Hard pion bremsstrahlung in the Coulomb region

TL;DR

This paper investigates high-energy pion-nucleus bremsstrahlung in the Coulomb region, focusing on measuring pion polarizability and analyzing the sensitivity of the process to the pion's internal structure using a model with meson exchanges.

Contribution

It introduces a detailed analysis of pion bremsstrahlung in the Coulomb region and examines the feasibility of extracting pion polarizability from such reactions.

Findings

Effective energy in virtual pion-Compton scattering is often very high.

Threshold approximation is generally not valid in these reactions.

Sensitivity to pion structure depends on the model with meson exchanges.

Abstract

Hard high-energy pion-nucleus bremsstrahlung, $\pi^- +A\to\pi^- +\gamma +A$, is studied in the Coulomb region, i.e. the small-angle region where the nuclear scattering is dominated by the Coulomb interaction. Special attention is focussed on the possibility of measuring the pion polarizability in such reactions. We study the sensitivity to the structure of the underlying the pion-Compton amplitude through a model with $\sigma$, $\rho$, and a_1 exchanges. It is found that the effective energy in the virtual pion-Compton scattering is often so large that the threshold approximation does not apply.