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Results on B Lifetimes from D Ø

Results on B Lifetimes from D Ø. Introduction Semileptonic lifetime measurements in J/ mode. Breese Quinn University of Mississippi for the D Ø Collaboration. B Lifetime Physics. All B hadrons predicted to have equal lifetimes by simple quark spectator model

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Results on B Lifetimes from D Ø

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  1. Results on B Lifetimesfrom DØ • Introduction • Semileptonic lifetime measurements • in J/ mode Breese Quinn University of Mississippi for the DØ Collaboration

  2. B Lifetime Physics • All B hadrons predicted to have equal lifetimes by simple quark spectator model • Heavy Quark Effective field Theory, on the other hand, predicts a lifetime hierarchy • τ(B+) ≥ τ(B0) ≈ τ(Bs) > τ(Λb) >> τ(Bc) • QCD expansions in orders of 1/mb • Measurements of lifetime ratios eliminate much systematic uncertainty B. Quinn University of Mississippi

  3. DØ Detector • Tracking • Coverage to =3 • New Layer 0 detector for improved vertexing and b-tagging • 2T Solenoid • Nearly hermetic muon system • High efficiency muon triggers • Toroids provide muon pT at Level 1 B. Quinn University of Mississippi

  4. Layer 0 Silicon • Installed April 2006 • 48 modules at r = 1.7 cm • Greatly improved resolution B. Quinn University of Mississippi

  5. Tevatron B’s • Tevatron has delivered in excess of 2 fb-1 • 1.68 fb-1 recorded at DØ • B physics at the Tevatron • Plus: all B hadrons produced there with large cross sections • Minus: very large backgrounds produced as well B. Quinn University of Mississippi

  6. Semileptonic B Decays • High statistics • Reconstruct primary and secondary vertices for B hadron • Lose some momentum via ν • Select events in triggers which are unbiased with regard to lifetime B. Quinn University of Mississippi

  7. Semileptonic B Decays • Must calculate proper decay length, , from the transverse decay length, Lxy. • But due to the missing neutrino, we do not measure pT(b), we measure pT(c), for a visible proper decay length. • Where K is a correction factor for the momentum difference obtained from Monte Carlo. z B. Quinn University of Mississippi

  8. b: Event Selection • Select events satisfying only triggers which do not bias lifetime distribution • pT(μ) > 2.0 Gev, at least 2 track segments in muon chambers • Reconstructed K0S: • pT(K0S) > 0.7 GeV • 480.0 < M(π π) < 507.5 MeV – mass constrained to PDG KS mass • pT(p) > 1.0 GeV, at least 2 hits in SMT • Λc vertex χ2 < 9 and Λb vertex χ2 < 9 • 3.4 < M(Λc) < 5.4 GeV • dT(PVΛc) – dT(PVΛb) >-3σ • dT(ΛbΛc) < 3.3σ • Isolation: Λb fraction of total momentum in cone [ (()2+()2)1/2 < 0.5 ] around Λc system > 0.5 B. Quinn University of Mississippi

  9. b: Likelihood Ratio BG Rejection • To reduce background further, construct a probability distribution function, y, by combining likelihood ratios of several discriminating variables, xi • Measure fifrom B0dD-+X(DKS) and B0sD-S+X(DSKSK) data • Similar kinematics to b signal • fis=fi(signal region)-fi(sidebands) B. Quinn University of Mississippi

  10. b: Likelihood Ratio BG Rejection • Variables used: • pT (K0S) • pT of proton • pT (Λ+c ) • M(Λ+c) • Isolation of Λ0b candidate • Cut at ln(y) < 0.1 B. Quinn University of Mississippi

  11. b: Final Sample • Fit is a Gaussian signal plus fourth order polynomial background • Red histogram shows MC estimated Bd and Bs reflected events • n(b) = 4437 ± 329 events • M(b) = 2285.8 ± 1.7 MeV • Width = 20.6 ± 1.7 MeV V > 0.02 cm B. Quinn University of Mississippi

  12. b: Lifetime Fit • There are several decay modes that will result in a cνX final state • Each one has a different K factor distribution • The individual distributions are determined from properly weighted Monte Carlo B. Quinn University of Mississippi

