Polarization and dilepton angular distribution in pion-nucleon collisions

TL;DR

This paper investigates how baryon resonances influence the angular distribution of dileptons in pion-nucleon collisions, revealing that resonance properties affect observable anisotropy patterns and can help identify resonance contributions.

Contribution

It introduces a consistent method to compute the impact of baryon resonances up to spin-5/2 on dilepton angular distributions, linking resonance quantum numbers to observable anisotropy features.

Findings

Resonance spin and parity affect the angular distribution of dileptons.

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

The anisotropy coefficient constrains resonance contributions in pion-nucleon reactions.

Abstract

We study hadronic polarization and the related anisotropy of the dilepton angular distribution for the reaction $\pi N \to Ne^+e^-$. We employ consistent effective interactions for baryon resonances up to spin-5/2 to compute their contribution to the anisotropy coefficient. We show that the spin and parity of the intermediate baryon resonance is reflected in the angular dependence of the anisotropy coefficient. We present results for 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 unraveling the resonance contributions to this process.