Observation of a new $\hat{I}{ž}_b^0$ 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 $\hat{I}{ž}_b^0$ resonance decaying to the $\hat{I}{ž}_b^{-}\ddot{I}{€}^{+}$ final state is presented. The state, referred to as $\hat{I}{ž}_b(6227{)}^0$, has a measured mass and natural width of $m(\hat{I}{ž}_b(6227{)}^0)=6227.1_{-1.5}^{+1.4}\pm 0.5$ MeV, $\hat{I}“(\hat{I}{ž}_b(6227{)}^0)=18.6_{-4.1}^{+5.0}\pm 1.4$ MeV, where the uncertainties are statistical and systematic. The production rate of the $\hat{I}{ž}_b(6227{)}^0$ state relative to that of the $\hat{I}{ž}_b^{-}$ baryon in the kinematic region $2<\hat{I}\cdot <5$ and $p_{\mathrm{T}}<30$ GeV is measured to be $\frac{f_{\hat{I}{ž}_b(6227{)}^0}}{f_{\hat{I}{ž}_b^{-}}}\mathcal{B}(\hat{I}{ž}_b(6227{)}^0\to \hat{I}{ž}_b^{-}\ddot{I}{€}^{+})=0.045\pm 0.008\pm 0.004$, where $\mathcal{B}(\hat{I}{ž}_b(6227{)}^0\to \hat{I}{ž}_b^{-}\ddot{I}{€}^{+})$ is the branching fraction of the decay, and $f_{\hat{I}{ž}_b(6227{)}^0}$ and $f_{\hat{I}{ž}_b^{-}}$ represent fragmentation fractions. Improved measurements of the mass and natural width of the previously observed $\hat{I}{ž}_b(6227{)}^{-}$ state, along with the mass of the $\hat{I}{ž}_b^{-}$ baryon, are also reported. Both measurements are significantly more precise than, and consistent with, previously reported values.

15 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