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Register a new userPrecision measurement of the mass and lifetime of the Xi_b^- baryon
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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.
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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.
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.
A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $sqrt{s}=7$ and 8 TeV, is used to reconstruct $63pm9$ $Omega_b^-toOmega_c^0pi^-$, $Omega_c^0to pK^-K^-pi^+$ decays. Using the $Xi_b^-toXi_c^0pi^-$, $Xi_c^0to pK^-K^-pi^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $Omega_b^-$ baryon are measured to be begin{align*} frac{tau_{Omega_b^-}}{tau_{Xi_b^-}} &= 1.11pm0.16pm0.03, tau_{Omega_b^-} &= 1.78pm0.26pm0.05pm0.06~{rm ps}, end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $tau_{Omega_b^-}$ only). A measurement is also made of the mass difference, $m_{Omega_b^-}-m_{Xi_b^-}$, and the corresponding $Omega_b^-$ mass, which yields begin{align*} m_{Omega_b^-}-m_{Xi_b^-} &= 247.4pm3.2pm0.5~{rm MeV}/c^2, m_{Omega_b^-} &= 6045.1pm3.2pm 0.5pm0.6~{rm MeV}/c^2. end{align*} These results are consistent with previous measurements.
Using a data sample of pp collisions corresponding to an integrated luminosity of $3~ rm fb^{-1}$, the $Xi_b^-$ and $Omega_b^-$ baryons are reconstructed in the $Xi_b^- rightarrow J/psi Xi^-$ and $Omega_b^- rightarrow J/psi Omega^-$ decay modes and their lifetimes measured to be $tau (Xi_b^-) = 1.55, ^{+0.10}_{-0.09}~{rm(stat)} pm 0.03,{rm(syst)}$ ps, $tau (Omega_b^-) = 1.54, ^{+0.26}_{-0.21}~{rm(stat)} pm 0.05,{rm(syst)}$ ps. These are the most precise determinations to date. Both measurements are in good agreement with previous experimental results and with theoretical predictions.
We perform a search for near-threshold $Xi_b^0$ resonances decaying to $Xi_b^- pi^+$ in a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by the LHCb experiment. We observe one resonant state, with the following properties: begin{eqnarray*} m(Xi_b^{*0}) - m(Xi_b^-) - m(pi^+) &=& 15.727 pm 0.068 , (mathrm{stat}) pm 0.023 , (mathrm{syst}) , mathrm{MeV}/c^2, Gamma(Xi_b^{*0}) &=& 0.90 pm 0.16 , (mathrm{stat}) pm 0.08 , (mathrm{syst}) , mathrm{MeV} . end{eqnarray*} This confirms the previous observation by the CMS collaboration. The state is consistent with the $J^P=3/2^+$ $Xi_b^{*0}$ resonance expected in the quark model. This is the most precise determination of the mass and the first measurement of the natural width of this state. We have also measured the ratio begin{align*} frac{sigma(pp to Xi_b^{*0} X){cal{B}}(Xi_b^{*0} to Xi_b^- pi^+)}{sigma(pp to Xi_b^- X)} = 0.28 pm 0.03 , (mathrm{stat}) pm 0.01 , (mathrm{syst}) . end{align*}
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