Quark helicity flip and the transverse spin dependence of inclusive DIS

TL;DR

This paper investigates how inclusive deep inelastic scattering (DIS) with unpolarized beams and transversely polarized targets can reveal quark helicity-flip amplitudes linked to non-perturbative QCD effects, providing insights into chiral symmetry breaking.

Contribution

It proposes that the transverse spin dependence in inclusive DIS primarily probes quark helicity-flip amplitudes caused by non-perturbative QCD vacuum structure, a novel interpretation.

Findings

Target spin asymmetry estimated at 10^{-4} for Jefferson Lab kinematics.

Helicity-flip amplitudes are linked to chiral symmetry breaking effects.

Helicity-conserving twist-3 contributions are expected to be small.

Abstract

Inclusive DIS with unpolarized beam exhibits a subtle dependence on the transverse target spin, arising from the interference of one-photon and two-photon exchange amplitudes in the cross section. We argue that this observable probes mainly the quark helicity-flip amplitudes induced by the non-perturbative vacuum structure of QCD (spontaneous chiral symmetry breaking). This conjecture is based on (a) the absence of significant Sudakov suppression of the helicity-flip process if soft gluon emission in the quark subprocess is limited by the chiral symmetry-breaking scale mu_chiral^2 >> Lambda_QCD^2; (b) the expectation that the quark helicity-conserving twist-3 contribution is small. The normal target spin asymmetry is estimated to be of the order 10^{-4} in the kinematics of the planned Jefferson Lab Hall A experiment.