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

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.

Figures (1)

• Figure 1: Analysing power in the $\sin \phi$ moment for $\pi ^0$ (circles) compared to previous results hermes_charged_pion_ssa:1999 for $\pi ^+$ (triangles) and $\pi ^-$ (squares) as a function of the pion fractional energy $z$, the Bjorken variable $x$, and of the pion transverse momentum $P_\perp$. Error bars include the statistical uncertainties only. The filled and open bands at the bottom of the panels represent the systematic uncertainties for neutral and charged pions, respectively. The data for charged pion production are slightly shifted in $z$, $x$, and $P_{\perp}$ for clarity. The shaded areas show a range of predictions of a model calculation Karo+:1998deSanctis:2000 applied to the case of $\pi ^0$ electroproduction (see text).