Observation of the doubly charmed baryon ${\Omega }_{cc}^{+}$

A search for the doubly charmed baryon ${\Omega }_{cc}^{+}$ in the ${\Omega }_c^0{\pi }^{+}$ decay channel is performed using proton-proton collision data corresponding to an integrated luminosity of $6.3{\text{fb}}^{-1}$, collected with the upgraded LHCb detector in 2024 at a center-of-mass energy of 13.6$\text{TeV}$. A peaking structure with a global significance of $8.7\sigma$ is observed in the ${\Omega }_c^0{\pi }^{+}$ mass spectrum, where the ${\Omega }_c^0$ baryon is reconstructed in the $p{K}^{-}{K}^{-}{\pi }^{+}$ final state. The structure is consistent with originating from a weakly decaying particle and is identified as the doubly charmed baryon ${\Omega }_{cc}^{+}$. Its mass is determined to be $3725.9\pm 1.0(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 0.2(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\pm 0.4(\mathrm{l}\mathrm{i}\mathrm{f}\mathrm{e}\mathrm{t}\mathrm{i}\mathrm{m}\mathrm{e})\pm 0.6(\mathrm{e}\mathrm{x}\mathrm{t})\text{MeV/}{c}^2$, where the third uncertainty arises from the dependence of the selection-induced bias on the unknown ${\Omega }_{cc}^{+}$ lifetime, and the fourth is due to the uncertainties on the masses of the ${\Omega }_c^0$, ${\Xi }_c^{+}$, and ${\Xi }_{cc}^{++}$ baryons.