Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data

Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality $Q^2>1(\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}c{)}^2$. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/$c$ polarised muon beam impinging on a polarised ${}^6$LiD target. By analysing the full range in hadron transverse momentum $p_{\mathrm{T}}$, the different $p_{\mathrm{T}}$-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation $\mathrm{\Delta }g\mathrm{/}g$ is evaluated at leading order in pQCD at a hard scale of $\mu^2= \langle Q^2 \rangle = 3 ({\rm GeV}/c)^2$. It is determined in three intervals of the nucleon momentum fraction carried by gluons, $x_{\mathrm{g}}$, covering the range $0.04\text{\hspace{0.17em}⁣}<\text{\hspace{0.17em}⁣}{x}_{\mathrm{g}}\text{\hspace{0.17em}⁣}<\text{\hspace{0.17em}⁣}0.28$~ and does not exhibit a significant dependence on $x_{\mathrm{g}}$. The average over the three intervals, $\langle \Delta g/g \rangle = 0.113 \pm 0.038_{\rm (stat.)}\pm 0.036_{\rm (syst.)}$at$\langle x_{\rm g} \rangle \approx 0.10$, suggests that the gluon polarisation is positive in the measured $x_{\mathrm{g}}$ range.