Results on Tau Physics from BaBar

Transcription

1 Results on Tau Physics from BaBar Eric Torrence University of Oregon Search for Lepton Flavor Violation Study of τ 3h 2h + ν τ (5 prong) Tau Lifetime

2 The BaBar Experiment Integrated Luminosity (fb -1 ) Jan 1 Nov fb -1 recorded, more data on its way Almost 22 million nb nb events! Results shown today use ~1 fb Jul 1 May 1 Mar 1 BABAR PEP-II Delivered /fb BABAR Recorded 244.6/fb BABAR off-peak 22.68/fb 96% Efficiency σ( e + e BB) = 1.5 Jan 1 Nov 1 Sep 1 2 Jul 1 May 1 Mar 1 Jan 1 Nov 1 Sep 1 21 Jul 1 May 1 Mar 1 Jan 1 Nov 1 Sep 1 22 Jul 1 May 1 Mar 1 Nov 1 Sep 1 23 Jul 1 May 1 Mar 1 Jan 1 σ( e + e τ + τ ) =.89 τ + τ 24

3 Lepton Flavor Violation Limits on Lepton Flavor Changing Decays before BaBar/Belle 11 B ( µ eγ ) < at 9% CL [MEGA/LAMPF] 12 B ( µ eee) < 1. 1 at 9% CL [SINDRUM] 6 B( τ µγ ) < at 9% CL [CLEO] 6 B( τ µµµ ) < at 9% CL [CLEO] Forbidden in SM, but no good theoretical motivation Neutrino Oscillations τ ν τ ν µ µ W γ LFV allowed in principle, but rate is very, very small. O(1-4 )? Signature of new physics! Search for τ µγ, τ lll,...

4 µ τ Η LFV in Tau Decays µ + µ Natural part of many models of new physics, particularly those trying to explain neutrino data τ ν χ µ + γ B(µ >eγ) 1-1 M 1/2 =5 µ eγ Experimental Bound B(τ >µγ) 1-4 M 1/2 =5 τ µγ Experimental Bound 1-14 M 1/2 =2 1-8 M 1/2 = M ν = 2 x 1 16 GeV M (GeV) 1-1 M ν = 2 x 1 16 GeV M (GeV) String inspired, heavy ν R SUSY [King and Oliveira, 1999] See E. Ma Tau2 proceedings for concise review

5 LFV Signature 1-prong tag 1-prong tag ν τ µγ ν τ lll One prong on tag side ( πν, ρν, eνν, µνν,...) ~ 85% Strict lepton identification No missing momentum on signal side Neutrinoless Decay m = m rec m τ E = E rec E beam Smeared by resolution and radiative effects E (GeV) Ε vs. m for MC signal τ - -> µ - e - e + Count events in signal box M (GeV)

6 τ lll Analysis E (GeV).4.2 qq.4.2 QED ττ.4.2 Data M (GeV) Require 1-3 topology, reject γ conversions, Particle ID, plus specific cuts per channel against major backgrounds 3 background PDFs, shape from MC/control, rate from data

7 BaBar τ lll LFV Limits 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 ) Mode e e + e µ + e e µ e + e e + µ µ e µ + µ µ µ + µ Eff [%] 7.3 ± ± ± ± ± ±.5 N bgd 1.51 ± ±.8.62 ±.1.21 ±.7.39 ±.8.31 ±.9 N obs B 9 UL No excess found! Limits ( 1 3) 9% CL L = 91.6 fb -1, σ τ =.89 nb PRL 92, (24) 7

8 Old Preliminary BaBar τ µγ Limits Significant background from e + e µ + µ γ and τ µν µ ν τ γ Require electron or rho tag (no muon or pion tags allowed) L = 63 fb -1, σ τ =.89 nb Bgd expected: 7.8 ± 1.4 Data observed: 13 ε = ( 5.2 ±.5) % m EC (GeV/c 2 ) B A B AR Preliminary Limit % CL Not competitive due to fluctuation Update with 22 fb -1 expected for Tau E (GeV)

9 Published Belle τ µγ Limits L = 86.3 fb -1, ε = ( 11. ±.5) % Expected: 2.2 ± 2.1 Observed: 19 7 BF Limit 3.1 9% CL PRL 92, (24) Also B( τ µη) < Submitted to PRL 7 Updates expected this week, see BSM-5 2:3 Tuesday

