BABAR results on Lepton Flavour Violating (LFV) searches for τ lepton + pseudoscalar mesons & Combination of BABAR and BELLE LFV limits

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1 BABAR results on Lepton Flavour Violating (LFV) searches for τ lepton + pseudoscalar mesons & Combination of BABAR and BELLE LFV limits Swagato Banerjee 9 th International Workshop on Tau Lepton Physics 19 th nd September 006, Pisa, Italy (Page: 1/3)

2 Outline Lepton Flavour is violated in Nature: but by how much? Results from BABAR Collaboration: Data from Runs 1-4: Luminosity = 3. fb 1 B(τ ± µ ± γ) < : Phys. Rev. Lett. 95(005)4180 B(τ ± e ± γ) < : Phys. Rev. Lett. 96(006)41801 Data from Runs 1-5: Luminosity = fb 1 τ ± l ± π 0, l ± η, l ± η (where l = e, µ): Preliminary Result Combination of results from BABAR and BELLE Collaborations: τ ± µ ± γ, τ ± e ± γ: Luminosity = 3. (BABAR) (BELLE) = 767. fb 1 τ ± l ± π 0, l ± η, l ± η : Luminosity = (BABAR) (BELLE) = fb 1 Constraints on New Physics LFV τ decays (Page: /3)

3 Introduction Lepton flavor violation (LFV) not forbidden by SM gauge symmetry most new models explicitly include LFV vertex In SM, LF is conserved for zero degenerate ν masses SM extended to include finite ν mass and mixing predicts LFV τ ν ν τ µ X W µ γ B(τ ± µ ± γ)[lee-shrock, Phys. Rev. D 16, 1444 (1977)] ( ) m 3 sin θ mix B(τ µ ν µ ν τ ) = 3α 18π M W With 3 ev, M W O( 11 ) ev O( 54 ) (θ mix : max)... many orders below experimental sensitivity! Observation for LFV unambiguous signature of new physics LFV τ decays (Page: 3/3)

4 LFV τ decays Predicted by many beyond SM processes... SUSY models: non-diagonal slepton mass matrix LFV Normal (Inverted) slepton hierarchy τ ± µ ± γ (τ ± e ± γ) Some models: LFV upto existing experimental bounds B(τ ± l ± γ) msugra+seesaw (EPJC14(000)319, PRD66(00)115013) 7 SUSY SO() (NPB649(003)189, PRD68(003)03301) SUSY Higgs (PLB549(00)159, PLB566(003)17) Non-Universal Z (PLB547(00)5) SM+Heavy Majorana ν R (PRD66(00)034008) Illustrative scenario: ν µ τ χ γ LFV τ decays (Page: 4/3)

5 Higgs induced tree level η final state enhanced due to color factor and Higgs-s s vertex MSSM + seesaw: (M.Sher, PRD66 (00) ) ( ) 6 ( ) 4 tanβ 0 GeV B(τ ± µ ± η) = m A where m A is the pseudoscalar Higgs mass and tanβ = H u / H d B(τ ± µ ± η) : B(τ ± µ ± γ) = 8.4 : 1.5 LFV τ decays (Page: 5/3)

6 e + e τ + τ (clean environment) Search for τ ± l ± γ/p 0, where P 0 = π 0, η, η ➋ decays: η γγ, η π + π π 0 ➋ decays: η π + π η (η γγ), η ρ 0 γ (ρ 0 π + π ) l γ γ Signal Side τ lγ(γ) 1 or 3 prong τ ± e ± γ, τ ± µ ± γ ν τ ± e ± π 0, τ ± µ ± π 0 : M π 0 γγ Tag Side [115, 150] MeV τ ± e ± η, τ ± µ ± η: M η γγ [515, 565] MeV h h τ lhhγ(γ) l 1 prong γ γ ν Signal Side Tag Side τ ± e ± η, τ ± µ ± η: M η π + π π 0 [537, 558] MeV τ ± e ± η, τ ± µ ± η : M η π + π η M η ρ 0 γ [950, 965] MeV [940, 970] MeV LFV τ decays (Page: 6/3)

