Observation of a Narrow Charmoniumlike State in Exclusive ${B}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{K}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ Decays

Observation of a Narrow Charmoniumlike State in Exclusive $B^{\pm} \to K^{\pm} π^{+} π^{-} J / ψ$ Decays

S.-K. Choi et al. (Belle Collaboration)

Phys. Rev. Lett. 91, 262001 – Published 23 December 2003

Abstract

We report the observation of a narrow charmoniumlike state produced in the exclusive decay process $B^{\pm} \to K^{\pm} π^{+} π^{-} J / ψ$ . This state, which decays into $π^{+} π^{-} J / ψ$ , has a mass of $3872.0 \pm 0.6 (s t a t) \pm 0.5 (s y s t) M e V$ , a value that is very near the $M_{D^{0}} + M_{D^{* 0}}$ mass threshold. The results are based on an analysis of 152M $B$ - $\bar{B}$ events collected at the $Υ (4 S)$ resonance in the Belle detector at the KEKB collider. The signal has a statistical significance that is in excess of $10 σ$ .