Hard Quasi-real Photo-production of Charged Hadrons at COMPASS energies

TL;DR

This paper reports on measurements of charged hadron production in quasi-real photon scattering at COMPASS, comparing experimental data with NLO pQCD calculations to understand proton structure and test theoretical models at various energies.

Contribution

It provides new experimental data on charged hadron production at low and high Q^2, testing the applicability of NLO pQCD in polarized scattering processes.

Findings

Unpolarized differential cross sections agree with NLO pQCD at certain energies.

Charged hadron spectra at different Q^2 ranges show consistency with theoretical predictions.

Results inform the understanding of polarized gluon distributions in the proton.

Abstract

The Common Muon Proton Apparatus for Structure and Spectroscopy (COMPASS) at CERN with its use of beams of naturally polarized muons scattered of a polarized deuteron target, provides an environment of hard scattering between quasi-real photons and partons. Hard hadron quasi-real photo-production with polarized initial states is sensitive to the polarized gluon distribution $\Delta$G through $\gamma$-gluon($g$) direct channels as well as $q$-$g$ resolved processes. Comparisons of unpolarized differential cross section measurements to next-to-leading order (NLO) pQCD calculations are essential to develop our understanding of proton-proton and lepton-nucleon scattering at varying center of mass energies. These measurements are important to asses the applicability of NLO pQCD in interpreting polarized processes. In this talk we will discuss unidentified charged separated hadron production at low $Q^{2}$ (Q$^{2}<0.1 GeV^{2}/c^{2}$) and high transverse momenta (p$_{T}>1.0\,GeV/c$). $<p_{T}^2>$ spectra of charged hadrons at $Q^{2}>1 GeV^{2}/c^{2}$ will also be discussed.