Parity-Violating Electron-Deuteron Scattering with a Twist

TL;DR

This paper proposes using parity-violating electron-deuteron scattering as a clean method to probe higher twist quark-quark correlations beyond the parton model, with simplified interpretation due to specific operator properties.

Contribution

It reformulates the Bjorken/Wolfenstein approach for interpreting experiments at JLab and estimates twist-four contributions using MIT Bag Model calculations.

Findings

The ratio R_{γZ} equals R_{γ} up to suppressed corrections.

MIT Bag Model estimates of twist-four effects as functions of x and Q^2.

Comparison of twist-four contributions with charge symmetry violation effects.

Abstract

We show that Parity-Violating Deep Inelastic Scattering (PVDIS) of longitudinally polarized electrons from deuterium can in principle be a relatively clean probe of higher twist quark-quark correlations beyond the parton model. As first observed by Bjorken and Wolfenstein, the dominant contribution to the electron polarization asymmetry, proportional to the axial vector electron coupling, receives corrections at twist-four from the matrix element of a single four-quark operator. We reformulate the Bjorken/Wolfenstein argument in a matter suitable for the interpretation of experiments planned at the Thomas Jefferson National Accelerator Facility (JLab). In particular, we observe that because the contribution of the relevant twist four operator satisfies the Callan-Gross relation, the ratio of parity-violating longitudinal and transverse cross sections, R_{\gamma Z}, is identical to that for purely electromagnetic scattering, R_{\gamma}, up to perturbative and power suppressed contributions. This result simplifies the interpretation of the asymmetry in terms of other possible novel hadronic and electroweak contributions. We use the results of MIT Bag Model calculations to estimate contributions of the relevant twist four operator to the leading term in the asymmetry as a function of Bjorken x and Q2 . We compare these estimates with possible leading twist corrections due to violation of charge symmetry in the parton distribution functions.