Quark orbital angular momentum from lattice QCD

We calculate the quark orbital angular momentum of the nucleon from the quark energy-momentum tensor form factors on the lattice with the quenched approximation. The disconnected insertion is estimated stochastically which employs the Z(2) noise with an unbiased subtraction. This reduced the error by a factor of 3-4 with negligible overhead. The total quark contribution to the proton spin is found to be 0.30 +/- 0.07. From this and the quark spin content we deduce the quark orbital angular momentum to be 0.17 +/- 0.06 which is similar to 34 % of the proton spin. We further predict that the gluon angular momentum is 0.20 +/- 0.07; i.e., similar to 40% of the proton spin is due to the glue.