μ-p scattering and the glue fraction of the proton

Abstract

The QCD version of the energy-momentum sum rule is tested against SLAC electroproduction and FNAL muon-proton scattering data. While providing only a single number for each Q2, the energy momentum sum rule is significant because the scaling violations due to gluons can be well determined. In particular, gluons carry 30±8% of the proton's energy-momentum at Q2=3.5 GeV2 (which means 22% at 1 GeV2). The largest single corrections of previous estimates of the glue fraction is the inclusion of gluon bremsstrahlung effects. Agreement with experiment is within the uncertainties in the μ-p data. However, the sum rule does not give a very sensitive test of the value of the quark-gluon coupling constant. The prediction for charm production agrees with the observed rates for dimuon and trimuon production in inelastic μ scattering.

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