Polarization and dilepton anisotropy in pion-nucleon collisions

TL;DR

This paper investigates how baryon resonance properties influence dilepton angular distributions in pion-nucleon collisions, providing insights into resonance contributions through anisotropy measurements.

Contribution

It introduces a consistent effective interaction framework for baryon resonances up to spin-5/2 and demonstrates how resonance characteristics affect dilepton anisotropy.

Findings

Anisotropy coefficients reflect the spin and parity of intermediate baryon resonances.

Including specific resonances like N(1520) and N(1440) aligns theoretical predictions with experimental data.

Anisotropy measurements can constrain resonance contributions in pion-nucleon reactions.

Abstract

Hadronic polarization and the related anisotropy of the dilepton angular distribution are studied for the reaction $\pi N \rightarrow Ne^+ e^-$. We employ consistent effective interactions for baryon resonances up to spin-5/2, where non-physical degrees of freedom are eliminated, to compute the anisotropy coefficients for isolated intermediate baryon resonances. It is shown that the spin and parity of the intermediate baryon resonance is reflected in the angular dependence of the anisotropy coefficient. We then compute the anisotropy coefficient including the $N(1520)$ and $N(1440)$ resonances, which are essential at the collision energy of the recent data obtained by the HADES collaboration on this reaction. We conclude that the anisotropy coefficient provides useful constraints for unravelling the resonance contributions to this process.