Azimuthal asymmetries of charged hadrons produced by high-energy muons scattered off longitudinally polarised deuterons

TL;DR

This study measures azimuthal asymmetries in charged hadron production from muon-deuteron scattering, finding no significant phi-modulation effects but observing nonzero constant asymmetries aligned with spin-dependent distributions.

Contribution

First measurement of azimuthal asymmetries in semi-inclusive charged hadron production from polarized deuterons at high energy, decomposing asymmetries into modulation terms related to parton functions.

Findings

All phi-modulation amplitudes are consistent with zero within errors.

Constant terms are nonzero and similar for positive and negative hadrons.

x dependence aligns with known longitudinal spin asymmetries.

Abstract

Azimuthal asymmetries in semi-inclusive production of positive (h^+) and negative hadrons (h^-) have been measured by scattering 160 GeV muons off longitudinally polarised deuterons at CERN. The asymmetries were decomposed in several terms according to their expected modulation in the azimuthal angle phi of the outgoing hadron. Each term receives contributions from one or several spin and transverse-momentum-dependent parton distribution and fragmentation functions. The amplitudes of all phi-modulation terms of the hadron asymmetries integrated over the kinematic variables are found to be consistent with zero within statistical errors, while the constant terms are nonzero and equal for h^+ and h^- within the statistical errors. The dependencies of the phi-modulated terms versus the Bjorken momentum fraction x, the hadron fractional momentum z, and the hadron transverse momentum p_h^T were studied. The x dependence of the constant terms for both positive and negative hadrons is in agreement with the longitudinal double-spin hadron asymmetries, measured in semi-inclusive deep-inelastic scattering. The x dependence of the sin phi-modulation term is less pronounced than that in the corresponding HERMES data. All other dependencies of the phi-modulation amplitudes are consistent with zero within the statistical errors.