Spin Structure of the Proton from Polarized Inclusive Deep-Inelastic Muon-Proton Scattering

Abstract

We have measured the spin-dependent structure function $g_1^p$ in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range $0.003<x<0.7$ and $1Ge{V}^2<Q^2<60Ge{V}^2$. A next-to-leading order QCD analysis is used to evolve the measured $g_1^p(x,Q^2)$ to a fixed $Q_0^2$. The first moment of $g_1^p$ at $Q_0^2=10Ge{V}^2$ is $\hat{I}{“}^p=0.136\pm 0.013(stat.)\pm 0.009(syst.)\pm 0.005(evol.)$. This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge $a_0$ is found to be $0.28\pm 0.16$. In the Adler-Bardeen factorization scheme, $\hat{I}”g\simeq 2$ is required to bring $\hat{I}”\hat{I}\pounds$ in agreement with the Quark-Parton Model. A combined analysis of all available proton and deuteron data confirms the Bjorken sum rule.

33 pages, 22 figures, uses ReVTex and smc.sty. submitted to Physical Review D