Lepton Flavor Violating  decays at B-factories: results and prospects Giovanni Marchiori Università di Pisa & I.N.F.N.

15/9/20062G. Marchiori - LFV tau decays at B-factories: results and prospects Introduction LFV in charged lepton sector in SM (via mixing) strongly suppressed (GIM)  Observation of LFV is a clear signal of NP Most SM extensions predict enhanced LFV effects in  decays (BR’s up to  ) Results reported in this talk:  l+   l+l’l’  l+hh’ (h = ,K)  l+h 0 (h 0 =  0, ,  ’,K S )  l+V 0 (V 0 = ,K*,  ) (  l=e  )  LFV as discriminating tool

15/9/20063G. Marchiori - LFV tau decays at B-factories: results and prospects Theoretical expectations for  LFV decays Also promising:    (enhanced in Higgs-mediated models)

15/9/20064G. Marchiori - LFV tau decays at B-factories: results and prospects B-factories (e  e ,  s  GeV=M  (4S) ) A B-factory is also a  -factory!  (  )~0.9nb,  (bb)~1.1nb ~5.6x10 8  -pairs at Belle, ~3.5x10 8  -pairs at BaBar  BR ~ O(10 -8 ) sensitivity! ~ 10 9  -pairs expected at each B-factory by 2008 Detectors BABAR:  90% tracking and e.m. calorimeter acceptance; 80% PID acceptance  e-ID: eff ~91%,  misid ~0.2%;  -ID: eff ~63%,  misid ~4.8% 400fb -1

15/9/20065G. Marchiori - LFV tau decays at B-factories: results and prospects Signal signature (example for    ) e + e   +   Event topology: thrust, number of charged tracks and neutral clusters in two (CM) hemispheres consistent with decay under study Signal side: positive lepton-ID, Tag side: p miss within detector acceptance, p T miss >0, M miss ~0  e e    generic  decay signal event  (signal side) 1/3 prong(s) + missing (tag side) signal MC 3  ellipse: blinded region

15/9/20066G. Marchiori - LFV tau decays at B-factories: results and prospects Background suppression Radiative Bhabhas and dimuon events: mostly leptons, high- momentum (and small p T ) tracks, jet-like Low-multiplicity hadronic events: more isotropic, more neutrals, Kaons Two-photon events: large E miss, small p T SM  decays: missing mass and momentum in both hemispheres signal data

15/9/20067G. Marchiori - LFV tau decays at B-factories: results and prospects Analysis strategy Signal extraction: M  -  E plane (2  ellipse/box around (m ,0) ) Background (B) extrapolated from M  -  E sidebands Signal (S) efficiency  from full MC simulation Selection optimized for best BR upper limit when S=0 Blind analysis Frequentist BR upper limits obtained from B, S, , N  with systematic uncertainties included (NIM A320,331)  B /B up to 100% (limited sidebands statistics)   /  <~ 8% (tracks and photons reconstruction efficiency; momentum scale and resolution; PID efficiency)  (N  )/N  ~2.3% (luminosity and   )

15/9/20068G. Marchiori - LFV tau decays at B-factories: results and prospects    Belle(535fb -1, preliminary ) BaBar(232fb -1, PRL 95, ) – Beam-energy constrained mass –  =7.4±0.5% (3-prong  tag : 1.2%) – N expected = 6.2±0.5 – N observed = 4 BR<6.8x10 -8 at 90% CL distribution in 2  band signal data blinded region signal region –  = 6.7% (only 1-prong  tag ) – N expected = 13.9 – N observed = 10 BR<4.5x10 -8 at 90% CL Main BGs: –  +ISR  (    ) –  +ISR 

15/9/20069G. Marchiori - LFV tau decays at B-factories: results and prospects   e  e Belle(535fb -1, preliminary ) BaBar(232fb -1, PRL 96, ) – Beam-energy constrained mass –  = 4.7±0.3% – N expected = 1.9 ± 0.4 – N observed = 1 BR<1.1x10 -7 at 90% CL –  = 3.0% – N expected = ? – N observed = 5 BR<1.2x10 -7 at 90% CL Main BGs: –  +ISR  (   e ) – ee+ISR 

