Tau Lepton Flavor Violation Search at Belle, tgmg/eg K.Hayasaka (Nagoya Univ.) 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Introduction LFV decays are forbidden in SM. Observation of LFV decay suggests existence of New Physics! t is a heaviest lepton and has decay mode including some hadrons. t is expected to be most sensitive lepton for New Physics! 7 March 2006 Mass Origin and SUSY Physics

LFV modes searched at Belle tglepton+g, 3 leptons (lepton=e,m) tglepton+2 charged meson (charged meson=p/K) tglepton+neutral meson (p0,h,h’,f,Ks,r0,K*) tgBaryon+meson (tgLp/Lp) 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics KEKB accelerator Asymmetric e+e- collider (e+:3.5GeV,e-:8.0GeV) Circumference~3Km s=Upsilon(4s) Integrated luminosity >560fb-1 B-factory is also 　t-factory! s(tt)~0.9nb s(bb)~1.1nb 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Belle detector F/B asymmetric m-ID:eff. 87.5% e-ID:eff. 92.4% 7 March 2006 Mass Origin and SUSY Physics

Signal and BG events for tgmg side tag side mm signal qq tt q=u,d,s s(mm)~1.0nb s(qq)~2.1nb s(tt)~0.9nb 7 March 2006 Mass Origin and SUSY Physics

Signal and BG events for tgeg qq tt signal bhabha q=u,d,s s(tt)~0.9nb s(bhabha)~124nb 7 March 2006 Mass Origin and SUSY Physics

Selection Criteria for tgeg 2 charged tracks + more than 1 g signal side : 1 charged+1 photon tag side : 1 charged e-ID>0.9 & e-ID<0.1 restrict kinematical variables momentum e,tag,g,missing polar angle e,tag,g,missing opening angle e-tag, e-g, tag-missing missing mass vs missing mom. analysis for 87fb-1 data sample e g 1-1 prong t e e t generic decay tag missing 7 March 2006 Mass Origin and SUSY Physics

Requirement for cosqegCM opening angle between e and g calculatable data MC total signal MC 7 March 2006 Mass Origin and SUSY Physics

Requirements for missing trks. Pmiss vs m2miss tt events have large missing mass n tt MC g signal MC e n t e e t n charged particle 98% of the t+t- bkg is removed. 7 March 2006 Mass Origin and SUSY Physics

Distribution for signal events generate 106 signal MC events 2 variables defined DE=Ee+Eg-Ebeam @CM Meg= (Pe+Pg)2 g ISR EgISR+EeISR<EgnoISR+EenoISR gDEISR<DEnoISR,MegISR~MegnoISR Energy leakage Egob<EgtruegDEob<DEtrue,Megob<Megtrue 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Meg and DE resolutions All selections applied for signal MC events Asymmetric Gaussian 6.5% Meg DE # of events. # of events. +1s - +1s - 25.7/14.3MeV/c2 84.8/36.0MeV eg +5s region - 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Blind Analysis Signal dominant region is masked. 42ev. 43.5ev. 60.8ev. Masked! side-band region +2.7(4.3) bhabha events. 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Signal extraction Unbinned Extended Maximum Likelihood Likelihood function s,b: # of events for signal and BG gfree parameter: search s and b which maximize L N: # of observed events, i: each found event PDFsig:fsignalMC(smoothing) PDFbg:express analytic func. 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics BG PDF Difficult to decide from data # of events is small. Blind region exists. Shape of BG distribution is evaluated from distribution of tt MC events. Its height is decided with data distribution of the side-band region. Masked! 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics BG distribution (MC) curve (Landau+Gauss) Estimate BG distribution from tt MC reproduce BG distribution by function 7 March 2006 Mass Origin and SUSY Physics

BG distribution (data) Estimate BG from MC and data data(side band) tt MC ee 65 = 61 4 ~ ttMC Masked! (Landau+Gauss) curve profile plot 7 March 2006 Mass Origin and SUSY Physics

Final Candidates (tgeg) 60 events found. (# of estimated BG:65) 20 events survived in +5s region - signal MC - signal events dominate +5s surviving data 7 March 2006 Mass Origin and SUSY Physics

Evaluation of signal events fit by unbinned expanded maximum likelihood with signal and BG shape g s0=0,b0=20 Estimation for U.L. of s90 @ 90%CL uby Toy MC: generate 10000 events result s90=3.8 events Branching fraction Signal yield : s0 e-ID ineff. 0.01 ev. BG function 0.07 ev. Efficiency & Luminosity : 2eNtt Track rec. eff. 2.0% Photon rec. eff. 3.0% Selection criteria 2.5% Luminosity 1.4% Trigger eff. 2.0% MC statistics 0.3% Total 5.0% Br=s0/2eNtt<3.9x10-7 e:detection efficiency Ntt:total event number 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Search for tgmg Almost same selection criteria as tgeg for tag side track, require not to be m Main BG: ttg & mmg(ffrom m-ID ineff.) Data (x ineff.) Masked! 7 March 2006 Mass Origin and SUSY Physics

Final Candidates ( tgmg ) 54 events survived in +5s region - 1.71<Minv<1.82GeV/c2 signal MC +5s - 11% fitting result(UEML) s=0 Evaluation for U.L. s=5.1ev. @90%C.L. Br<3.1x10-7 @90%C.L. including systemaric uncertaunties 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Future prospect Super B-factory : >10 times more data B.R. sensitivity: ~1/L for negligible BG case ~1/ L for BG dominated modes We need 2~3ab-1 data sample to reach Br<a few x 10-8. 7 March 2006 Mass Origin and SUSY Physics

Mass Origin and SUSY Physics Conclusion & Summary Obtain BR UL’s with blind analyses. BG distributions are modeled well. Results are 10 times more sensitive than CLEO’s. tgeg(86.7fb-1) Ntt=7.90x107 20 observed events e=6.5% s=3.8ev. @90%C.L. Br<3.9x10-7 @90%C.L. tgmg(86.3fb-1) Ntt=7.87x107 54 observed events e=11% s=5.1ev. @90%C.L. Br<3.1x10-7 @90%C.L. Phys. Lett. B613(2005) 20 Phys. Rev. Lett. 92(2004) 171802 7 March 2006 Mass Origin and SUSY Physics