Subleading-twist effects in single-spin asymmetries in semi-inclusive deep-inelastic scattering on a longitudinally polarized hydrogen target

TL;DR

Single-spin asymmetries in the semi-inclusive production of charged pions in deep-inelastic scattering from transversely and longitudinally polarized proton targets are combined to evaluate the subleading-twist contribution to the longitudinal case.

Abstract

Single-spin asymmetries in the semi-inclusive production of charged pions in deep-inelastic scattering from transversely and longitudinally polarized proton targets are combined to evaluate the subleading-twist contribution to the longitudinal case. This contribution is significantly positive for (π^+) mesons and dominates the asymmetries on a longitudinally polarized target previously measured by \hermes. The subleading-twist contribution for (π^-) mesons is found to be small.

Figures (2)

• Figure 1: The definitions of the azimuthal angle $\phi$ of the hadron production plane, relative to the plane containing the momentum $\hbox{\boldmath $l$}$ ($\hbox{\boldmath $l'$}$) of the incident (scattered) lepton, the polar angle $\theta_{\gamma^*}$ between the virtual photon and the incoming lepton directions, and of the transverse component $\hbox{\boldmath ${S}_\perp$}$ of the target spin $\hbox{\boldmath $S$}$ with respect to the photon direction $\hbox{\boldmath $q$}\equiv \hbox{\boldmath $l$}-\hbox{\boldmath $l'$}$.
• Figure 2: The various azimuthal moments appearing in the measurement of the $\sin\phi$ modulations of single-spin asymmetries on a longitudinally polarized hydrogen target for charged pions as functions of $x$ and $z$. The open symbols are the measured lepton-axis moments. The ones from a transversely polarized target are multiplied by $-\sin\theta_{\gamma^*}$ according to their appearance in the longitudinal lepton-axis moments. The closed symbol is the subleading-twist contribution to the measured lepton-axis asymmetries on a longitudinally polarized target. The triangles are slightly shifted horizontally for distinction. An overall systematic error of 0.003 is not included in the figure.