Observation of Two Resonant Structures in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\psi}(2S)$ via Initial-State Radiation at Belle

Observation of Two Resonant Structures in $e^{+} e^{-} \to π^{+} π^{-} ψ (2 S)$ via Initial-State Radiation at Belle

X. L. Wang et al. (Belle Collaboration)

Phys. Rev. Lett. 99, 142002 – Published 1 October 2007

Abstract

The cross section for $e^{+} e^{-} \to π^{+} π^{-} ψ (2 S)$ between threshold and $\sqrt{s} = 5.5 GeV$ is measured using $673 {fb}^{- 1}$ of data on and off the $Υ (4 S)$ resonance collected with the Belle detector at KEKB. Two resonant structures are observed in the $π^{+} π^{-} ψ (2 S)$ invariant-mass distribution, one at $4361 \pm 9 \pm 9 MeV / c^{2}$ with a width of $74 \pm 15 \pm 10 MeV / c^{2}$ , and another at $4664 \pm 11 \pm 5 MeV / c^{2}$ with a width of $48 \pm 15 \pm 3 MeV / c^{2}$ , if the mass spectrum is parametrized with the coherent sum of two Breit-Wigner functions. These values do not match those of any of the known charmonium states.