Coherent η-meson production in the reaction π^{-}+^{3}He→η+t

Abstract

The reaction ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${+}^{3}$He\ensuremath{\rightarrow}\ensuremath{\eta}+t has been observed by detecting \ensuremath{\eta}\ensuremath{\rightarrow}2\ensuremath{\gamma} decays. The observed forward-angle cross sections vary from \ensuremath{\sim}100 \ensuremath{\mu}b/sr at 680 MeV/c to \ensuremath{\sim}2 \ensuremath{\mu}b/sr at 590 MeV/c. Distorted-wave impulse-approximation calculations reproduce the shape but underestimate the magnitude of the observed cross section. These cross sections are approximately 100 times larger than those for the reaction p+d\ensuremath{\rightarrow}\ensuremath{\eta}${+}^{3}$He measured at similar \ensuremath{\eta} center-of-mass energies.