Pion emission in 2H, 12C, 27Al, gamma pi+ reactions at threshold

TL;DR

This paper presents initial measurements of pion production in photonuclear reactions near threshold energies, comparing experimental data with model predictions and highlighting areas needing further theoretical refinement.

Contribution

First experimental data from MAX-lab on pion production at threshold energies, providing insights into nuclear interactions and model validation.

Findings

Total pi+ yield decreases below 200 MeV for 12C and 27Al

Differential cross sections align with intranuclear cascade model predictions

Deviations at 176 MeV suggest need for model refinements

Abstract

The first data from MAX-lab in Lund, Sweden on pion production in photonuclear reactions at threshold energies, is presented. The decrease of the total yield of pi+ in gamma + 12C, 27Al reactions below 200 MeV as well as differential, dsigma/dOmega, cross sections follow essentially predictions from an intranuclear cascade model with an attractive potential for pion-nucleus interaction in its simplest form. Double differential, d2sigma/dOmegadT, cross sections at 176 MeV show, however, deviations from the model, which call for refinements of nuclear and Coulomb potentials and possibly also for coherent pion production mechanisms.