Update on BaBar Searches for Lepton Flavor Violation using Tau Decays Richard Kass for the BaBar Collaboration Outline of Talk Introduction some facts about BaBar & PEPII Searches for Lepton Flavor Violation 2-body decays 3-body decays Baryon number violating decays Summary & Conclusions Richard Kass

Since the cross section for e+e-®Y(4S)®BB Fact #1 Since the cross section for e+e-®Y(4S)®BB is about the same as the cross section for e+e-®t+t- a B factory is also a t factory. Cross Section sBB 1.05 nb stt 0.92 nb July 2006 Richard Kass

BaBar is a great detector for t physics! Fact #2 BaBar is a great detector for t physics! 1.5 T Solenoid Electromagnetic Calorimeter (EMC) Detector of Internally Recflected Cherenkov Light (DIRC) e+ (3.1 GeV) e- (9 GeV) Drift Chamber (DCH) Instrumented Flux Return (IFR) Silicon Vertex Tracker (SVT) SVT, DCH: charged particle tracking Þ vertex &mom. resolution, K0s, L’s EMC: electromagnetic calorimetry Þ g/e/p0/h DIRC, IFR, DCH: charged particle ID Þ p/m/K/p Highly efficient trigger for t events Richard Kass

The BaBar Detector BaBar (and Belle) has: r-f view x-z view BaBar (and Belle) has: excellent charged particle tracking excellent EM calorimetry excellent Particle ID and LOTS of data. Richard Kass

PEP-II is a great accelerator Fact #3 PEP-II is a great accelerator BaBar recorded data ~477 fb-1 Total # of t decays: ~8.7x108 Expect ~ 1.5x109 by Sept. 2008 Peak Luminosity 1.2 x 1034 cm-2 s-1 Richard Kass

t LFV Search Technique All of the analyses to be discussed rely on the following: i) only 2 t’s produced in the event, each t has the beam energy ii) divide event into 2 hemispheres; “Tag” and “Signal” Tag side assumes the tau decays via standard model (e.g. τ-→π- ν, τ-→e νv) Signal side contains the LFV decay. Since the LFV decays are neutrinoless no missing mom/energy allowed on Signal side t   MC τ+→μ+μ+μ- τ-→π- ν iii) Rely heavily on kinematics for signal/bkgd separation signal box For signal events: ΔE~0 and MEC~Mτ iv) Use data (if possible) & MC to estimate backgrounds Use MC to estimate signal efficiency Richard Kass

Introduction to Lepton Flavor Violation (LFV) in τ decay In the neutrino sector there is large LFV! neutrino oscillations Þ q23 »450, q12 »320 solar neutrinos: ne ®ne/3+nm/3+nt/3 But in the standard model charged LFV is heavily suppressed. t m g nt nm W · Lee-Shrock, Phys. Rev. D 16, 1444 (1977) However LFV OK in many extensions to standard model. SUSY models can bring B(t®mg) all the way to 10-7 Richard Kass

Theory Says….. (a small sampling of the models) = within range Observe LFV Þ Observe New Physics Don’t Observe LFV Þ Rule out some models Richard Kass

Search for t   & t  e BaBar used 232 fb-1 data (~430·106 τ’s) to search for τ→μγ & τ→eγ τ→eγ Main backgrounds: Bhabha & t+t- [t→enn with ISR, FSR t→ enng] # bckd expected =1.9±0.4 evts # of observed events = 1 efficiency=(4.7±0.3)% BF(t -  e- g ) < 11 x10-8 t - m- g Main backgrounds: dimuon (m+m-), t+t- [t ->mnn with ISR, FSR] PRL 96, 041801 (2006) # bckd expected =6.2±0.5 # of observed events = 4 efficiency=(7.4±0.7)% BF (t -  m- g ) < 6.8 x10-8 PRL 95, 041802 (2005) Richard Kass

