Observation of Doubleφ-Meson Production inπ−pInteractions

Abstract

We report a measurement of the reaction ${\pi }^{-}p\to \varphi \varphi n$ at 22.6 GeV/c. The $\varphi \varphi$ effectivemass spectrum shows a concentration of events from threshold to about 2.4 GeV/${\mathit{c}}^2$. From the data near 2.8 GeV/${\mathit{c}}^2$ effective mass, we place an upper limit on $\sigma$ times the branching ratio of 2 nb (90% confidence level) for the production of ${\eta }_c$ and its decay into $\varphi \varphi$.