The Kappa in J/Psi -> Kpplus-piminus-Kminus-piplus

TL;DR

This paper analyzes BES II data on J/Psi decays to K pi, revealing a strong kappa resonance near threshold, with phase and magnitude measurements consistent with elastic scattering data, and provides a detailed fit including a pole position.

Contribution

It presents a combined fit of BES and LASS data to determine the kappa resonance parameters, including a pole position and scattering length, with a model incorporating an Adler zero.

Findings

Kappa pole at 760+-20(stat)+-40(syst) - i(420+-45+-60syst) MeV

S-wave I=0 scattering length a_0 = 0.23+-0.04

Phase variation agrees with elastic scattering data

Abstract

BES II data for J/Psi->K*(890)Kpi reveal a strong kappa peak in the Kpi S-wave near threshold. Both magnitude and phase are determined in slices of Kpi mass by interferences with strong Ko(1430), K1(1270) and K1(1400) signals. The phase variation with mass agrees within errors with LASS data for Kpi elastic scattering. A combined fit is presented to both BES and LASS data. The fit uses a Breit-Wigner amplitude with an s-dependent width containing an Adler zero. The kappa pole is at 760+-20(stat)+-40(syst) - i(420+-45+-60syst) MeV. The S-wave I=0 scattering length a_0 = 0.23+-0.04 (in units of m(pi)) is close to the prediction 0.19+-0.02 of Chiral Perturbation Theory.