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Search for LFV tau decays

Weak Interactions and Neutrinos workshop 2003/10/6-11 @ Lake Geneva. Search for LFV tau decays. t  mg and t  e g, mh, e h, lll. K.Inami (Nagoya-u) for the Belle collaboration. KEKB collider. Asymmetric energy e + :3.5 GeV, e - : 8 GeV for CPV search with B 0 Very high luminosity

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Search for LFV tau decays

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  1. Weak Interactions and Neutrinos workshop 2003/10/6-11 @ Lake Geneva Search for LFV tau decays tmg and teg, mh, eh, lll K.Inami (Nagoya-u) for the Belle collaboration

  2. KEKB collider • Asymmetric energy • e+:3.5 GeV, e-: 8 GeV • for CPV search with B0 • Very high luminosity • Lpeak=1.061034cm-2s-1 • Int. L > 158fb-1 • World record 1.44108 tau-pair events

  3. Belle detector • F/B asymmetric detector • KLM (KL and m detector) • Efficiency > 90% • Fake rate < 1.5% for P>1.0 GeV/c • ECL (Elec. calorimeter) • Electron and gamma • e ID efficiency > 95% • Fake rate < 1% • Energy resolution 1.8% at E=1.0 GeV

  4. tmg • Forbidden in SM, while new physics allows LFV. • ex. SUSY GUT with nR(PRD59, 116005) • LFV through slepton mixing in the SUSY loop • Br() = <10-6

  5. Analysis of tmg • 86.3fb-1 data (7.9x107 tau-pairs) • Select low-multiplicity events • Signal side • Muon-ID • High-momentum photon • Tag side • Not-muon (to reject e+e- m+m-g) • Missing momentum (n) • tenn, pn, rn, a1n,… • Main background • e+e- t+t- • e+e- m+m- g g ...

  6. Event selection

  7. Event selection (2) Tau-pair: neutrinos in both side  Larger effective missing mass Removed events by this selection - 24% signal - 98% tau-pair BG

  8. Signal MC Signal • Signal yield is evaluated by likelihood fit method from DE-vs-Minv plot. (DE = Emg-Ebeam in CM) • Signal distribution : tail due to initial radiation and energy leakage in calorimeter • To avoid bias on analysis, Blinded signal region 1.70<Minv<1.85 GeV/c2 Resolution by asymmetric Gaussian sDE:75.4/33.7MeV, sM:23.1/15.0MeV

  9. Background • Main background • e+e- t+t- (Ntt) with initial-state radiation, beam BG • e+e- m+m- g g ... (Nmm) due to muon inefficiency in tag side • Background shape (p.d.f. for likelihood fit) • estimated byMC for Ntt and data (both tracks be muons) for Nmm • expressed by Gaussian + Landau function. Data (x ineff.= Nmm)

  10. Selected sample 1.71<Minv<1.82GeV/c2 - Good agreement between BG function and selected data - No peak around signal region 5s region: 54 observed events

  11. Likelihood fit • Unbinned Extended Maximum Likelihood fit • Si : Signal probability density from MC simulation • Bi : BG probability density from MC(Ntt) and data(Nmm) • s, b : Number of signal and BG events (free param.)  s = 0, b = 54 5s region

  12. Result of Br(tmg) • Upper limit : Toy-MC ( I.Narsky, NIM A450,444(2000) )  s0 = 5.1 eventfor 90% C.L. • Systematic uncertainty • Signal yield : s0 Muon-ID ineff. +0.06/-0.11 ev. BG function ±0.3 ev. Fit region 0.07 ev. • Efficiency & Luminosity : 2eNtt Track rec. eff. 2.0% Photon rec. eff. 2.8% Selection criteria 2.2% Luminosity 1.4% Trigger eff. 1.6% MC statistics 0.8% Total 4.7% e = 11.0% Ntt = 78.5106 (86.3fb-1) Result Br(tmg)<3.110-7at 90%C.L.

  13. teg • Analysis : same as tmg • 87.1fb-1 data (7.9x107 tau-pairs) • Background source • tau-pair (fake gamma) • 5s signal region • 20 observed events • 6.5% efficiency • S0= 3.8 for 90%C.L. teg, preliminary Preliminary result by likelihood fit Br(teg)<3.610-7at 90%C.L.

  14. tmh, eh and tlll • Constrained MSSM Higgs-mediated model • The anomalous LFV Yukawa coupling for Higgs boson is generated radiatively and not suppressed by the SUSY scale. • LFV is generated by Higgs mediation and B.R.s are comparable. M. Sher, PR D66 057301 (2002) K.S. Bubu and C. Kolda, PRL 89, 241802 (2002) A. Dedes, J. Ellis, and M. Raidal, PL B549, 159 (2002)

  15. preliminary Result of Br(tmh, eh) tmh hgg hp+p-p0 • 84.3fb-1 (7.8x107 tau-pairs) • Event selection: Essentially same as tmg • BG: trn • Signal region: ellipse • Bayesian method signal MC data teh hgg Preliminary result

  16. Selected data, preliminary Result of Br(tlll) • 87.1fb-1 (7.9x107 tau-pairs) • Select 1-3 topology • BG: e+e- qq • Count with signal box • Feldman&Cousins method Preliminary result 1 observed event: two-photon(eeee)?

  17. Summary • Search for LFV • use 7.9x107 tau-pairs • Br(tmg)<3.110-7 • Br(teg)<3.610-7 • Br(tmh)<3.410-7 • Br(teh)<6.910-7 • Br(tlll)<1.4~3.110-7 at 90%C.L. • 3~30 times higher sensitivity than previous results • 1.44108 tau-pairs are ready. • Br ~ 10-8 level in near future.

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