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Search for t g e g / mg

Search for t g e g / mg. K.Hayasaka(Nagoya U.) Belle Collaboration. Introduction. Lepton Flavour Violating ( LFV ) process: forbidden in SM n probe of new physics SUSY model predicts: most sensitive mode in the LFV decays. We SHOULD search for

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Search for t g e g / mg

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  1. Search fortgeg / mg K.Hayasaka(Nagoya U.) Belle Collaboration

  2. Introduction • Lepton Flavour Violating (LFV) process: forbidden in SM n probe of new physics • SUSY model predicts: most sensitive mode in the LFV decays. • We SHOULD search for not only fortgmg but also for tgeg . ~ ~ B B Tau04 @ Nara

  3. KEKB accelerator/Belle detector • asymmetric collider • cross section@ s~110GeV2 s(bb):s(tt)=1.05:0.912 uA B-factoryis also a t-factory! • asymmetric detector Peak Lum. 1.4x1034 cm-2s-1 Total Logged Lum. 288fb-1 • m-ID:eff. 87.5% • e-ID:eff. 92.4% _ Tau04 @ Nara

  4. Signatures of the Signal and of the BGs • Signal Event • (e+g)+(e+ng) • Expected BG Events • Bhabha process / • tt process n e g g e e n g t t e e e e e e t t e generic decay generic decay Tau04 @ Nara

  5. Selection Criteria • 2 charged tracks + more than 1 g • signal side :1 charged+1 photon • tag side :1 charged+ n photons • 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 Tau04 @ Nara

  6. Nagoya Cut • 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. Tau04 @ Nara

  7. 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 DE=Ee+Eg-Ebeam @CM Meg= (Pe+Pg)2 eg - +5s region Tau04 @ Nara

  8. Blind Analysis • Signal dominant region is masked. ttBG : ttMC Bhabha BG : data Shape of BG distribution is evaluated. Its height is decided with data distribution of the side-band region. Masked! side-band region Tau04 @ Nara

  9. BG distribution (MC) curve (Landau+Gauss) • Estimate BG distribution from tt MC reproduce BG distribution by function Tau04 @ Nara

  10. BG distribution (data) • Estimate BG from MC and data data(side band) tt MC ee 64 = 61 3 ~ ttMC Masked! curve (Landau+Gauss) profile plot Tau04 @ Nara

  11. Final Candidates (tgeg) • 60 events found. (# of estimated BG:64) • 20 events survived in +5s region - signal MC - signal events dominate +5s surviving data Tau04 @ Nara

  12. 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. 0.01/0.02 ev. BG function 0.13 ev. Efficiency & Luminosity : 2eNtt Track rec. eff. 2.0% Photon rec. eff. 2.8% Selection criteria 2.5% Luminosity 1.4% Trigger eff. 5.0% MC statistics 0.2% Total 6.8% Br=s0/2eNtt<3.8x10-7 e:detection efficiency Ntt:total event number Tau04 @ Nara

  13. 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.) Tau04 @ Nara

  14. 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 Tau04 @ Nara

  15. 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<3.8x10-7@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. Preliminary result Phys. Rev. Lett. 92(2004) 171802 cf. Br<2.7x10-6@90%C.L. (CLEO) cf. Br<1.1x10-6@90%C.L. (CLEO) Tau04 @ Nara

  16. Unbinned Extended Maximum Likelihood fit • s:#signal,b:#BG • Si:signalprob. of i-th event • Bi:BGprob. of i-th event • N: #remaining events Search for s and b which maximizeL we fit over 5s region Tau04 @ Nara

  17. Belle detector • Asymmetric detector:forward/backward • KLMgdetection for m/KL mID:eff. 87.5% • ECLgdetectionfor e,g eID:eff. 92.4% Tau04 @ Nara

  18. Upper bound of cosqmiss-tag • Bhabha events restrict: cosqmiss-tag<0.99 g e e e e matter e g more than a half of bhabha events removed missing Tau04 @ Nara

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