7 Signal vs. Background ln(p T miss /E beam) τ ± e ± γ/p 0 e + e τ + τ γ e + e e + e γ m ν = E/ T ag p/ T ag p T miss /E beam large large small ln(p T miss /E beam) τ ± e ± γ e + e τ + τ γ e + e e + e γ m ν ( GeV ) m ν ( GeV ) Bhabha rejection for searches with electron: (m ν /1.8 GeV ) ln(p T miss /E beam)/ < 1 electron / Tag-side, p CM T ag < 4.75 GeV, θlab miss m ν ( GeV ) detector acceptance Di-muon rejection for searches with muon: ln(p T miss /E beam) <.5, p CM T ag < 4.75 GeV, θlab miss detector acceptance LFV τ decays (Page: 7/3)

8 Signal Characteristics (GeV) M EC (Energy, Mass) daughters ( s, m τ ) (upto resolution & radiation) Photon at edge of acceptance Initial State Radiation E (GeV) 1 τ µγ simulation E = E rec s 0 σ( E) 50 MeV M EC (σ 9 MeV) Beam energy constrained mass after vertexing γ at µ POCA(XY) [Inv. mass: σ 4 MeV ] Signal Region: ± σ around ( E, M EC ) LFV τ decays (Page: 8/3)

9 Signal Characteristics (GeV) M EC (Energy, Mass) daughters ( s, m τ ) (upto resolution & radiation) E (GeV) 1 τ µγ simulation E = E rec s 0 σ( E) 50 MeV M EC (σ 9 MeV) Beam energy constrained mass after vertexing γ at µ POCA(XY) [Inv. mass: σ 4 MeV ] Blinded Region: ± 3 σ around ( E, M EC ) LFV τ decays (Page: 8/3)

10 Background estimation τ ± l ± γ: Background rate from PDF(m EC ) in ±σ band in E (GeV/c m EC Events/(0.05 GeV/c ) ) 5 Data Bhabha e + e - τ + τ - τ ± e ± γ E (GeV) (GeV/c ) m EC τ ± l ± P 0 : Unbinned maximum likelihood fit to (m EC, E) 3σ GSB N data σ = σ PDF tot GSB 3σ PDF N data tot GSB 3σ LFV τ decays (Page: 9/3)

11 Modeling m EC & E PDF tot = (f e+ e /µ + µ PDF e + e /µ + µ ) +(f τ + τ PDF τ + τ )+([1 f e + e /µ + µ f τ + τ ] PDF qq) Signal MC τ ± e ± η (η γγ) PDF e+ e : Data control samples with electron Tag-side others: multi-variate PDF(s) kernel density estimated from MC E (Projection) Bhabha : 6.8 Data: etag BABAR preliminary GeV MEC (Projection) Bhabha : 6.8 Data: etag BABAR preliminary E (Projection) MC: Data: 18 BABAR preliminary GeV M EC (Projection) MC:.5 Data: 18 BABAR preliminary Events / ( 0.1 GeV ) Events / ( 0.05 GeV ) BABAR preliminary E (GeV) BABAR preliminary Bhabha τ + τ GeV GeV (GeV) M EC LFV τ decays (Page: /3)

12 τ ± l ± P 0 : Results ) (GeV/c 1.8 e π 0 (π 0 γγ) e η (η γγ) e η (η π + π - π 0 ) + π - + e η (η π η) e η (η π π - γ) M EC 1.6 BABAR preliminary µ π 0 (π 0 γγ) µ η (η γγ) + µ η (η π π - π 0 ) + µ η (η π π - η) + µ η (η π π - γ) E (GeV) N bkg /channel = ( ), Total expected = 3.1, Observed = LFV τ decays (Page: 11/3)

