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Single-Transverse Spin Asymmetry in Dijet Correlations at Hadron Colliders

C. J. Bomhof, P. J. Mulders, W. Vogelsang, F. Yuan

TL;DR

The paper analyzes single-transverse spin asymmetries in dijet correlations in proton-proton collisions at RHIC, focusing on the Sivers mechanism and the role of gauge links that cause process dependence. By formulating the spin-dependent cross section and introducing the sin(delta) moment, the authors connect the observable to twist-3 quark-gluon correlators (Qiu-Sterman T_F) and process-specific hard factors, enabling predictions that respect the nonuniversality of Sivers functions. Using SIDIS-tuned T_F inputs, they predict a sizable reduction of the dijet SSA relative to universal-Sivers expectations, with final-state interactions dominating; preliminary STAR data hint at a vanishing asymmetry. The work provides a framework to test Sivers nonuniversality in hadronic collisions and motivates future refinements in TMD factorization and higher-order corrections.

Abstract

We present a phenomenological study of the single-transverse spin asymmetry in azimuthal correlations of two jets produced nearly "back-to-back" in pp collisions at RHIC. We properly take into account the initial- and final-state interactions of partons that can generate this asymmetry in QCD hard-scattering. Using distribution functions fitted to the existing single-spin data, we make predictions for various weighted single-spin asymmetries in dijet correlations that are now readily testable at RHIC.

Single-Transverse Spin Asymmetry in Dijet Correlations at Hadron Colliders

TL;DR

The paper analyzes single-transverse spin asymmetries in dijet correlations in proton-proton collisions at RHIC, focusing on the Sivers mechanism and the role of gauge links that cause process dependence. By formulating the spin-dependent cross section and introducing the sin(delta) moment, the authors connect the observable to twist-3 quark-gluon correlators (Qiu-Sterman T_F) and process-specific hard factors, enabling predictions that respect the nonuniversality of Sivers functions. Using SIDIS-tuned T_F inputs, they predict a sizable reduction of the dijet SSA relative to universal-Sivers expectations, with final-state interactions dominating; preliminary STAR data hint at a vanishing asymmetry. The work provides a framework to test Sivers nonuniversality in hadronic collisions and motivates future refinements in TMD factorization and higher-order corrections.

Abstract

We present a phenomenological study of the single-transverse spin asymmetry in azimuthal correlations of two jets produced nearly "back-to-back" in pp collisions at RHIC. We properly take into account the initial- and final-state interactions of partons that can generate this asymmetry in QCD hard-scattering. Using distribution functions fitted to the existing single-spin data, we make predictions for various weighted single-spin asymmetries in dijet correlations that are now readily testable at RHIC.

Paper Structure

This paper contains 4 sections, 12 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Spin-dependent cross section and $\sin\delta$-moment
  3. Phenomenological results for RHIC
  4. Conclusions

Figures (2)

  • Figure 1: The weighted single-transverse-spin asymmetry for dijet-correlations in polarized proton-proton scattering at RHIC, as a function of the sum of the jet pseudo-rapidities. The jet transverse momenta are in the range $5-10$ GeV. The solid line is our main result, based on Eqs. (\ref{['hsivers']})-(\ref{['tfdist']}). In the left panel we also plot the individual contributions due to the $u$-quark (dashed line) and $d$-quark (dotted line) Qiu-Sterman matrix elements. For comparison, in the right panel we also show the results that would be obtained if the Sivers functions contributing to dijet production were the same as those in SIDIS (upper curve) or the Drell-Yan process (lower curve).
  • Figure 2: Same as Fig. 1, but for the SSA defined in Eq. (\ref{['eqan']}).