{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b1216002d00032f1fec920f5b29b44ccf26aaa62a2b36aab069978b141a1b09a","created":"2026-10-03T07:18:07Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","58e430b37105a7ee04896df7e09da38151b5a1073a3284062adbf2d3bc0ab888"],"salt":"8cae3df20a5e1491ef3254614a09131c4b0cc7e678e13f8f7d70db8c52e3e6a1","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":"1","parents":[{"note":"","parent_revision":"58e430b37105a7ee04896df7e09da38151b5a1073a3284062adbf2d3bc0ab888","relation":"special_case"}],"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 $J_q = (1/2)\\,\\operatorname{integral} dx\\, x\\, [H_q(x,0,0) + E_q(x,0,0)]$, 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":null,"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":"43e6b835146db14bd1b426a6a865acb8bf50720a1000b6a2c5c5d637adc5063d"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"35f41452b4a5862da9c8afca82610251dbcfee316e1d5e16787090a409968578","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"31913b3f278408b04bbb58af5be0e4b6832badc75299266a79410ec87a322e61","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"nPinjd-cCVZFR2ibYV-WVbD3hZTeKUTuI4nL1GIEzlmQM7m5mqzGV9sNhUsc43IfkUhoJAqzgPkAZ19xc-9XDA"},"schema":"pubphys.envelope/1"},"record_hash":"35f41452b4a5862da9c8afca82610251dbcfee316e1d5e16787090a409968578","leaf_index":1797}