15/9/200610G. Marchiori - LFV tau decays at B-factories: results and prospects  ll’l’ (l,l’=e,  ) BaBar(91.5fb -1, PRL 92, ) – only 1-prong  tag decays –  =7-11% – N expected = 3.41±0.22 in total – N observed = 3 BR<( )x10 -7 at 90% CL ~similar results from Belle (87.1fb -1, PLB 589, 103 ) signal box data Main BGs: higher order radiative e + e ,  +   : e + e   lll’l’

15/9/200611G. Marchiori - LFV tau decays at B-factories: results and prospects    BaBar(315fb -1, hep-ex/ )  2  box data     : 7.0±0.5 % N exp : 0.64±0.08 N obs : 1          : 3.7±0.3 % N exp : 0.07±0.02 N obs : 0 BR<1.6x % ellipse (MC) Belle(401fb -1, preliminary ) BR<6.5x10 -8     : 6.4% N expected : 0.40 N observed : 0          : 6.8% N expected : 0.24 N observed : 0 signal data 90% ellipse (MC)

15/9/200612G. Marchiori - LFV tau decays at B-factories: results and prospects   h 0 / eh 0 (h 0 =  , ,  ’) Belle(401fb -1, preliminary ) Based on previous analysis (154fb -1, PLB622, 218)   e  ’ /  ’ :  ’   mode is now included. –eff.: 4.3%(   e  ’,  ’      ), 4.8%(   e  ’,  ’   ) 4.9%(    ’,  ’      ), 5.4%(    ’,  ’   ) Main BGs: –     :    –others  negligibly small BGs BR(e  )<9.2x10  BR(e  ’)<1.6x10  BR(e   )<8.0x10  BR(   )<1.2x10  BR(  ’)<1.3x10  signal data 3-6 times more sensitive results obtained

15/9/200613G. Marchiori - LFV tau decays at B-factories: results and prospects  lhh’ (l=e,  ; h,h’= ,K) – only 1-prong  tag decays –  ~3% for each mode – N expected = 11.3  0.7 in total ( depending on channel) – N observed = 10 BR<( )x10 -7 at 90% CL ~similar results from Belle (158fb -1, hep-ex/ ) BaBar(221fb -1, PRL 95, ) signal data Main BGs: low-multiplicity qq evts  hh’h”

15/9/200614G. Marchiori - LFV tau decays at B-factories: results and prospects   K S / eK S (K S      ) Belle(281fb -1, PLB639, 159 )    Ks   eKs Main BGs: D  lK S,  K S - but negligible Main syst. on  : K S reco. (4.5%), tracking eff. (4%) signal data signal region  : (13.5±0.9)% N expected =0.2  0.2 N observed =0 BR<4.9*10 -8  : (11.8±0.8)% N expected =0.2  0.2 N observed =0 BR<5.6*10 -8 previous result CLEO:14fb -1  Ks:<9.5x10 -7 eKs:<9.1x times improvement wrt previous UL (CLEO) blind region

15/9/200615G. Marchiori - LFV tau decays at B-factories: results and prospects   V 0 / eV 0 (V 0 = ,K*,  )       ee  e    e  ee Belle(158fb -1, hep-ex/ ) –  ~3-5% – N expected = 2.55±1.04 in e   ; negligible for non-  modes (V 0 mass cut) – N observed = 5 in e  0 ; 0 in all other channels BR<( )x10 -7 at 90% CL signal box data  K  K  K*  K        e e   lepton h h V0V0 generic  decay Main BGs:  +qq (    V 0 )  +2photon (   eV 0 )

15/9/200616G. Marchiori - LFV tau decays at B-factories: results and prospects Summary of  LFV searches mode x10 -7 mode x10 -7    Belle0.45   lll 1.1  3.5 ee BaBar1.1     + e  e  BaBar1.1    Belle0.65      e  e + Belle1.9 ee Belle0.92   lhh BaBar 0.7  4.8    ' Belle1.3 ++ BaBar0.7 e'e' Belle1.6 lV0lV0 Belle 2.0  7.7     Belle1.2    0 Belle2.0 ee Belle0.80      BaBar0.59    Ks Belle0.52      BaBar0.58   e Ks Belle0.60      BaBar0.72      BaBar1.5 red: results shown in this talk * : bkg currently negligible Starting to constrain the parameter space of some NP (SUSY/Higgs/mSUGRA) models * * * * * * * * * * *

