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Search for Lepton Flavor Violating Tau decays at B-factory

This international workshop will discuss the search for Lepton Flavor Violating (LFV) Tau decays at B-factories, including experimental results, future prospects, and summaries. The workshop will cover the importance of LFV decays in the Standard Model and the potential for new physics effects. It will also highlight the detectors and analysis methods used at B-factories, as well as the latest results and future prospects for improving LFV sensitivity. Join us to explore the exciting possibilities for discovering new physics at B-factories!

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Search for Lepton Flavor Violating Tau decays at B-factory

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  1. International workshop e+e- collisions from phi to psi Search for Lepton Flavor Violating Tau decays at B-factory • Introduction • Experimental results • Future prospects • Summary 2006/2/27-3/2 K.Inami Nagoya university, Belle

  2. Introduction • Lepton flavor violating decays have a very small probability in the Standard Model (even with neutrino oscillation). • New physics effects (SUSY, Extra-D, etc.) may allow us to observe LFV with the present experimental sensitivity. • Previous results from CLEO were sensitive to Br~O(10-6). • The B factories (Belle and BaBar) have sensitivities of O(10-7~10-8).

  3. B-factories • Asymmetric-energy e+e- collider at Upsilon(4S) • For CPV search with B0 • Very high luminosity • Integrated luminosity • >500fb-1 for Belle • >300fb-1 for BaBar • Tau factory! • s(tt)~0.9nb, s(BB)~1.1nb 500fb-1 300fb-1

  4. Detectors at B-factories • F/B asymmetric detectors • Good vertex resolution and particle ID ability • Accumulated data: • >4.5x108t-pairs at Belle, >3.0x108t-pairs at BaBar  Br~O(10-8) sensitivity!

  5. Analysis method • Event Selection • Low multiplicity events • Separate into hemispheres • Signal and tag sides • Missing momentum • Low missing mass • Small Ng • Lepton tag etc.

  6. Analysis method (2) • Signal extraction • Calc. Minv and DE • DE=Erec-Ebeam • Blinded signal region •  Event selection study • Estimate background using sideband data • Open blind and estimate signal yield • Estimate upper limits • BG reduction is important to improve the sensitivity. Signal MC of tmg Signal region Background

  7. Belle 86.3fb-1 data Br<3.1x10-7 at 90%C.L. PRL 92, 171892 (2005). BaBar 232fb-1 data Br<0.68x10-7 PRL 95, 041802 (2005). tmg • Background: tmnn + ISR • Small contamination of mm BG in DE>0

  8. Belle : Br<3.1x10-7 / 86.3 fb-1 e = 11.1% 2D EML fit with 5s signal box Nsignal= 0, NBG= 54 Nsignal is constrained to be 0. BaBar : Br<0.68x10-7 / 232 fb-1 e = 9.4% 1D EML fit with 2sDE band Nsignal= -2.2, NBG= 143 N is allowed to be negative. Negative yield gives lower U.L. than expected. Belle : 5s box tmg : Belle vs BaBar BaBar : 2s band

  9. BaBar 232fb-1 data Br<1.1x10-7 PRL 96, 041801 (2006). Belle 86.7fb-1 data Br<3.9x10-7 at 90%C.L. PLB 613, 20 (2005). teg • Background: tenn + ISR

  10. t3l • Belle: 87.1fb-1, BaBar: 91.5fb-1 PLB 598, 103 (2004), PRL 92, 121801 (2004). • Br<(1.1~3.5)x10-7 at 90%C.L. • Background: low level • qq around DE<0, QED(mm or Bhabha) around DE>0 Belle’s results Signal region

  11. tlhh • Belle: 158fb-1, BaBar: 221fb-1 • Br<(1.6~8.0)x10-7 by Belle (preliminary) • Br<(0.7~4.8)x10-7 by BaBar, PRL 95, 191801 (2005). • Background: qq(flat) and tt(corner) • tehh: negligible BG level BaBar’s results

  12. Data ttqq tlp0/h/h’ tmh teh • Lepton + Pseudoscalar meson • Belle: 154fb-1 • Br(tmh)<1.5x10-7 • Br < (1.5~10)x10-7 PLB 622, 218 (2005). • Background • m: tt + qq • e: negligible tmp0 tep0 Signal region tmh’ teh’

  13. tlKs Belle preliminary • Belle: 281fb-1 • Br(tmKs)<0.52x10-7 • Br(teKs)<0.60x10-7 (Preliminary, hep-ex/0509014) • Most stringent U.L. among tau LFV searches • High efficiency (14%,12%) and Low BG • Background: negligible • D± l±Ksn, p±Ks tmKs teKs

  14. tlV0 • Lepton+Vector meson • Belle: 158fb-1 • Br<(2.0~7.7)x10-7 (Preliminary) • Background: tt • tmV0: + qq • teV0: +2photon (eeeeuu, eess etc.) Belle preliminary ter0 teK* tmr0 tmK* teK* tef tmK* tmf Signal region

  15. tpg, pp0 Belle (preliminary) B(tpg)<3.0x10-7 (87fb-1) B(tpp0)<6.5x10-7 (154fb-1) Background: many tt, qq p/p misidentification tLp Belle: 154fb-1 B(tLp)<1.4x10-7 B(tLp)<0.72x10-7 PLB 632, 51 (2006). Background: tt(a1n), qq tBaryons t-Lp- t-Lp-

  16. B.R. summary • Br < O(10-6) in PDG (by CLEO) •  Br < O(10-7) by Belle and BaBar New Physics

  17. For Future • B-factories are accumulating data stably. • Currently, >7.5x108t-pairs in two B-factories. • However, improvement of LFV sensitivity will be slow. • Non-negligible backgrounds • Need better m/p separation • Low energy t-factory may have an advantage. • Effects of ISR and qq may be reduced. m/p

  18. Future prospect • Super B-factory : >10 times more data • B.R. sensitivity: ~1/n for negligible BG case ~1/n for BG dominated modes

  19. Future prospect (2) • Possible sensitivity with Super B-factory • Red band for 5~10ab-1 Super B-factory

  20. Summary • A data sample of >7.5x108t-pairs has been successfully obtained by the B-factories. • LFV sensitivities are Br~1x10-7. • Exploring possible parameter space of New Physics • For some modes, it will be hard to improve the sensitivity due to backgrounds. • Better muon identification • Tau-factory at around energy threshold may be better to reduce ISR effects.? • Super B-factory will produce 1010t-pairs at 10ab-1.  LFV sensitivity will reach Br~O(10-9).

  21. Effect to physics parameter • MSSM with Seesaw PRD 60, 055008 (1999). • Higgs mediated in MSSM PRD 66, 057301 (2002). • Heavy Dirac neutrino model PRD 62, 0306010 (2000). • B(tlV0) constrain y2te and y2tm.

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