Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Transversity Distribution Does Not Contribute to Hard Exclusive Electroproduction of Mesons

J. C. Collins, M. Diehl

TL;DR

The paper investigates whether hard exclusive electroproduction can probe quark transversity via transversely polarized vector meson production. It proves that the leading-twist hard-scattering coefficient vanishes to all orders after proper collinear subtractions, negating the use of this process to measure skewed transversity and clarifying a prior conflicting NLO result. By providing a regulator-aware all-orders argument and discussing the axial anomaly, it reinforces helicity-conservation-based arguments for chirality in perturbative QCD and extends the reasoning to related processes. The results establish a helicity selection rule and demonstrate the general validity of chirality-based constraints in hard-scattering coefficients beyond this specific case.

Abstract

We show that in hard exclusive electroproduction, ep-->eVp, the leading-twist hard-scattering coefficient for the production of a transversely polarized vector meson V vanishes to all orders of perturbation theory. This implies that this process cannot be used to measure the skewed transversity distribution of quarks in a hadron. In contrast, a recent calculation obtained a non-zero value at NLO. We show that this calculation is incorrect because it failed to include the necessary collinear subtractions. Our method of proof also applies to other processes whose hard-scattering coefficients are constrained by chirality and helicity conservation, and thus validates helicity selection rules based on these symmetries.

Transversity Distribution Does Not Contribute to Hard Exclusive Electroproduction of Mesons

TL;DR

The paper investigates whether hard exclusive electroproduction can probe quark transversity via transversely polarized vector meson production. It proves that the leading-twist hard-scattering coefficient vanishes to all orders after proper collinear subtractions, negating the use of this process to measure skewed transversity and clarifying a prior conflicting NLO result. By providing a regulator-aware all-orders argument and discussing the axial anomaly, it reinforces helicity-conservation-based arguments for chirality in perturbative QCD and extends the reasoning to related processes. The results establish a helicity selection rule and demonstrate the general validity of chirality-based constraints in hard-scattering coefficients beyond this specific case.

Abstract

We show that in hard exclusive electroproduction, ep-->eVp, the leading-twist hard-scattering coefficient for the production of a transversely polarized vector meson V vanishes to all orders of perturbation theory. This implies that this process cannot be used to measure the skewed transversity distribution of quarks in a hadron. In contrast, a recent calculation obtained a non-zero value at NLO. We show that this calculation is incorrect because it failed to include the necessary collinear subtractions. Our method of proof also applies to other processes whose hard-scattering coefficients are constrained by chirality and helicity conservation, and thus validates helicity selection rules based on these symmetries.

Paper Structure

This paper contains 7 sections, 9 equations, 3 figures.

Table of Contents

  1. Introduction
  2. One-loop calculation with subtractions
  3. General proof
  4. Previous proof
  5. Completed proof
  6. The axial anomaly
  7. Conclusions

Figures (3)

  • Figure 1: A lowest order graph for the hard-scattering coefficient.
  • Figure 2: An NLO graph for the hard-scattering coefficient.
  • Figure 3: Hard-scattering coefficient with spinor labels. The external photon is not shown, and diagrams (a) and (b) show the two possibilities for connecting the external quark lines.