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Register a new userObservation of a new $Xi_b^0$ state
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Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 8.5 fb$^{-1}$, the observation of a new excited $Xi_b^0$ resonance decaying to the $Xi_b^-pi^+$ final state is presented. The state, referred to as $Xi_b(6227)^0$, has a measured mass and natural width of $m(Xi_b(6227)^0) = 6227.1^{,+1.4}_{,-1.5}pm0.5$ MeV, $Gamma(Xi_b(6227)^0) = 18.6^{,+5.0}_{,-4.1}pm1.4$ MeV, where the uncertainties are statistical and systematic. The production rate of the $Xi_b(6227)^0$ state relative to that of the $Xi_b^-$ baryon in the kinematic region $2<eta<5$ and $p_{rm T}<30$ GeV is measured to be $frac{f_{Xi_b(6227)^0}}{f_{Xi_b^-}}{mathcal{B}}(Xi_b(6227)^0toXi_b^-pi^+) = 0.045pm0.008pm0.004$, where ${mathcal{B}}(Xi_b(6227)^0toXi_b^-pi^+)$ is the branching fraction of the decay, and $f_{Xi_b(6227)^0}$ and $f_{Xi_b^-}$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed $Xi_b(6227)^-$ state, along with the mass of the $Xi_b^-$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.
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From samples of $pp$ collision data collected by the LHCb experiment at $sqrt{s}=7$, $8$ and $13$ TeV corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb$^{-1}$, respectively, a peak in both the $Lambda_b^0K^-$ and $Xi_b^0pi^-$ invariant mass spectra is observed. In the quark model, radially and orbitally excited $Xi_b^-$ resonances with quark content $bds$ are expected. Referring to this peak as $Xi_b(6227)^-$, the mass and natural width are measured to be $m_{Xi_{b}(6227)^-}=6226.9pm2.0pm0.3pm0.2$ MeV/$c^2$ and $Gamma_{Xi_b(6227)^-}=18.1pm5.4pm1.8$ MeV/$c^2$, where the first uncertainty is statistical, the second is systematic, and the third, on $m_{Xi_b(6227)^-}$, is due to the knowledge of the $Lambda_b^0$ baryon mass. Relative production rates of the ${Xi_b(6227)^-toLambda_b^0K^-}$ and ${Xi_b(6227)^-toXi_b^0pi^-}$ decays are also reported.
Two structures are observed close to the kinematic threshold in the $Xi_b^0 pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = frac{1}{2}^+$ and $J^P=frac{3}{2}^+$ states, denoted $Xi_b^{prime -}$ and $Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(Xi_b^{prime -}) - m(Xi_b^0) - m(pi^{-}) = 3.653 pm 0.018 pm 0.006$ MeV$/c^2$, $m(Xi_b^{*-}) - m(Xi_b^0) - m(pi^{-}) = 23.96 pm 0.12 pm 0.06$ MeV$/c^2$, $Gamma(Xi_b^{*-}) = 1.65 pm 0.31 pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $Gamma(Xi_b^{prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.
A structure is observed in the $B^+K^-$ mass spectrum in a sample of proton--proton collisions at centre-of-mass energies of 7, 8, and 13 TeV, collected with the LHCb detector and corresponding to a total integrated luminosity of 9 fb${}^-1$. The structure is interpreted as the result of overlapping excited $B_s^0$ states. With high significance, a two-peak hypothesis provides a better description of the data than a single resonance. Under this hypothesis the masses and widths of the two states, assuming they decay directly to $B^+K^-$, are determined to be $m_1 = 6063.5 pm 1.2 text{ (stat)} pm 0.8text{ (syst) MeV},$ $Gamma_1 = 26 pm 4 text{ (stat)} pm 4text{ (syst) MeV},$ $m_2 = 6114 pm 3 text{ (stat)} pm 5text{ (syst) MeV},$ $Gamma_2 = 66 pm 18 text{ (stat)} pm 21text{ (syst) MeV}.$ Alternative values assuming a decay through $B^{*+}K^-$, with a missing photon from the $B^{*+} rightarrow B^+gamma$ decay, which are shifted by approximately 45 MeV are also determined. The possibility of a single state decaying in both channels is also considered. The ratio of the total production cross-section times branching fraction of the new states relative to the previously observed $B_{s2}^{*0}$ state is determined to be $0.87 pm 0.15 text{ (stat)} pm 0.19 text{ (syst)}$.
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*}
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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