  13. b: Lifetime Fit • M prob. Dist. for events in the signal peak • Measure V and its error for each event and split sample into V bins and fit the mass distribution of each bin to a Gaussian signal and 4th order polynomial to determine bin by bin yields and errors, niand I • Minimize: • NTOT: total number of signal events, free parameter • F(M): M probability distribution for events in the signal peak B. Quinn University of Mississippi

  14. b: Lifetime Fit • M prob. Dist. for events in the signal peak • fcc: fraction of prompt c + c hadron in signal peak • Gcc: double Gaussian VPDL dist. from MC • M prob. Dist. for signal • H(K): total K factor distribution • Resolution function • p(): error prob. dist. for signal • s: scale factor for mis-estimation of errors Free Parameters • NTOT • b • Fcc B. Quinn University of Mississippi

  15. b: Lifetime Fit DØ RunII Preliminary B. Quinn University of Mississippi

  16. b: Systematic Uncertainties • Mass fitting variations • Linear BG • Variation of binning • Scale factor varied by ±20% • K factor • Unknown BR varied over a wide range • Dependence on pT() cut • Uncertainties in B hadron generation and decay • cc BG • Widths and fractions of two Gaussians varied by their uncertainties • Many consistency checks also performed • Fit method tested on full and toy signal MC • Variety of data splits B. Quinn University of Mississippi

  17. b: S.L. Decay Lifetime Result DØ RunII Preliminary PDG: CDF (prelim.): 1.3 fb-1 B. Quinn University of Mississippi

  18. Previous S.L. Results: (B+)/(B0) • As a function of VPDL, measure the ratio of the number of events of • Dominated by B+ decays • To the number of • Dominated by B0 decays • Binned likelihood fit gives the lifetime ratio • October, 2004 • 0.44 fb-1 • World’s best measurement until Belle’s 100’s of fb-1 B. Quinn University of Mississippi

  19. Previous S.L. Results: B0S • Unbinned maximum log-likelihood fit to the VPDL distribution • April, 2006 • 0.4 fb-1 WORLD’s BEST! PDG: DØ RunII Preliminary DØ RunII Preliminary B. Quinn University of Mississippi

  20. b: J/  Mode • Select bevents with dimuon trigger • +- reconstruct to a J/ • 2 addl. tracks reconstruct to , with p assigned to higher pT track • Reconstruct b via  +- fit to common vertex with +- constrained to J/ mass • Similar process to select B0d J/KS events for ratio measurement B. Quinn University of Mississippi

  21. bJ/ : Lifetime/Mass Fit • Information on mass and proper decay length are used simultaneously in an unbinned likelihood fit to determine lifetime. • Ns, Nb: number of signal, bg • SM: signal mass dist. – single gaussian • BM[sh)lg)]: prompt(non-prompt) bg mass dist. – flat (2nd O polyn.) • S: signal PDL dist.: exp. convoluted with gauss. Resolution function, G(j,j) • B[sh)lg)]: prompt(non-prompt) bg PDL dist. – G(j,j) (+ and – exp. For combinatoric bg plus exp. for long-lived bg) • SE, BE:  ( error) dist. for signal (bg) – gauss. + 1 exp. (guass. + 2 exp.) • f0: prompt bg fraction B. Quinn University of Mississippi

  22. bJ/ : Systematic Uncertainties • Lifetime and mass dist. models: vary functional forms • Long-lived bg: replace single exp. with separate low and high mass exp. To investigate effect of any difference • Contamination: 6.5% of B0 pass b cuts, add model distributions to fit B. Quinn University of Mississippi

  23. bJ/ : Fit Results DØ RunII Preliminary DØ RunII Preliminary DØ RunII Preliminary 1.2 fb-1 B. Quinn University of Mississippi

  24. b: Comparison of Results • Both DØ results are consistent with the world average and theoretical prediction B. Quinn University of Mississippi

  25. Conclusions • DØ has produced several very nice B hadron lifetime measurements in RunII • Two recent (b) results with more than 1 fb-1 of data are consistent with world average and with NLO prediction. • Good (B+)/(B0) measurement with only 0.4 fb-1 in good agreement with world average and theory • World’s best (B0S) measurement (in PRL shortly!) in good agreement with world averages B. Quinn University of Mississippi

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