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

TL;DR

This study analyzes $ o o J/ o o o$ decays using a large dataset, providing evidence for the production of the $ o$ meson and determining its pole position with a covariant amplitude analysis.

Contribution

It presents the first covariant helicity amplitude analysis of $ o o J/ o$, confirming the existence of the $ o$ meson and measuring its pole position.

Findings

Evidence for $ o$ production in $ o J/ o$ decays.

Determination of the $ o$ pole position as $(552^{+84}_{-106}) - i(232^{+81}_{-72})$ MeV/$c^2$.

Results consistent with the existence of the $ o$ meson.

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/$c^2$.