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Tau Lepton Flavor Violation Search at Belle, t g mg /e g

Tau Lepton Flavor Violation Search at Belle, t g mg /e g. K.Hayasaka (Nagoya Univ.). 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.

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Tau Lepton Flavor Violation Search at Belle, t g mg /e g

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

  2. 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! Mass Origin and SUSY Physics

  3. LFV modes searched at Belle • tglepton+g, 3leptons (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) Mass Origin and SUSY Physics

  4. 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 Mass Origin and SUSY Physics

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

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

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

  8. 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 Mass Origin and SUSY Physics

  9. Requirement for cosqegCM • opening angle between e and g • calculatable data MC total signal MC Mass Origin and SUSY Physics

  10. Requirements for missing trks. • Pmiss vs m2misstt 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. Mass Origin and SUSY Physics

  11. 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 Mass Origin and SUSY Physics

  12. 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 Mass Origin and SUSY Physics

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

  14. 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. Mass Origin and SUSY Physics

  15. 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! Mass Origin and SUSY Physics

  16. BG distribution (MC) curve (Landau+Gauss) • Estimate BG distribution from tt MC reproduce BG distribution by function Mass Origin and SUSY Physics

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

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

  19. Evaluation of signal events • fit by unbinned expanded maximum likelihood with signal and BG shape gs0=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 Mass Origin and SUSY Physics

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

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

  22. 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. Mass Origin and SUSY Physics

  23. 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 Mass Origin and SUSY Physics

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