Swagato Banerjee. HEP Seminar University of Wisconsin, Madison 16 October 2006

Transcription

1 TAU PHYSICS AT BABAR Swagato Banerjee HEP Seminar University of Wisconsin, Madison 16 October 2006

2 SLAC-Based B-Factory The BABAR Detector:

3 PEP II Records: better than ever

4 τ-factory /13/ :19 B-Factories are also τ-factories s =.58 GeV (Υ (4S)): σ(e + e BB) = 1.05 nb σ(e + e τ + τ ) = 0.89 nb Experiment # of τ-pairs LEP 3 5 CLEO 1 7 BABAR 3 8 Precision measurements: systematics limited on-going efforts ] -1 Integrated Luminosity [fb Delivered Luminosity Recorded Luminosity Off Peak BaBar Run 1-5 PEP II Delivered Luminosity: /fb BaBar Recorded Luminosity: /fb Off Peak Luminosity: 37.43/fb Ideal for search of rare decays

5 τ Physics at BABAR Tests of Standard Model τ-lifetime Tests of CPT Lepton-universality Strange Spectral Function Extraction of V us, m s New decay modes A typical τ + τ event Search for new Physics Lepton Flavor Violation τ µγ, τ eγ τ lπ 0 /η/η τ lll, τ lhh

6 τ-lifetime

7 Strange Spectral Function Excellent K/π separation using dedx, Cherenkov angle Inclusive study of strange spectral functions from final states with net strangeness of unity (Branching Fraction = (29.3 ± 0.8) 3 ) the route to world s best measurement of V us, m s Branching Fractions of τ K π 0 ν τ, τ K π π + ν τ reported with better precision than the world average with 230 fb 1, 344 fb 1 of data respectively (BaBar Preliminary, TAU06)

8 New decay modes FIRST MEASUREMENTS of Branching Fractions O( 5 ) Significances: τ π φν τ : 5.5 σ, τ K K K + ν τ :.6 σ τ π φν τ consistent with saturating τ K K K + ν τ decays

9 Search for New Physics 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 But, now we have clear indication that ν s have finite mass Lepton Flavor is violated in Nature: but by how much? 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 sin 2 2θ mix B(τ µ ν µ ν τ ) = 3α 128π M 2 W With 3 ev 2, M W O( 11 ) ev O( 54 ) (θ mix : max)... many orders below experimental sensitivity! Observation for LFV unambiguous signature of new physics

10 LFV τ decays Mass dependent couplings enhance tau LFV w.r.t. lighter leptons Some models predict LFV upto existing experimental bounds eg. SUSY models: non-diagonal slepton mass matrix LFV Normal (Inverted) hierarchy for slepton τ µγ ( τ eγ) O( 6 ) (CLEO 00) (J. Ellis, J. Hisano, M. Raidal and Y. Shimizu, Phys. Rev. D 66 (2002) )

11 LFV τ decays Neutrinoless 2 and 3 body τ decays have different sensitivity B(τ lγ) B(τ lll) msugra+seesaw (EPJC14(2000)319, PRD66(2002)115013) 7 9 SUSY SO() (NPB649(2003)189, PRD68(2003)033012) 8 SUSY Higgs (PLB549(2002)159, PLB566(2003)217) 7 Non-Universal Z (PLB547(2002)252) 9 8 SM+Heavy Majorana ν R (PRD66(2002)034008) 9 Illustrative scenarios... ν µ τ χ γ τ µ µ H 0 µ + Search for τ lγ/p 0, τ lll, τ lhh decays (l = e, µ; h = π, K)

12 Higgs induced tree level η final state enhanced due to color factor and Higgs-s s vertex MSSM + seesaw: (M.Sher, PRD66 (2002) ) ( ) 6 ( ) 4 tanβ 0 GeV B(τ µη) = m A where m A is the pseudoscalar Higgs mass and tanβ = H u / H d B(τ µη) : B(τ µγ) : B(τ µµµ) = 8.4 : 1.5 : 1

