Searching for Lepton Flavor Violation Decays J/ e μ, μ τ , e τ at BES Guoliang Tong

Guoliang TONG Tau04,Nara,Septemper 16,2004 1

Searching for Lepton Flavor Violation Decays J/ e μ, μ τ , e τ

at BESGuoliang Tong

( BES Collaboration)IHEP CAS, Beijing ChinaE-mail: [email protected]

8th International Workshop on Tau Lepton Physics

Nara, September 14 – 17, 2004


Outline

1.Introduction2.Search for LFV in J/ e μ3.Search for LFV in J/ μ τ , e τ4.Summary


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/,, Z0) in recent years

-Super-Kamiokande and Kamland, SNO experimental results indicate strongly m0, and mix with each others


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)


Theoretical limits and predictions for LFVD on BR

Boson Mode

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 τe τe μ

< 6x10-7

<6x10-7

<4x10-13

3.0x10-8

3.0x10-8

3.5x10-15

Υ(1S)μ τe τe μ

< 10-2

<10-2

<2x10-9

1.3x10-7

1.3x10-7

4.1x10-12


The Beijing Electron Positron Collider

L ~ 51030 /cm2s at J/ peak Ecm~2-5 GeV


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.


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


Korea (4)Korea University

Seoul National University Chonbuk National University

Gyeongsang Nat. Univ.

Japan (5)

Nikow UniversityTokyo Institute of Technology

Miyazaki UniversityKEK

U. Tokyo

USA (4)University of Hawaii

University of Texas at DallasColorado 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.


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 BE S I BE S II

(2S)

World J/ and (2S) Samples (×106)

BESII 14M (2S)

BESII 58M J/

(99.11-01.03) (01.11-02.03)


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


• 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)

J/ e (con’t)


Cuts for isolated photon are

we need no isolated photon.

MeVEsc 5015c18 E/P of electron and μ (data)

• particle identification - identify e: E/P>0.7, μhit=0 - identify μ: E/P<0.3, μhit pass Pxy cuts , Pxy -transverse momentum.

J/ e (con’t)

BES counter: Iron a bsorber-1st layer: 120 mm (67%, solid angle)-2nd layer: 140 mm (67%)-3rd layer: 140 mm (63%)


J/ e (con’t)

E/P of electron and μ (data)

With data sample.


J/ e (con’t)


Survivals events cuts Survivals events

Nchrg = 2 38045098Vertical cuts and M_fit=2 or

-19 16119944

Qi = 0 158788361.45 < P <1.65GeV/c 4114702

|cos| < 0.8 396314512 > 178.50 1947195

Reject cosmic ray 1843853Niso = 0 1799597

One of two track is identified as

152820The other is identified as e 4

2.95 < Me < 3.25GeV/c2 4

J/ e (con’t)


ResultThe upper limit of BR(J/e) with 58 M

J/Ψ sample at BES could be got:

Background,candidates andUpper limit1.490.79

Total number of backgrounds

2.2

4The upper limit(conservatively calculated with 0 background)

1.1 10-6(90% C.L)

/J

KKJ /

eJ /

J/ e (con’t)

PLB 561(2003)49-54

Br < (NOB)/[NTJ/e]


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 Ebsc<0.3 for μ • Muonhit=3 for μ Muonhit=0 for electron

3. J/ μ τ , e τ

(a)

(b)


J/ e(con’t) Detector efficiency

μ ID efficiency in μ counter is determined from real μ data. Others are from MC simulation. Efftotal = effMC*eff μ ID. eff μ ID= ii here, i is the weight of events, i is the ith efficiency from μ real data sample.

Systematic error Systematic error is incorporat

ed when calculating upper limit: Un=Un0(1+En

2 ) where En=

Un0-1


J/ e(con’t)

J/ candidate J/ e candidate

2 σ regions from MCBackground event is 0 for J/ to .

Background event is 0.4 for J/ to e . which is from J/ to K*K.


J/ e(con’t)

J/

J/ e


Upper Limits (@ 90% C.L.)J/ e(con’t)

Paper has been accepted by PLB(hep-ex/0406018)

( ) ( )

PLB 598(2004)172-177


The results of three decay modes:

Decay mode

Nsignal Nbackground Upper limit (@90%C.L.)

J/Ψ→e 4 2 1.110-6J/Ψ→ 0 0 2.010-6J/Ψ→e 1 0 8.310-6

J/ e μ, μ τ, e τ


4.SummaryNo evidence for direct LFV has been found in these searches. These searches reached new upper limits for LFV processes

Br(J/Ψ→e) < 1.110-6 ;

Br(J/Ψ→) < 2.010-6 ;

Br(J/Ψ→e) < 8.310-6

(@ 90%C.L.)

Prospect

BEPCII/BESIII Project is making good progress Nov. 2006: commissioning detector/machine


BEPCII/BESIII Project

Two rings

Beam energy 1 – 2.1 GeV

Optimal energy 1.89 GeV

Luminosity 1 x 10 33 cm-2s-1 @ 1.89 GeV

Linac requirements Full energy injection: 1.55 1.89 GeV Positron injection rate > 50 mA/min

Dedicated SR 250 mA @ 2.5 GeV


工

BESIII Detector

system BES 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


Sub-system BES III BESII 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 /√EToF T (ps) = 90-100 ps barrel 110 ps endcap 180 ps barrel

350 ps endcapCounter 9- 10 layers 3 layers

Magnet 1.0 tesla 0.4 tesla

Comparison between BESIII and BESII


BESIII Schedule2-3/2005: endcap muon chamber installation5/2005: magnet installation10/2005: magnetic field mapping2/2006: EMC installation3/2006: MDC/TOF installation7/2006: BESIII debug and commissioning,

Cosmic ray11/2004: supporting structure/yoke installation10/2006: BESIII detector in beam-line11/2006: commissioning detector/machine


Physics

Channel

C. M. Energy (GeV) Peak Lumi.

(1033cm-2s-1)

Cross Section(nb)

Events per Year

J/ 3.097 0.6 ~3400 10109 3.670 1.0 ~2.4 12106 3.686 1.0 ~640 3.0109D 3.770 1.0 ~5 25106Ds 4.030 0.6 ~0.32 1.0106Ds 4.140 0.6 ~0.67 2.0106

Expected Number of Events in One Year’s Running

With such a data sample, a precise measurements are expected


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

Thank you !

Searching for Lepton Flavor Violation Decays J/ e μ, μ τ , e τ at BES Guoliang Tong

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