Measurement of inclusive $D_s$, $D^0$, and $Jpsi$ rates and determination of the $B_s^{()}
a r X i v :h e p -e x /0608015v 4 17 J a n 2007
Measurement of inclusive D s ,D 0,and J/ψrates and determination of the B (?)s ˉB (?)
s
production fraction in b ˉb events at the Υ(5S)resonance
A.Drutskoy,4K.Abe,8K.Abe,46I.Adachi,8H.Aihara,48D.Anipko,1K.Arinstein,1V.Aulchenko,1
T.Aushev,19,14S.Banerjee,44E.Barberio,22M.Barbero,7I.Bedny,1K.Belous,13U.Bitenc,https://www.360docs.net/doc/2116432109.html,jak,15S.Blyth,25A.Bondar,1A.Bozek,28M.Braˇc ko,8,21,15J.Brodzicka,28T.E.Browder,7P.Chang,27Y.Chao,27A.Chen,25K.-F.Chen,27W.T.Chen,25B.G.Cheon,3R.Chistov,14Y.Choi,42Y.K.Choi,42A.Chuvikov,36
S.Cole,43J.Dalseno,22M.Danilov,14M.Dash,52J.Dragic,8S.Eidelman,1D.Epifanov,1S.Fratina,15
N.Gabyshev,1T.Gershon,8A.Go,25G.Gokhroo,44P.Goldenzweig,4B.Golob,20,15H.Ha,17J.Haba,8T.Hara,33
K.Hayasaka,23H.Hayashii,24M.Hazumi,8D.He?ernan,33T.Higuchi,8Y.Hoshi,46S.Hou,25W.-S.Hou,27Y.B.Hsiung,27T.Iijima,23A.Imoto,24K.Inami,23A.Ishikawa,48R.Itoh,8M.Iwasaki,48Y.Iwasaki,8J.H.Kang,53N.Katayama,8H.Kawai,2T.Kawasaki,30H.R.Khan,49H.Kichimi,8S.K.Kim,40Y.J.Kim,6K.Kinoshita,4S.Korpar,21,15P.Kriˇz an,20,15P.Krokovny,8R.Kulasiri,4R.Kumar,34C.C.Kuo,25A.Kuzmin,1Y.-J.Kwon,https://www.360docs.net/doc/2116432109.html,nge,5G.Leder,12J.Lee,40M.J.Lee,40T.Lesiak,28J.Li,7A.Limosani,8S.-W.Lin,27D.Liventsev,14J.MacNaughton,12G.Majumder,44F.Mandl,12T.Matsumoto,50A.Matyja,28S.McOnie,43W.Mitaro?,12K.Miyabayashi,24H.Miyake,33H.Miyata,30Y.Miyazaki,23R.Mizuk,14G.R.Moloney,22T.Nagamine,47Y.Nagasaka,9E.Nakano,32M.Nakao,8Z.Natkaniec,28S.Nishida,8O.Nitoh,51T.Nozaki,8S.Ogawa,45T.Ohshima,23S.Okuno,16S.L.Olsen,7Y.Onuki,37P.Pakhlov,14G.Pakhlova,14H.Park,18K.S.Park,42R.Pestotnik,15L.E.Piilonen,52A.Poluektov,1Y.Sakai,8N.Satoyama,41T.Schietinger,19O.Schneider,19C.Schwanda,12A.J.Schwartz,4R.Seidl,10,37K.Senyo,23M.E.Sevior,22M.Shapkin,13H.Shibuya,45B.Shwartz,1V.Sidorov,1J.B.Singh,34A.Sokolov,13A.Somov,4S.Staniˇc ,31M.Stariˇc ,15H.Stoeck,43K.Sumisawa,8T.Sumiyoshi,50S.Suzuki,38S.Y.Suzuki,8F.Takasaki,8K.Tamai,8N.Tamura,30
M.Tanaka,8G.N.Taylor,22Y.Teramoto,32X.C.Tian,35K.Trabelsi,7T.Tsukamoto,8S.Uehara,8T.Uglov,14K.Ueno,27Y.Unno,3S.Uno,8P.Urquijo,https://www.360docs.net/doc/2116432109.html,ov,1G.Varner,7S.Villa,19C.C.Wang,27C.H.Wang,26Y.Watanabe,49J.Wiechczynski,28E.Won,17Q.L.Xie,11B.D.Yabsley,43A.Yamaguchi,47Y.Yamashita,29M.Yamauchi,8Y.Yusa,52L.M.Zhang,39Z.P.Zhang,39V.Zhilich,1and A.Zupanc 15
(The Belle Collaboration)
1
Budker Institute of Nuclear Physics,Novosibirsk
2
Chiba University,Chiba
3
Chonnam National University,Kwangju 4
University of Cincinnati,Cincinnati,Ohio 45221
5
University of Frankfurt,Frankfurt
6
The Graduate University for Advanced Studies,Hayama
7
University of Hawaii,Honolulu,Hawaii 96822
8
High Energy Accelerator Research Organization (KEK),Tsukuba
9
Hiroshima Institute of Technology,Hiroshima
10
University of Illinois at Urbana-Champaign,Urbana,Illinois 6180111
Institute of High Energy Physics,Chinese Academy of Sciences,Beijing
12
Institute of High Energy Physics,Vienna 13
Institute of High Energy Physics,Protvino
14
Institute for Theoretical and Experimental Physics,Moscow
