Production of $σ$ in $ψ(2S)\to π^{+}π^{-}J/ψ$

Using 14M $ψ(2S)$ events accumulated by BESII at the BEPC, a Covariant Helicity Amplitude Analysis is performed for $ψ(2S)\toπ^+π^-J/ψ, J/ψ\to μ^+μ^-$. The $π^+π^-$ mass spectrum, distinctly different from phase space, suggests $σ$ 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 $σ$. The $σ$ pole position is determined to be $(552^{+84}_{-106})-i(232^{+81}_{-72})$ MeV/$c^2$.

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