Observation of a new ${\Xi }_b^0$ state

Abstract

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 $m({\Xi }_b(6227{)}^0)=6227.1_{-1.5}^{+1.4}\pm 0.5$ MeV, $\Gamma ({\Xi }_b(6227{)}^0)=18.6_{-4.1}^{+5.0}\pm 1.4$ 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 $p_{\mathrm{T}}<30$ GeV is measured to be $\frac{f_{{\Xi }_b(6227{)}^0}}{f_{{\Xi }_b^{-}}}\mathcal{B}({\Xi }_b(6227{)}^0\to {\Xi }_b^{-}{\pi }^{+})=0.045\pm 0.008\pm 0.004$, where $\mathcal{B}({\Xi }_b(6227{)}^0\to {\Xi }_b^{-}{\pi }^{+})$ 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.

arXiv comment15 pages, 5 figures. All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2020-032.html

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