Precision measurement of the proton spin structure function g1p

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