Spin Asymmetry in Muon--Proton Deep Inelastic Scattering on a Transversely-Polarized Target

TL;DR

This study measures the spin asymmetry in muon-proton deep inelastic scattering with a transversely polarized target, finding results compatible with zero and setting upper limits on related spin structure functions.

Contribution

It provides the first measurement of spin asymmetry in muon-proton scattering with a transversely polarized target, establishing new upper limits for $A_2$ and $g_2$.

Findings

Asymmetry compatible with zero across the measured kinematic range.

Upper limits set for the virtual photon--proton asymmetry $A_2$.

For $x<0.15$, $A_2$ is significantly below the positivity limit.

Abstract

We measured the spin asymmetry in the scattering of 100 GeV longitudinally-polarized muons on transversely polarized protons. The asymmetry was found to be compatible with zero in the kinematic range $0.006<x<0.6$, $1<Q^2<30\,~\mbox{GeV}^2$. {}From this result we derive the upper limits for the virtual photon--proton asymmetry $A_2$, and for the spin structure function $g_2$. For $x<0.15$, $A_2$ is significantly smaller than its positivity limit $\sqrt{R}$.