Target and Beam-Target Spin Asymmetries in Exclusive $\pi^+$ and $\pi^-$ Electroproduction with 1.6 to 5.7 GeV Electrons

TL;DR

This study measures beam-target and target single-spin asymmetries in exclusive pion electroproduction over a broad energy range, providing new data to constrain nucleon resonance models at moderate to high Q^2.

Contribution

It presents extensive new measurements of spin asymmetries in pion electroproduction across a wide kinematic range, improving constraints on nucleon resonance amplitudes at higher energies.

Findings

Large target-spin asymmetries observed for W>1.6 GeV.

Results agree with previous data at low Q^2, discrepancies grow at higher Q^2.

Data will help refine nucleon resonance models.

Abstract

Beam-target double spin asymmetries and target single-spin asymmetries in exclusive $\pi^+$ and $\pi^-$ electroproduction were obtained from scattering of 1.6 to 5.7 GeV longitudinally polarized electrons from longitudinally polarized protons (for $\pi^+$) and deuterons (for $\pi^-$) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The kinematic range covered is $1.1<W<2.6$ GeV and $0.05<Q^2<5$ GeV$^2$, with good anglular coverage in the forward hemisphere. The asymmetry results were divided into approximately 40,000 kinematic bins for $\pi^+$ from free protons and 15,000 bins for $\pi^-$ production from bound nucleons in the deuteron. The present results are found to be in reasonable agreement with fits to previous world data for $W<1.7$ GeV and $Q^2<0.5$ GeV$^2$, with discrepancies increasing at higher values of $Q^2$, especially for $W>1.5$ GeV. Very large target-spin asymmetries are observed for $W>1.6$ GeV. When combined with cross section measurements, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of $Q^2$, for resonances with masses as high as 2.3 GeV.