic rays (CR s)were discovered in 1911by Victor Hess through a series of balloon ﬂights in which he carried electrometers to over 5000m [1].Originally being thought of as penetrating γ-radiation,in the late twenties Compton and others realized that CR smainly consist of charged particles.By performing coincidence measurements in 1938us-ing Geiger counters at mountain altitudes and later also at sea level in Paris,Pierre Auger discovered the phenomenon of “extensive air showers”;A high energy CR entering the at-mosphere initiates a cascade of secondary particles which is large enough and sufﬁciently penetrating to reach ground level.From his observations,Pierre Auger already concluded that primary particles up to energies of 1015eV are found in CR s,and speculations were raised how to generate particles of such high energy.Present day simulations predict that,e.g.a single 1015eV CR particle produces about 106secondary particles at sea level,mainly photons and electrons plus some muons and hadrons being spread out over about a hectare.Indeed,the present particle physics has taken origin from the observations and measure-ments of CR s performed in the ﬁrst half of our century,starting from the discovery of the positron in 1932,muons in 1937,to that of pions and strange particles (Λand K )in 1947,xxxxx-xxx/2000c 2000EP Systema Bt.,Debrecen2K.-H.KampertCosmic Rays and Particle Physics34K.-H.KampertHe might in principlealso be produced in high en-ergy cosmic ray interactions,their contribution to theHe4/He4of10−6at rigidities between1and16GV/c.SimilarCosmic Rays and Particle Physics5He4/He4≤10−8probing the antimatter contents of the Universe to more than150Mpc.Finally,absoluteﬂuxes of proton,helium,and atmospheric muons are important also for the derivation of the neutrino oscillation parameters e.g.from Super-Kamiokande[19],since the atmospheric neutrinoﬂux is proportional to the normalization of the dominating CR proton and heliumﬂuxes.Presently,new balloon borne experiments are in preparation to reduce particularly the uncertainties of the muonﬂux at different atmospheric depths.This is of great importance also for upcoming long-baseline neutrino experiments and is a good example of the interconnection between cosmic ray and particle physics.3.Extensive Air Showers and High Energy InteractionsCosmic ray measurements at energies above some1014eV are performed by large area air shower experiments.An extensive air shower(EAS)is a cascade of particles generated by the interaction of a single high energy primary cosmic ray nucleus or nucleon near the top of the atmosphere.The secondary particles produced in each collision,mostly charged and neutral pions and kaons,may either decay or interact with another nucleus,thereby multi-plying the number of particles within an EAS.After reaching a maximum in the number of secondary particles,the shower attenuates as more and more particles fall below the thresh-old for further particle production.A disk of relativistic particles extended over an area with a diameter of some tens of metres at1014eV to several kilometres at1020eV can then be observed at ground.This magnifying effect of the earth atmosphere allows to instrument only a very small portion of the EAS area and to still reconstruct the major properties of the primary particles.It is a lucky coincidence that at the energy where direct detection of CR s rays becomes impractical,the resulting air showers become big enough to be easily detectable at ground level.Due to the nature of the involved hadronic and electromagnetic interactions and the different decay properties of particles,an EAS has three components, electromagnetic,muonic,and hadronic.Extracting the primary energy and mass from such measurements is not straightforward and a model must be adopted to relate the observed EAS parameters(total number of electrons,muons,hadrons,shapes of their lateral density distributions,reconstructed height of the shower maximum,etc.)to the properties of the primary particle[20].A large body of experimental data from heavy-ion collisions studied at CERN and Brookhaven and from pp-collisions studied at the CERN SPS and Fermilab Tevatron is available and has been used to constrain the phenomenological QCD-inspired models entering EAS simulations.However,CR interactions above the knee are already be-yond the maximum CMS-energy of the Tevatron.Furthermore,the very forward kinematic region being mostly relevant to the propagation of air showers is basically uncovered by collider experiments.Finally,effects of possible quark-gluon plasma formation may affect EAS observables[21].Testing air shower simulations and thereby hadronic interaction models by means of EAS data thus is of interest for particle and CR physics.6K.-H.KampertCosmic Rays and Particle Physics78K.-H.KampertCosmic Rays and Particle Physics910K.-H.KampertCosmic Rays and Particle Physics1112K.-H.KampertCosmic Rays and Particle Physics13。

