First 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 collision data, measuring its mass, confirming its existence with high significance, and providing initial lifetime constraints.

Contribution

The first experimental observation of the Xi_cc^+ baryon, including its mass measurement and statistical significance, using data from the SELEX experiment at Fermilab.

Findings

Mass measured at (3519 +/- 1) MeV/c^2

Statistical significance of 6.3 sigma

Lifetime less than 33 femtoseconds at 90% confidence

Abstract

We observe a signal for the doubly charmed baryon Xi_cc^+ in the charged decay mode Xi_cc^+ --> Lambda_c^+ K- pi+ in data from SELEX, the charm hadro-production experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1 +/- 0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is (3519 +/- 1) MeV/c^2. The Gaussian mass width of this state is 3MeV/c^2, consistent with resolution; its lifetime is less than 33fsec at 90% confidence.