Observation of two resonancelike structures in the ${\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1}$ mass distribution in exclusive ${\overline{B}}^{0}\ensuremath{\rightarrow}{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}{\ensuremath{\chi}}_{c1}$ decays

Observation of two resonancelike structures in the $π^{+} χ_{c 1}$ mass distribution in exclusive ${\bar{B}}^{0} \to K^{-} π^{+} χ_{c 1}$ decays

R. Mizuk et al. (Belle Collaboration)

Phys. Rev. D 78, 072004 – Published 10 October 2008

Abstract

We report the first observation of two resonancelike structures in the $π^{+} χ_{c 1}$ invariant mass distribution near $4.1 GeV / c^{2}$ in exclusive ${\bar{B}}^{0} \to K^{-} π^{+} χ_{c 1}$ decays. From a Dalitz plot analysis in which the $π^{+} χ_{c 1}$ mass structures are represented by Breit-Wigner resonance amplitudes, we determine masses and widths of: $M_{1} = (4051 \pm 14_{- 41}^{+ 20}) MeV / c^{2}$ , $Γ_{1} = (82_{- 17 - 22}^{+ 21 + 47}) MeV$ , $M_{2} = (4248_{- 29 - 35}^{+ 44 + 180}) MeV / c^{2}$ , and $Γ_{2} = (177_{- 39 - 61}^{+ 54 + 316}) MeV$ ; and product branching fractions of $B ({\bar{B}}^{0} \to K^{-} Z_{1, 2}^{+}) \times B (Z_{1, 2}^{+} \to π^{+} χ_{c 1}) = ({3.0}_{- 0.8 - 1.6}^{+ 1.5 + 3.7}) \times 10^{- 5}$ and $({4.0}_{- 0.9 - 0.5}^{+ 2.3 + 19.7}) \times 10^{- 5}$ , respectively. Here the first uncertainty is statistical, the second is systematic. The significance of each of the $π^{+} χ_{c 1}$ structures exceeds $5 σ$ , including the systematic uncertainty from various fit models. This analysis is based on $657 \times 10^{6}$ $B \bar{B}$ events collected at the $Υ (4 S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider.