Study of resonant structure of S-wave amplitudes in pi(-)p->pi(-)pi(+)n measured on polarized target at 17.2 GeV/c in the mass range of 580-1080 MeV

Abstract

We have performed a new model independent amplitude analysis of reaction $\pi^- p \to \pi^- \pi^+ n$ measured at CERN at 17.2 GeV/c on polarized target. The analysis extends the range of dipion mass from 600--880 MeV used in the previous study to 580--1080 MeV. Our purpose is to study the role of $f_0(980)$ interference and to better determine the resonance parameters of $\sigma(750)$ resonance from fits to both S-wave amplitudes $|\bar S|^2\Sigma$ and $|S|^2\Sigma$ with recoil nucleon transversities ``up'' and ``down'', respectively. This work is the first attempt to determine resonance parameters of a resonance from Breit-Wigner fits to production amplitudes of opposite transversity. We used several fitting procedures to understand the resonant structure of the S-wave amplitudes in this mass range. The simultaneous fit to $|\bar S|^2\Sigma$ and $|S|^2\Sigma$ with two common $\sigma$ poles yields an excellent fit with a lower $\chi^2/dpt$ than the separate fits. All amplitudes are dominated by a $\sigma$ state with $m_\sigma = 786 \pm 24$ MeV and $\Gamma_\sigma = 130\pm 47$ MeV. All amplitudes receive a weaker contribution from a narrower $\sigma'$ state with $m_{\sigma'} = 670 \pm 30$ MeV and $\Gamma_{\sigma'} = 59 \pm 58$ MeV. We propose to identify $\sigma'(670)$ and $\sigma(786)$ with colour-electric and colour-magnetic modes of lowest mass scalar gluonium $0^{++} (gg)$.