Evidence for the Existence of a New Meson in the 955-MeV Mass Region

Abstract

We report evidence for the existence of a new meson, which we call the $M\left(953\right)\mathrm{}$, with mass 953 ± 2 MeV and width <10 MeV, produced in the final state $K^{-}p\to p{K}^{-}{M}^0$ at incident momenta 3.9 and $4.6\frac{\mathrm{GeV}}{c}$. These results are based primarily on a signal of 68 ± 12 events in the decay mode $M\to {\pi }^{+}{\pi }^{-}\gamma$ where the $\pi \pi$ system does not show a ${\rho }^0$ signal, in sharp distinction to the ${\rho }^0\gamma$ decay mode of the ${\eta }^{\prime }\mathrm{}\left(958\right)\mathrm{}$.