Observation of two new $\hat{I}{ž}_b^{-}$ baryon resonances

Abstract

Two structures are observed close to the kinematic threshold in the $\hat{I}{ž}_b^0\ddot{I}{€}^{-}$ 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 $\hat{I}{ž}_b^{\prime -}$ and $\hat{I}{ž}_b^{\ast -}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\hat{I}{ž}_b^{\prime -})-m(\hat{I}{ž}_b^0)-m(\ddot{I}{€}^{-})=3.653\pm 0.018\pm 0.006$ MeV$/c^2$, $m(\hat{I}{ž}_b^{\ast -})-m(\hat{I}{ž}_b^0)-m(\ddot{I}{€}^{-})=23.96\pm 0.12\pm 0.06$ MeV$/c^2$, $\hat{I}“(\hat{I}{ž}_b^{\ast -})=1.65\pm 0.31\pm 0.10$ 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 $\hat{I}“(\hat{I}{ž}_b^{\prime -})<0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.

17 pages, 2 figures