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Register a new userMeasurement of the properties of the $Xi_b^{*0}$ baryon
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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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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.
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.
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 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.
A search for baryon-number-violating $Xi_b^0$ oscillations is performed with a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of 3 fb$^{-1}$. The baryon number at the moment of production is identified by requiring that the $Xi_b^0$ come from the decay of a resonance $Xi_b^{*-} to Xi_b^0 pi^-$ or $Xi_b^{prime-} to Xi_b^0 pi^-$, and the baryon number at the moment of decay is identified from the final state using the decays $Xi_b^0 to Xi_c^+ pi^-, ~ Xi_c^+ to p K^- pi^+$. No evidence of baryon number violation is found, and an upper limit at the 95% confidence level is set on the oscillation rate of $omega < 0.08$ ps$^{-1}$, where $omega$ is the associated angular frequency.
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