B0 Lifetimes Research Articles

Phenomenological study of heavy hadron lifetimes

The lifetimes of bottom and charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as weak W-annihilation and Pauli interference. Spectator effects originating from dimension-7 four-quark operators are derived. Hadronic matrix elements of four-quark operators are parameterized in a model-independent way. Using the dimension-6 bag parameters recently determined from HQET sum rules and the vacuum insertion approximation for meson matrix elements of dimension-7 operators, the calculated B meson lifetime ratios τ(B+)/τ(Bd0) = 1.074− 0.016+ 0.017 and τ(Bs0)/τ(Bd0) = 0.9962 ± 0.0024 are in excellent agreement with experiment. Likewise, based on the quark model evaluation of baryon matrix elements, the resulting baryon lifetime ratios τ(Ξb−)/τ(Λb0), τ(Ξb−)/τ(Ξb0), τ(Ωb−)/τ(Ξb−) and the Λb − B0 lifetime ratio τ(Λb0)/τ(Bd0) = 0.953 also agree well with the data. Contrary to the bottom hadron sector where the HQE in 1/mb works well, the HQE to 1/mc3 fails to give a satisfactory description of the lifetimes of both charmed mesons and charmed baryons. This calls for the subleading 1/mQ corrections to spectator effects. The relevant dimension-7 spectator effects are in the right direction for explaining the large lifetime ratio of τ(Ξc+)/τ(Λc+). However, the destructive 1/mc corrections to Γ(Ωc0) are too large to justify the validity of the HQE, namely, the predicted Pauli interference and semileptonic rates for Ωc0 become negative. Demanding these rates to be positive for a sensible HQE, we find the lifetime pattern τ(Ξc+) > τ(Ωc0) > τ(Λc+) > τ(Ξc0), contrary to the current hierarchy τ(Ξc+) > τ(Λc+) > τ(Ξc0) > τ(Ωc0). We conclude that the Ωc0, which is naively expected to be shortest-lived in the charmed baryon system owing to the large constructive Pauli interference, could live longer than the Λc+ due to the suppression from 1/mc corrections arising from dimension-7 four-quark operators. The new charmed baryon lifetime pattern needs to be tested in forthcoming experiments.

Results on b hadron properties in CMS

The lifetime is among the fundamental properties of particles and is one of the important observables in heavy hadrons allowing to test the theoretical tools describing their physics. This report presents lifetime measurements of B0, B0s, Λ0b and B+c hadrons performed on data, corresponding to 19.7 fb-1, collected by the CMS experiment at the LHC at a center-of-mass energy of √s = 8 TeV. The B0 lifetime is measured to be 453:0± 1:6 (stat) ± 1:5 (syst) μm in J/ψK0S and 457:8 ± 2:7 (stat) ± 2:7 (syst) μm in J/ψK*(892)0. The B0s meson lifetime is measured in two decay modes with differing contributions from the heavy and light eigenstates, resulting in two different measured lifetimes: 504:3 ± 10:5 (stat) ±3:7 (syst) μm in J/ψπ+π- and 443:9±2:0 (stat) ±1:2 (syst) μm in J/ψϕ(1020) respectively. The lifetime of the Λ0b hadron is found to be 443:1±8:2 (stat) ±2:7 (syst) μm. The B+c lifetime is measured with respect to the B+ lifetime and is found to be 162:3 ± 8:2 (stat) ± 4:7 (syst) ± 0:1 (τB+) μm.

Measurement of theBs0Lifetime in Fully and Partially ReconstructedBs0→Ds−(ϕπ−)XDecays inp¯pCollisions ats=1.96 TeV

We present a measurement of the Bs0 lifetime in fully and partially reconstructed Bs0→Ds−(ϕπ−)X decays in 1.3 fb−1 collected in pp¯ collisions at s=1.96 TeV by the CDF II detector at the Fermilab Tevatron. We measure τ(Bs0)=1.518±0.041(stat)±0.027(syst) ps. The ratio of this result and the world average B0 lifetime yields τ(Bs0)/τ(B0)=0.99±0.03, which is in agreement with recent theoretical predictions.Received 10 March 2011DOI:https://doi.org/10.1103/PhysRevLett.107.272001© 2011 American Physical Society

Measurement of theΛbLifetime in the Exclusive DecayΛb→J/ψΛ

We have measured the Lambda b lifetime using the exclusive decay Lambda b --> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda b decays, where the J/psi and Lambda are identified via the decays J/psi --> mu+ mu- and Lambda --> ppi, we measured the Lambda b lifetime to be tau(Lambda b)=1.218 (+0.130)/(-0.115) (stat) +/- 0.042(syst) ps. We also measured the B0 lifetime in the decay B0 --> J/psi(mu+ mu-)K(0)/(S)(pi+ pi-) to be tau(B0)=1.501 (+0.078)/(-0.074) (stat) +/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda b)/tau(B0)=0.811 (+0.096)/(-0.087) (stat) +/- 0.034(syst).

