{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"b73724be25e32128b35d62f5775160479abf69915076b8f8dc9cda396262110d","created":"2026-10-03T07:18:08Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"ae2ae7e65386479d7e313e64f4c8ac8f6cad42897e8eaa244bf9d13582e4b8dd","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"nuc.quark-gluon-plasma.small-system-collectivity","kind":"phenomenon","literature_status":"contested","n":"1","parents":[],"plain":"When two lead nuclei collide, the produced particles flow together as if from a drop of liquid. The same flow pattern appears in collisions of single protons, where few expected a liquid to form.","posed_since":"2010","precise":"High-multiplicity pp and p-Pb collisions at the LHC show long-range two-particle correlations (the ridge), azimuthal anisotropies $v_{2}$ and $v_{3}$ from multi-particle cumulants, and strangeness enhancement comparable to Pb-Pb. Determine the mechanism (hydrodynamic response of a quark-gluon plasma droplet, initial-state gluon correlations, or kinetic transport with few rescatterings) and the minimum system size for hydrodynamic behavior. Answer: one model reproducing $v_{n}$ versus multiplicity and system size from pp to Pb-Pb with fixed parameters.","problem_ref":null,"references":"","settled_by":"Flow-fluctuation and correlation measurements in pp, p-O, O-O, Ne-Ne and Pb-Pb compared with models that include both initial-state and final-state effects.","status_note":"LHC O+O and Ne+Ne collisions (July 2025) gave flow consistent with hydrodynamic predictions using ab initio nuclear shapes; the origin of flow in pp collisions remained unsettled as of 2026.","title":"Why small collision systems show collective flow","topic_ref":"ec5bb29d3c4ec6576273c8009fdd00011a21f5672430b3080013ab67a0a1a41c"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"0ab26281418884a1b39082d100d1eaca1a318ef57ef7cbc23970e65432cbc30e","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"fcfc24c9df1ce55d2c1f5b8df27c3676e1c8d6f1aadbf8ffedd8e169e2a28f8e","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"s3mvx8KG72FUe9rVoo-G2ajZg3qhYx-7CGIVbyi3ysp4_YWwDOtis_s3Tr_GUUwOXp4cF-fQlVk7s6qzf5XtBQ"},"schema":"pubphys.envelope/1"},"record_hash":"0ab26281418884a1b39082d100d1eaca1a318ef57ef7cbc23970e65432cbc30e","leaf_index":1806}