13 Neighbouring & Signal boxes Decay modes ±3σ to ±11σ box ±σ box observed expected observed expected τ ± e ± π 0 (π 0 γγ) ± ±0.04 τ ± µ ± π 0 (π 0 γγ) ± ±0.15 τ ± e ± η (η γγ) ± ±0.05 τ ± µ ± η (η γγ) ± ±0.08 τ ± e ± η (η π + π π 0 ) ± ±0.01 τ ± µ ± η (η π + π π 0 ) 3.01± ±0.0 τ ± e ± η (η π + π η) ± ±0.01 τ ± µ ± η (η π + π η) 1.4± ±0.0 τ ± e ± η (η ρ 0 γ).97± ±0.03 τ ± µ ± η (η ρ 0 γ) ± ±0.03 Good modeling of background in data No evidence of signal LFV τ decays (Page: 1/3)

14 Upper Limit B 90 UL = N 90 UL /(N τ ε) ε: high statistics signal MC simulated for different Data-taking periods ε = Trigger. Reco. Topology. PID. Cuts. Signal Box Cumulative: 90% 70% 70% 50% 50% 50% 90% 63% 44% % 11% ~5% σ τ + τ (.6 GeV) 0.89 nb, L 339 fb 1 ( BABAR Summer 006) N τ = L σ τ + τ NUL: 90 90% C.L. Upper Limit for (N obs, N bkg ) from Data Naive Sensitivity : N 90 UL =.3 N bkg, N bkg O(1) B 90 UL O( 7 ) LFV τ decays (Page: 13/3)

15 B-Factories: Status Channel BABAR BELLE BUL 90 ) L ( fb 1 ) BUL 90 ) L ( fb 1 ) τ ± e ± γ PRL96(006)41801 Tau06: Preliminary result τ ± µ ± γ PRL95(005)4180 Tau06: Preliminary result τ ± e ± π Tau06: Preliminary result ICHEP06: hep-ex/ τ ± µ ± π Tau06:Preliminary result ICHEP06: hep-ex/ τ ± e ± η Tau06: Preliminary result ICHEP06: hep-ex/ τ ± µ ± η Tau06: Preliminary result ICHEP06: hep-ex/ τ ± e ± η Tau06: Preliminary result ICHEP06: hep-ex/ τ ± µ ± η Tau06: Preliminary result ICHEP06: hep-ex/ LFV τ decays (Page: 14/3)

16 B-Factories: Combinations Signal and Background PDF paramerterizations vary Signal regions not same for all analysis: σ ellipse vs. rectangle BABAR uses m EC, BELLE uses m inv : resolutions different Efficiency combined by weighting with luminosity Observed & background events added (asymmetric errors averaged) 6 Toy MC generated: Poisson distribution with mean (s + b) where the background, b, and signal, s, are each drawn randomly from Gaussian distributions describing their respective PDFs. Mean and s.d. of background Gaussian: (b ± σ b ) Mean and s.d. of signal Gaussian: Lσ τ τ B UL (ε ± σ ε ) Vary B UL till % of the sample yields a number of events < n obs = the number of events observed in the data upper limit at 90% confidence level (C.L.) [Ref: Cousins-Highland NIM A30, 331 (199), Barlow CPC 149, 97 (00)] LFV τ decays (Page: 15/3)

17 B-Factories: Combinations τ ± e ± γ Luminosity ε Background events (%) Expected Observed BABAR 3. fb ± ± BELLE fb 1.99 ± BABAR & BELLE 767. fb ± ±.3 6 B(τ ± e ± γ) < % C.L. τ ± µ ± γ Luminosity ε Background events (%) Expected Observed BABAR 3. fb ± ± BELLE fb ± BABAR & BELLE 767. fb ± ± B(τ ± µ ± γ) < % C.L. LFV τ decays (Page: 16/3)