15
J.Stefan Institute,Ljubljana 16
Kanagawa University,Yokohama 17
Korea University,Seoul
18
Kyungpook National University,Taegu
19
Swiss Federal Institute of Technology of Lausanne,EPFL,Lausanne
20
University of Ljubljana,Ljubljana 21
University of Maribor,Maribor 22
University of Melbourne,Victoria 23
Nagoya University,Nagoya 24
Nara Women’s University,Nara 25
National Central University,Chung-li 26
National United University,Miao Li
2 27Department of Physics,National Taiwan University,Taipei
28H.Niewodniczanski Institute of Nuclear Physics,Krakow
29Nippon Dental University,Niigata
30Niigata University,Niigata
31University of Nova Gorica,Nova Gorica
32Osaka City University,Osaka
33Osaka University,Osaka
34Panjab University,Chandigarh
35Peking University,Beijing
36Princeton University,Princeton,New Jersey08544
37RIKEN BNL Research Center,Upton,New York11973
38Saga University,Saga
39University of Science and Technology of China,Hefei
40Seoul National University,Seoul
41Shinshu University,Nagano
42Sungkyunkwan University,Suwon
43University of Sydney,Sydney,New South Wales
44Tata Institute of Fundamental Research,Bombay
45Toho University,Funabashi
46Tohoku Gakuin University,Tagajo
47Tohoku University,Sendai
48Department of Physics,University of Tokyo,Tokyo
49Tokyo Institute of Technology,Tokyo
50Tokyo Metropolitan University,Tokyo
51Tokyo University of Agriculture and Technology,Tokyo
52Virginia Polytechnic Institute and State University,Blacksburg,Virginia24061
53Yonsei University,Seoul
(Dated:February7,2008)
The inclusive production of D s,D0,and J/ψmesons is studied using a1.86fb?1data sample col-
lected on theΥ(5S)resonance with the Belle detector at the KEKB asymmetric energy e+e?collider.
The number of bˉb events in thisΥ(5S)data sample is determined.We measure the branching frac-
tions B(Υ(5S)→D s X)/2=(23.6±1.2±3.6)%,B(Υ(5S)→D0X)/2=(53.8±2.0±3.4)%,and
B(Υ(5S)→J/ψX)/2=(1.030±0.080±0.067)%.From the D s and D0inclusive branching frac-
tions the ratio f s=(18.0±1.3±3.2)%of B(?)
s ˉB(?)
s to the total b
ˉb quark pair production at the
Υ(5S)energy is obtained in a model-dependent way. PACS numbers:13.25.Gv,13.25.Hw,14.40.Gx,14.40.Nd
The possibility of studying B s decays at very high luminosity e+e?colliders running at the energy of the Υ(5S)resonance has been discussed in several theoret-ical papers[1,2,3].Studies of the B s meson proper-ties at theΥ(5S),both alone and in comparison with those of its lighter cousins B0and B+,may provide im-portant insights into the Cabibbo-Kobayashi-Maskawa matrix and hadronic structure,as well as sensitivity to new physics phenomena[4].To date,most studies of B s have been performed at hadron colliders,where high production rates are tempered by limited triggering and detection capabilities.As B factories have amply demonstrated for the B0and B+,the kinematic cleanli-ness of resonant near-threshold exclusive pair production (e+e?→Υ(4S)→BˉB),combined with a high trigger-ing e?ciency and the ability to measure neutral particles, can open up a complementary realm of sensitivity to new phenomena.TheΥ(5S)could play a similar role for B s that theΥ(4S)has played for B.
