Target and Double Spin Asymmetries of Deeply Virtual $\pi^0$ Production with a Longitudinally Polarized Proton Target and CLAS

TL;DR

This paper reports the first measurement of target and double spin asymmetries in deeply virtual $$ production using polarized beams and targets, providing new insights into chiral-odd GPDs and constraining theoretical models.

Contribution

It presents the first experimental data on spin asymmetries in deeply virtual $$ production, offering critical constraints on chiral-odd GPDs and advancing understanding of nucleon structure.

Findings

Large asymmetries indicate significant transverse virtual photon contributions.

Data provide first insights into chiral-odd GPDs $ ilde{H}_T$ and $E_T$.

Results will influence theoretical GPD models.

Abstract

The target and double spin asymmetries of the exclusive pseudoscalar channel $\vec e\vec p\to ep\pi^0$ were measured for the first time in the deep-inelastic regime using a longitudinally polarized 5.9 GeV electron beam and a longitudinally polarized proton target at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS). The data were collected over a large kinematic phase space and divided into 110 four-dimensional bins of $Q^2$, $x_B$, $-t$ and $\phi$. Large values of asymmetry moments clearly indicate a substantial contribution to the polarized structure functions from transverse virtual photon amplitudes. The interpretation of experimental data in terms of generalized parton distributions (GPDs) provides the first insight on the chiral-odd GPDs $\tilde{H}_T$ and $E_T$, and complement previous measurements of unpolarized structure functions sensitive to the GPDs $H_T$ and $\bar E_T$. These data provide necessary constraints for chiral-odd GPD parametrizations and will strongly influence existing theoretical handbag models.