Proton spin content from lattice QCD

We calculate the form factor of the quark energy momentum tensor and thereb y extract the quark orbital angular momentum of the nucleon. The calculatio n is done on a quenched 16(3) x 24 lattice at beta = 6.0 and with Wilson fe rmions at kappa = 0.148, 0.152, 0.154 and 0.155. We calculate the disconnec ted insertion stochastically which employs the Z(2) noise with an unbiased subtraction. This proves to be an efficient method of reduce the error from the noise. We find that the total quark contribution to the proton spin is 0.29 +/- 0.07. From this we deduce that the quark orbital angular momentum is 0.17 +/- 0.08 and predict the gluon spin to be 0.21 +/- 0.07, i.e. abou t 40% of the proton spin is due to the glue.