$A_{LL}(p_T)$ for single hadron photoproduction at high $p_T$

TL;DR

This paper presents preliminary measurements of double longitudinal spin asymmetries in single hadron production at COMPASS, aiming to constrain gluon polarization in the nucleon through high transverse momentum data.

Contribution

It provides new experimental data on $A_{LL}(p_T)$ for single hadron production at COMPASS, complementing RHIC results and testing NLO pQCD predictions without gluon resummation.

Findings

Preliminary $A_{LL}(p_T)$ results for proton and deuteron targets.

Comparison with NLO theoretical predictions.

Analysis based on 10 million hadrons with $p_T>1$ GeV/c.

Abstract

In order to understand the gluon contribution to the nucleon spin, some experiments can study the production of hadrons at high transverse momemtum from lepton-nucleon or nucleon-nucleon scattering. RHIC has recently measured such double spin asymmetries $A_{LL}(p_T)$ for pion production at high center of mass energies, and inclusion of its data to global fits based on NLO collinear pQCD calculations gives some constraints on the gluon polarization in the range $0.05<x_g<0.2$. To complement these results at COMPASS range, we will present preliminary COMPASS results on double longitudinal spin asymmetries $A_{LL}(p_T)$ for single hadron production measured on deuteron and proton target at $Q^2<1$ GeV$^2$, $p_T>1$ GeV/c and center of mass energy $\sqrt{s}\approx 18$ GeV. All COMPASS data taken from 2002 to 2011 by scattering 160 GeV polarized muons on longitudinally polarized $^6$LiD and NH$_3$ targets have been used, and the number of hadrons collected with $p_T>1$ GeV/c for this analysis amounts to about 10 millions. The obtained asymmetries will be compared to theoretical predictions of at NLO without gluon resummation calculation.