1. Guoliang TONGTau04,Nara,Septemper 16,20041 Searching for Lepton Flavor Violation Decays J/   e μ, μ τ, e τ at BES Guoliang Tong ( BES Collaboration) IHEP CAS, Beijing China E-mail: tonggl@mail.ihep.ac.cn 8th International Workshop on Tau Lepton Physics Nara, September 14 – 17, 2004

2. Guoliang TONGTau04,Nara,Septemper 16,20042 Outline 1.Introduction 2.Search for LFV in J/   e μ 3.Search for LFV in J/   μ τ, e τ 4.Summary

3. Guoliang TONGTau04,Nara,Septemper 16,20043 1.Introduction -In the SM of electroweak theory, the lepton flavor symmetries are conserved -In many extensions of the SM, such as SUSY,GUT, left-right symmetric models,lepton flavor symmetries speculated to be violated -Some theorists predicted LFV decay branching-ratio of vector bosons( ,J/ , , Z 0 ) in recent years -Super-Kamiokande and Kamland, SNO experimental results indicate strongly m  0, and mix with each others

4. Guoliang TONGTau04,Nara,Septemper 16,20044 Experimental status - Experimentally, no evidence for direct LFV has been reported so far. -Many research for LFV have been done in μ and τ decays. - Direct searches at the Z peak performed by the LEP experiments yielded 95% C.L. upper limits BR(Z  e μ, e τ,μ τ) <1.7x10 -6, 9.8x10 -6 and 1.2x10 -5 respectively. - J/Ψ  e μ’s search was reported by BES with 58M J/  sample and U.L. BR(J/Ψ  e μ )<1.1x10 -6 reached (@ 90%C.L.)(PLB 561(2003)49-54)

5. Guoliang TONGTau04,Nara,Septemper 16,20045 Theoretical limits and predictions for LFVD on BR BosonMode Theoretical limits (Peccei, Nussinov and Zhang; PRD63,016003,(2001)) Theoretical Predictions (Leptoquark model, SUSY model, Huo, Feng, Yue; PRD67,114001,(2003)) J/Ψ(1S) μ τ e τ e μ < 6x10 -7 <4x10 -13 3.0x10 -8 3.5x10 -15 Υ(1S) μ τ e τ e μ < 10 -2 <2x10 -9 1.3x10 -7 4.1x10 -12

6. Guoliang TONGTau04,Nara,Septemper 16,20046 The Beijing Electron Positron Collider L ~ 5  10 30 /cm 2  s at J/  peak E cm ~2-5 GeV

7. Guoliang TONGTau04,Nara,Septemper 16,20047 BEPC consists of Linac 、 Storage Ring 、 Detector(BES ） and Synchrotron Facility(BSRF). Ground breaking in 1984 ， completed in 1988 within budget and according to the schedule. Soon after reached the designed performances.

8. Guoliang TONGTau04,Nara,Septemper 16,20048 BESII Detector VC:  xy = 100  m TOF:  T = 180 ps  counter:  r  = 3 cm MDC:  xy = 220  m BSC:  E/  E= 22 %  z = 5.5 cm  dE/dx = 8.5 %   = 7.9 mr B field: 0.4 T  p/p=1.7%  (1+p 2 )  z = 2.3 cm

9. Guoliang TONGTau04,Nara,Septemper 16,20049 Korea (4) Korea University Seoul National University Chonbuk National University Gyeongsang Nat. Univ. Japan (5) Nikow University Tokyo Institute of Technology Miyazaki University KEK U. Tokyo USA (4) University of Hawaii University of Texas at Dallas Colorado State University Stanford Linear Accelerator Center UK (1) Queen Mary University China (18) IHEP of CAS Univ. of Sci. and Tech. of China Shandong Univ., Zhejiang Univ. Huazhong Normal Univ. Shanghai Jiaotong Univ. Peking Univ., CCAST Wuhan Univ., Nankai Univ. Henan Normal Univ. Hunan Univ., Liaoning Univ. Tsinghua Univ., Sichuan Univ. Guangxi Univ., Guangxi Normal Univ. Jiangsu Normal Univ.

