Production of $\sigma$ in $\psi(2S)\to \pi^{+}\pi^{-}J/\psi$

Abstract

Using 14M $\psi(2S)$ events accumulated by BESII at the BEPC, a Covariant Helicity Amplitude Analysis is performed for $\psi(2S)\to\pi^+\pi^-J/\psi, J/\psi\to \mu^+\mu^-$. The $\pi^+\pi^-$ mass spectrum, distinctly different from phase space, suggests $\sigma$ production in this process. Two different theoretical schemes are used in the global fit to the data. The results are consistent with the existence of the $\sigma$. The $\sigma$ pole position is determined to be $(552^{+84}_{-106})-i(232^{+81}_{-72})$ MeV/$c^2$.