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Transversity distribution function in hard scattering of polarized protons and antiprotons in the PAX experiment

A. V. Efremov, K. Goeke, P. Schweitzer

TL;DR

This paper assesses the feasibility of measuring the transversity distribution h1^a(x) through the double-spin asymmetry A_TT in Drell–Yan lepton-pair production using polarized protons and antiprotons at the proposed PAX experiment. Relying on LO QCD and transversity predictions from the chiral-quark-soliton model, the authors find potentially large A_TT values driven by h1^u(x) in the valence region, with higher Q^2 enhancing the effect. They discuss kinematic reach (x>0.2–0.5), experimental practicality, and the impact of depolarization and backgrounds, noting that NLO corrections will modestly reduce LO estimates. The work argues that PAX offers a promising avenue to probe h1^u(x) and to test nonperturbative QCD descriptions of transversity, while highlighting the need to understand backgrounds and K-factors for a clean interpretation.

Abstract

Estimates are given for the double spin asymmetry in lepton pair production from collisions of transversely polarized protons and antiprotons for the kinematics of the recently proposed PAX experiment at GSI on the basis of predictions for the transversity distribution from the chiral quark soliton model.

Transversity distribution function in hard scattering of polarized protons and antiprotons in the PAX experiment

TL;DR

This paper assesses the feasibility of measuring the transversity distribution h1^a(x) through the double-spin asymmetry A_TT in Drell–Yan lepton-pair production using polarized protons and antiprotons at the proposed PAX experiment. Relying on LO QCD and transversity predictions from the chiral-quark-soliton model, the authors find potentially large A_TT values driven by h1^u(x) in the valence region, with higher Q^2 enhancing the effect. They discuss kinematic reach (x>0.2–0.5), experimental practicality, and the impact of depolarization and backgrounds, noting that NLO corrections will modestly reduce LO estimates. The work argues that PAX offers a promising avenue to probe h1^u(x) and to test nonperturbative QCD descriptions of transversity, while highlighting the need to understand backgrounds and K-factors for a clean interpretation.

Abstract

Estimates are given for the double spin asymmetry in lepton pair production from collisions of transversely polarized protons and antiprotons for the kinematics of the recently proposed PAX experiment at GSI on the basis of predictions for the transversity distribution from the chiral quark soliton model.

Paper Structure

This paper contains 6 sections, 6 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Lepton pair production in collisions of transversely polarized $p\bar{p}$
  3. Chiral quark-soliton model prediction for $h_1^a(x)$
  4. Double spin asymmetry $A_{TT}$ at PAX
  5. Summary
  6. Acknowledgements.

Figures (2)

  • Figure 1: a. The transversity distribution function $h_1^a(x)$ vs. $x$ from the chiral quark soliton model Schweitzer:2001sr. b. Comparison of $h_1^u(x)$ from the chiral quark soliton model (solid) to $f_1^u(x)$ (dashed) and $g_1^u(x)$ (dotted) and the Soffer bound $(f_1^u+g_1^u)(x)/2$ (dashed-dotted line) with the parameterizations of Gluck:1994uf. All curves in Figures 1a and 1b are multiplied by $x$ and are LO evolved to a scale of $Q^2=16\,{\rm GeV}^2$.
  • Figure :