Guoliang TONGICHEP04,Beijing,August 17,20041 Searching for Lepton Flavor Violation and Other Rare Decays at BES Guoliang Tong ( BES Collaboration) IHEP CAS, Beijing China 32rd International Conference on High Energy Physics Beijing, August 16 – 22, 2004

Guoliang TONGICHEP04,Beijing,August 17,20042 Outline 1.Introduction 2.Search for LFV in J/   e μ, μ τ, e τ 3.Search for CP violating process  ’, J/   K S K S 4.Summary

Guoliang TONGICHEP04,Beijing,August 17, 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 -  ’, J/   K S K S test for CP violating and EPR(Einstein- Podolsky-Rosen) paradox

Guoliang TONGICHEP04,Beijing,August 17,20044 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) - J/   K S K S was searched by Mark-III with 2.7 million J/  to reach the U.L. for the decay <5.2x %C.L.)

Guoliang TONGICHEP04,Beijing,August 17,20045 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 <4x x x Υ(1S) μ τ e τ e μ < <2x x x10 -12

Guoliang TONGICHEP04,Beijing,August 17,20046 The Beijing Electron Positron Collider L ~ 5  /cm 2  s at J/  peak E cm ~2-5 GeV

Guoliang TONGICHEP04,Beijing,August 17,20047 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

Guoliang TONGICHEP04,Beijing,August 17, M 14M J/   (2S) World J/  and  (2S) Samples (×10 6 ) BESII 14M  (2S) BESII 58M J/ 

Guoliang TONGICHEP04,Beijing,August 17,20049 Event selection For charged tracks: mfit=2 or – 19 |cos  | < 0.8 θ 12 >178.5 ° the angle between two charged tracks θ Search for J/   e μ, μ τ, e τ 2.1 J/   e 

Guoliang TONGICHEP04,Beijing,August 17, 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 

Guoliang TONGICHEP04,Beijing,August 17, Cuts for isolated photon are we need no isolated photon. P xy (GeV/c) P xy < <P xy <0.95 P xy >0.95 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 

Guoliang TONGICHEP04,Beijing,August 17, Survivals events cutsSurvivals events N chrg = Vertical cuts and M_fit=2 or  Q i = < P <1.65GeV/c |cos  | <  12 > Reject cosmic ray N iso = One of two track is identified as  The other is identified as e < M e  < 3.25GeV/c 2 4 J/   e 

Guoliang TONGICHEP04,Beijing,August 17, Result The upper limit of BR(J/  e  ) with 58 M J/Ψ sample at BES could be got: Background, candidates and Upper limit Total number of backgrounds The upper limit (conservatively calculated with 0 background) 1.1  (90% C.L) J/   e  PLB 561(2003)49-54 Br < (N OB )/[N T  J/  e  ]

Guoliang TONGICHEP04,Beijing,August 17, Events selection 2 good charged tracks Q(sum) = 0 |cos  | < <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 2.2 J/   μ τ, e τ (a) (b)

Guoliang TONGICHEP04,Beijing,August 17, J/    e  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

Guoliang TONGICHEP04,Beijing,August 17, J/    e  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.

Guoliang TONGICHEP04,Beijing,August 17, Upper Limits 90% C.L.) J/    e  Paper has been accepted by PLB(hep-ex/ ) ()()

Guoliang TONGICHEP04,Beijing,August 17, The results of three decay modes: Decay modeN signal N background Upper limit J/ Ψ → e   J/ Ψ → e   J/ Ψ →   J/   e μ, e τ, μ τ

Guoliang TONGICHEP04,Beijing,August 17, CP violating process Test EPR paradox (Einstein-Podolsky-Rosen) MarkIII: 2.7M J/  B(J/   K S K S )< 5.2  C.L.) BESII: 58M J/  14M  ’ Events selection 4 good charged tracks Q(sum) = 0 |cos  | < 0.8 K S decay length Lxy > 3 mm |M  - M K S | < 2 σ M 3. Search for  ’, J/   K S K S

Guoliang TONGICHEP04,Beijing,August 17, J/   K S K S candidate  ’  K S K S candidate 2 circles – 1 σ & 2 σ regions from MC 1 evt in 2 σ region  ’, J/   K S K S bkg=1.0 ± 0.4 eff=21% bkg=0.7 ± 0.3 eff=20%

Guoliang TONGICHEP04,Beijing,August 17, Upper Limits C.L.) 1st upper limit for B(  ’  K S K S ). Higher sensitivity for B( J/   K S K S ) upper limit. Sensitivity insufficient for testing EPR paradox and CP violation. The expectations on the CP violation in K S K S is at level for both J/  and  ’, and that for EPR is at level by some theories.  ’, J/   K S K S PLB 589, 7 (2004)

Guoliang TONGICHEP04,Beijing,August 17, Event Display J/   K S K S Most like J/   And  ’  K S K S and with an isolated photon(126MeV)  K S K S Most like  ’  Ecm=3.097GeVEcm=3.686GeV

Guoliang TONGICHEP04,Beijing,August 17, 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  ; Br(J/Ψ→  ) < 2.0  ; Br(J/Ψ→e  ) < 8.3  %C.L.) CP Violation search:the upper limit for Br(   K S K S ) < 1.0  and B(  ’  K S K S ) < 4.6  %C.L.)

Guoliang TONGICHEP04,Beijing,August 17, Prospect BES III with J/Ψ events and 3  10 9 Ψ(2S) 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. 谢谢！ Thank you !