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Single-Transverse Spin Asymmetries: From DIS to Hadronic Collisions

Werner Vogelsang, Feng Yuan

TL;DR

This paper investigates single-transverse spin asymmetries in SIDIS and hadronic collisions within a QCD TMD framework, focusing on Sivers and Collins effects. It proposes simple, flavor-dependent parameterizations for the Sivers and Collins functions and fits them to HERMES data, achieving good agreement and cross-consistency with COMPASS. Using the SIDIS fits, it predicts sizable Sivers-induced asymmetries in Drell-Yan, di-jet, and jet-photon production at RHIC, highlighting forward-rapidity regions as most sensitive. It discusses universality and process-dependence of Sivers functions, including sign changes between SIDIS and Drell-Yan and possible nontrivial color factors in jet-related processes, signaling areas for future theoretical and experimental tests.

Abstract

We study single-spin asymmetries in semi-inclusive deep inelastic scattering with transversely polarized target. Based on the QCD factorization approach, we consider Sivers and Collins contributions to the asymmetries. We fit simple parameterizations for the Sivers and Collins functions to the recent HERMES data, and compare to results from COMPASS. Using the fitted parameterizations for the Sivers functions, we predict the single transverse spin asymmetries for various processes in $pp$ collisions at RHIC, including the Drell-Yan process and angular correlations in dijet and jet-plus-photon production. These asymmetries are found to be sizable at forward rapidities

Single-Transverse Spin Asymmetries: From DIS to Hadronic Collisions

TL;DR

This paper investigates single-transverse spin asymmetries in SIDIS and hadronic collisions within a QCD TMD framework, focusing on Sivers and Collins effects. It proposes simple, flavor-dependent parameterizations for the Sivers and Collins functions and fits them to HERMES data, achieving good agreement and cross-consistency with COMPASS. Using the SIDIS fits, it predicts sizable Sivers-induced asymmetries in Drell-Yan, di-jet, and jet-photon production at RHIC, highlighting forward-rapidity regions as most sensitive. It discusses universality and process-dependence of Sivers functions, including sign changes between SIDIS and Drell-Yan and possible nontrivial color factors in jet-related processes, signaling areas for future theoretical and experimental tests.

Abstract

We study single-spin asymmetries in semi-inclusive deep inelastic scattering with transversely polarized target. Based on the QCD factorization approach, we consider Sivers and Collins contributions to the asymmetries. We fit simple parameterizations for the Sivers and Collins functions to the recent HERMES data, and compare to results from COMPASS. Using the fitted parameterizations for the Sivers functions, we predict the single transverse spin asymmetries for various processes in collisions at RHIC, including the Drell-Yan process and angular correlations in dijet and jet-plus-photon production. These asymmetries are found to be sizable at forward rapidities

Paper Structure

This paper contains 11 sections, 35 equations, 14 figures.

Table of Contents

  1. Introduction
  2. SSA in Semi-inclusive Deep Inelastic Scattering
  3. Theoretical Formalism and Approximations
  4. Model for the Sivers functions
  5. Model for the Collins functions
  6. Comparison with SIDIS Data
  7. Single-Transverse Spin Asymmetries at Hadron Colliders
  8. Drell-Yan Dimuon Production $p^{\uparrow}p\to \mu^+\mu^-X$
  9. Correlations in $p^{\uparrow}p\to {\rm jet}_1 (\vec{P}_{1\perp})+{\rm jet}_2(\vec{P}_{2\perp})+X$
  10. Jet-Photon Correlations in $p^{\uparrow}p\to {\rm jet} +\gamma+X$
  11. Conclusions

Figures (14)

  • Figure 1: Sivers SSA fit to the HERMES data HERMESnew; see text. The bands correspond to the 1-$\sigma$ error of the fitted parameters. Note that the data have not yet been corrected for acceptance and smearing.
  • Figure 2: Predicted Sivers SSA asymmetries for $\pi^0$ production at HERMES.
  • Figure 3: Sivers asymmetries compared to the COMPASS data COMPASS.
  • Figure 4: Same as Fig. \ref{['fig1']} for the Collins asymmetries, using the Set I parameterization of the Collins functions. The data HERMESnew and the theory curves are for the so-called lepton beam asymmetries. Note that the data have not yet been corrected for acceptance and smearing.
  • Figure 5: Same as Fig. \ref{['fig4']}, for the Set II parameterizations for the Collins functions.
  • ...and 9 more figures