To test the experimental feasibility of B s studies in Υ(5S)events,a sample of1.86fb?1was collected with the Belle detector over3days in June2005.Earlier anΥ(5S) data sample of～0.1fb?1was taken at CESR[5,6,7] and,more recently,a dataset of0.42fb?1was collected by CLEO[8,9].We report here the?rst results obtained by Belle,a determination of the number of bˉb events in theΥ(5S)data sample,a measurement of the inclusive rate ofΥ(5S)events to D s,D0,and J/ψand derivation of the fraction of bˉb events containing B s.
The Belle detector[10]has operated since1999at KEKB[11],an asymmetric-energy double storage ring designed to collide8GeV electrons and3.5GeV positrons and produceΥ(4S)mesons with a boost ofβγ=0.425. The recent data sample of1.86fb?1was taken at the Υ(5S)energy of～10869MeV,under exactly the same experimental conditions as inΥ(4S)and continuum runs, except that both beam energies were increased by～2.7%, keeping the center-of-mass(CM)boost unchanged.An-other data sample of3.67fb?1collected at a CM energy 60MeV below theΥ(4S)just before theΥ(5S)data tak-ing is used in this analysis to evaluate continuum contri-butions.
3
Only clean decay modes D+s→φπ+(φ→K+K?), D0→K?π+and J/ψ→μ+μ?are reconstructed. Charge-conjugate modes are implicitly included every-where in this Letter.The standard track
reconstruction and particle identi?cation procedures are used[10].The invariant mass ofφ→K+K?candidates is required to be within±12MeV/c2of the nominalφmass.For the D+s→φπ+decay mode,the helicity angle distribution
is expected to be proportional to cos2θD s
hel ;therefore,the
requirement|cosθD s
hel |>0.25is applied.The helicity an-
gleθD s
hel is de?ned as the angle between the directions of
the K+and D+s momenta in theφrest frame.
In the energy region of theΥ(5S),hadronic events can be classi?ed into three physics categories:uˉu,dˉd,sˉs,cˉc continuum events,bˉb continuum events,andΥ(5S) events.The bˉb continuum and theΥ(5S)events always produce?nal states with a pair of B or B s mesons and, therefore,cannot be topologically separated.We de-?ne the bˉb continuum andΥ(5S)events collectively as bˉb events,everywhere in this analysis.All bˉb events are expected to hadronize in one of the following?nal states: BˉB,BˉB?,B?ˉB,B?ˉB?,BˉBπ,BˉB?π,B?ˉBπ,B?ˉB?π, BˉBππ,B0sˉB0s,B0sˉB?s,B?sˉB0s or B?sˉB?s.Here B denotes a B0or a B+meson andˉB denotes aˉB0or a B?me-son.The excited states decay to their ground states via B?→Bγand B?s→B0sγ[12].
An energy scan was performed just before theΥ(5S) data taking to?nd the peak position of theΥ(5S)res-onance.An integrated luminosity of～30pb?1was collected at?ve values of e+e?CM energy between 10825MeV and10905MeV at intervals of20MeV.The ratio of the number of hadronic events with R2>0.2to the number of Bhabha events is measured as a function of the CM energy(Fig.1).Here,R2is the normalized second Fox-Wolfram moment[13].This ratio is expected to have a Breit-Wigner function shape corresponding to theΥ(5S)resonance,above a?at background.Fixing the width value to the PDG valueΓ=110MeV/c2 [12],the mean mass value is found from the?t to be M=(10868±6±14)MeV/c2,where the?rst error is sta-tistical and the second error is a systematic uncertainty, dominated by the variation of background contributions with CM energy.This value is in good agreement with the PDG value MΥ(5S)=(10865±8)MeV/c2[12].The ?t value obtained above is treated only as a systematic check rather than as a measurement,as the energy range scanned is small compared to theΥ(5S)width,and un-certainties due to background contributions are not well known.Finally,the energy of10869MeV was set for subsequentΥ(5S)runs.
The uˉu,dˉd,sˉs,cˉc continuum subtraction method is ap-plied to obtain the number of bˉb events in theΥ(5S)data sample:
N bˉb5S=1
L cont
·
E2cont
?con
cont
.(1)
E
CM
(GeV)
N
(
H
a
d
r
o
n
,
R
2
<
.
