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Azimuthal asymmetries at CLAS: Extraction of e^a(x) and prediction of A_{UL}

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

TL;DR

<3-5 sentence high-level summary>

Abstract

First information on the chirally odd twist-3 proton distribution function e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the electro-production of pions from deeply inelastic scattering of longitudinally polarized electrons off unpolarized protons, which has been recently measured by CLAS collaboration. Furthermore parameter-free predictions are made for azimuthal asymmetries, A_{UL}, from scattering of an unpolarized beam on a polarized proton target for CLAS kinematics.

Azimuthal asymmetries at CLAS: Extraction of e^a(x) and prediction of A_{UL}

TL;DR

<3-5 sentence high-level summary>

Abstract

First information on the chirally odd twist-3 proton distribution function e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the electro-production of pions from deeply inelastic scattering of longitudinally polarized electrons off unpolarized protons, which has been recently measured by CLAS collaboration. Furthermore parameter-free predictions are made for azimuthal asymmetries, A_{UL}, from scattering of an unpolarized beam on a polarized proton target for CLAS kinematics.

Paper Structure

This paper contains 10 sections, 18 equations, 3 figures.

Table of Contents

  1. Introduction
  2. The twist-3 distribution function $e^a(x)$
  3. The Collins fragmentation function
  4. The azimuthal asymmetry $A_{LU}^{\sin\phi}$
  5. $A_{LU}^{\sin\phi}$ in the CLAS experiment.
  6. $A_{LU}^{\sin\phi}$ in theory.
  7. The extraction of $e^a(x)$ from preliminary CLAS data.
  8. $A_{LU}^{\sin\phi}$ in the HERMES experiment.
  9. Predictions for $A_{UL}$ asymmetries at CLAS
  10. Conclusions

Figures (3)

  • Figure 1: Kinematics of the process $ep\rightarrow e'h X$ in the lab frame.
  • Figure 2: The flavour combination $e(x)\!=\!(e^u\!+\!\frac{1}{4}e^{\bar{d}})(x)$ extracted from preliminary CLAS data vs. $x$ at $\langle Q^2\rangle \!=\! 1.5\,{\rm GeV}^2$. The error bars are due to statistical error of the data. For comparison the same flavour combinations of $f_1^a(x)$ and the twist-3 Soffer lower bound are shown.
  • Figure 3: Predictions for azimuthal asymmetries $A_{UL}^{W(\phi)}(x)$ vs. $x$ for different beam energies and the corresponding kinematical cuts at CLAS. The thick lines correspond to $W(\phi) = \sin\phi$, the thin lines correspond to $W(\phi) = \sin2\phi$. Hereby solid lines refer to $\pi^+$, long-dashed lines to $\pi^0$, and short-dashed lines to $\pi^-$.