Observation of a narrow charmoniumlike state in exclusive B+/--->K+/-pi+pi-J/psi decays

Phys Rev Lett. 2003 Dec 31;91(26 Pt 1):262001. doi: 10.1103/PhysRevLett.91.262001. Epub 2003 Dec 23.

Abstract

We report the observation of a narrow charmoniumlike state produced in the exclusive decay process B+/--->K+/-pi(+)pi(-)J/psi. This state, which decays into pi(+)pi(-)J/psi, has a mass of 3872.0+/-0.6(stat)+/-0.5(syst) MeV, a value that is very near the M(D0)+M(D(*0)) mass threshold. The results are based on an analysis of 152M B-Bmacr; events collected at the Upsilon(4S) resonance in the Belle detector at the KEKB collider. The signal has a statistical significance that is in excess of 10sigma.