15/9/200617G. Marchiori - LFV tau decays at B-factories: results and prospects Prospects For many modes at present the expected background is negligible. probably the case also at the end of the B-factories era (2ab -1 in total)  UL  1/L (5-10 improvement)  UL ~10 -8 may not be the case at a Super flavor factory (50 ab -1 )  UL improvement  ~1/  L (another x5 improvement AT LEAST) –detailed studies (simulations) to be done –detector design to be optimized: improve  and bkg suppression: Increased hermiticity Better particle-ID performance Improved tracking/neutral resolution  Sensitivity to BR ~ could be reached  Potential for LFV observation in  decays

15/9/200618G. Marchiori - LFV tau decays at B-factories: results and prospects Conclusion Data sample of B-factories (  -factories): >900*10 6  pairs now ~2*10 9 by 2008 Studies of  LFV decays now reach the O(10 -8 ) level: No signals are found in any of the LFV decay modes Many ULs for  LFV updated by B-factories’ results A Super flavor factory (50x more data, more optimized detector) can set O( ) limits and has potential for LFV discovery in many NP scenarios

15/9/200619G. Marchiori - LFV tau decays at B-factories: results and prospects Backup

15/9/200620G. Marchiori - LFV tau decays at B-factories: results and prospects Extracting BR upper limits (NIM A320, 331) Cousins-Highland method: extension to frequentist method to include syst. uncertainties. MC samples generated according to Poisson distribution with mean (S+B) –B drawn randomly from Gaussian distribution with mean = N expected, std. dev. =  (N expected ) –S drawn randomly from Gaussian distribution with mean = L*   *2*BR* , std. dev. =  (L*   *2*BR*  ) BR varied until 10% of the sample yields a # of events < then the # observed in data

15/9/200621G. Marchiori - LFV tau decays at B-factories: results and prospects Nested subdetectors: Vertex detector (SVT) (5 Si layers) Drift chamber (DCH) (gas based, 40 cell layers) Cherenkov detector (DIRC) (fused silica bars) Electromagnetic calorimeter (EMC) (CsI(Tl) crystals) Superconducting Magnet (1.5 T solenoidal field) Muon and neutral hadron calorimeter (IFR) (Iron + RPC/LST) The BaBar detector “Multi-purpose” detector with full azimuthal and ~90% polar angle coverage Optimized for CP violation studies in B decays (energies in the range 100 MeV – 4 GeV) –Vertex resolution –Material budget (momentum resolution, low-energy photon efficiency) –Lepton/Kaon identification (B flavor tagging) ee SVT DCH EMC Solenoid IFR DIRC e+ e+ B decay vertex, soft  from D* K-ID e-ID  -ID

15/9/200622G. Marchiori - LFV tau decays at B-factories: results and prospects performances SVT: –90% acceptance in CM, 4% X 0 thickness –  (vtx): 70  m fully reco, 150  m tag –  (d 0 ),  (z 0 ) ~ 50  m –Low-p T trk. eff. : >80% at p T =70 MeV/c DCH: –90% acceptance in CM, 1.08% X 0 thickness –Trk. eff.: 98% for p T >200 MeV/c –  (p T )/p T =0.13%p T /(GeV/c) % –3  K/  separation (dE/dx) up to 700 MeV/c DIRC: –78% acceptance in CM, 17% X 0 thickness –  (  C )2.5 mrad,  (t  )~1.7 ns –K/  separation: 4.2 3GeV/c, 2.5 4GeV/c EMC: –90% acceptance in CM, 17 X 0 thickness –  (E)/E: 2.3%/(E/GeV)^(1/4)  1.85% –  ( ,  ) = 3.9 mrad/(E/GeV)^(1/2) –  (  0 mass)=6.9 MeV/c 2 –e-ID: eff=91%,  misid=0.2% IFR –65 cm of steel (+brass) –18 plates of RPCs (being replaced by LSTs) –  -ID: eff=63%,  misid=4.8% (eff. > 90% with LSTs)

15/9/200623G. Marchiori - LFV tau decays at B-factories: results and prospects Typical selection variables charged tracks: –d 0, z 0 –momentum, # of hits photons: –Energy –Lateral shower shape –Not matched to tracks K/  : –dE/dx –Cherenkov angle Unstable particles: –invariant mass of daughters –  2 probability of vertex fit  : m EC,  E K S : –Distance of flight –Line of flight vs p direction , K *, , D *0 : –helicity angle (polarization)