{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"22b631c7cfba7115fe15379a86920e01fba2861587fceb8360856960f5e1b915","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["35f41452b4a5862da9c8afca82610251dbcfee316e1d5e16787090a409968578","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"e46a3a893ea00c9b5784976946195fb5e859fb88e0e492c8ec318099f17e2aad","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"nuc.proton-structure.orbital-angular-momentum","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Quarks and gluons circulate inside the proton, and this circulating motion carries part of its spin. 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 proton","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"dae4b4abe7562bc46920a25a161b95ad7919fb530f54d7b55f39e36f3c3ae4a7","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"2dd23045fe71be5cbd15f3e9c72fed04bfbcb0e3afa655f264d4ed4e33c03c51","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"uSB91ZGSZQR8vFiah-aK-H9WaqnDbRt_iV5R0rbkuFt-aHpzrOVKHvP7VWtSVK_D0EniwAhwP8PgGVst2e9-Cg"},"schema":"pubphys.envelope/1"},"record_hash":"dae4b4abe7562bc46920a25a161b95ad7919fb530f54d7b55f39e36f3c3ae4a7","leaf_index":3524}