Precision measurement of the proton spin structure function $g^{p}_{1}$

We have measured the ratio g[sup p][sub 1]/F[sup p][sub 1] over the range 0.029 < x < 0.8 and 1.3 < Q2 < 10 (GeV/c)2 using deep-inelastic scattering of polarized electrons from polarized ammonia. An evaluation of the integral (integral)g[sup p][sub 1](x,Q2)dx at fixed Q2 = 3 (GeV/c)2 yields 0.127 ± 0.004(stat) ± 0.010(syst), in agreement with previous experiments, but well below the Ellis-Jaffe sum rule prediction of 0.160 ± 0.006. In the quark-parton model, this implies Delta q = 0.27 ± 0.10.