2
)
/
N
(
B
h
a
b
h
a
)
FIG.1:The ratio of the number of hadronic events with
R2>0.2to the number of Bhabha events,as a function of
the e+e?CM energy.Only statistical errors are shown.The
curve is the result of the?t described in the text.
Here N bˉb5S is the number of bˉb events in theΥ(5S)data
sample,and N had
5S
and N had
cont
are the numbers of hadronic
events in theΥ(5S)and continuum data samples,re-
spectively.A few percent contribution ofτ+τ?,QED,
γγand beam-gas events partially cancels in Eq.(1),
and the corresponding small systematic uncertainty is
included in the full systematic uncertainty.The e?-
ciency to select a bˉb event in theΥ(5S)data sample,
?bˉb5S=(99±1)%,and the e?ciency ratio for contin-
uum events in theΥ(5S)and continuum data samples,
?con
5S
/?con
cont
=1.007±0.003,are obtained from Monte Carlo
(MC)simulation.The hadronic cross section varies with
the CM energy as1/E2and a corresponding correction is
applied.The CM energies for theΥ(5S)and continuum
data sets are E5S=10869MeV and E cont=10520MeV,
respectively,with a～5MeV accuracy of the collider ab-
solute CM energy calibration.The integrated luminosity
ratio L5S/L cont=0.5061±0.0020is calculated using the
standard Belle luminosity measurement procedure with
Bhabha events.The small statistical uncertainty on this
ratio can be neglected.
The value of and uncertainty on the luminosity ratio
is further checked using high-momentum charged tracks,
K0S mesons,and D0mesons.To compareΥ(5S)and
continuum production,normalized momentum distribu-
tions are used.The normalized momentum of a particle
h is de?ned as x(h)=P(h)/P max(h),where P(h)is the
measured momentum of that particle,and P max(h)is the
expected value of its momentum if it were produced in
the process e+e?→hˉh at the same CM energy.Fitting a
constant to the distributions of theΥ(5S)and continuum
dataset ratios x(h)5S/x(h)cont for0.5 applying small corrections due to the di?erence between theΥ(5S)and continuum?nal state particle multiplici- ties,which were obtained from MC simulation,the ratios 0.471±0.005,0.471±0.005,and0.477±0.005are de- termined for h=π+,K0S,and D0,respectively.These values agree with the energy-corrected luminosity ratio of0.4740±0.0019obtained from Bhabha event measure- ments,where the factor E2cont/E25S was applied to correct for the hadronic cross-section energy dependence. 4 From Eq.(1)we obtain the number of bˉb events in the Υ(5S)data sample,N bˉb5S=(5.61±0.03stat±0.29syst)×105. The total systematic uncertainty of～5%includes all sys-tematic errors on parameters used in Eq.(1).Finally,the bˉb production cross-section at theΥ(5S)is measured to be(0.302±0.015)nb,in good agreement with the CLEO value of(0.310±0.052)nb[8]. The method for inclusive D s(D s≡D±s)analysis of Υ(5S)data developed in Ref.[8]is applied here.The D s signals(D+s→φπ+,φ→K+K?)in theΥ(5S)and continuum data samples are shown in Fig.2(a)for the normalized D s momentum region x(D s)<0.5,where a bˉb contribution is expected.Here and throughout this Letter,the continuum distributions are normalized to the Υ(5S)distributions using the energy-corrected luminos-ity ratio.To extract the number of D s mesons,the D s mass distribution is?tted by a Gaussian to describe the signal and a linear function to describe the background. The Gaussian width is?xed to the value obtained from MC simulation;the Gaussian mean value and normal-ization,and the background parameters are allowed to ?oat.The same mass?t procedure,but with the Gaus-sian mean value?xed to that obtained from the?t of the D s signal in the x(D s)<0.5range,is repeated in each bin of x(D s)in order to obtain the D s yield as a func-tion of the normalized momentum,x(D s).The x(D0) and x(J/ψ)distributions discussed below are obtained using the same?t procedures. The normalized momentum x(D s)distributions are shown in Fig.2(b)for theΥ(5S)and continuum data samples.These two distributions agree well in the region x(D s)>0.5,where bˉb events cannot contribute.The ex-cess of