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Lepton Flavor Violation Searches at B-Factories

Lepton Flavor Violation Searches at B-Factories. K.Hayasaka (Nagoya U.) On behalf of Belle and BaBar. Introduction. New Physics (NP) search with t Lepton Flavor Violating (LFV) decays LFV decays are forbidden in the SM

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Lepton Flavor Violation Searches at B-Factories

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  1. Lepton Flavor ViolationSearches at B-Factories K.Hayasaka (Nagoya U.) On behalf of Belle and BaBar ICHEP06 - Moscow

  2. Introduction • New Physics (NP) search with t Lepton Flavor Violating (LFV) decays • LFV decays are forbidden in the SM Observation of LFV is a clear signal of NP. • t lepton is expected to be strongly coupled to NP. proportional to (mt)n >> (mm)n,(me)n • Results to be reported in this talk • tgl+g • tgl+h0(h0=p0,h,h’,Ks) • tgh+L/L (h=p,K) • tgl+V0(V0=r,K*,K*,f) • e+egt+l (l=e,m ) ICHEP06 - Moscow

  3. B-factories • A B-factory is also a t-factory! • s(tt)~0.9nb, s(bb)~1.1nb • Detectors -F/B asymmetric -high momentum particle ID capability • Accumulated data: >4.5x108t-pairs at Belle, >3.0x108t-pairs at BaBar  Br~O(10-8) sensitivity! 500fb-1 ICHEP06 - Moscow

  4. Results of t LFV searches • results up to 2005 ICHEP06 - Moscow

  5. History of tgmg searches # of t pairs Before B factories B factories 10-1/10-year improvement achieved 10-1/4or5-year improvement? ICHEP06 - Moscow

  6. New physics and tgm+g • Most promising LFV decay mode e.g. MSSM+ seesaw model • Br(tmee) / Br(tmg) ~1/94 • Br(tmmm)/ Br(tmg) ~ 1/440 • assuming g gaugino m t slepton hep-ex/0406071 ICHEP06 - Moscow

  7. 1 prong + missing ( tag side) m+g (signal side) Analysis of tgm+g search I m • e+e-gt+t- signal event g t e e t generic t decay signal MC for signal event Signalextraction:Mmg-DE plane • Blind analysis 3s ellipse: blinded region ICHEP06 - Moscow

  8. signal data Analysis of tgm+g search II • Main BGs: • tt+ISR g (tgmnn) • mm+ISR g • Requirement on missing mass useful to reduce t+t- BG (signal: 1or2n; tt :>2n) • Signal extraction: • Unbinned Extended Maximum Likelihood fit likelihood function: BG: tt+ISR g BG: mm+ISR g m ISR g n m ISR g n t e e e e t m generic t decay ICHEP06 - Moscow

  9. Previous tgm+g search • BaBar( 232 fb-1) • Signal detection eff.: 9.4% • Not only 1-prong but 3-prong events in tag side; 8.8%g9.4% • Neural Network selection • Beam energy constraint mass • Signal distribution: a • 1D UEML fit with 2sDE band • s= -2.2, b= 143 (prob. 30%) Br<6.8x10-8 at 90%CL Phys. Rev. Lett. 95, 041802 (2005) ICHEP06 - Moscow

  10. signal data New tgm+g search • Belle(535fb-1) • Analysis similar to the previous one of 86fb-1 data sample • Tighter requirements to reduce BG • Remaining events: 54ev./86fb-1g 94ev./535fb-1 • Signal detection eff.: 11%g 6.7% • Signal region: 5s boxg 2s ellipse • Signal extraction: UEML fit • Result:s=-3.9, b=13.9 (allow negative s and its prob. 25%) Br<4.5x10-8 at 90%C.L. blinded region projection 2D fit on Mmg-DE plane distribution in 2s band no signal events are found. preliminary ICHEP06 - Moscow

  11. Development of results on tgm+g • MSSM + seesaw 100 80 New result 60 tanb 40 20 0 0 1 2 3 4 oldnew Luminosity: 86fb-1g535fb-1 (x 6.2) U.L. of Br: 3.1x10-7g4.5x10-8 (x 6.8) negative signal yield: forbidden gallowed mSUSY (TeV/c2) ICHEP06 - Moscow

  12. New results on tge+g • BaBar(232fb-1) • Belle(535fb-1) Select 2 or 4 tracks events Signal extraction Counting method in 2s box eff: 4.7% Br<11.0x10-8 at 90%CL Select 2 tracks events Signal extraction:2D UEML fit in 2s ellipse eff: 3.0% Phys. Rev. Lett. 96, 041801(2006) Br<12.0x10-8 at 90%CL preliminary ICHEP06 - Moscow

  13. New physics and tgm+h • Higgs mediated model predicts a process … PRD 66, 057301 (2002). In the case of Higgs mediated model, tgmh decay may be observed earlier than tgmg. ICHEP06 - Moscow

  14. Previous result for tgm+h • Belle(154fb-1) • Not only hggg but hg3p are used for analysis. • eff. 8.0%(hggg),7.2%(hg3p) • By reconstructing h mass, BG can be suppressed. • main BGs: tt + qq • Signal extraction • Counting method • Br(tgmh)<1.5x10-7 m m p g p h g g h t t g e e e p0 t e t generic t decay generic t decay • Phys. Lett. B622, 218 (2005) ICHEP06 - Moscow