夸克理论

20世纪60年代，美国物理学家默里·盖尔曼和G.茨威格各自独立提出了中子、质子这一类强子是由更基本的单元——夸克（quark）组成的。

它们具有分数电荷，是电子电量的2/3或-1/3倍，自旋为1/2。

夸克理论认为，所有的重子都是由三个夸克组成的，比如质子（uud），中子（udd）；反重子则是由三个相应的反夸克组成的。

夸克理论还预言了存在一种由三个奇异夸克组成的粒子（sss），这种粒子于1964年在氢气泡室中观测到，叫做负ω粒子。

顶、底、奇、魅夸克由于质量太大（参见下表），很短的时间内就会衰变成上夸克或下夸克。

夸克按其特性分为三代，如下表所示：世代自旋名称符号 e 质量/ MeV.c-21 + 1/2 上夸克u + 2/3 1.5 to 4.01 − 1/2 下夸克 d − 1/34 to 82 − 1/2 奇异夸克s − 1/3 80 to 1302 + 1/2 魅夸克 c + 2/3 1150 to 13503 − 1/2 底夸克 b − 1/3 4100 to 44003 + 1/2 顶夸克t + 2/3 171400 ± 2100在量子色动力学中，夸克除了具有“味”的特性外，还具有三种“色”(color)的特性，分别是红、绿和蓝。

这里“色”并非指夸克真的具有颜色，而是借“色”这一词形象地比喻夸克本身的一种量子数。

量子色动力学认为，一般物质是没有“色”的，组成重子的三种夸克的“颜色”分别为红、绿和蓝，因此叠加在一起就成了无色的。

因此计入6种味和3种色的属性，共有18种夸克，另有它们对应的18种反夸克。

夸克理论还认为，介子是由同色的一个夸克和一个反夸克组成的束缚态。

例如，日本物理学家汤川秀树预言的π+介子是由一个上夸克和一个反下夸克组成的，π-介子则是由一个反上夸克和一个下夸克组成的，它们都是无色的。

除顶夸克外的五种夸克已经通过实验发现它们的存在，华裔科学家丁肇中便因发现魅夸克而获诺贝尔物理学奖。

1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。

arXiv:hep-ph/9904447v1 25 Apr 1999ChargeandcriticaldensityofstrangequarkmatterG.X.Peng,1,2,3H.C.Chiang,2P.Z.Ning,3andB.S.Zou21ChinaCenterofAdvancedScienceandTechnology(WorldLaboratory),Beijing100080,China

2InstituteofHighEnergyPhysics,AcademiaSinica,Beijing100039,China

3DepartmentofPhysics,NankaiUniversity,Tianjin300071,China

(Received16November1998)

Theelectricchargeofstrangequarkmatterisofvitalimportancetoexperiments.Arecentin-vestigationshowsthatstrangeletsaremostlikelyhighlynegativelycharged,ratherthanslightlypositivelychargedaspreviouslybelieved.Ourpresentstudyindicatesthatnegativechargescanindeedlowerthecriticaldensity,andthusbefavorabletotheexperimentalsearchesinheavyioncollisions.However,toomuchnegativechargescanmakeitimpossibletomaintainﬂavorequilib-rium.{S0556-2813(99)02506-6}

PACSnumbers:24.85.+p,12.39.-x,12.38.Mh,25.75.-q

Thelast20yearshavewitnessedanever-increasingin-terestinstrangequarkmatter(SQM)[1].Earlyin1970’s[2],ithadalreadybeenknownthattheappearanceofsfractionintwoﬂavorquarkdropletsprovidesanaddi-tionaldegreeoffreedom,andthuscouldlowertheenergyofthesystem.In1984,Wittenconjecturedthatquarkmatterwithstrangenessperbaryonoforderunitymightbebound[3],whichhasarousedagreatfocusofinvesti-gationsintothestabilityanddetectabilityofSQM.IntheframeworkofMITbagmodel,Jaﬀeetal.ﬁndthatSQMisabsolutelystablearoundthenormalnucleardensityforawiderangeofparameters[4]whileotherauthorsﬁndafewdestabilityfactors[5,6].Onapplicationofthequarkmass-density-dependentmodel,Chakrabartyetal.car-riedoutalotofinvestigationswithsigniﬁcantlydiﬀerentresults[7,8].However,theinvestigationsbyBenvenutoandLugonesgivesimilarresultstothoseinthebagmodel[9].AmorerecentinvestigationindicatesalinkofSQMtothestudyofquarkcondensates[10].ThemostimportantwayoftheterritorialsearchesforSQMisinthealtra-relativisticheavyioncollisions[11].OfvitalimportancetotheexperimentalsearchesistheelectricchargeofSQM.Previously,itisgenerallybe-lievedthatSQMisslightlypositivelycharged[4].Con-trarytopreviousﬁndings,arecentinvestigationshowsthatmetastablestrangeletsaremostlikelyhighlynega-tivelycharged[12].Thissigniﬁcantresultmay,ifreallythecase,haveaseriousimpactonthehighsensitivitysearchesinheavyionexperimentsattheAGSandCERNfacilities.Ourpresentstudy,inaverysimplemanner,in-dicatesthatpropernegativechargescanindeedlowerthecriticaldensityunderwhichSQMcannotmaintainitsﬂavorequilibrium,andthusnolongerexist.FollowingRef.[4],WeassumetheSQMtobeaFermigasmixtureofu,d,squarksandelectronswithchemicalequilibriummaintainedbytheweakinteractions:d,s↔u+e+

