First Observation of the Doubly Charmed Baryon [Formula presented]

Abstract

We observe a signal for the doubly charmed baryon [Formula presented] in the charged decay mode [Formula presented] in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of [Formula presented] events, a statistical significance of [Formula presented]. The observed mass of this state is [Formula presented]. The Gaussian mass width of this state is [Formula presented], consistent with resolution; its lifetime is less than 33 fs at 90% confidence. © 2002 The American Physical Society.