Measurement of the Lifetime Difference in theBs0System

We present a study of the decay Bs0→J/ψϕ. We obtain the CP-odd fraction in the final state at time zero, R⊥=0.16±0.10(stat)±0.02(syst), the average lifetime of the (Bs0, B¯s0) system, τ¯(Bs0)=1.39−0.16+0.13(stat)−0.02+0.01(syst) ps, and the relative width difference between the heavy and light mass eigenstates, ΔΓ/Γ¯≡(ΓL−ΓH)/Γ¯=0.24−0.38+0.28(stat)−0.04+0.03(syst). With the additional constraint from the world average of the Bs0 lifetime measurements using semileptonic decays, we find τ¯(Bs0)=1.39±0.06 ps and ΔΓ/Γ¯=0.25−0.15+0.14. For the ratio of the Bs0 and B0 lifetimes we obtain τ¯(Bs0)τ(B0)=0.91±0.09(stat)±0.003(syst).Received 20 July 2005DOI:https://doi.org/10.1103/PhysRevLett.95.171801©2005 American Physical Society

Measurement of theΛb0Lifetime in the DecayΛb0→J/ψΛ0with the D0 Detector

We present measurements of the Lambda(0)(b) lifetime in the exclusive decay channel Lambda(0)(b)--> J/psiLambda(0), with J/psi--> mu(+)mu(-) and Lambda(0)--> ppi(-), the B0 lifetime in the decay B0-->J/psiK(0)(S) with J/psi--> mu(+)mu(-) and K(0)(S)-->pi(+)pi(-), and the ratio of these lifetimes. The analysis is based on approximately 250 pb(-1) of data recorded with the D0 detector in pp collisions at sqrt[s] = 1.96 TeV. The Lambda(0)(b) lifetime is determined to be tau(Lambda(0)(b)) = 1.22(+0.22)(-0.18)(stat) +/- 0.04(syst) ps, the B0 lifetime tau(B0) = 1.40(+0.11)(-0.10)(stat) +/- 0.03(syst) ps, and the ratio tau(Lambda(0)(b))/tau(B0) = 0.87(+0.17)(-0.14)(stat) +/- 0.03(syst). In contrast with previous measurements using semileptonic decays, this is the first determination of the Lambda(0)(b) lifetime based on a fully reconstructed decay channel.

Improved measurements of the B0 and B+ meson lifetimes

Updated measurements of the B0 and B+ meson lifetimes are presented. From a data sample of 1.72 million hadronic Z0 decays recorded during the period 1991 to 1993, a sample of approximately 1000 semileptonic B meson decays containing a D0, D+ or D*+ has been isolated. From the distribution of decay times in the different samples the lifetimes of the B0 and B+ mesons are determined to be 1.53±0.12±0.08 ps and 1.52±0.14±0.09 ps, respectively, where the first error is statistical and the second systematic. The ratio of the B+ to B0 lifetimes is measured to be 0.99±0.14−0.04+0.05, confirming expectations that the lifetimes are similar.

A measurement of B+ and B0 lifetimes using $$\bar D\ell ^ + $$ events

A measurement of B meson lifetimes is presented using data collected from 1991 to 1993 by the DELPHI detector at the LEP collider. Samples of events with a D meson and a lepton in the same jet are selected where\(\bar D^{^0 } \ell ^ + \) and D*l+ events originate mainly from the semileptonic decays of B+ and B0 mesons, respectively. From the reconstructed B decay length and the estimated B momentum, taking into account the dilution due to B decays into\(\bar D^{^{**} } \ell ^ + v\), the following B meson lifetimes and lifetime ratio are measured: $$\begin{gathered} \tau (B^ + ) = 1.61_{ - 0.16}^{ + 0.16} (stat.) \pm 0.12(syst.) ps \hfill \tau (B^0 ) = 1.61_{ - 0.13}^{ + 0.14} (stat.) \pm 0.08(syst.) ps \hfill \tau (B^ + )/\tau (B^0 ) = 1.00_{ - 0.15}^{ + 0.17} (stat.) \pm 0.10(syst.) \hfill \end{gathered} $$ and an average lifetime of B+ and B0 mesons is obtained: $$\tau (B) = 1.61_{ - 0.07}^{ + 0.08} (stat.) \pm 0.05(syst.) ps$$

Kinematic suppression of D** in B-decay analysis using heavy-quark effective theory

There is considerable interest in the measurement of the individual lifetimes of the different B-hadron species. At LEP, it is possible to measure these in the channels B- to l- nu lD0 to l- nu lK- pi + and Bd0 to l- nu lD+* to l- nu l(K- pi +) pi + by complete reconstruction of the final states (except the neutrino). A preliminary result has been given by ALEPH: tau (B0)=1.40-0.48+0.52(stat.) -0.40+0.18(syst.)*10-12 s and tau (B+or-)=1.35-0.35+0.37(stat.) -0.40+0.26(syst.)*10-12 s. The charge of the decaying B meson is found from the sum of the charges of its decay products, which are found kinematically. Jets containing high-pT leptons are searched for combinations of tracks which made a D0 or D+* meson. Such events are strong candidates for semileptonic B decays. It is assumed that any missing mass is carried by the neutrino and any pi 0s. Nonresonant D pi states or higher-mass D states in the decay products of the B, which the authors generically call D**, may well involve the production of an extra charged pion, and in these cases the charge of the B meson will be incorrectly determined. Use of this method to obtain the individual B+ and B0 lifetimes therefore requires that the fraction of semileptonic B decays to D** is small and well known. Currently the CLEO estimate is B(B0 to D*l nu n pi )=3.9+or-2.7% compared with B(B to Xl nu )=10.4+or-0.3%. This uncertainty dominates the systematic errors on the lifetimes given in (2). The authors make a suggestion for reducing that contribution.

Measurement of the B0-meson lifetime.

We report a measurement of the lifetime of the B0 meson based upon 29-GeV e+e− annihilation data taken with the Mark II detector at the SLAC storage ring PEP. The B0 mesons are tagged by their decays into D*−e+ν and D*−μ+ν, where the D*− is tagged by its decay into π−D¯ 0. We reconstruct the decay vertices of 15 B0-meson candidates and measure the B0 lifetime to be 1.20−0.360.14+0.52+0.16 psec.Received 20 November 1989DOI:https://doi.org/10.1103/PhysRevLett.64.1095©1990 American Physical Society