13 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

14 e + e τ + τ (clean environment) τ lγ l 1 or 3 prong γ ν Signal Side Tag Side Backgrounds: τ lll (τ lhh ) l 1 prong l(h) l(h) ν Signal Side Tag Side Backgrounds: τ eγ (τ µγ): τ l l + l : Radiative Bhabha (di-muon) Bhabha, di-muon τ + τ γ(τ lνν) τ l + l l, τ lhh : qq (γ) τ + τ, qq # of ν(s) in Signal-side Signal: 0 τ + τ : 1-2 Bhabha, di-muon, qq: 0 # of ν(s) in Tag-side Signal: 1-2 τ + τ : 1-2 Bhabha, di-muon, qq: 0

15 Highlights of Search Signal MC: simulated with background and detector conditions (lγ) mass: Beam energy constrained fit with vertex corrections τ eγ search: Correlation between [m 2 ν, p T miss ] to reject Bhabha τ µγ search: MultiLayerPerceptron (NN) to reject di-muons Extended Un-binned Likelihood Fits: Background estimation

16 Signal Characteristics (GeV) M EC (Energy, Mass) daughters ( s 2, m τ ) (upto resolution & radiation) Photon at edge of acceptance Initial State Radiation E (GeV) 2 1 τ µγ simulation E = E rec s 2 0 σ( E) 50 MeV M EC (σ 9 MeV) Beam energy constrained mass after vertexing γ at µ POCA(XY) [Inv. mass: σ 24 MeV ] Signal Region: ± 2 σ around ( E, M EC )

17 Signal Characteristics (GeV) M EC (Energy, Mass) daughters ( s 2, m τ ) (upto resolution & radiation) E (GeV) 2 1 τ µγ simulation E = E rec s 2 0 σ( E) 50 MeV M EC (σ 9 MeV) Beam energy constrained mass after vertexing γ at µ POCA(XY) [Inv. mass: σ 24 MeV ] Blinded Region: ± 3 σ around ( E, M EC )

18 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 2 ν = E/ 2 T ag p/2 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 2 ν ( GeV2 ) m 2 ν ( GeV2 ) Bhabha rejection for searches with electron: (m 2 ν /1.8 GeV2 ) ln(p T miss /E beam)/2 < 1 electron / Tag-side, p CM T ag < 4.75 GeV, θlab miss m 2 ν ( GeV2 ) detector acceptance Di-muon rejection for searches with muon: ln(p T miss /E beam) < 2.5, p CM T ag < 4.75 GeV, θlab miss detector acceptance

19 τ µγ: Neural-Net Selection Signal: MC Background: Data / ±3σ Common Input Variables: µ Helicity angle Event Missing p T Event Missing Mass Tag-side Missing Mass Tag-side Momentum

20 τ µγ: Neural-Net Selection Signal: MC Background: Data / ±3σ Common Input Variables: µ Helicity angle Event Missing p T Event Missing Mass Tag-side Missing Mass Tag-side Momentum MC Optimized/ tagging modes: electron electron gamma muon hadron hadron gamma 3 hadrons Events/ Data µ ± γ τ + τ- + - e-tag µ µ qq eγ-tag µ-tag h-tag hγ-tag 3h-tag NN Output

21 Background estimation: τ lγ/p 0 τ ± l ± γ: Background rate from PDF(m EC ) in ±2σ band in E (GeV/c m EC Events/(0.05 GeV/c 2 2 ) ) 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 2σ = 2σ PDF tot GSB 3σ PDF N data tot GSB 3σ

22 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

23 τ ± l ± P 0 ) 2 (GeV/c 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 2 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 = 2

24 Neighboring & Signal boxes Decay modes ±3σ to ±11σ box ±2σ 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 ) ± ±0.02 τ ± e ± η (η π + π η) ± ±0.01 τ ± µ ± η (η π + π η) ± ±0.02 τ ± e ± η (η ρ 0 γ) ± ±0.03 τ ± µ ± η (η ρ 0 γ) ± ±0.03 Good modeling of background in data No evidence of signal