10 Limits 7 ( 1 ) at 9% CL based on ~ 9 fb -1 per experiment Mode BaBar Belle My Combination B( τ µ µ + µ ) B( τ µ µ + e ) B( τ µ e + µ ) B( τ µ e + e ) B( τ e µ + e ) B( τ e e + e ) Published Lepton Flavor Violation Limits BaBar: PRL 92, (24) Belle: PLB 589, 13 (24) 7 Also B( τ µγ ) < and B( τ µη) < (Belle) B-factories have lowered these limits Over 5 fb -1 (.5 ab -1 ) expected in next few years 5 distinct modes listed in PDG with LF, L, or B violation Many interesting channels: τ lhh, τ µη', τ pγ,... τ lll limits should approach O(1-8 ) soon Many models predictions are above this level!

11 Five Prong Tau Decays τ W ν τ e + e - γ/z Tau Decays provide a clean laboratory to study QCD τ π π ν τ and τ π π + π ν τ extensively studied worldwide 5-prong modes suffer from lack of statistics... Events/(.1 GeV/c 2 ) 2 1 CLEO 1pr tag lept tag 3h 2h + ν τ 5 25 CLEO saw 295 events (1.7 fb -1 ) PRL 73, 934 (1994) M 5 (GeV/c 2 )

12 BaBar 5-prong Analysis 3h 2h + mass compared to TAUOLA (phase space) 2 3 Events/.4 GeV/c τ BABAR preliminary 3h 2h + ν τ Data 3π 2π + MC other tau qqbar h - 2h + 2 Mass (GeV/c ) 1-5 topology, lepton tag, thrust, P t /E miss, no kaon id (yet) veto e -, π, and conversions from signal side Efficiency: 7.5%, Purity: 79%, Events: 15,869, Lumi: 11.7 fb -1 Backgrounds mostly from other tau decays with π or K s

13 Preliminary 5-prong Results Tag Efficiency [%] Purity [%] Events B(τ 3h 2h + ν τ ) Electron (8.52 ±.9 ±.4) 1 4 Muon (8.54 ±.11 ±.45) 1 4 Babar Preliminary: hep-ex/485 Branching Fraction Hadronic Structure in h + h - pairs BaBar 8.5 ±.4 Preliminary Opal 9.1 ± 1.5 Aleph 8. ± 1.7 Cleo 7.7 ± 1. PDG 8.2 ± B(τ 3h - 2h + ν) [1-4 ] 2 Events/.125 GeV/c pairs/ev. BABAR preliminary Phase Space Monte Carlo h + h - Data 3π 2π + MC background ρ 2 Mass (GeV/c ) Future Plans: Measure 5h π, 5h 2π modes Separate kaons from pions Study hadronic structure in detail

14 Preliminary Tau Lifetime Very clean 1-3 sample Reconstruct r-φ decay length from primary IP to 3-track vertex Use simple mean <λ> to reduce syst. 1-prong λ 3-prong µm Events per BABAR preliminary decay_length_allcuts_unblinded_tau Entries Entries Mean Underflow RMS.462 Overflow Data tau uds cc bb BaBar 29.8 ± 2.2 Preliminary cm Lifetime with 3 fb ± 1.5( stat) ± 1.6( syst) fs (prelim.) Uncertainties will be significantly reduced for publication (8 fb -1 ) λ τ Delphi ± 3. L ± 2.5 Opal ± 2.1 Aleph 29.1 ± 1.9 Cleo 289. ± 4.9 PDG 29.6 ± Tau Lifetime (fs)

15 Summary Lepton Flavor Violation B( τ lll) < ( 1 3) 1 published Prelim. result on B( τ µγ ) to be updated shortly 7 Hadronic Structure Prelim. results with 16k Much more to come here τ 3h 2h + ν τ events Tau Lifetime Prelim. lifetime measurement among world s best Improvements and publication expected soon First results on tau physics from BaBar are just now being published There is a lot of physics to be extracted from this huge data sample See Tau4 (Nara, Japan, September 14-17) for more