Semi-Inclusive $\pi_0$ target and beam-target asymmetries from 6 GeV electron scattering with CLAS

TL;DR

This paper reports precise measurements of spin asymmetries in neutral pion electroproduction from polarized protons at Jefferson Lab, providing insights into transverse-momentum distributions and quark-gluon correlations in deep-inelastic scattering.

Contribution

First detailed multidimensional measurements of target and beam-target asymmetries in neutral pion electroproduction at 6 GeV, revealing the behavior of spin asymmetries and quark-gluon correlations.

Findings

Double spin asymmetries depend weakly on transverse momentum.

$ ext{sin} 2 ext{phi}_h$ moments are consistent with suppression of Collins fragmentation.

$ ext{sin} ext{phi}_h$ moments indicate significant quark-gluon correlations at large x.

Abstract

We present precision measurements of the target and beam-target spin asymmetries from neutral pion electroproduction in deep-inelastic scattering (DIS) using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. We scattered 6-GeV, longitudinally polarized electrons off longitudinally polarized protons in a cryogenic $^{14}$NH$_3$ target, and extracted double and single target spin asymmetries for $ep\rightarrow e^\prime\pi^0X$ in multidimensional bins in four-momentum transfer ($1.0<Q^2<3.2$ GeV$^2$), Bjorken-$x$ ($0.12<x<0.48$), hadron energy fraction ($0.4<z<0.7$), transverse pion momentum ($0<P_T<1.0$ GeV), and azimuthal angle $\phi_h$ between the lepton scattering and hadron production planes. We extracted asymmetries as a function of both $x$ and $P_T$, which provide access to transverse-momentum distributions of longitudinally polarized quarks. The double spin asymmetries depend weakly on $P_T$. The $\sin 2\phi_h$ moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed $\sin\phi_h$ moments suggest that quark gluon correlations are significant at large $x$.