events in the region x(D s)<0.5corresponds to inclusive D s production in bˉb events. The fully corrected x(D s)distribution for bˉb events is obtained,subtracting the continuum contribution and applying a bin-by-bin e?ciency correction,obtained from the MC simulation.Summing over all bins within the interval x(D s)<0.5and dividing by the D+s andφdecay branching fractions and by the number of bˉb events in theΥ(5S)data sample,the inclusive branching fraction B(Υ(5S)→D s X)/2=(23.6±1.2±3.6)%is obtained. In the calculations the PDG value B(D+s→φπ+)= (4.4±0.6)%[12]is used.TheΥ(5S)inclusive branching fraction is multiplied by a factor of1/2to compare with B(s)branching fractions.As explained above,continuum bˉb production cannot be separated fromΥ(5S)events and therefore continuum bˉb production is included in the Υ(5S)→D s X branching fraction.The latter is therefore de?ned as the average number of D s mesons produced in bˉb events at theΥ(5S)energy. The dominant contributions to the systematic uncer-tainty on the branching fraction measurement are the uncertainties due to the B(D+s→φπ+)measurement of 14%,to the number of bˉb events of5%,to the track re-construction e?ciency and particle identi?cation of4%, M(φπ+) (GeV/c2) E v e n t s / 5 M e V 2 x(D s ) E v e n t s / . 5 FIG.2:The D s signal in the region x(D s)<0.5(a)and the D s normalized momentum x(D s)(b).The points with error bars are theΥ(5S)data,while the histograms show the normalized continuum(here and in Figs.3and4). and to the?t procedure of2%. The obtained inclusive branching fraction agrees well with the branching fraction B(Υ(5S)→D s X)/2= (22.4±2.1±5.0)%obtained by CLEO[8].The value of B(Υ(5S)→D s X)/2is signi?cantly larger than the branching fraction B(B→D s X)=(8.7±1.2)%,which we calculate by combining the PDG average[12]with the recent CLEO result[8]adjusted to the value B(D+s→φπ+)=(4.4±0.6)%.The signi?cant increase of D s pro-duction at theΥ(5S)as compared to that at theΥ(4S) indicates a sizable B s production rate. The fraction f s of B(?)sˉB(?)s events among all bˉb events at theΥ(5S)satis?es the following relation: B(Υ(5S)→D s X)/2=f s·B(B s→D s X)+ (1?f s)·B(B→D s X),(2) where B(B s→D s X)and B(B→D s X)are the average number of D s mesons produced in B s and B decays,https://www.360docs.net/doc/2116432109.html,ing our measurement of B(Υ(5S)→D s X), the measured value of B(B→D s X)=(8.7±1.2)% [8,12],and the model-dependent estimate B(B s→ D s X)=(92±11)%[8],we determine f s=(17.9±1.4± 4.1)%.The systematic uncertainty on f s is obtained by propagating the systematic uncertainties on the branch-ing fractions included in Eq.(2),taking into account the correlation induced by B(D+s→φπ+). The inclusive production of D0mesons(including both D0andˉD0)at theΥ(5S)is studied applying a proce-dure similar to that used for the D s case.As shown in Fig.3(a),large D0signals(D0→K?π+)are seen in theΥ(5S)and continuum data samples.The number of D0mesons as a function of x(D0)is shown in Fig.3(b) for both samples.These two distributions agree well in the region x(D0)>0.5. After continuum subtraction and e?ciency correction, the inclusive branching fraction B(Υ(5S)→D0X)/2= (53.8±2.0±3.4)%is determined.This branching fraction is de?ned as the average number of D0andˉD0mesons produced per bˉb event.The dominant sources of system-atic uncertainties are similar to the D s analysis,except 5 M(K -π+ ) (GeV/c 2 ) E v e n t s / 5 M e V /c 2 x(D 0 ) E v e n t s / 0.05 FIG.3:The D 0signal in the region x (D 0)<0.5(a)and the D 0normalized momentum x (D 0)(b). that the PDG value B (D 0→K ?π+)=(3.80±0.07)% has much better accuracy than B (D + s →φπ+). The value obtained for B (Υ(5S)→D 0X )/2is lower than the PDG value B (B →D 0X )=(64.0±3.0)%[12],as expected,if there is sizable B s production at the Υ(5S).The rate of D 0production in B s decays can be estimated in a way similar to that described in Ref.