Search for t   & t  e τ l Upper Limits Vs time S. Banerjee (Tau06) Nucl. Phys. Proc., Suppl. 169, 199 (2007) Richard Kass

t  & b®s! SUSY GUT models can relate CP asymmetry in B®fKs to B(t®mg) SU(5), right handed neutrino GUT relation: b®s penguin processes and t   are related in SUSY GUTs. J. Hisano & Y.Shimizu, PLB 565 (2003), 182. PDG 2000 scalar mass gaugino mass CP asymmetry in Bd ®fKs Richard Kass

mSUGRA mixing at GUT scale t  & SUSY! BaBar (L=232 fb-1) Belle (L=535 fb-1) preliminary Hisano & Y.Shimizu PDG 2000 BaBar 2007 HFAG: SφKs=0.39±0.17 SUSY SO(10) + seesaw Masiero et al. – NJP 6 (2004) 202 Excluded mSUGRA mixing at GUT scale Brignole, Rossi NJB701 (2004) 3 mSUGRA + Seesaw Igonkina, hep-ex/0606009v1 Richard Kass

Searches for τ→l+(π0, η, η′) Signal box (±2 in DE and MEC) Shaded region covers 68% of signal MC ● =data Using 339 fb-1 data (~620·106 τ’s) t decay mode UL (10-7) ep0 1.3 mp0 1.1 eh (h->gg) 2.5 mh (h-> gg) 1.9 eh (h->ppp0) 5.4 mh (h->ppp0) 4.5 eh 1.6 mh 1.5 eh’ (h’->pph) 5.8 mh’ (h’->pph) 3.6 eh’ (h’->rg) 4.2 mh’ (h’->rg) 2.7 eh’ 2.4 mh’ 1.4 Background events: 0.1-1.3 depending on mode Total expected events = 3.1 Total observed events = 2 NO Signals PRL 98, 061803 (2007) Richard Kass

τ→lη and New Physics 2007 Exclusion regions in tanβ=<Hu>/<Hd>, A0= pseudoscalar CPodd Higgs A0= pseudoscalar CPodd Higgs M.Sher, PRD 66, 057301 (2002) 2007 Exclusion regions in the mA and tanb plane by different experiments @ 95%CL Competitive with the direct Higgs searches at CDF & D0 CDF: pp  H  τ+τ- (310 fb-1) D0: pp  H  τ+τ- (325 fb-1) D0: pp  H  bb (260 fb-1) S.Banerjee (Tau 06) Nucl. Phys. Proc. Suppl. 169, 199 (2007) Richard Kass

Search for τ→lw Mode Eff.(%) expected bckd observed bckd UL@90%CL τ→eω Use 384.1 fb-1 data (~710·106 τ’s) for this analysis Use ω→π+π-π0 τ→ew τ→mw Signal box ±3 in DE-MEC ● =data ● =data Mode Eff.(%) expected bckd observed bckd UL@90%CL τ→eω 2.96±0.21 0.35±0.06 1.1·10-7 τ→μω 2.56±0.23 0.73±0.03 1.0·10-7 NO Signals arXiv:0711.0980 [hep-ex] submitted to PRL Richard Kass

Search for τ→lll m- t- h0 m+ SUSY Models: B(τ→lll) & B(τ→lhh) in range 10-17 to 10-6 Many Modes to search: t- -> e+e-e- , m+m-m-, e-m+m-, m-e+e- , m+e-e-, e+m-m- m- h0 t- m+ Babu, Kolda PRL 89 241802 (2002) t Signal Mode m-m+m- e-e+e- μ-e+e- e-m+m- μ+e-e- e+m-m- Dominant Background tt uds eemm Bhabha eeee mm Event selection is optimized separately for each signal mode accounting for different background compositions Richard Kass

