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

TL;DR

This paper reports the first observation of the doubly charmed baryon $\\Xi_{cc}^{++}$ in proton-proton collisions at the LHCb experiment, measuring its mass and confirming its existence with high significance.

Contribution

The paper provides the first experimental evidence and precise mass measurement of the doubly charmed baryon $\Xi_{cc}^{++}$, confirming its existence.

Findings

Observation of a significant structure in the $\Lambda_c^+K^-\pi^+\pi^+$ mass spectrum.

Mass of $\Xi_{cc}^{++}$ measured to be approximately 3621 MeV/c^2.

Confirmed the state in data collected at 8 TeV and 13 TeV.

Abstract

A highly significant structure is observed in the $\Lambda_c^+K^-\pi^+\pi^+$ mass spectrum, where the $\Lambda_c^+$ baryon is reconstructed in the decay mode $pK^-\pi^+$. The structure is consistent with originating from a weakly decaying particle, identified as the doubly charmed baryon $\Xi_{cc}^{++}$. The difference between the masses of the $\Xi_{cc}^{++}$ and $\Lambda_c^+$ states is measured to be $1334.94 \pm 0.72 (\mathrm{stat}) \pm 0.27 (\mathrm{syst}~\mathrm{MeV}/c^2$, and the $\Xi_{cc}^{++}$ mass is then determined to be $3621.40 \pm 0.72 (\mathrm{stat}) \pm 0.27 (\mathrm{syst} \pm 0.14 \, (\Lambda_c^+)~\mathrm{MeV}/c^2$, where the last uncertainty is due to the limited knowledge of the $\Lambda_c^+$ mass. The state is observed in a sample of proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 $\mathrm{fb}^{-1}$, and confirmed in an additional sample of data collected at 8 TeV.