The mass of the sigma pole

Abstract

BES data on the sigma pole are refitted taking into account new information on coupling of sigma to KK and eta-eta. The fit also includes Cern-Munich data on pi-pi elastic phases shifts and Ke4 data, and gives a pole position of 500 +- 30 - i(264 +- 30) MeV. However, there is a clear discrepancy with the sigma pole position recently predicted by Caprini et al. using the Roy equation. This discrepancy may be explained naturally by uncertainties arising from inelasticity in KK and eta-eta channels and mixing between sigma and f0(980). Adding freedom to accomodate these uncertainties gives an optimum compromise with a pole position of 472 +- 30 - i(271 +- 30) MeV.