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The cos 2 phi asymmetry of Drell-Yan and J/psi production in unpolarized ppbar scattering

Vincenzo Barone, Zhun Lu, Bo-Qiang Ma

TL;DR

This paper studies the cos 2φ azimuthal asymmetry in unpolarized p pbar collisions at GSI-HESR energies, focusing on how the leading-twist Boer-Mulders function h1^⊥(x, k_T^2) generates the asymmetry in Drell–Yan and J/ψ production. The authors adopt a spectator scalar diquark model for h1^⊥ and f1, and compute the ν coefficient from transverse-momentum convolutions, with u-quark dominance in the GSI regime. They find the cos 2φ asymmetry to be sizable both in the Drell–Yan continuum and on the J/ψ peak, with ν ≈ 0.2–0.3, and show that the J/ψ channel yields much higher event rates. The results suggest that unpolarized pp̄ experiments at GSI could provide a viable, early-access probe of the Boer-Mulders function, pending consideration of perturbative effects.

Abstract

We investigate the cos 2 phi azimuthal asymmetry in Drell--Yan and J/psi production from unpolarized ppbar scattering at GSI-HESR energies. The contribution to this asymmetry arising from the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which describes a correlation between the transverse momentum and the transverse spin of quarks in an unpolarized hadron, is explicitly evaluated, and predictions for the GSI-HESR kinematic regime are presented. We show that the cos 2 phi asymmetry is quite sizable both on the J/psi peak and in the Drell-Yan continuum region. Therefore these processes may offer an experimentally viable access to the Boer-Mulders function in the early unpolarized stage of GSI experiments.

The cos 2 phi asymmetry of Drell-Yan and J/psi production in unpolarized ppbar scattering

TL;DR

This paper studies the cos 2φ azimuthal asymmetry in unpolarized p pbar collisions at GSI-HESR energies, focusing on how the leading-twist Boer-Mulders function h1^⊥(x, k_T^2) generates the asymmetry in Drell–Yan and J/ψ production. The authors adopt a spectator scalar diquark model for h1^⊥ and f1, and compute the ν coefficient from transverse-momentum convolutions, with u-quark dominance in the GSI regime. They find the cos 2φ asymmetry to be sizable both in the Drell–Yan continuum and on the J/ψ peak, with ν ≈ 0.2–0.3, and show that the J/ψ channel yields much higher event rates. The results suggest that unpolarized pp̄ experiments at GSI could provide a viable, early-access probe of the Boer-Mulders function, pending consideration of perturbative effects.

Abstract

We investigate the cos 2 phi azimuthal asymmetry in Drell--Yan and J/psi production from unpolarized ppbar scattering at GSI-HESR energies. The contribution to this asymmetry arising from the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which describes a correlation between the transverse momentum and the transverse spin of quarks in an unpolarized hadron, is explicitly evaluated, and predictions for the GSI-HESR kinematic regime are presented. We show that the cos 2 phi asymmetry is quite sizable both on the J/psi peak and in the Drell-Yan continuum region. Therefore these processes may offer an experimentally viable access to the Boer-Mulders function in the early unpolarized stage of GSI experiments.

Paper Structure

This paper contains 4 sections, 13 equations, 3 figures.

Table of Contents

  1. Introduction
  2. The $\cos 2 \phi$ asymmetry in Drell-Yan and $J/\psi$ production
  3. Calculation of the $\cos 2 \phi$ asymmetry
  4. Conclusion

Figures (3)

  • Figure 1: The $\cos 2 \phi$ azimuthal asymmetry of Drell--Yan production in $p\bar{p}$ collisions as a function of $Q_T$, for $s = 45$ GeV$^2$ and $M^2 = 5$ GeV$^2$. The solid curve is our prediction. The dashed curve is the result of bbh03 extended to the kinematic region of interest here.
  • Figure 2: The $\cos 2 \phi$ azimuthal asymmetry of $p\bar{p} \rightarrow J/\psi \, X\rightarrow l^+l^- X$ as a function of $Q_T$, for two values of $s$ in the GSI-HESR kinematic domain.
  • Figure 3: The $\cos 2 \phi$ azimuthal asymmetry of $p\bar{p} \rightarrow J/\psi X\rightarrow l^+l^- X$ as a function of $x_F$, for two values of $s$ in the GSI-HESR kinematic domain.