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Guoliang TONG Tau04,Nara,Septemper 16,2004 1
Searching for Lepton Flavor Violation Decays J/ e μ, μ τ , e τ
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.
Guoliang TONG Tau04,Nara,Septemper 16,2004 8
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+p2) z = 2.3 cm
Guoliang TONG Tau04,Nara,Septemper 16,2004 9
Korea (4)
Korea University Seoul National University
Chonbuk National UniversityGyeongsang Nat. Univ.
Japan (5)
Nikow UniversityTokyo Institute of Technology
Miyazaki UniversityKEK
U. Tokyo
USA (4)
University of HawaiiUniversity 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 ChinaShandong 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.
Guoliang TONG Tau04,Nara,Septemper 16,2004 10
0
2
4
6
8
10
12
14
MKI MKII MKIII CBAL BESI BESII CLEOc
3.0M
14M
J/
0
10
20
30
40
50
60
MarkI I I DM2 BES I BES I I
(2S)
World J/ and (2S) Samples (×106)
BESII 14M
(2S)
BESII 58M J/
(99.11-01.03) (01.11-02.03)
Guoliang TONG Tau04,Nara,Septemper 16,2004 11
Event selection
For charged tracks:
• mfit=2 or –19 • |cos| < 0.8 • • θ12>178.5°
4,0,2 neuchrg NQN
cmzcmycmx 15,5.1,5.1
the angle between two charged tracks θ12
2. Search for J/ e μ
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• The invariant mass of two charged tracks
• The momentum of
charge tracks, 1.45<P<1.65GeV/c
2/25.395.2 cGeVM e
the invariant mass of electron and μ and the momenta of electron and μ ( MC)
With such a data sample, a precise measurements are expected
Guoliang TONG Tau04,Nara,Septemper 16,2004 30
BES III with 1010 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