Measurement of the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ Cross Section Via Initial-State Radiation at Belle

Measurement of the $e^{+} e^{-} \to π^{+} π^{-} J / ψ$ Cross Section Via Initial-State Radiation at Belle

C. Z. Yuan et al. (Belle Collaboration)

Phys. Rev. Lett. 99, 182004 – Published 2 November 2007

Abstract

The cross section for $e^{+} e^{-} \to π^{+} π^{-} J / ψ$ between 3.8 and $5.5 GeV / c^{2}$ is measured using a $548 {fb}^{- 1}$ data sample collected on or near the $Υ (4 S)$ resonance with the Belle detector at KEKB. A peak near $4.25 GeV / c^{2}$ , corresponding to the so called $Y (4260)$ , is observed. In addition, there is another cluster of events at around $4.05 GeV / c^{2}$ . A fit using two interfering Breit-Wigner shapes describes the data better than one that uses only the $Y (4260)$ , especially for the lower-mass side of the 4.25 GeV enhancement.