Study of theη′Meson from the ReactionK−p→Λη′at 2.18 GeV/c

We present new data on the ${\eta }^{\prime }$ meson based on 1414 ${\eta }^{\prime }$ events obtained from a 1 100 000-picture exposure of the BNL 31-inch hydrogen bubble chamber to a 2.18-GeV/c $K^{-}$ beam. We have measured the ${\eta }^{\prime }$ mass, width, and branching ratios. We find that the very-forward-produced ${\eta }^{\prime }$ mesons have anisotropic angular distributions with respect to the incident $K^{-}$ beam, suggesting that possibly $J^{\mathrm{PC}}=2^{-+}$; however, the standard Dalitz-plot analyses favor $J^{\mathrm{PC}}=0^{-+}$ over $2^{-+}$.