Radiative pion capture in 3He

Abstract

The rates for the radiative and charge exchange capture of stopped pions in 3He are calculated in the impulse approximation. The Panofsky ratio is considered in detail; the S, S′ and D state components of the nuclear wave functions are included and an estimate of the capture rate from a 2p state is made. We show that the recent experimental measurement of the Panofsky ratio by Truöl et al. implies that there are small corrections to the impulse approximation and that these corrections are similar in magnitude to those that occur in the related process, the β-decay of 3H. The radiative breakup rates are calculated using the Amado model to describe the final states and the results are compared with closure approximations. We show that each spin-isospin channel is dominated by the contribution of the state with the lowest threshold energy; that the impulse approximation can account for the experimental branching ratios and the shape of the photon spectrum; and that the radiative breakup reaction does not provide any evidence for the existence of a three-nucleon resonance.