Discovery of the doubly charmed baryon $\Xi_{cc}^{++}$ at LHCb

The LHCb collaboration announced the first observation of the doubly charmed baryon $\Xi_{cc}^{++}$, which was discovered decaying to a $\Lambda_{c}^{+}K^{-}\pi^{+}\pi^{+}$ final state. A highly significant structure is found in the $\Lambda_{c}^{+}K^{-}\pi^{+}\pi^{+}$ mass spectrum in proton-proton collision data collected by the LHCb experiment at center-of-mass energies of 13 TeV and 8 TeV. The peak contains $313 \pm 33$ decays in the 13 TeV sample and $113 \pm 21$ decays in the 8 TeV, with local significances in excess of $12\sigma$ and $7\sigma$ respectively. The narrow structure has a width that is consistent with experimental resolution, and its properties are consistent with those of a weakly decaying state and inconsistent with those of a strongly decaying state. The difference between the masses of the structure, identified as $\Xi_{cc}^{++}$, and the $\Lambda_{c}^{+}$ baryon is $1334.94 \pm 0.72(\mbox{stat.}) \pm 0.27(\mbox{syst.})\,\mbox{MeV}/c^{2}$, and the mass of the $\Xi_{cc}^{++}$ baryon is $3621.40 \pm 0.72(\mbox{stat.}) \pm 0.27(\mbox{syst.}) \pm 0.14(\Lambda^+_c)\,\mbox{MeV}/c^{2}$.