Results for τ→lll search ● =data Used 376 fb-1 (~690·106 τ’s) of data Efficiency: 5.5-12.4% Background events: 0.3-1.3 depends on mode Total background = 4.20.8 events Total number of observed events =6 BR(t)<(3.7-8.0)x10-8 @ 90%CL 2-5 X lower limits than previous Babar results NO Signals arXiv:0708.3650 [hep-ex] accepted by PRL. Richard Kass

Results For τ→lhh′ (221.5 fb-1) Many Modes Searched No signals, just upper limits · DATA (221.5 fb-1) Used 221 fb-1 (~410·106 τ’s) of data Selection criteria and signal region optimized for each mode for best Upper Limit Signal efficiency varies by mode, 2.1-3.8% Number of background events estimated for each mode, 0.1-3 events, data 0-3events Upper limits calculated according to method of Cousins and Highland (NIM A 320 (1992) 331.) BR’s < (0.7-4.8)10-7 (90% CL) Published in PRL 95 (2005) 191801 Richard Kass

Summary of 3 Body LFV Decays No signals found Set limits O(10-8-10-7) for 20 LFV modes (6 lll and 14 lhh′) Limits at the upper end of theoretical predictions eg: SUSY with Higgs Triplet: B(→ lll) is 10-7 Can probe 10-8 (SUSY) region with higher statistics: Þ backgrounds are under control (~ 1 channel): For t → lll analysis expect 4.2 events find 6. For t → lhh′ analysis expect 11.1 events find 10. Richard Kass

Lepton & Baryon number violation in τ Decay Baryon asymmetry in the universe is an outstanding question. Standard model (SM) has lepton (L) & baryon (B) number conservation built in. Once you go beyond the SM B & L do not have to be conserved But in some supersymmetric models B-L is conserved t-→Lp- pp- t-→«p- pp+ t- L p- B 1 B-L -1 +1 t- « p- B -1 L 1 B-L (B-L) violating (B-L) conserving Also searched for decays with a K- instead of π Richard Kass

L & B # violation in τ Decay t-→«p- t-→Lp- 237 fb-1 BaBar data ( ~440·106 τ’s) used for this analysis. ● =data hep-ex: 0607040 Signal MC with arbitrary normalization t- →«K- t- →LK- Elliptical signal region NO Signals Mode B-L Eff.(%) expected bckd observed bckd UL@90%CL t-→«p- conserve 12.28 0.42±0.42 5.9·10-8 t-→Lp- violate 12.21 0.56±0.56 5.8·10-8 t-→«K- 10.63 0.26±0.26 7.2·10-8 t-→LK- 9.47 0.12±0.12 1 15·10-8 Richard Kass

Summary & Conclusions ►BaBar has performed many searches for LFV in τ decay 2-body decays: t  l, τ→l+(π0, η, η′), τ→lω 3-body decays: τ→lll, τ→lhh′ baryon number violating LNO evidence for LFV in τ decay similar results from Belle starting to limit the parameter space of models ►Since most channels are not background limited expect better limits with more data BaBar takes data until Sept. 2008 Expect ~2X improvement in UL’s with full data set ►What are the long(er) term chances of seeing LFV in τ decay? Lots of τ’s produced at LHC but HUGE backgrounds: BaBar B(τ→3m)<5.3·10-8 Vs 1 year of LHCb: B(τ→3m)<1.2·10-7 Best chance to see LFV in τ decay is at a Super B-factory produce ~1.5·1011 τ’s at Super B factory M. Shapkin, Nuc. PhysB 169 (2007) 363 Richard Kass

LFV in t decays: SuperB capability t , hh’ : the sensitivity is not likely to be limited by irreducible backgrounds: the sensitivity scales as 1/L. For SuperB @ 75 ab-1 expect ~2x10-10 Principal backgrounds From: Hitlin, Giorgi, SuperB workshops Richard Kass 23

Extra slides Richard Kass

BaBar K/p ID D*+ → D0p+ D0→ K+ p- BaBar DIRC Richard Kass