$\Deltag/g$ results from the Open Charm production at COMPASS

TL;DR

This paper reports on the measurement of the gluon polarization in the nucleon using charm meson production at COMPASS, employing neural networks and NLO-QCD analysis to improve accuracy and incorporate corrections.

Contribution

It introduces a novel neural network method for better D0 meson mass spectrum reconstruction and applies NLO-QCD corrections to the gluon polarization measurement for the first time.

Findings

Improved statistical significance of D0 mass spectra.

First application of NLO-QCD corrections to experimental gluon polarization data.

Quantitative results for Δg/g at specific kinematic points.

Abstract

One of the main goals of the COMPASS experiment at CERN is the determination of the gluon contribution to the nucleon spin. To achieve this goal COMPASS uses a naturally polarised muon beam with an energy of 160 GeV and a fixed polarised target. Two types of materials are used for the latter: $^{6}$LiD (polarised deuterons) during the years of 2002-2006 and NH$_{3}$ (polarised protons) in 2007. The gluons in the nucleon can be accessed directly via the Photon Gluon Fusion (PGF) process. Among the channels studied by COMPASS, the production of charmed mesons is the one that tags a PGF interaction in the most clean and efficient way. This talk presents a result for the gluon polarisation, $\Delta g/g$, which is based on a measurement of the spin asymmetry resulting from the production of D$^{0}$ mesons. These mesons are reconstructed through the invariant mass of their decay products. The statistical significance of the $D^{0}$ mass spectra has been improved significantly using a new method based on Neural Networks. The $\Delta g/g$ result is also presented using a next-to-leading order (NLO-QCD) analysis of the $\mu N \rightarrow q\bar{q}$ reaction. Such correction is relevant and was for the first time applied to an experimental measurement of the gluon polarisation.