Searches for Lepton Flavor Violation. Update on BaBar Searches for Lepton Flavor Violation using Tau Decays

Transcription

1 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 Miami

2 Fact #1 Since the cross section for e + e Y(4S) BB is about the same as the cross section for e + e τ + τ a B factory is also a τ factory. σ ΒB σ ττ Cross Section July nb 0.92 nb Richard Kass Miami

3 Fact #2 BaBar is a great detector for τ physics! Detector of Internally Recflected Cherenkov Light (DIRC) 1.5 T Solenoid Electromagnetic Calorimeter (EMC) Drift Chamber (DCH) e - (9 GeV)e + (3.1 GeV) Instrumented Flux Return (IFR) Silicon Vertex Tracker (SVT) SVT, DCH: charged particle tracking vertex &mom. resolution, K 0 s, Λ s EMC: electromagnetic calorimetry γ/e/π 0 /η DIRC, IFR, DCH: charged particle ID π/µ/k/p Highly efficient trigger for τ events Richard Kass Miami

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

5 Fact #3 PEP-II is a great accelerator BaBar recorded data~477 fb fb -1-1 Total # of of τ decays: ~8.7x10 88 Expect ~ 1.5x by by Sept Peak Luminosity 1.2 x cm -2 s -1 Richard Kass Miami

6 τ LFV Search Technique All of the analyses to be discussed rely on the following: i) only 2 τ s produced in the event, each τ 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 τ µγ MC τ + µ + µ + µ - τ - π - ν iii) Rely heavily on kinematics for signal/bkgd separation E = E beam E measured M EC = E 2 beam 2 measured For signal events: E~0 and M EC ~M τ iv) Use data (if possible) & MC to estimate backgrounds Use MC to estimate signal efficiency Richard Kass Miami P signal box

7 Introduction to Lepton Flavor Violation (LFV) in τ decay In the neutrino sector there is large LFV! neutrino oscillations θ , θ solar neutrinos: ν e ν e /3+ν µ /3+ν τ /3 But in the standard model charged LFV is heavily suppressed. ν τ 2 ν µ 2 3α m 2 54 ( ) ( ) 23 sin 2 ( ) 10 τ µ B τ µγ = θ B O 2 mix τ µν µ ν τ W W γ 128π m W Lee-Shrock, Phys. Rev. D 16, 1444 (1977) However LFV OK in many extensions to standard model. SUSY models can bring B(τ µγ) all the way to 10-7 Richard Kass Miami

8 Theory Says.. (a small sampling of the models) = within range Observe LFV Observe New Physics Don t Observe LFV Rule out some models Richard Kass Miami

9 Search for τ µγ & τ eγ BaBar used 232 fb-1 data (~ τ s) to search for τ µγ & τ eγ τ eγ Main backgrounds: Bhabha & τ+τ [τ eνν with ISR, FSR τ eννγ] # bckd expected =1.9±0.4 evts # of observed events = 1 efficiency=(4.7±0.3)% BF(τ e γ ) < 11 x10-8 PRL 96, (2006) τ µ γ Main backgrounds: dimuon (µ+µ ), τ+τ [τ >µνν with ISR, FSR] # bckd expected =6.2±0.5 # of observed events = 4 efficiency=(7.4±0.7)% BF (τ µ γ ) < 6.8 x10-8 PRL 95, (2005) Richard Kass Miami

10 Search for τ µγ & τ eγ τ lγ Upper Limits Vs time S. Banerjee (Tau06) Nucl. Phys. Proc., Suppl. 169, 199 (2007) Richard Kass Miami

11 τ µγ & b s! SUSY GUT models can relate CP asymmetry in B φk s to B(τ µγ) SU(5), right handed neutrino 2 2 ( ) ( ) m m e ϕ ϕ i( ) 1 2 GUT relation: d% R l% L b s penguin processes and τ µγare related in SUSY GUTs. scalar mass gaugino mass PDG 2000 J. Hisano & Y.Shimizu, PLB 565 (2003), 182. m m U A ν τ ν R 32 0 = = 5 10 = 5 10 = 1/ ev ev trilinear coupling CP asymmetry in B d φk s Richard Kass Miami

