1 / 23

Lepton Flavor Violating  decays at B-factories: results and prospects

Lepton Flavor Violating  decays at B-factories: results and prospects. Giovanni Marchiori Università di Pisa & I.N.F.N. Introduction. LFV in charged lepton sector in SM (via  mixing) strongly suppressed (GIM)  Observation of LFV is a clear signal of NP

jens
Download Presentation

Lepton Flavor Violating  decays at B-factories: results and prospects

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. 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 10-610-7) • Results reported in this talk: LFV as discriminating tool •  l+g • t  l+l’l’ t  l+hh’ (h = ,K) t l+h0 (h0 = p0,h,h’,KS) t  l+V0 (V0 = r,K*,f) (l=e,m ) G. Marchiori - LFV tau decays at B-factories: results and prospects

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

  4. B-factories (e+e-,s10.58 GeV=M(4S)) 400fb-1 • A B-factory is also a t-factory! s(tt)~0.9nb, s(bb)~1.1nb ~5.6x108t-pairs at Belle, ~3.5x108t-pairs at BaBar  BR ~ O(10-8) sensitivity! ~ 109t-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% G. Marchiori - LFV tau decays at B-factories: results and prospects

  5. Signal signature (example for   ) 1/3 prong(s) + missing (tag side) m+g (signal side) m signal event g t e • e+e-t+t- 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: pmiss within detector acceptance, pTmiss>0, Mmiss~0 e t generic t decay signal MC 3s ellipse: blinded region G. Marchiori - LFV tau decays at B-factories: results and prospects

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

  7. Analysis strategy • Signalextraction:M-E plane (2s 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 ) G. Marchiori - LFV tau decays at B-factories: results and prospects

  8.    signal data • Main BGs: • tt+ISR g (tgmnn) • mm+ISR g • Belle(535fb-1, preliminary) • BaBar(232fb-1, PRL 95, 041802) signal region blinded region distribution in 2s band • Beam-energy constrained mass • =7.4±0.5% (3-prong tag: 1.2%) • Nexpected= 6.2±0.5 • Nobserved= 4 • BR<6.8x10-8 at 90% CL • = 6.7% (only 1-prong tag) • Nexpected= 13.9 • Nobserved= 10 • BR<4.5x10-8 at 90% CL G. Marchiori - LFV tau decays at B-factories: results and prospects

  9.   e • Main BGs: • tt+ISR g (tgenn) • ee+ISR g Belle(535fb-1, preliminary) BaBar(232fb-1 , PRL 96, 041801) • Beam-energy constrained mass •  = 4.7±0.3% • Nexpected= 1.9 ± 0.4 • Nobserved= 1 • BR<1.1x10-7 at 90% CL •  = 3.0% • Nexpected= ? • Nobserved= 5 • BR<1.2x10-7 at 90% CL G. Marchiori - LFV tau decays at B-factories: results and prospects

  10.  ll’l’ (l,l’=e,) signal box data Main BGs: higher order radiative e+e-, +-: e+e-lll’l’ BaBar(91.5fb-1 , PRL 92, 121801) • only 1-prong tag decays •  =7-11% • Nexpected= 3.41±0.22 in total • Nobserved= 3 • BR<(1.1-3.3)x10-7 at 90% CL • ~similar results from Belle (87.1fb-1, PLB 589, 103) G. Marchiori - LFV tau decays at B-factories: results and prospects

  11.    signal data BaBar(315fb-1, hep-ex/0607045) Belle(401fb-1, preliminary) hgg 2s box 70% ellipse (MC) data 90% ellipse (MC) hggg •  : 7.0±0.5 % • Nexp: 0.64±0.08 • Nobs: 1 hgp+p-p0 •  : 3.7±0.3 % • Nexp: 0.07±0.02 • Nobs: 0 hggg •  : 6.4% • Nexpected: 0.40 • Nobserved: 0 hgp+p-p0 •  : 6.8% • Nexpected: 0.24 • Nobserved: 0 BR<1.6x10-7 BR<6.5x10-8 G. Marchiori - LFV tau decays at B-factories: results and prospects