  15. New tgm+h result from BaBar • BaBar(315fb-1) • Counting method in 2s box on MEC-DE plane • hggg mode • eff: 7.0% • Nexpexted=0.64 • Nobserved=1 • hgp+p-p0mode • eff: 3.7% • Nexpexted=0.07 • Nobserved=0 • combined 2 modes hggg 2s box data a region which contains 70% of signal MC events Br<1.6x10-7 hep-ex/0607045 preliminary ICHEP06 - Moscow

  16. signal data New tgm+h result from Belle • Belle(401fb-1) • Based on previous analysis of Belle • Counting method in 90% ellipse on Mmh-DE plane • hggg mode • eff: 6.4% • Nexpected=0.40 • Nobserved=0 • hgp+p-p0mode • eff: 6.8% • Nexpected=0.24 • Nobserved=0 • combined 2 modes 90% ellipse: a region which contains 90% of signal MC events Br<6.5x10-8 preliminary ICHEP06 - Moscow

  17. Impact on SUSY of tgm+h Higgs mediated model predicts D0 BaBar(90%CL) CDF Belle(95%CL) Belle(90%CL) • CDF • fgtt search/310pb-1 • D0 • fgtt search/325pb-1 • fgbb search/260pb-1 Our result has good sensitivity in comparison with Tevatron results. ICHEP06 - Moscow

  18. New results on tgm+h0 / e+h0(h0=p0,h,h’) signal • Belle(401fb-1) • Based on previous analysis, optimized requirements mode by mode.(Lum.:154fb-1g401fb-1) • tgeh’ / mh’ : h’grg mode is now included. • eff.: 4.3%(tgeh’ ,h’ghp+p-), 4.8%(tgeh’ ,h’grg) • 4.9%(tgmh’ ,h’ghp+p-), 5.4%(tgmh’ ,h’grg) • Main BGs: • tgmp0 : tgrn • others: negligible small BGs data Br(eh)<9.2x10-8 preliminary Br(eh’)<1.6x10-7 Br(mh’)<1.3x10-7 Br(ep0)<8.0x10-8 Br(mp0)<1.2x10-7 3-6 times more sensitive results obtained ICHEP06 - Moscow

  19. New result on tgm+Ks / e+Ks signal signal region data • Belle(281fb-1) tmKs teKs previous result CLEO:14fb-1 mKs:<9.5x10-7 eKs:<9.1x10-7 eff.:13.5% Nexpected=0.2 Nobserved=0 eff.:11.8% Nexpected=0.2 Nobserved=0 Br(tgmKs)<4.9x10-8 Br(tgeKs)<5.6x10-8 • Main BGs:Dg lKsn, pKs But negligible 20 times improvement! Phys. Lett. B639, 159(2006) ICHEP06 - Moscow

  20. signal box data Results on tgm+V0 / e+V0 (V0=f,K*,K*,r) • Belle(158fb-1) • Br<(2.0~7.7)x10-7 ter0 teK* tmr0 tmK* lepton h V0 h t e e teK* tef tmK* tmf t generic t decay BGs for some modes are negligible because requirements for V0 mass efficiently reduce BGs. Main BGs: tt+qq (tgmV0) tt+2photon (tgeV0) hep-ex/0603036 accepted by PLB ICHEP06 - Moscow

  21. t-Lp- t-Lp- Previous resulton tgL+h (h=p,K) p • Belle(154fb-1) • First search • Baryon number violating process • Not only (B-L) conserving process but (B-L) violating process • Lgpp (Br~64%) eff.:11.8%(t-gLp-), 11.7%(t-gLp-) Main BGs: tt (tga1n), qq • Br(t-gLp-)<1.4x10-7 • Br(t-gLp-)<7.2x10-8 p L p t e e t generic t decay signal data Phys. Lett. B632, 51 (2006) ICHEP06 - Moscow

  22. signal data New results on tgL+h (h=p,K) • BaBar(237fb-1) • First search for tgLK • t-gLp- eff.:12.3% Nobs=0 Br<5.9x10-8 • t-gLK- eff.:10.6% Nobs=0 Br<7.2x10-8 t-gLp- t-gLp- • t-gLp- • eff.:12.2% • Nobs=0 • Br<5.8x10-8 • t-gLK- • eff.:9.5% • Nobs=1 • Br<15x10-8 (B-L) violating (B-L) conserving Consistent with proton decay prediction Br~O(10~-30) (Phys. Rev. D72 095001) t-gLK- t-gLK- preliminary hep-ex/0607040 ICHEP06 - Moscow

  23. Result on e+egt+l(l=e,m) • BaBar(211fb-1) e+ • signal extraction • 2D UEML fit (mt-pl plane) • s(eegtm)<4.6fb • s(eegte)<10.1fb at 95%CL e/m p e- t n eegte tg3pn e:eff. Br:Br of tag side mode L:lum. tgpn hep-ex/0607044 submitted to PRD lepton momentum t mass preliminary ICHEP06 - Moscow

  24. Summary • Data samples of B-factory ( t-factory ):>500fb-1 • Studies of t LFV decays have made great progress and now reach the O(10-8) level. • No signals are found in any of the LFV decay modes. • tgmg is the most sensitive to possible NP. • tgmh is predicted to have largest BR by Higgs mediated model. • Many ULs of Br for t LFV are updated by the results of B-factories… ICHEP06 - Moscow

  25. Results of t LFV searches red: shown results in this talk ICHEP06 - Moscow

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