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Register a new userPrecision measurement of the Lambda_b baryon lifetime
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The ratio of the Lambda b baryon lifetime to that of the B0 meson is measured using 1.0/fb of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC. The Lambda b baryon is observed for the first time in the decay mode Lambda b -> J/psi pK-, while the B0 meson decay used is the well known B0 -> J/psi pi+K- mode, where the pi+ K- mass is consistent with that of the K*0(892) meson. The ratio of lifetimes is measured to be 0.976 +/- 0.012 +/- 0.006, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the B0 meson lifetime, the Lambda b lifetime is found to be 1.482 +/- 0.018 +/- 0.012 ps. In both cases the first uncertainty is statistical and the second systematic.
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We report on measurements of the mass and lifetime of the Xi_b^- baryon using about 1800 Xi_b^- decays reconstructed in a proton-proton collision data set corresponding to an integrated luminosity of 3.0 fb^{-1} collected by the LHCb experiment. The decays are reconstructed in the Xi_b^- --> Xi_c^0 pi^-, Xi_c^0 --> pK-K-pi+ channel and the mass and lifetime are measured using the Lambda_b^0 --> Lambda_c^+ pi- mode as a reference. We measure M(Xi_b^-) - M(Lambda_b^0) = 178.36 +- 0.46 +- 0.16 MeV/c^2 and tau(Xi_b^-)/tau(Lambda_b^0) = 1.089 +- 0.026 +- 0.011, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of two better precision on the Xi_b^- mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.
Using a proton-proton collision data sample corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at center-of-mass energies of 7 and 8 TeV, about 3800 $Xi_b^0toXi_c^+pi^-$, $Xi_c^+to pK^-pi^+$ signal decays are reconstructed. From this sample, the first measurement of the $Xi_b^0$ baryon lifetime is made, relative to that of the $Lambda_b^0$ baryon. The mass differences $M(Xi_b^0)-M(Lambda_b^0)$ and $M(Xi_c^+)-M(Lambda_c^+)$ are also measured with precision more than four times better than the current world averages. The resulting values are $frac{tau_{Xi_b^0}}{tau_{Lambda_b^0}} = 1.006pm0.018pm0.010$, $M(Xi_b^0) - M(Lambda_b^0) = 172.44pm0.39pm0.17 MeV/c^2$, $M(Xi_c^+) - M(Lambda_c^+) = 181.51pm0.14pm0.10 MeV/c^2$, where the first uncertainty is statistical and the second is systematic. The relative rate of $Xi_b^0$ to $Lambda_b^0$ baryon production is measured to be $frac{f_{Xi_b^0}}{f_{Lambda_b^0}}frac{{cal{B}}(Xi_b^0toXi_c^+pi^-)}{{cal{B}}(Lambda_b^0toLambda_c^+pi^-)}frac{{cal{B}}(Xi_c^+to pK^-pi^+)}{{cal{B}}(Lambda_c^+to pK^-pi^+)} = (1.88pm0.04pm0.03)times10^{-2}$, where the first factor is the ratio of fragmentation fractions, $btoXi_b^0$ relative to $btoLambda_b^0$. Relative production rates as functions of transverse momentum and pseudorapidity are also presented.
We report a measurement of the lifetime of the $Omega_c^0$ baryon using proton-proton collision data at center-of-mass energies of 7 and 8~TeV, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb experiment. The sample consists of about 1000 $Omega_b^-toOmega_c^0mu^-bar{ u}_{mu} X$ signal decays, where the $Omega_c^0$ baryon is detected in the $pK^-K^-pi^+$ final state and $X$ represents possible additional undetected particles in the decay. The $Omega_c^0$ lifetime is measured to be $tau_{Omega_c^0} = 268pm24pm10pm2$ fs, where the uncertainties are statistical, systematic, and from the uncertainty in the $D^+$ lifetime, respectively. This value is nearly four times larger than, and inconsistent with, the current world-average value.
Bottom baryons decaying to a J/psi meson and a hyperon are reconstructed using 1.0 fb^{-1} of data collected in 2011 with the LHCb detector. Significant Lambda_b^0 rightarrow J/psi Lambda, Xi_b^-rightarrow J/psi Xi^- and Omega_b^- rightarrow J/psi Omega^- signals are observed and the corresponding masses are measured to be M(Lambda_b^0) = 5619.53 pm 0.13 (stat) pm 0.45 (syst) MeV/c^2, M(Xi_b^-) = 5795.8 pm 0.9 (stat) pm 0.4 (syst) MeV/c^2, M(Omega_b^-) = 6046.0 pm 2.2 (stat) pm 0.5 (syst) MeV/c^2, while the differences with respect to the Lambda_b^0 mass are M(Xi_b^-)-M(Lambda_b^0) = 176.2 pm 0.9 (stat) pm 0.1 (syst) MeV/c^2, M(Omega_b^-)-M(Lambda_b^0) = 426.4 pm 2.2 (stat) pm 0.4 (syst) MeV/c^2. These are the most precise mass measurements of the Lambda_b^0, Xi_b^- and Omega_b^- baryons to date. Averaging the above Lambda_b^0 mass measurement with that published by LHCb using 35 pb^{-1} of data collected in 2010 yields M(Lambda_b^0) = 5619.44 pm 0.13 (stat) pm 0.38 (syst) MeV/c^2.
A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Lambda_b^0toLambda_c^+mu^-overline{ u}$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Lambda_c^+mu^-overline{ u}$(+ anything) final states are reconstructed through the detection of a muon and a $Lambda_c^+$ baryon decaying into $pK^-pi^+$, and the decays $Lambda_b^0toLambda_c^+pi^+pi^-mu^-overline{ u}$ are used to determine contributions from $Lambda_b^0to Lambda_c^{star+}mu ^-bar{ u}$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.
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