[8].Assuming that D 0mesons are dominantly produced from conventional b →c processes through a fragmentation mechanism with additional u ˉu quark pair creation,the branching fraction is expected to be B (B s →D 0X )=(8±7)%.Using the inclusive D 0production branching fraction of the Υ(5S),B ,and B s decays and replacing D s by D 0in Eq.(2),the ratio f s =(18.1±3.6±7.5)%of B (?)s ˉB (?) s events to all b ˉb events at the Υ(5S)is obtained.The systematic er-ror is dominated by the systematic uncertainties from B (Υ(5S)→D 0X )/2and B (B →D 0X )and is slightly a?ected by the uncertainty on the model-dependent as-sumption for the B (B s →D 0X )value.Although the D s inclusive analysis provides better accuracy on f s ,the D 0inclusive analysis is an independent method,where the uncertainty due to the D 0decay branching fraction is small and the uncertainty on the number of b ˉb events dominates.Moreover,the correlation between f s and the number of b ˉb events is positive in the D 0analysis and is negative in the D s analysis. Using the f s value obtained in the D 0inclusive anal-ysis,the inclusive branching fraction B (B s →D s X )can be extracted from Eq.(2).Using the results of the present analysis,and taking into account the correla-tion between our measurements of B (Υ(5S)→D s X )and B (Υ(5S)→D 0X ),we obtain B (B s →D s X )=(91±18±41)%,in agreement with expectations within large errors. The inclusive production of J/ψmesons is studied in the decay mode J/ψ→μ+μ?.As shown in Fig.4(a),the Υ(5S)data sample contains a prominent J/ψsig-nal,whereas the J/ψsignal in continuum is small.The x (J/ψ)distributions are shown in Fig.4(b)for the Υ(5S)and continuum data samples.As expected,J/ψproduc-tion in the continuum region x (J/ψ)>0.5is smaller M(μ+μ-) (GeV/c 2 ) E v e n t s / 10 M e V /c 2 x(J/ψ) E v e n t s / 0.1 FIG.4:The J/ψsignal in the region x (J/ψ)<0.5(a)and the J/ψnormalized momentum x (J/ψ)(b). than in the low x (J/ψ)region where B and B s mesons can contribute. The di?erence of these distributions in the region x (J/ψ)<0.5is corrected for e?ciency to obtain the inclusive J/ψspectrum in b ˉb https://www.360docs.net/doc/2116432109.html,ing the PDG value B (J/ψ→μ+μ? )=(5.88±0.10)%[12],the inclu-sive branching fraction B (Υ(5S)→J/ψX )/2=(1.030±0.080±0.067)%is obtained.Systematic uncertainties are similar to those in the D s analysis and are domi-nated by the uncertainty on the number of b ˉb events.The Υ(5S)branching fraction can be compared with B (B →J/ψX )=(1.094±0.032)%[12],because the inclusive J/ψproduction rates in B and B s decays are expected to be approximately equal.Conversely,assum-ing the equality of inclusive J/ψbranching fractions in B and B s decays,we can obtain the number of b ˉb events.This cross-check can be important for future large statis-tics Υ(5S)measurements. In conlusion,the inclusive production of D s ,D 0,and J/ψmesons has been studied in e +e ?colli-sions at the Υ(5S)energy.The precise measure-ment of B (Υ(5S)→D s X )and the ?rst measurement of B (Υ(5S)→D 0X )and B (Υ(5S)→J/ψX )branching fractions are performed.Clear evidence of sizable B s production is observed.The fraction of B (?)s ˉB (?) s events among all b ˉb events produced at the Υ(5S)energy is de-termined from the inclusive D s and D 0analyses to be f s =(17.9±1.4±4.1)%and f s =(18.1±3.6±7.5)%,https://www.360docs.net/doc/2116432109.html,bining these two f s measurements and taking into account the anticorrelated systematic un-certainty due to the number of b ˉb events,the value f s =(18.0±1.3±3.2)%is obtained.This measurement agrees with the CLEO value of f s =(16.0±2.6±5.8)%[8],but has a total relative uncertainty that is a factor of two smaller.The B s production rate over all b ˉb events at the Υ(5S)is somewhat larger than the fraction of B s mesons produced from the ˉb quark in Z →b ˉb decays at LEP,B (ˉb →B s )=(10.2±0.9)%[12].The large f s value measured here indicates very good potential for future B s studies at high luminosity asymmetric-energy B factories running at the Υ(5S)resonance. 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