We report the first lattice QCD calculation of the glue spin in the nucleon. The lattice calculation is carried out with valence overlap fermions on 2+1 flavor DWF gauge configurations on four lattice spacings and four volumes including an ensemble with physical values for the quark masses. The glue spin $S_{ G}$ in the Coulomb gauge in the $\overline{ \text{ MS}}$ scheme is obtained with the 1-loop perturbative matching. We find the results fairly insensitive to lattice spacing and quark masses. We also find that the proton momentum dependence of $S_G$ in the range $0\leq |\vec{ p}| < 1.5$ GeV is very mild, and we determine it in the large momentum limit to be $S_{ G}=0.251(47)(16)$ at the physical pion mass in the $\overline{ \text{ MS}}$ scheme at $\mu^2=10$ GeV$^2$. If the matching procedure in large momentum effective theory is neglected, $S_G$ is equal to the glue helicity measured in high-energy scattering experiments.
Categories: hep-ph hep-lat nucl-th