Quark orbital angular momentum from lattice QCD - art. no. 114504

We calculate the quark orbital angular momentum of the nucleon from the qua rk energy-momentum tensor form factors on the lattice with the quenched app roximation. The disconnected insertion is estimated stochastically which em ploys the Z(2) noise with an unbiased subtraction. This reduced the error b y 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 w hich is similar to 34 % of the proton spin. We further predict that the glu on angular momentum is 0.20 +/- 0.07; i.e., similar to 40% of the proton sp in is due to the glue.