Scaling study of the pion electroproduction cross sections and the pion form factor

TL;DR

This study measures pion electroproduction cross sections at high momentum transfer, finding that the longitudinal component follows Q^2-scaling predictions, indicating applicability of perturbative QCD at relatively low Q^2, but the pion form factor magnitude remains inconsistent with theoretical calculations.

Contribution

It provides new high-Q^2 measurements of pion electroproduction, testing QCD scaling predictions and the applicability of perturbative QCD concepts at low to moderate Q^2.

Findings

Longitudinal cross section follows Q^2-scaling predictions.

Pion form factor aligns with Q^2-scaling but not with perturbative QCD magnitude.

Transverse contributions remain significant at Q^2=3.91 GeV^2.

Abstract

The $^{1}$H($e,e^\prime \pi^+$)n cross section was measured for a range of four-momentum transfer up to $Q^2$=3.91 GeV$^2$ at values of the invariant mass, $W$, above the resonance region. The $Q^2$-dependence of the longitudinal component is consistent with the $Q^2$-scaling prediction for hard exclusive processes. This suggests that perturbative QCD concepts are applicable at rather low values of $Q^2$. Pion form factor results, while consistent with the $Q^2$-scaling prediction, are inconsistent in magnitude with perturbative QCD calculations. The extraction of Generalized Parton Distributions from hard exclusive processes assumes the dominance of the longitudinal term. However, transverse contributions to the cross section are still significant at $Q^2$=3.91 GeV$^2$.