10. Guoliang TONGTau04,Nara,Septemper 16,200410 3.0M 14M J/  (2S) World J/  and  (2S) Samples (×10 6 ) BESII 14M  (2S) BESII 58M J/  (99.11-01.03) (01.11-02.03)

11. Guoliang TONGTau04,Nara,Septemper 16,200411 Event selection For charged tracks: mfit=2 or – 19 |cos  | < 0.8 θ 12 >178.5 ° the angle between two charged tracks θ 12 2. Search for J/   e μ

12. Guoliang TONGTau04,Nara,Septemper 16,200412 The invariant mass of two charged tracks The momentum of charge tracks, 1.45<P<1.65GeV/c the invariant mass of electron and μ and the momenta of electron and μ ( MC) J/   e  (con’t)

13. Guoliang TONGTau04,Nara,Septemper 16,200413 Cuts for isolated photon are we need no isolated photon. E/P of electron and μ (data) particle identification - identify e: E/P>0.7, μ hit =0 - identify μ: E/P<0.3, μ hit pass P xy cuts, P xy -transverse momentum. J/   e  (con’t) BES  counter: Iron a bsorber -1 st layer: 120 mm (67%, solid angle) -2 nd layer: 140 mm (67%) -3 rd layer: 140 mm (63%)

14. Guoliang TONGTau04,Nara,Septemper 16,200414 J/   e  (con’t) E/P of electron and μ (data) With data sample.

15. Guoliang TONGTau04,Nara,Septemper 16,200415 J/   e  (con’t)

16. Guoliang TONGTau04,Nara,Septemper 16,200416 Survivals events cutsSurvivals events N chrg = 238045098 Vertical cuts and M_fit=2 or - 19 16119944  Q i = 0 15878836 1.45 < P <1.65GeV/c4114702 |cos  | < 0.8 3963145  12 > 178.5 0 1947195 Reject cosmic ray1843853 N iso = 01799597 One of two track is identified as  152820 The other is identified as e4 2.95 < M e  < 3.25GeV/c 2 4 J/   e  (con’t)

17. Guoliang TONGTau04,Nara,Septemper 16,200417 Result The upper limit of BR(J/  e  ) with 58 M J/Ψ sample at BES could be got: Background, candidates and Upper limit 1.49 0.79 Total number of backgrounds 2.2 4 The upper limit (conservatively calculated with 0 background) 1.1  10 -6 (90% C.L) J/   e  (con’t) PLB 561(2003)49-54 Br < (N OB )/[N T  J/  e  ]

18. Guoliang TONGTau04,Nara,Septemper 16,200418 Events selection 2 good charged tracks Q(sum) = 0 |cos  | < 0.8 1.0<P  (e)  GeV/c Pe(  )<1.4GeV/c E/P>0.7 for electron E bsc <0.3 for μ Muon hit =3 for μ Muon hit =0 for electron 3. J/   μ τ, e τ (a) (b)

19. Guoliang TONGTau04,Nara,Septemper 16,200419 J/    e  (con’t) Detector efficiency μ ID efficiency in μ counter is determined from real μ data. Others are from MC simulation. Eff total = eff MC *eff μ ID. eff μ ID=  i  i here,  i is the weight of events,  i is the ith efficiency from μ real data sample. Systematic error Systematic error is incorporated when calculating upper limit: U n =U n0 (1+E n  2 ) where E n= Un0-1

20. Guoliang TONGTau04,Nara,Septemper 16,200420 J/    e  (con’t) J/    candidateJ/   e  candidate 2 σ regions from MC  Background event is 0 for J/  to .  Background event is 0.4 for J/  to e . which is from J/  to K*K.