12 τ µγ & SUSY! Hisano & Y.Shimizu PDG 2000 Belle (L=535 fb -1 ) preliminary BaBar (L=232 fb -1 ) BaBar 2007 HFAG: S φks =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/ v1 Richard Kass Miami

13 Searches for τ l+(π 0, η, η ) Signal box (±2σ in E and M EC ) Shaded region covers 68% of signal MC = data Using 339 fb -1 data (~ τ s) Background events: depending on mode Total expected events = 3.1 Total observed events = 2 τ decay mode UL (10-7 ) τ decay mode UL (10-7 ) eπ µπ eη (η >γγ) 2.5 µη (η > γγ) 1.9 eη (η >πππ 0 ) 5.4 µη (η >πππ 0 ) 4.5 eη 1.6 µη 1.5 NO Signals PRL 98, (2007) eη (h ->ππη) 5.8 µη (η ->ππη) 3.6 eη (h ->ργ) 4.2 µη (η ->ργ) 2.7 eη Richard Kass Miami µη 1.4

14 τ lη and New Physics A 0 = pseudoscalar CP odd Higgs ( 6 tan β 100 GeV ) B τ µ η = m A tanβ=<h u >/<H d >, A 0 = pseudoscalar CP odd Higgs 6 4 M.Sher, PRD 66, (2002) 2007 Exclusion regions in the m A and tanβ plane by different 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 Miami

15 Search for τ lω Use fb -1 data (~ τ s) for this analysis Use ω π + π - π 0 τ eω τ µω Signal box ±3σ in E-M EC = data = data Mode Eff.(%) expected bckd observed bckd UL@90%CL τ eω 2.96± ± τ µω 2.56± ± NO Signals arxiv: [hep-ex] submitted to PRL Richard Kass Miami

16 Search for τ lll SUSY Models: B(τ lll) & B(τ lhh) in range to 10-6 Many Modes to search: τ > e + e e, µ + µ µ, e µ + µ, µ e + e, µ + e e, e + µ µ µ - τ - h 0 µ - 6 µ + Babu, Kolda PRL (2002) ( 7 tan β 100 GeV 3 ) B τ µ m A τ lll Signal Mode Dominant Background 4 µ µ + µ ττ uds eeµµ e - e + e - Bhabha eeee ττ µ - e + e - e - µ + µ Richard Kass Miami eeµµ ττ µµ µ + e - e - e + µ µ ττ uds Event selection is optimized separately for each signal mode accounting for different background compositions

17 Results for τ lll search = data Used 376 fb -1 (~ τ s) of data Efficiency: % Background events: depends on mode Total background = 4.2±0.8 events Total number of observed events =6 BR(τ 90%CL 2-5 X lower limits than previous Babar results NO Signals arxiv: [hep-ex] accepted by PRL. Richard Kass Miami

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

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

20 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 B L B-L τ Λπ τ Lepton & Baryon number pπ - Λ (B-L) violating violation in τ Decay π τ «π pπ + (B-L) conserving Also searched for decays with a K - instead of π B L B-L τ « π Richard Kass Miami

21 L & B # violation in τ Decay τ «π τ «Κ τ Λπ τ ΛΚ 237 fb -1 BaBar data ( ~ τ s) used for this analysis. = data hep-ex: Signal MC with arbitrary normalization Elliptical signal region NO Signals Mode B-L Eff.(%) expected bckd observed bckd UL@90%CL τ «π conserve ± τ Λπ violate ± τ «Κ conserve ± τ ΛΚ violate ± Richard Kass Miami

22 Summary & Conclusions BaBar has performed many searches for LFV in τ decay 2-body decays: τ lγ, τ l+(π 0, η, η ), τ lω 3-body decays: τ lll, τ lhh baryon number violating NO 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 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 3µ)< Vs 1 year of LHCb: B(τ 3µ)< Best chance to see LFV in τ decay is at a Super B-factory produce ~ τ s at Super B factory M. Shapkin, Nuc. PhysB 169 (2007) 363 Richard Kass Miami

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

24 Extra slides Richard Kass Miami

25 BaBar K/π ID D * + D 0 π + D 0 K + π - BaBar DIRC Richard Kass Miami