Semi-Inclusive ${\pi }_0$ target and beam-target asymmetries from 6 GeV electron scattering with CLAS

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 $ep\to e^{\prime }{\pi }^{0}X$ 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 ${\varphi }_h$ 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 $\sin 2{\varphi }_h$ moments are zero within uncertainties, which is consistent with the expected suppression of the Collins fragmentation function. The observed $\sin {\varphi }_h$ moments suggest that quark gluon correlations are significant at large $x$.

arXiv comment18 preprint pages, 3 figures

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• Applications of the WW-type approximation to SIDIS