Final COMPASS results on the deuteron spin-dependent structure function g 1 d and the Bjorken sum rule

摘要

Final results are presented from the inclusive measurement of deep-inelastic polarised-muon scattering on longitudinally polarised deuterons using a 6 LiD target. The data were taken at 160?GeV beam energy and the results are shown for the kinematic range 1 ( GeV / c ) 2 Q 2 100 ( GeV / c ) 2 in photon virtuality, 0.004 x 0.7 in the Bjorken scaling variable and W 4 GeV / c 2 in the mass of the hadronic final state. The deuteron double-spin asymmetry A 1 d and the deuteron longitudinal-spin structure function g 1 d are presented in bins of x and Q 2 . Towards lowest accessible values of x , g 1 d decreases and becomes consistent with zero within uncertainties. The presented final g 1 d values together with the recently published final g 1 p values of COMPASS are used to again evaluate the Bjorken sum rule and perform the QCD fit to the g 1 world data at next-to-leading order of the strong coupling constant. In both cases, changes in central values of the resulting numbers are well within statistical uncertainties. The flavour-singlet axial charge a 0 , which is identified in the MS ￣ renormalisation scheme with the total contribution of quark helicities to the nucleon spin, is extracted at next-to-leading order accuracy from only the COMPASS deuteron data: a 0 ( Q 2 = 3 ( GeV / c ) 2 ) = 0.32 ± 0.02 stat ± 0.04 syst ± 0.05 evol . Together with the recent results on the proton spin structure function g 1 p , the results on g 1 d constitute the COMPASS legacy on the measurements of g 1 through inclusive spin-dependent deep inelastic scattering.