48π2󰀁µi(2µ2i−5m2i)󰀌

µ2i−m2i

∂µi

=gi

3(nu+nd+ns)=nb,(5)23nd−1

3(µ2e−m2e)3/2−π2(2nb−Q),(10)whereµ=µe+󰀎3(µ2e−m2e)3/2]2/3.(11)

1Becausems>mu,d,theequationF(µe)=0forµehassolutionifandonlyif

µ≥ms,(12)F(µe)≤0.(13)

Atthecriticaldensityncofbaryonnumber,theequal-itysignsintheabovetwoinequalitiesshouldbetaken.Sowecaneasilyﬁndtheequation

󰀂ms−󰀎

π2(m2s−m2d)3/2−1

m2u+󰀁3π2nc−(m2s−m2d)3/2󰀄2/3.(16)Inordertomaketheinversesquarerootmeaningful,wemustrequire

󰀈m2s−m2d󰀉3/2≤3π2nc.(17)

Whentakingtheequalitysign,andthensolvingthecorrespondingequation,weobtaintheminimumcriticaldensityncmin.SubstitutingintoEq.(15)gives

Qmin=−ncmin−1

󰀍q󰀋nb|¯qq|nb󰀊(22)

≡mq0+mI.(23)ThephysicalmeaningofEq.(23)isclear:theﬁrsttermontherightistheoriginalmass,i.e.,thequarkcurrentmass,whilethesecondtermmIistheinter-actingpartmimickingthestronginteractionbetweenquarks.Obviously,mIisﬂavor-independentanddensity-dependent.Becausethecharacteristicofstronginter-actionsistheconﬁnementofquarks,weshouldrequirelimnb→0mI=∞.Apopularlyusedparametrizationformis[7–9]

mq=mq0+Bconcludethatpropernegativechargescanlowerthecrit-icaldensity,andthusbefavorabletotheexperimentalsearches.Toexploreiftheaboveconclusiondependsonmassformulasused,wenowadoptthefollowingexpression:

mq=mq0+D

[1]G.X.Peng,P.Z.Ning,andS.J.Luo,CCAST-WLWork-shopSeries,57,1(1996).[2]A.R.Bodmer,Phys.Rev.D4,1601(1971);S.A.ChinandA.K.Kerman,Phys.Rev.Lett.43,1292(1979).[3]E.Witten,Phys.Rev.D30,272(1984).[4]E.FarhiandRL.Jaﬀe,Phys.Rev.D30,2379(1984);M.S.BergerandR.L.Jaﬀe,Phys.Rev.C35,213(1987);E.P.GilsonandR.L.Jaﬀe,Phys.Rev.Lett.71,332(1993).[5]JesMadsen,Phys.Rev.Lett.61,2909(1993);Phys.Rev.D47,5156(1993);50,3328(1994);JesMadsen,DanM.Jensen,andMichaelB.Christiansen,Phys.Rev.C53,1883(1996).[6]B.C.Parija,1993,Phys.Rev.C48,2483(1993);51,1473(1995).[7]S.Chakrabarty,S.Raha,andB.Sinha,Phys.Lett.B229,112(1989).[8]S.Chakrabaty,Phys.Rev.D43,627(1991);48,1409(1993);54,1306(1996).[9]O.G.BenvenutoandG.Lugones,Phys.Rev.D51,1989(1995);G.LugonesandO.G.Benvenuto,ibid.52,1276(1995).[10]G.X.Peng,P.Z.Ning,andH.C.Chiang,Phys.Rev.C56,491(1997).[11]C.Greiner,P.Kock,andH.St¨ocker,Phys.Rev.Lett.58,1825(1987);C.Greiner,D.H.Rischke,H.St¨ocker,andP.Koch,Phys.Rev.D38,2797(1988).C.Greiner,P.Koch,andH.St¨ocker,ibid.44,3517(1991).[12]J¨urgenSchaﬀner-Bielich,CarstenGreiner,AlexanderDi-ener,andHorstSt¨ocker,Phys.Rev.D55,3038(1997).