Single-spin Azimuthal Asymmetries in Electroproduction of Neutral Pions in Semi-inclusive Deep-inelastic Scattering

TL;DR

This paper reports the first measurement of single-spin azimuthal asymmetries in neutral pion electroproduction during deep-inelastic scattering, revealing insights into quark transverse polarization effects.

Contribution

It introduces the first measurement of neutral pion asymmetries in polarized deep-inelastic scattering and compares these to charged pion asymmetries, enhancing understanding of spin-dependent fragmentation.

Findings

The pi^0 asymmetry is approximately 0.019 with statistical and systematic uncertainties.

Pi^0 asymmetry is similar in size and behavior to pi^+ asymmetry in the same kinematic range.

Results align with phenomenological models based on spin-sensitive fragmentation functions.

Abstract

A single-spin asymmetry in the azimuthal distribution of neutral pions relative to the lepton scattering plane has been measured for the first time in deep-inelastic scattering of positrons off longitudinally polarized protons. The analysing power in the sin(phi) moment of the cross section is 0.019 +/- 0.007(stat.) +/- 0.003(syst.). This result is compared to single-spin asymmetries for charged pion production measured in the same kinematic range. The pi^0 asymmetry is of the same size as the pi^+ asymmetry and shows a similar dependence on the relevant kinematic variables. The asymmetry is described by a phenomenological calculation based on a fragmentation function that represents sensitivity to the transverse polarization of the struck quark.