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Search for Lepton Flavor Violating Tau decays at B-factory

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. Introduction.

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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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