Results on B Lifetimes from DØ Breese Quinn University of Mississippi for the DØ Collaboration Introduction Semileptonic lifetime measurements in J/ mode Explain plots more More physics, less technical, esp after slide 25,26 Watch jargon

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 CKM2006, Nagoya, Japan 12/14/06

DØ Detector Tracking 2T Solenoid Nearly hermetic muon system 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 CKM2006, Nagoya, Japan 12/14/06

Layer 0 Silicon Installed April 2006 48 modules at r = 1.7 cm Greatly improved resolution B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

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 fi from 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 CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

b: Final Sample V > 0.02 cm 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 B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

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, ni and 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 CKM2006, Nagoya, Japan 12/14/06

b: Lifetime Fit Free Parameters NTOT b Fcc 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 CKM2006, Nagoya, Japan 12/14/06

b: Lifetime Fit DØ RunII Preliminary B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

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 Source Systematic Uncertainty in c(m) Detector alignment ±5.4 Mass fitting method ±20 K factor determination ±12 cc background ±2.6 Scale factor ±10 Total ±26 B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

b: S.L. Decay Lifetime Result DØ RunII Preliminary PDG: CDF (prelim.): 1.3 fb-1 B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

b: J/  Mode Select b events 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 CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06

bJ/ : Systematic Uncertainties Source b(m) B0(m) Ratio Detector alignment 5.4 Models for lifetime and mass distributions 0.7 13.0 0.026 Long-lived background components 1.0 0.4 0.001 Contamination 13.9 - 0.031 Total 15.0 14.1 0.041 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 CKM2006, Nagoya, Japan 12/14/06

bJ/ : Fit Results 1.2 fb-1 DØ RunII Preliminary B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

b: Comparison of Results Both DØ results are consistent with the world average and theoretical prediction B. Quinn University of Mississippi CKM2006, Nagoya, Japan 12/14/06

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 CKM2006, Nagoya, Japan 12/14/06