Choi, SK (reprint author), Gyeongsang Natl Univ, Chinju, South Korea.
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-D(0)+M-D*0 mass threshold. The results are based on an analysis of 152M B-(B) over bar events collected at the Y(4S) resonance in the Belle detector at the KEKB collider. The signal has a statistical significance that is in excess of 10sigma.