  12.  h0 / eh0(h0=p0,h,h’) signal data Belle(401fb-1, preliminary) • Based on previous analysis (154fb-1, PLB622, 218) • tgeh’ / mh’ : h’grg mode is now included. • eff.: 4.3%(tgeh’ ,h’ghp+p-), 4.8%(tgeh’ ,h’grg) 4.9%(tgmh’ ,h’ghp+p-), 5.4%(tgmh’ ,h’grg) • Main BGs: • tgmp0 : tgrn • others: negligibly small BGs BR(eh)<9.2x10-8 BR(eh’)<1.6x10-7 BR(mh’)<1.3x10-7 BR(ep0)<8.0x10-8 BR(mp0)<1.2x10-7 3-6 times more sensitive results obtained G. Marchiori - LFV tau decays at B-factories: results and prospects

  13.  lhh’ (l=e,; h,h’=,K) Main BGs: low-multiplicity qq evts hh’h” signal data BaBar(221fb-1 , PRL 95, 191801) • only 1-prong tag decays •  ~3% for each mode • Nexpected= 11.30.7 in total (0.1-3.0 depending on channel) • Nobserved= 10 • BR<(0.7-4.8)x10-7 at 90% CL • ~similar results from Belle (158fb-1, hep-ex/0603036) G. Marchiori - LFV tau decays at B-factories: results and prospects

  14.  KS / eKS (KS +-) signal data Belle(281fb-1, PLB639, 159) signal region tmKs teKs previous result CLEO:14fb-1 mKs:<9.5x10-7 eKs:<9.1x10-7 blind region  : (13.5±0.9)% Nexpected=0.20.2 Nobserved=0 BR<4.9*10-8  : (11.8±0.8)% Nexpected=0.20.2 Nobserved=0 BR<5.6*10-8 20 times improvement wrt previous UL (CLEO) • Main BGs: Dg lKSn, pKS - but negligible • Main syst. on : KS reco. (4.5%), tracking eff. (4%) G. Marchiori - LFV tau decays at B-factories: results and prospects

  15.  V0 / eV0 (V0=f,K*,r) lepton h V0 h t e e t generic t decay signal box Main BGs: tt+qq (tgmV0) tt+2photon (tgeV0) data K+K- K*K+- +- Belle(158fb-1, hep-ex/0603036) ter0 t eK* t mr0 t mK* t mK* t mf t ef teK* •  ~3-5% • Nexpected= 2.55±1.04 in er0; negligible for non- modes (V0 mass cut) • Nobserved= 5 in er0; 0 in all other channels • BR<(2.0-7.7)x10-7 at 90% CL G. Marchiori - LFV tau decays at B-factories: results and prospects

  16. Summary of  LFV searches red: results shown in this talk * : bkg currently negligible * * * * * * * * * * * Starting to constrain the parameter space of some NP (SUSY/Higgs/mSUGRA) models G. Marchiori - LFV tau decays at B-factories: results and prospects

  17. 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 ~10-9-10-10 could be reached • Potential for LFV observation in t decays G. Marchiori - LFV tau decays at B-factories: results and prospects

  18. Conclusion • Data sample of B-factories (-factories): >900*106t pairs now ~2*109 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(10-9-10-10) limits and has potential for LFV discovery in many NP scenarios G. Marchiori - LFV tau decays at B-factories: results and prospects

  19. Backup G. Marchiori - LFV tau decays at B-factories: results and prospects

  20. 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 = Nexpected , std. dev. = (Nexpected) • 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 G. Marchiori - LFV tau decays at B-factories: results and prospects

  21. 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) EMC 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) B decay vertex, soft p from D* Solenoid DIRC K-ID e+ K-ID e-ID e- DCH IFR m-ID SVT G. Marchiori - LFV tau decays at B-factories: results and prospects

  22. performances SVT: 90% acceptance in CM, 4% X0 thickness (vtx): 70 m fully reco, 150 m tag (d0), (z0) ~ 50 m Low-pT trk. eff. : >80% at pT=70 MeV/c DCH: 90% acceptance in CM, 1.08% X0 thickness Trk. eff.: 98% for pT>200 MeV/c (pT)/pT=0.13%pT/(GeV/c) + 0.45% 3 K/ separation (dE/dx) up to 700 MeV/c DIRC: 78% acceptance in CM, 17% X0 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 X0 thickness • (E)/E: 2.3%/(E/GeV)^(1/4)  1.85% • (,) = 3.9 mrad/(E/GeV)^(1/2) • (0 mass)=6.9 MeV/c2 • 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) G. Marchiori - LFV tau decays at B-factories: results and prospects

  23. Typical selection variables charged tracks: d0, z0 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 : mEC, E KS: Distance of flight Line of flight vs p direction , K*, , D*0: helicity angle (polarization) G. Marchiori - LFV tau decays at B-factories: results and prospects

More Related