Search for Rare and Forbiddenη′Decays

Abstract

We have searched for rare and forbidden decays of the ${\eta }^{\prime }$ meson in hadronic events at the CLEO II detector. The search is conducted on 4.80 ${\mathrm{fb}}^{-1\mathrm{}}$ of $e^{+}{e}^{-}$ collisions at 10.6 GeV center-of-mass energy at the Cornell Electron Storage Ring. We find no signals, and set $90\%$ confidence level upper limits of their branching fractions: $B({\eta }^{\prime }\to e^{+}{e}^{-}\eta )<2.4\mathrm{}\times {10}^{-3\mathrm{}}$, $B({\eta }^{\prime }\to e^{+}{e}^{-}{\pi }^0)<1.4\mathrm{}\times {10}^{-3\mathrm{}}$, $B({\eta }^{\prime }\to e^{+}{e}^{-}\gamma )<0.9\mathrm{}\times {10}^{-3\mathrm{}}$, and $B({\eta }^{\prime }\to e\mu )<4.7\mathrm{}\times {10}^{-4\mathrm{}}$. We also fit the matrix element of the ${\eta }^{\prime }\to {\pi }^{+}{\pi }^{-}\eta$ Dalitz plot with the parametrization $|M{|}^2=A|1+\alpha y{|}^2$, where $y$ is a linear function of the kinetic energy of the $\eta$, and find Re $\left(\alpha \right)=-0.021\mathrm{}\pm 0.025$.