a Measurement and Next to Leading Order Evaluation of the Spin Dependent Structure Function G(1) of the Proton.

In 1992 the Spin Muon Collaboration began a program of fixed target deep inelastic scattering experiments in the muon hall in the north extraction area of the CERN SPS. The beam used during most of the data taking had an energy of 190 GeV and a polarization of.80 +/-.03 +/-.20. In 1993, a solid butanol target was used. Protons in the target accounted for 12% of the total mass and had a polarization of.86 +/-.03. In that year 13.6 million events were recorded and reconstructed, 4.4 million of which were accepted as deep inelastic scattering events. Using this sample, in conjunction with deep inelastic scattering data involving unpolarized beams and targets, the structure function g_1 of the proton was determined in twelve x bins. A next to leading order analysis of this structure function allowed for an evaluation of its first moment at a fixed Q^2 as well as a determination of polarized parton densities. A comparison with the Ellis-Jaffe sum rule prediction shows a discrepancy of two standard deviations, indicating that anomalous scaling violations in the singlet component of the relevant matrix element are not negligible.