Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Azimuthal asymmetries in SIDIS off unpolarized targets at COMPASS

Andrea Bressan

TL;DR

This work analyzes azimuthal asymmetries in unpolarized SIDIS to probe the nucleon’s transverse structure via $k_ot$-dependent PDFs, notably the Boer-Mulders function, while disentangling kinematic effects such as the Cahn term and perturbative QCD. Using COMPASS data from a $160\ \mathrm{GeV}$ muon beam on a $^6$LiD target collected in 2004, the authors extract $\\ extcos{\\phi_h}$ and $\\cos 2\\phi_h$ modulations for positive and negative hadrons after a thorough acceptance correction implemented with a full Monte Carlo chain. They observe sizable $\\cos \\phi$ modulations and a clear charge dependence in $\\cos 2\\phi$, with $\\sin \\phi$ consistent with zero, and find reasonable agreement with models that include the Cahn effect and Boer-Mulders contributions, supporting a nonzero Boer-Mulders PDF and demonstrating COMPASS’s sensitivity to transverse spin–momentum correlations.

Abstract

Azimuthal asymmetries measured in unpolarized semi-inclusive deep inelastic scattering bring important information on the inner structure of the nucleons, and can be used both to estimate the average quark transverse momentum k_T and to access the so-far unmeasured Boer-Mulders functions. COMPASS results using part of the 2004 data collected with a 6LiD target and a 160 GeV positive muon beam are presented separately for positive and negative hadrons.

Azimuthal asymmetries in SIDIS off unpolarized targets at COMPASS

TL;DR

This work analyzes azimuthal asymmetries in unpolarized SIDIS to probe the nucleon’s transverse structure via -dependent PDFs, notably the Boer-Mulders function, while disentangling kinematic effects such as the Cahn term and perturbative QCD. Using COMPASS data from a muon beam on a LiD target collected in 2004, the authors extract and modulations for positive and negative hadrons after a thorough acceptance correction implemented with a full Monte Carlo chain. They observe sizable modulations and a clear charge dependence in , with consistent with zero, and find reasonable agreement with models that include the Cahn effect and Boer-Mulders contributions, supporting a nonzero Boer-Mulders PDF and demonstrating COMPASS’s sensitivity to transverse spin–momentum correlations.

Abstract

Azimuthal asymmetries measured in unpolarized semi-inclusive deep inelastic scattering bring important information on the inner structure of the nucleons, and can be used both to estimate the average quark transverse momentum k_T and to access the so-far unmeasured Boer-Mulders functions. COMPASS results using part of the 2004 data collected with a 6LiD target and a 160 GeV positive muon beam are presented separately for positive and negative hadrons.

Paper Structure

This paper contains 4 sections, 3 equations, 3 figures.

Table of Contents

  1. Introduction
  2. The COMPASS experiment
  3. Analysis and Systematic Studies
  4. Results and Comments

Figures (3)

  • Figure 1: Top:measured azimuthal distribution after weighting for the two target polarization. Middle: acceptance distribution as calculated by the Monte Carlo data. Bottom: azimuthal distribution corrected for the acceptance effects.
  • Figure 2: $\cos \phi$ asymmetries from COMPASS deuteron data for positive (upper row) and negative (lower raw) hadrons; the asymmetries includes the kinematical factor $\varepsilon_1$ and the bands indicate the size of the systematic errors. The superimposed curves are the values predicted by anselmino2 taking into account the Cahn effect only.
  • Figure 3: $\cos 2 \phi$ asymmetries from COMPASS deuteron data for positive (upper row) and negative (lower raw) hadrons; the asymmetries are divided by the kinematical factor $\varepsilon_1$ and the red bands indicate size of the systematic errors.