Measurement of azimuthal modulations in SIDIS off proton target at COMPASS

TL;DR

This paper reports the first measurement of azimuthal modulations in semi-inclusive deep inelastic scattering off a proton target at COMPASS, providing new insights into nucleon structure through detailed angular distributions of produced hadrons.

Contribution

It presents the first corrected measurements of azimuthal modulations in SIDIS off protons at COMPASS, including QED radiative effects, advancing understanding of nucleon transverse momentum structure.

Findings

Measured azimuthal modulations $ ext{cos}\phi_h$, $ ext{cos}2\phi_h$, and $ ext{sin}\phi_h$

Corrected for QED radiative effects for the first time

Provides new data on nucleon structure functions

Abstract

The azimuthal angle ($\phi_h$) distribution of hadrons produced in deep inelastic scattering serves as a powerful tool for probing the nucleon structure in terms of transverse momentum dependent parton distribution functions and fragmentation functions. For an unpolarized nucleon, three azimuthal modulations arise: $\cos\phi_h$ related to the Cahn effect, $\cos2\phi_h$ linked to the Boer--Mulders function, and $\sin\phi_h$ known as beam-spin asymmetry, each revealing insights into combinations of twist-two or higher-twist distribution and fragmentation functions. The COMPASS collaboration at CERN collected semi-inclusive deep inelastic scattering events in 2016 and 2017 using a longitudinally polarized 160 GeV/$c$ muon beam scattering off a liquid hydrogen target. Data from 2016 corresponding to about 1/3 of the full sample have been analyzed to measure the azimuthal modulations of charged hadrons. For the first time, the results were corrected for QED radiative effects using the DJANGOH MC generator.