Leading and next-to-leading order gluon polarization in the nucleon and longitudinal double spin asymmetries from open charm muoproduction

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Abstract

The gluon polarization in the nucleon was measured using open charm production by scattering $160\text{ }\text{ }\mathrm{GeV}/c$ polarized muons off longitudinally polarized protons or deuterons. The data were taken by the COMPASS Collaboration between 2002 and 2007. A detailed account is given of the analysis method that includes the application of neural networks. Several decay channels of ${\mathrm{D}}^{0}$ mesons are investigated. Longitudinal spin asymmetries of the D meson production cross sections are extracted in bins of ${\mathrm{D}}^{0}$ transverse momentum and energy. At leading order QCD accuracy, the average gluon polarization is determined as $⟨\ensuremath{\Delta}g/g{⟩}^{\mathrm{LO}}=\ensuremath{-}0.06\ifmmode\pm\else\textpm\fi{}0.21(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.08(\mathrm{syst}.)$ at the scale $⟨{\ensuremath{\mu}}^{2}⟩\ensuremath{\approx}13\text{ }\text{ }(\mathrm{GeV}/c{)}^{2}$ and an average gluon momentum fraction $⟨x⟩\ensuremath{\approx}0.11$. The average gluon polarization is also obtained at next-to-leading order QCD accuracy as $⟨\ensuremath{\Delta}g/g⟩$ $\mathrm{NLO}=\ensuremath{-}0.13\ifmmode\pm\else\textpm\fi{}0.15(\mathrm{stat}.)\ifmmode\pm\else\textpm\fi{}0.15(\mathrm{syst}.)$ at the scale $⟨{\ensuremath{\mu}}^{2}⟩\ensuremath{\approx}13\text{ }\text{ }(\mathrm{GeV}/c{)}^{2}$ and $⟨x⟩\ensuremath{\approx}0.20$.

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