First Measurement of the Double Spin Asymmetry in $\vec{e}\vec{p}\to e' \pi^+ n$ in the Resonance Region

TL;DR

This paper reports the first measurement of the double spin asymmetry in the pion production reaction on protons within the resonance region, providing new insights into resonance contributions and helicity transitions.

Contribution

It presents the inaugural measurement of the double spin asymmetry in $oldsymbol{e}oldsymbol{p} o e' oldsymbol{ ext{π}}^+ oldsymbol{n}$ in the resonance region, revealing strong resonance sensitivities and helicity dominance.

Findings

Helicity-1/2 transitions dominate in the second and third resonance regions.

Measured asymmetry aligns with a faster increase of $A_1$ for the $F_{15}(1680)$ resonance with $Q^2$.

Data show strong sensitivity to resonance contributions.

Abstract

The double spin asymmetry in the $\vec{e}\vec{p}\to e' \pi^+ n$ reaction has been measured for the first time in the resonance region for four-momentum transfer $Q^2=0.35-1.5$ GeV$^2$. Data were taken at Jefferson Lab with the CLAS detector using a 2.6 GeV polarized electron beam incident on a polarized solid NH$_3$ target. Comparison with predictions of phenomenological models shows strong sensitivity to resonance contributions. Helicity-1/2 transitions are found to be dominant in the second and third resonance regions. The measured asymmetry is consistent with a faster rise with $Q^2$ of the helicity asymmetry $A_1$ for the $F_{15}(1680)$ resonance than expected from the analysis of the unpolarized data.