New Upper Limit on the Width of theX0(958)

Abstract

An upper limit ${\Gamma }_{X^0}<0.8\mathrm{}$ MeV${/\mathit{c}}^2$ (95% confidence level) is deduced from the missing-mass spectrum near 958 MeV${/\mathit{c}}^2$ in the reaction ${\pi }^{-}+p\to \mathrm{MM}+n$ close to threshold. Measurement of those missing masses which decay to $2\gamma$ shows a single peak with a central mass of 957.4 ± 0.5 MeV${/\mathit{c}}^2$ close to the value of 957.46 ± 0.33 MeV${/\mathit{c}}^2$ deduced from the total missing-mass spectrum.