Test of isospin symmetry via low energy $^1$H($\pi^-$,$\pi^o$)$n$ charge exchange

TL;DR

This study measures differential cross sections for low-energy pion-proton charge exchange to test isospin symmetry, revealing discrepancies with previous data and implications for isospin violation claims.

Contribution

It provides new experimental data on pion-nucleon charge exchange at low energies, challenging prior findings of large isospin symmetry breaking.

Findings

New differential cross section measurements at 104-143 MeV/c

Discrepancies with previous data sets

Implications for isospin violation in pion-nucleon interactions

Abstract

We report measurements of the $\pi^- p \to \pi^o n$ differential cross sections at six momenta (104-143 MeV/c) and four angles (0-40 deg) by detection of $\gamma$-ray pairs from $\pi^o \to \gamma \gamma$ decays using the TRIUMF RMC spectrometer. This region exhibits a vanishing zero-degree cross section from destructive interference between s-- and p--waves, thus yielding special sensitivity to pion-nucleon dynamics and isospin symmetry breaking. Our data and previous data do not agree, with important implications for earlier claims of large isospin violating effects in low energy pion-nucleon interactions.