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No experiment has yet measured this orbital part directly.","posed_since":"1997","precise":"Extract the quark orbital angular momentum $L_q = J_q - \\Delta \\Sigma_q/2$ with $J_q = (1/2)\\,\\int dx\\, x\\, [H_q(x,0,0) + E_q(x,0,0)]$, where $H$ and $E$ are generalized parton distributions (GPDs, functions encoding both momentum and transverse position of partons) measured in deeply virtual Compton scattering and exclusive meson production, together with the gluon $J_g$. Answer: $L_u, L_d\\ \\text{and}\\ J_g$ at $\\mu^2 = 4\\,\\mathrm{GeV}^2$ with uncertainties below 0.05, satisfying the spin sum rule.","problem_ref":"35f41452b4a5862da9c8afca82610251dbcfee316e1d5e16787090a409968578","references":"","settled_by":"Global GPD extraction from JLab 12 GeV and EIC exclusive data with controlled extrapolation to zero momentum transfer, compared with lattice QCD values.","status_note":"Lattice QCD provided values by 2020, but experimental extraction of $E_{q}$, needed for $J_{q}$, remained model dependent as of 2026.","title":"Measuring quark and gluon orbital angular momentum in the 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