Coherent Pion Production near Threshold with aHe3Projectile

Abstract

Pion production in ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^3{}_{}{}^{}\mathrm{He}$ collisions has been measured at energies below the threshold for production in free ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-nucleon reactions, with use of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ beam from the Orsay synchrocyclotron. Discrete states of the recoil nucleus, corresponding to the coherent process ${}_{}{}^3{}_{}{}^{}\mathrm{He}$(${}_{}{}^3{}_{}{}^{}\mathrm{He}$,${\pi }^{+}$) ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, have been observed with sizable cross sections at 268.5- and 282-MeV kinetic energy. The ground-state data are consistent with pionic atom information.