Deeply inelastic pions in the exclusive reaction $p(e,e'\pi^+)n$ above the resonance region

TL;DR

This paper presents a model combining meson-exchange currents and deep-inelastic scattering to explain the transverse and longitudinal responses in the $p(e,e'\pi^+)n$ reaction, resolving longstanding discrepancies in observed cross sections.

Contribution

It introduces a unified model that accurately describes both transverse and longitudinal responses in pion electroproduction above the resonance region, integrating DIS and hadronic effects.

Findings

DIS dominates the transverse response at high $Q^2$

Longitudinal response is governed by hadronic degrees of freedom

Large transverse cross sections are sensitive to parton transverse momentum

Abstract

A model for the $p(e,e'\pi^+)n$ reaction which combines an improved treatment of gauge invariant meson--exchange currents and hard deep--inelastic scattering (DIS) of virtual photons off nucleons is proposed. It is shown that DIS dominates and explains the transverse response at moderate and high photon virtualities $Q^2$ whereas the longitudinal response is dominated by hadronic degrees of freedom and the pion electromagnetic form factor. This leads to a combined description of the longitudinal and transverse components of the cross section in a wide range of photon virtuality $Q^2$ and momentum transfer to the target $t$ and solves the longstanding problem of the observed large transverse cross sections. The latter are shown to be sensitive to the intrinsic transverse momentum distribution of partons.