18 B-Factories: Combinations τ ± e ± π 0 Luminosity ε Background events (%) Expected Observed BABAR fb 1.83 ± ± BELLE fb ± ± BABAR & BELLE fb ± ± B(τ ± e ± π 0 ) < % C.L. τ ± µ ± π 0 Luminosity ε Background events (%) Expected Observed BABAR fb ± ± BELLE fb ± ± BABAR & BELLE fb ± ± 0.37 B(τ ± µ ± π 0 ) < % C.L. LFV τ decays (Page: 17/3)

19 B-Factories: Combinations τ ± e ± η Luminosity ε Background events (%) Expected Observed BABAR fb 1.1 ± ± BELLE fb 1.86 ± ± BABAR & BELLE fb 1.5 ± ± B(τ ± e ± η) < % C.L. τ ± µ ± η Luminosity ε Background events (%) Expected Observed BABAR fb ± ± BELLE fb ± ± BABAR & BELLE fb ± ± B(τ ± µ ± η) < % C.L. LFV τ decays (Page: 18/3)

20 B-Factories: Combinations τ ± e ± η Luminosity ε Background events (%) Expected Observed BABAR fb ± ± BELLE fb 1.15 ± BABAR & BELLE fb ± ± B(τ ± e ± η ) < % C.L. τ ± µ ± η Luminosity ε Background events (%) Expected Observed BABAR fb 1.18 ± ± BELLE fb 1.45 ± BABAR & BELLE fb 1.33 ± ± B(τ ± µ ± η ) < % C.L. LFV τ decays (Page: 19/3)

21 B-Factories: Projections B 90 UL = N 90 UL /(N τ ε) τ ± µ ± γ search: Optimize NUL 90 /ε for expected 90% C.L. N 90 UL Baseline: B 90 UL 1. 7 (BaBar 3. fb 1 ) Background free search.3 N obs O(1) Background limited search L B 90 UL 1/L 1/ L BaBar, Belle: 1 ab 1 each (008) L ( ab 1 ) 0.5 (Now) B 90 UL ( 8 ).5 (5) 0.05 (0.7) Super B-Factory: 50 ab 1 B 90 UL < O ( ) / O ( 9 ) no/with Background LFV τ decays (Page: 0/3)

22 τ µγ & S φks SUSY SU(5) GUT: Flavour changing right-handed currents Correlations between CP asymmetry in b-s penguins and τ µγ BABAR BELLE BABAR & BELLE J. Hisano, Y. Shimizu (PLB565(003)183) tan β =, A 0 = 0, m 0 m 1/ m νr = 5 14 GeV, m ντ = 5 ev Current measurement: S(B φk S ) = 0.47 ± 0.19 (HFAG, 005). More sensitive B(τ ± µ ± γ) < exclude some regions. LFV τ decays (Page: 1/3)

23 Search for Supersymmetric Higgs BABAR and BELLE upper 95% C.L. on search of τ ± µ ± η: competetive with direct searches at CDF: τ + τ (3 pb 1 ), D0: b b (60 pb 1 ), τ + τ (35 pb 1 ) complementary to region excluded by LEP BELLE BABAR & BELLE and no-mixing: stop mixing benchmark models (M. Carena et.al, hep-ph/9913) m max h LFV τ decays (Page: /3)

24 Summary of LFV Limits - -4 B(τ e γ) MARKII CRYSTAL BALL ARGUS DELPHI - -4 MARKII B(τ µ γ) ARGUS DELPHI msugra + Seesaw SUSY + SO() SUSY + Higgs CLEO BELLE BABAR BELLE BABAR+BELLE Technicolor + Z msugra + Seesaw SUSY + SO() SUSY + Higgs CLEO BELLE BABAR BELLE BABAR+BELLE Technicolor + Z Channel BABAR BELLE BABAR & BELLE BUL 90 ) L ( fb 1 ) BUL 90 ) L ( fb 1 ) BUL 90 ) L ( fb 1 ) τ ± e ± γ τ ± µ ± γ τ ± e ± π τ ± µ ± π τ ± e ± η τ ± µ ± η τ ± e ± η τ ± µ ± η LFV τ decays (Page: 3/3)