Observation ofη-Meson Production in the Reactionπ−+He3→η+t

Pion-induced $\eta$-meson production populating a discrete nuclear state is observed for the first time in the reaction ${\pi }^{-}+{}_{}{}^3{}_{}{}^{}\mathrm{He}\to \eta +t$. At 680 MeV/c ${\pi }^{-}$ momentum, this reaction is identified by measurement of the recoiling tritons. The measured cross sections are approximately 3 orders of magnitude greater than the $p+d\to \eta +{}_{}{}^3{}_{}{}^{}\mathrm{He}$ and the $d+d\to \eta +{}_{}{}^4{}_{}{}^{}\mathrm{He}$ cross sections. Distorted-wave impulse-approximation calculations underpredict the observed cross sections by a factor of 2-4.