Two-Body Mechanisms in Pion Photoproduction on the Trinucleon

Abstract

A breakdown of the Impulse Approximation is studied in pion photoproduction on 3 He at high momentum transfers. The usual DWIA formalism with Faddeev wave functions which works well for small momentum transfers deviates from experimental measurements by up to two orders of magnitude for Q 2 > 6f m −2 . It is found that the explicit inclusion of two-body mechanisms, where the photon is absorbed on one nucleon and the pion is emitted from another nucleon can restore agreement with the data.

Neutral pion photoproduction on deuterium in baryon chiral perturbation theory to order q4

“…refs. [18]- [21]), it is worth emphasizing why we use chiral perturbation theory here. As first stressed by Weinberg [13], chiral perturbation theory allows one to systematically construct the many-body interactions between nucleons, pions and photons following the power counting rules.…”

Coherent photoproduction ofπ+fromHe3

“…Our new data suggest that there are other mechanisms that produce much larger contributions than the 1-body (impulse approximation) and the 2-body mechanisms that were proposed in Ref. [10]. It is possible that two-or even three-body effects are driving the large cross sections, but it is not precisely known to what extent.…”

“…12-15). The curves show plane-wave impulse approximation PWIA (dotted line), distorted-wave impulse approximation DWIA (dashed line), and the DWIA + 2-body mechanism [10](solid lines).…”

“…In 1995, the two-body mechanisms were explicitly included in the model [10] where the photon is absorbed by one nucleon and the pion is emitted from the other nucleon (Fig. 1).…”

“…Studying this production process is ideal for understanding the interaction of pions with nuclei and to search for possible effects mediated by nucleon resonances in nuclear matter. Reactions such as γ+ 3 He→ π + + t, γ+ 3 He→ π 0 + 3 He, γ + t → π − + 3 He, and γ + t → π 0 + t have been studied by both experimental and theoretical groups over the last four decades( [1]- [10]). Studying these processes is useful in developing our understanding of nuclear structure and the long-range part of the nucleon-nucleon interaction described by the one-pion exchange model.…”