21. Guoliang TONGTau04,Nara,Septemper 16,200421 J/    e  (con’t) J/    J/   e 

22. Guoliang TONGTau04,Nara,Septemper 16,200422 Upper Limits (@ 90% C.L.) J/    e  (con’t) Paper has been accepted by PLB(hep-ex/0406018) ()() PLB 598(2004)172-177

23. Guoliang TONGTau04,Nara,Septemper 16,200423 The results of three decay modes: Decay modeN signal N background Upper limit (@90%C.L.) J/ Ψ → e  42 1.1  10 -6 J/ Ψ →  00 2.0  10 -6 J/ Ψ → e  10 8.3  10 -6 J/   e μ, μ τ, e τ

24. Guoliang TONGTau04,Nara,Septemper 16,200424 4.Summary No evidence for direct LFV has been found in these searches. These searches reached new upper limits for LFV processes Br(J/Ψ→e  ) < 1.1  10 -6 ; Br(J/Ψ→  ) < 2.0  10 -6 ; Br(J/Ψ→e  ) < 8.3  10 -6 (@ 90%C.L.) Prospect BEPCII/BESIII Project is making good progress Nov. 2006: commissioning detector/machine

25. Guoliang TONGTau04,Nara,Septemper 16,200425 BEPCII/BESIII Project Two rings

26. Guoliang TONGTau04,Nara,Septemper 16,200426 工 工 BESIII Detector systemBES III  XY = 130  m MDT(Drift Chamber)  P/P = 0.5 %(1 GeV)  dE/dx = 6-7 % EMC(CsI Crystal)  E/√E = 2.5 %(1 GeV)  z,  = 5-6mm (1 GeV) TOF  T = 90-100 ps Barrel 110 ps endcap  counter(RPC) 9- 8 layers Magnet(S.C.) 1.0 tesla BESIII Main Parameters

27. Guoliang TONGTau04,Nara,Septemper 16,200427 Sub-systemBES IIIBESII  XY (  m) = 130 250 MDC  P/P ( 0 / 0 ) = 0.5 %(1 GeV) 2.4% (1 GeV)  dE/dx ( 0 / 0 ) = 6-7 % 8.5% E.M. Calorimeter  E/√E( 0 / 0 ) = 2.5 %(1 GeV)  z,  (cm) = 0.6cm/ √E 22% (1 GeV) 3 cm / √E ToF  T (ps) = 90-100 ps barrel 110 ps endcap 180 ps barrel 350 ps endcap  Counter 9- 10 layers3 layers Magnet 1.0 tesla 0.4 tesla Comparison between BESIII and BESII

28. Guoliang TONGTau04,Nara,Septemper 16,200428 BESIII Schedule 2-3/2005: endcap muon chamber installation 5/2005: magnet installation 10/2005: magnetic field mapping 2/2006: EMC installation 3/2006: MDC/TOF installation 7/2006: BESIII debug and commissioning, Cosmic ray 11/2004: supporting structure/yoke installation 10/2006: BESIII detector in beam-line 11/2006: commissioning detector/machine

29. Guoliang TONGTau04,Nara,Septemper 16,200429 Physic s Chann el C. M. Energy (GeV) Peak Lumi. (10 33 cm -2 s - 1 ) Cross Section (nb) Events per Year J/  3.0970.6~3400 10  10 9  3.6701.0~2.4 12  10 6  3.6861.0~640 3.0  10 9 D3.7701.0~5 25  10 6 DsDs 4.0300.6~0.32 1.0  10 6 DsDs 4.1400.6~0.67 2.0  10 6 Expected Number of Events in One Year’s Running With such a data sample, a precise measurements are expected

30. Guoliang TONGTau04,Nara,Septemper 16,200430 BES III with 10 10 J/Ψ events in one year’s running can further improve these measurements with much higher sensitivities, and may reach the level to test the prediction for some theoretical model Thank you !