Experimental Review on Lepton Flavor Violating Tau decays 2008/4 K.Inami Nagoya university International workshop e + e - collisions from phi to psi PHIPSI08

2008/4 International workshop e+e- collisions from phi to psi2 Lepton Flavor Violation (LFV) Standard Model (SM) exactly forbids LFV. Extended SM including neutrino mixing term includes LFV. Charged Lepton Flavor Violation can occur through loop diagram. But, extremely tiny branching ratio below experimental sensitivity Br(    )<O( ) (X.-Y. Pham, EPJ C8(1999)513) Many new models include LFV vertex naturally. Observation of charged LFV  Clear signal of new physics! Tau lepton has many possible LFV decay modes.  Wide window to probe New Physics effect.

2008/4 International workshop e+e- collisions from phi to psi3 LFV tau decays Predicted by many new physics models Normal NP models enhance    For some NP parameters, other modes may be enhanced instead. Many models allow measurable BR of O(10 -8 ) within the parameter space. Reference      SM+ mixing EPJ C8(1999) SM + heavy Maj R PRD 66(2002) Non-universal Z’PLB 547(2002) SUSY SO(10)PRD 68(2003) mSUGRA+seesawPRD 66(2002) SUSY HiggsPLB 566(2003)

2008/4 International workshop e+e- collisions from phi to psi4 Most famous SM extension LFV are generated through slepton mixing. Independent parameter for   e  SUSY seesaw (J.Hisano et. al.,PRD 60 (1999) ) Achievable BR of O(10 -7~-8 ) if tan  ~60 and m SUSY ~1TeV/c 2 SUSY

2008/4 International workshop e+e- collisions from phi to psi5 When sleptons are heavy (>weak scale), Br(    ) is suppressed. Higgs in SUSY enhances other LFV modes, such as   3l, l+hadrons,... Higgs-mediated MSSM   3  (A.Brignole, A.Rossi, PLB 566 (2003) 217) Enhanced if tan  is large and Higgs mass is small. SUSY Higgs

2008/4 International workshop e+e- collisions from phi to psi6 SUSY Higgs Higgs-mediated MSSM (M.Sher, PRD 66 (2002) ) Br(    ) : Br(    ) = 8.4 : 1 Phase space, color factor, mass MSSM seesaw (E.Arganda, arXiv: v1) Large BR of O(10 -7 ) for   ,  ’,     Need to search for all possible LFV modes To probe unknown physics and discriminate models

2008/4 International workshop e+e- collisions from phi to psi7 Experiment Recent results obtained by B-factories High intensity e + e - collider on  (4S) KEKB/Belle; World highest luminosity of 1.7x10 34 /cm 2 /s Similar cross-section with BB (~0.9nb)   -factory Detectors; Good PID ability and vertex resolution Lepton ID eff. : ~90%  fake rate : ~2% e fake rate : ~0.3 %

2008/4 International workshop e+e- collisions from phi to psi8 Status of LFV search at spring 2007 Current accumulated luminosity; >700fb -1 at Belle and >500fb -1 at BaBar. Searches for 3l, lhh modes should be updated. BelleBaBarBelleBaBar UL90 (10 -7 ) Lum (fb -1 ) UL90 (10 -7 ) Lum (fb -1 ) UL90 (10 -7 ) Lum (fb -1 ) UL90 (10 -7 ) Lum (fb -1 )  ee ee l3l  l hh  ’ V0V   eV ee  Ks e’e’ eKs0.6281

2008/4 International workshop e+e- collisions from phi to psi9 LFV analysis Signal extraction Calc. M inv and  E  E=E rec -E beam Blinded signal region  Event selection study Estimate background using sideband data Open blind and estimate signal yield Estimate upper limits by Likelihood fit or number of events in signal region BG reduction is important to improve the sensitivity. Find effective ways to use all information Signal MC Signal region Background M inv

2008/4 International workshop e+e- collisions from phi to psi10 LFV  decays; Signal and Background    qq _ 2photon process  f=leptons,quarks signal Only tag side has neutrino(s). Both sides have neutrino(s). radiative Bhabha process e+e+ ee ee ee ee ee  many tracks e + e -      1 prong tau decay (BR~85%)

2008/4 International workshop e+e- collisions from phi to psi11   3 leptons; BG reduction Signal topology BG events -  conversion veto (e - e + e - and  - e + e - ) - Electron-veto on the tag-side (e - e + e - and e -  +  - ) Bhabha(  ) ee  (eeee) Optimized event selection for each mode separately because the BG processes are different.

