Symmetry Tests in Photo-Pion Production

TL;DR

This paper discusses using small angle electron scattering with intense beams to perform near-real photon reactions, enabling new tests of fundamental symmetries and interactions in photo-pion production.

Contribution

It introduces a novel experimental approach for photo-pion reactions that allows precise tests of charge symmetry, isospin breaking, and chiral effective theories.

Findings

Potential to measure neutron-neutron scattering length $a_{nn}$

Tests of charge symmetry and isospin breaking

Validation of chiral effective theories

Abstract

Small angle electron scattering with intense electron beams opens up the possibility of performing almost real photon induced reactions with thin, polarized hydrogen and few body targets, allowing for the detection of low energy charged particles.This promises to be much more effective than conventional photon tagging techniques. For photo-pion reactions some fundamental new possibilities include: tests of charge symmetry in the N-N system by measurement of the neutron-neutron scattering length $a_{nn}$ in the $\gamma D \rightarrow \pi^{+} nn$ reaction; tests of isospin breaking due to the mass difference of the up and down quarks; measurements with polarized targets are sensitive to $\pi$N phase shifts and will test the validity of the Fermi-Watson (final state interaction) theorem. All of these experiments will test the accuracy and energy region of validity of chiral effective theories.