Understanding the Forward Muon Deficit in Coherent Pion Production

TL;DR

This paper investigates the forward muon deficit in coherent pion production, analyzing how lepton mass effects and interference phenomena might explain the observed suppression in experimental data.

Contribution

It provides a theoretical analysis of lepton mass effects and interference mechanisms that could account for the forward suppression in coherent pion production.

Findings

Lepton mass induces a dynamical 'PCAC-screening' effect.

Interference between spin-zero and spin-one exchanges affects cross sections.

Potential explanation for the forward muon deficit observed experimentally.

Abstract

For any inelastic process $v_{\ell} + I \to \ell^- + F$ with $m_{\ell} = 0$, the cross section at $\theta_{\ell} = 0$ is given by Adler's PCAC theorem. Inclusion of the lepton mass has a dynamical effect (``PCAC-screening'') caused by interference of spin-zero ($\pi^+$) and spin-one exchanges. This effect may be relevant to the forward suppression reported in recent experiments.