Observation of the doubly charmed baryon $\hat{I}{ž}_{cc}^{+}$ with the LHCb Run 3 detector

Abstract

The first observation of the doubly charmed baryon $\hat{I}{ž}_{cc}^{+}$ is reported through its decay to the $\hat{I}{›}_c^{+}{K}^{-}\ddot{I}{€}^{+}$ final state, with a statistical significance exceeding seven standard deviations. The observation is made using proton-proton collision data collected in 2024 with the LHCb Run 3 detector at a center-of-mass energy of 13.6 TeV, corresponding to a total integrated luminosity of $6.9{\mathrm{fb}}^{-1}$. The $\hat{I}{ž}_{cc}^{+}$ mass is measured to be $3619.97\pm 0.83\pm 0.26{}_{-1.30}^{+1.90}\mathrm{MeV}/c^2$, where the first uncertainty is statistical, the second is systematic, and the third is due to the unknown $\hat{I}{ž}_{cc}^{+}$ lifetime, which is assumed to lie in the range 15-160 fs with a baseline value of 45 fs. The difference between the masses of the $\hat{I}{ž}_{cc}^{+}$ and $\hat{I}{ž}_{cc}^{++}$ baryons is determined to be $-1.77\pm 0.84\pm 0.15{}_{-1.30}^{+1.90}\mathrm{MeV}/c^2$. This is the first observation of a new particle made with the LHCb Run 3 detector.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/5952/ (LHCb public pages)