25 Background estimation: τ lll,lhh qq: uniform E (GeV) qq E (GeV) QED QED: E M (GeV) M (GeV) τ + τ : M 0 E 0 E (GeV) ττ E (GeV) data τ lll: after PID & Preselection M (GeV) M (GeV) 2-dim PDF s: shape from MC/control sample, rate fitted to Data

26 τ lll E (GeV) τ e - e + e - - τ - µ + e - e τ - e - µ + µ - BABAR τ - µ - e + e - τ e + µ µ τ - µ - µ + µ M (GeV/c N bkg /channel = ( ), Total expected = 3.4, Observed = 3 )

27 τ lhh E (GeV) e - + τ K K τ - e - K π- - τ- e - π + K τ - e - π + π- BABAR e + - τ K K τ- e + K π- τ - e + π - π τ µ K K τ - µ K π µ π + - τ K τ - µ π + π τ µ K K τ- µ K π- + τ - µ π - π M (GeV/c ) N bkg /channel = ( ), Total expected = 11.3, Observed =

28 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% 22% 11% ~5% σ τ + τ (.6 GeV) 0.89 nb, L 339 fb 1 ( BABAR Summer 2006) N τ = 2 L σ τ + τ NUL: 90 90% C.L. Upper Limit for (N obs, N bkg ) from Data Naive Sensitivity : N 90 UL = 2.3 N bkg, N bkg O(1) B 90 UL O( 7 )

29 B-Factories: Status Channel BABAR BELLE BUL 90 ) L ( fb 1 ) BUL 90 ) L ( fb 1 ) τ ± e ± γ PRL96(2006)41801 ICHEP06: Preliminary result τ ± µ ± γ PRL95(2005)41802 ICHEP06: 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 lll (1-3) 91.5 (2-4) 87.1 PRL92(2004) PLB589(2004)3 τ lhh (1-5) (2-16) PRL95(2005) NPB(Proc)144(2005)173

30 B-Factories: Combinations Signal and Background PDF parameterizations vary Signal regions not same for all analysis: 2σ 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: 2Lσ 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 A320, 331 (1992), Barlow CPC 149, 97 (2002)]

31 B-Factories: Combinations τ ± e ± γ Luminosity ε Background events (%) Expected Observed BABAR fb ± ± BELLE fb ± BABAR & BELLE fb ± ± B(τ ± e ± γ) < % C.L. τ ± µ ± γ Luminosity ε Background events (%) Expected Observed BABAR fb ± ± BELLE fb ± BABAR & BELLE fb ± ± B(τ ± µ ± γ) < % C.L.

32 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 (BaBar fb 1 ) Background free search 2.3 N obs O(1) Background limited search L B 90 UL 1/L 1/ L BaBar, Belle: 1 ab 1 each (2008) L ( ab 1 ) 0.25 (Now) B 90 UL ( 8 ) 2.5 (5) 0.05 (0.7) Super B-Factory: 50 ab 1 B 90 UL < O ( ) / O ( 9 ) no/with Background

33 τ µγ: LHC expectations Energy of τ not known, Mass(daughters) m τ Signal qq W τ( µγ)ν σ B = 14.8 nb N τ (for fb 1 low luminosity 1yr data) Backgrounds FSR qq W µνγ qq W τ( µν ν)νγ Radiative production qq W γ µνγ L. Serin and R. Stroynowski (ATL-PHYS ): ε = 5.4%, N bkg = 17 events/yr ( fb 1 ) Sensitivity B(τ µγ) = (2.3 N bkg ) / (N τ ε) 6 For 30 fb 1 data : B(τ µγ) < E. Barberio (SMU, 2002): Signal: Z ττ decays N τ = 2 L σ B For 30 fb 1 data : B(τ µγ) < 0.5 7

34 τ µµµ: LHC expectations Event Signature: 3 prong vertex µ ID m(µµµ) m τ N τ / yr (low lumi) W τν Z ττ D S τx B 0 τx B ± τx B S τx 7.9 CMS Simulation

