Observation of Cabibbo-Suppressed Two-Body Hadronic Decays and Precision Mass Measurement of the $\hat{I}{\text{c◯}}_c^0$ Baryon

Abstract

The first observation of the singly Cabibbo-suppressed $\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}{K}^{+}$ and $\hat{I}{\text{c◯}}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+}$ decays is reported, using proton-proton collision data at a center-of-mass energy of $13\mathrm{TeV}$, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$, collected with the LHCb detector between 2016 and 2018. The branching fraction ratios are measured to be $\frac{\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}{K}^{+})}{\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+})}=[6.08\pm 0.51(\mathrm{stat})\pm 0.40(\mathrm{syst})]\%$, $\frac{\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})}{\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+})}=[15.81\pm 0.87(\mathrm{stat})\pm 0.44(\mathrm{syst})\pm 0.16(\mathrm{ext})]\%$. In addition, using the $\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+}$ decay channel, the $\hat{I}{\text{c◯}}_c^0$ baryon mass is measured to be $M(\hat{I}{\text{c◯}}_c^0)=2695.28\pm 0.07(\mathrm{stat})\pm 0.27(\mathrm{syst})\pm 0.30(\mathrm{ext})\mathrm{MeV}$, improving the precision of the previous world average by a factor of 4.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-011.html (LHCb public pages)