Observation of the doubly charmed baryon $\it{\Xi}_{cc}^+$ with the LHCb Run 3 detector

TL;DR

The paper reports the first observation of the doubly charmed baryon $ ext{ extit{Xi}}_{cc}^+$ using LHCb Run 3 data, measuring its mass and confirming its existence with high statistical significance.

Contribution

This work provides the first observation and precise mass measurement of the doubly charmed baryon $ ext{ extit{Xi}}_{cc}^+$ with the LHCb Run 3 detector, advancing understanding of heavy baryons.

Findings

$ ext{ extit{Xi}}_{cc}^+$ mass measured at 3619.97 MeV/c²

Statistical significance exceeds seven standard deviations

Mass difference between $ ext{ extit{Xi}}_{cc}^+$ and $ ext{ extit{Xi}}_{cc}^{++}$ is -1.77 MeV/c²

Abstract

The first observation of the doubly charmed baryon $\it{\Xi}_{cc}^+$ is reported through its decay to the $\it{\Lambda}_c^+ K^-\pi^+$ 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 $\it{\Xi}_{cc}^+$ mass is measured to be $3619.97 \pm 0.83 \pm 0.26 \,^{+1.90}_{-1.30}\,\mathrm{MeV}/c^2$, where the first uncertainty is statistical, the second is systematic, and the third is due to the unknown $\it{\Xi}_{cc}^+$ 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 $\it{\Xi}_{cc}^+$ and $\it{\Xi}_{cc}^{++}$ baryons is determined to be $-1.77 \pm 0.84 \pm 0.15 \,^{+1.90}_{-1.30}\,\mathrm{MeV}/c^2$. This is the first observation of a new particle made with the LHCb Run 3 detector.