Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Sivers effect in semi-inclusive deeply inelastic scattering and Drell-Yan

J. C. Collins, A. V. Efremov, K. Goeke, M. Grosse Perdekamp, S. Menzel, B. Meredith, A. Metz, P. Schweitzer

TL;DR

The paper extracts the Sivers function from HERMES SIDIS data using a Gaussian transverse-momentum framework and a large-$N_c$ flavor structure, validating the approach against preliminary and final data. It demonstrates compatibility with a model-independent extraction and uses the results to predict the Sivers effect in Drell-Yan, including a sign reversal between SIDIS and DY as a crucial test of QCD factorization. The work also discusses the role of antiquark Sivers distributions and assesses experimental prospects at COMPASS, PAX, and RHIC, noting that SIDIS data strongly constrain DY predictions while leaving room to probe sea quark spin dynamics. Overall, the study supports a Gaussian TMD description, confirms flavor-symmetric expectations, and outlines concrete measurements to test universality and the underlying nucleon structure.

Abstract

The Sivers function is extracted from HERMES data on single spin asymmetries in semi-inclusive deeply inelastic scattering. The result is used for making predictions for the Sivers effect in the Drell-Yan process.

Sivers effect in semi-inclusive deeply inelastic scattering and Drell-Yan

TL;DR

The paper extracts the Sivers function from HERMES SIDIS data using a Gaussian transverse-momentum framework and a large- flavor structure, validating the approach against preliminary and final data. It demonstrates compatibility with a model-independent extraction and uses the results to predict the Sivers effect in Drell-Yan, including a sign reversal between SIDIS and DY as a crucial test of QCD factorization. The work also discusses the role of antiquark Sivers distributions and assesses experimental prospects at COMPASS, PAX, and RHIC, noting that SIDIS data strongly constrain DY predictions while leaving room to probe sea quark spin dynamics. Overall, the study supports a Gaussian TMD description, confirms flavor-symmetric expectations, and outlines concrete measurements to test universality and the underlying nucleon structure.

Abstract

The Sivers function is extracted from HERMES data on single spin asymmetries in semi-inclusive deeply inelastic scattering. The result is used for making predictions for the Sivers effect in the Drell-Yan process.

Paper Structure

This paper contains 8 sections, 8 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Sivers function from preliminary $P_{h\perp}$-weighted data [1]
  3. Transverse parton momenta and the Gaussian ansatz
  4. Sivers function from final (published) HERMES data [2]
  5. Sivers effect from deuteron at COMPASS [3]
  6. Sivers function from most recent preliminary data [4]
  7. Sivers effect in the Drell-Yan process
  8. Conclusions

Figures (2)

  • Figure 1: Left: $\langle P_{h\perp}(z)\rangle$ of pions produced at HERMES$^{17}$ vs. $z$. The dashed (dotted) curve follows from the Gaussian ansatz with the parameters from our approach$^{33}$ (from a study of the Cahn effect$^{31}$). Middle: The two alternative fits$^{30}$ of $xf_{1T}^{\perp(1)u}(x)$ to the $P_{h\perp}$-weighted preliminary data$^1$ and the 1-$\sigma$ region of the fit$^{33}$ to final (non-$P_{h\perp}$-weighted) data$^2$ Right: The 1-$\sigma$ regions of the fits to the final data$^2$ and to the preliminary data$^4$.
  • Figure 2: The Sivers SSA $A_{UT}^{\sin(\phi-\phi_S)}$ in $p^\uparrow p\to l^+l^- X$ as function of $y$ for the kinematics of the RHIC experiment with $\sqrt{s}=200\,{\rm GeV}$, and $Q^2=(4\,{\rm GeV})^2$. The inner error band (thick lines) shows the 1-$\sigma$ uncertainty of the fit$^{33}$. The $x$-region explored at HERMES is included to indicate where the SIDIS data constrain the prediction. The outer error band (thin lines) arises from assuming Sivers $\bar{q}$-distribution functions according to model I (left) and model II (right) in Eq. (\ref{['Eq:model-Sivers-qbar']}). Also shown are the regions in which PHENIX and STAR can detect $\mu^+\mu^-$ or $e^+e^-$ pairs.