35 τ µµµ: LHC expectations Level 1 Trigger: single-muon p T > 14 GeV, di-muon p T > 3 GeV Backgrounds: D S µνφ φ µµ, φ µµγ ε 1%, B(τ µµµ) < (A.Stahl, Heraeus Flavor School 2005)

36 BABAR Physics Reach Assessment (2005) msugra mixing at GUT scale: L = M 2 L L L M 2 Ẽ ẼẼ Model-independent calculation 0.35 τ µγ 0.3 (A.Brignole, A.Rossi, NPB701(2004)3) RGE using SPheno (W. Porod, CPC153(2003)275) Cold Dark Matter (WMAP) with micromegas (CPC149(2002)3) M 2 L23 /M 2 L m 0 (GeV) m GUT = 5 15 GeV, tan β = 55 µ > 0, A 0 = 0, m 1/2 = m 0 B 90 UL ( 8 ) msugra + Seesaw: ν-mixing induces LFV at EW scale via RGE Normal Hierarchy Inverted Hierarchy m 1/2 (GeV) τ is LSP Allowed by Ω CDM h 2 m 1/2 (GeV) τ is LSP Allowed by Ω CDM h B(τ µγ) < 7, 5, 2, 1 ( 8 ) B(τ eγ) < 11, 5, 2, 1 ( 8 ) m 0 (GeV) m 0 (GeV) Excluded by LEP No REWSB Excluded by LEP No REWSB m νr = 5 14 GeV, tan β = 55, µ > 0, A 0 = 0, m 0, m 1/2, M 2 L, M 2 Ẽ : Diagonal

37 τ µγ & S φks SUSY SU(5) GUT: Flavor changing right-handed currents Correlations between CP asymmetry in b-s penguins and τ µγ BABAR BELLE BABAR & BELLE J. Hisano, Y. Shimizu (PLB565(2003)183) tan β =, A 0 = 0, m 0 m 1/2 m νr = 5 14 GeV, m ντ = 5 2 ev Current measurement: S(B φk S ) = 0.47 ± 0.19 (HFAG, 2005). More sensitive B(τ ± µ ± γ) < exclude some regions.

38 τ lll predictions SUSY + Higgs (A.Brignole, A.Rossi, PLB566(2003)217) B(τ 3µ) 7 ( tan β 50 )6 ( 0GeV m A ) 4 ( 50 L R 2 3 ) If Higgs light, s-particles O( TeV), tan β 50 No direct observation, but τ µµµ observable (?) Sensitivity 8 at B-Factories, LHC Non Universal Z (Technicolor) (C.Yue, Y.Zhang, L.Liu, PLB547(2002)252) τ lll most sensitive Flavor mixing (k 1 ) = 0.2, B(τ lll) < 8 m Z < 1.2 TeV

39 Search for Supersymmetric Higgs Mixing between left-handed smuons and staus with m νr = 14 GeV via seesaw τ ± µ ± η limit translates into exclusion plot in tan β vs. m A plane (M.Sher, PRD66 (2002) ) BELLE BABAR & BELLE Light and dark shade: m max h and no-mixing stop mixing benchmark models (M. Carena et.al, hep-ph/ ) 95% C.L. from BABAR-BELLE competetive with direct searches at CDF: τ + τ (3 pb 1 ), D0: b b (260 pb 1 ), τ + τ (325 pb 1 ), and complementary to region excluded by LEP2

40 Summary of LFV Limits -2-4 B(τ e γ) MARKII CRYSTAL BALL ARGUS DELPHI -2-4 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

41 Conclusions B-Factories are also τ-factories Dataset expected to be doubled by 2008 On-going effort to better understand systematic errors Expect lots of more τ-physics in near future: Leptonic Branching Fractions, Lepton Universality Structure of non-strange and strange hadronic states High precision tests of QCD: V us, m s Search for new Physics are very close to theoretical predictions: already probing LFV predictions O( 8 ). Please Stay tuned to update of Experiment vs. Theory plots...