2008/4 International workshop e+e- collisions from phi to psi12   lll search; Belle Data; 535fb -1 Efficiency; ( )% N BG ; events N obs ; 0 events for all modes Br<( )×10 -8 at 90%C.L. (Y.Miyazaki et. al., PLB 660 (2008) 154) eeeeee  datasignal signal region

2008/4 International workshop e+e- collisions from phi to psi13   lll search; BaBar Data; 376fb -1 Efficiency; ( )% N BG ; events Total BG; 4.2±0.8 N obs ; 6 events in total Br<( )×10 -8 at 90%C.L. (B.Aubert et. al.,PRL 99 (2007) ) =M inv  M 

2008/4 International workshop e+e- collisions from phi to psi14   lV 0 search Belle; 543fb -1 data Ten modes are investigated, l=e,  and V 0 = ,K* 0,K* 0,  Main BG: SM  decay ;      Signal Efficiency; % Expected N BG ; events Observed number of events; 1 event for   , e , eK* 0 0 events for others Br<(5.9-18)×10 -8 (Y.Nishio et. al., arXiv: ) BaBar; 384fb -1 data Searched for , e  Br<(10-11)×10 -8 (B.Aubert et. al., PRL 100; ) datasignal

2008/4 International workshop e+e- collisions from phi to psi15   lf 0 search Scalar Higgs mediation No search yet. Belle; 671fb -1 Use f 0       No event is observed. Preliminary result Br(  →lf 0 )xBr(f 0 →     )  f 0 : <3.3X10 -8, ef 0 : <3.4X10 -8 signal MC ● data f0f0 ef 0 efficiencyN BG f0f0 6.0%0.11±0.08 ef 0 5.8%0.10±0.07 Br(  →  f 0 ):Br(  →  ):Br (  →  ) = 1.3 : 0.54 :1 (C.H.Chen et.al, PRD74:035010,2006 )

2008/4 International workshop e+e- collisions from phi to psi16 Current status of LFV search Sensitivity is improved by factors of It comes from the luminosity increase and successful BG reduction. Search for   3leptons sets most stringent upper limit. BelleBaBarBelleBaBar UL90 (10 -7 ) Lum (fb -1 ) UL90 (10 -7 ) Lum (fb -1 ) UL90 (10 -7 ) Lum (fb -1 ) UL90 (10 -7 ) Lum (fb -1 )  ee ee l3l  l hh  ’ V0V (  ) 384   eV (e  ) 384 ee f0f e’e’ ef

2008/4 International workshop e+e- collisions from phi to psi17 Current status of LFV search Experimental results have already ruled out some parts of the parameter space. Exclude large tan , small SUSY/Higgs mass Accessing other models and other parameter space reference      SM+ mixing EPJ C8(1999) SM + heavy Maj R PRD 66(2002) Non-universal Z’PLB 547(2002) SUSY SO(10)PRD 68(2003) mSUGRA+seesawPRD 66(2002) SUSY HiggsPLB 566(2003)

2008/4 International workshop e+e- collisions from phi to psi18 Int. Luminosity at B-factory; >1300fb -1 ~1.2x10 9  -pairs At super B-factory >10 times more data BR sensitivity It depends on background.   l  ; scale as ~1/  L e  e        is irreducible BG. ~10 -8 level at super B-factory   lll, lX 0 ; scale as ~1/L BG can be reduced by lepton-ID or mass requirement for X 0 O(10 -9 ) level at super B-factory Future prospect

2008/4 International workshop e+e- collisions from phi to psi19 Summary A data sample of >10 9  -pairs has been successfully obtained by the B-factories. New searches for 3-prong final state   3l, lV 0, lf 0 using 400~700 fb -1 of data Better sensitivity than previous analysis Applied event selection optimized for each mode separately LFV sensitivities are Br~O(10 -8 ). Exploring some parameter space of New Physics Many models predict possible BR of O(10 -7~-8 ). Super B-factory is planned to produce >10 10  -pairs.  LFV sensitivity will reach Br~O(10 -9 ).

2008/4 International workshop e+e- collisions from phi to psi20 LFV  decays; where we are. Sensitivity of Br~O(10 -8 )

2008/4 International workshop e+e- collisions from phi to psi21    237 fb -1 BaBar data used for this analysis. (hep-ex: )

2008/4 International workshop e+e- collisions from phi to psi22   3 leptons; Results No signal events No BG events in sideband except for e - e + e -