Using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of $8.5{\mathrm{fb}}^{-1}$, the observation of a new excited ${\mathrm{\Xi }}_b^0$ resonance decaying to the ${\mathrm{\Xi }}_b^{-}{\pi }^{+}$ final state is presented. The state, referred to as ${\mathrm{\Xi }}_b(6227{)}^0$, has a measured mass and natural width of $m({\mathrm{\Xi }}_b(6227{)}^0)=6227.1_{-1.5}^{+1.4}\pm 0.5\mathrm{MeV}$ and $\mathrm{\Gamma }({\mathrm{\Xi }}_b(6227{)}^0)=18.6_{-4.1}^{+5.0}\pm 1.4\mathrm{MeV}$, where the uncertainties are statistical and systematic. The production rate of the ${\mathrm{\Xi }}_b(6227{)}^0$ state relative to that of the ${\mathrm{\Xi }}_b^{-}$ baryon in the kinematic region $2<\eta <5$ and $p_{\mathrm{T}}<30\mathrm{GeV}$ is measured to be $\frac{f_{{\mathrm{\Xi }}_b(6227{)}^0}}{f_{{\mathrm{\Xi }}_b^{-}}}\mathcal{B}({\mathrm{\Xi }}_b(6227{)}^0\to {\mathrm{\Xi }}_b^{-}{\pi }^{+})=0.045\pm 0.008\pm 0.004,$ where $\mathcal{B}({\mathrm{\Xi }}_b(6227{)}^0\to {\mathrm{\Xi }}_b^{-}{\pi }^{+})$ is the branching fraction of the decay, and $f_{{\mathrm{\Xi }}_b(6227{)}^0}$ and $f_{{\mathrm{\Xi }}_b^{-}}$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed ${\mathrm{\Xi }}_b(6227{)}^{-}$ state, along with the mass of the ${\mathrm{\Xi }}_b^{-}$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.

• Received 28 October 2020
• Accepted 23 November 2020

DOI:https://doi.org/10.1103/PhysRevD.103.012004

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