{"paper":{"title":"Tilted geometry of the pion emission source in Au+Au collisions in the RHIC Beam Energy Scan","license":"http://creativecommons.org/licenses/by-nc-nd/4.0/","headline":"The tilt angle of the pion emission source in Au+Au collisions decreases rapidly with rising collision energy and depends strongly on pair transverse momentum.","cross_cats":[],"primary_cat":"nucl-ex","authors_text":"STAR Collaboration","submitted_at":"2026-05-14T16:13:56Z","abstract_excerpt":"We present the first systematic measurement of the tilt of the pion emission source in relativistic Au+Au collisions at center-of-mass energies per nucleon pair, $\\sqrt{s_{NN}}$ = 7.7, 14.5, 17.3 and 27 GeV, using data from the STAR experiment. The tilt angle and final freeze-out eccentricity are extracted through azimuthally sensitive femtoscopy of identical pion pairs. Our results reveal a strong dependence of the tilt parameter on the pair transverse momentum, indicating that the apparent source geometry is strongly coupled to expansion dynamics. Moreover, we observe a rapid decrease of the"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"Our results reveal a strong dependence of the tilt parameter on the pair transverse momentum, indicating that the apparent source geometry is strongly coupled to expansion dynamics. Moreover, we observe a rapid decrease of the tilt magnitude with increasing collision energy, consistent with the emission source approaching longitudinal boost invariance at higher energies.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The azimuthally sensitive femtoscopy analysis assumes that the extracted tilt angle and freeze-out eccentricity faithfully reflect the true source geometry without large biases from detector acceptance, pair selection cuts, or the specific parametrization of the correlation function.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"The pion emission source in Au+Au collisions is tilted with magnitude decreasing rapidly as collision energy rises from 7.7 to 27 GeV, indicating departure from longitudinal boost invariance.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"The tilt angle of the pion emission source in Au+Au collisions decreases rapidly with rising collision energy and depends strongly on pair transverse momentum.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"01b908b1ecbfdadeb780c1f5fa379c6378d38089ad2053af277613ff50e79af4"},"source":{"id":"2605.15013","kind":"arxiv","version":1},"verdict":{"id":"254cc87c-826d-485b-8cd8-9322a9de1b1d","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-15T02:37:35.508657Z","strongest_claim":"Our results reveal a strong dependence of the tilt parameter on the pair transverse momentum, indicating that the apparent source geometry is strongly coupled to expansion dynamics. Moreover, we observe a rapid decrease of the tilt magnitude with increasing collision energy, consistent with the emission source approaching longitudinal boost invariance at higher energies.","one_line_summary":"The pion emission source in Au+Au collisions is tilted with magnitude decreasing rapidly as collision energy rises from 7.7 to 27 GeV, indicating departure from longitudinal boost invariance.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The azimuthally sensitive femtoscopy analysis assumes that the extracted tilt angle and freeze-out eccentricity faithfully reflect the true source geometry without large biases from detector acceptance, pair selection cuts, or the specific parametrization of the correlation function.","pith_extraction_headline":"The tilt angle of the pion emission source in Au+Au collisions decreases rapidly with rising collision energy and depends strongly on pair transverse momentum."},"references":{"count":65,"sample":[{"doi":"","year":2023,"title":"Hot QCD White Paper","work_id":"64dd8cb3-cf9f-4092-8986-bad0715f028d","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2024,"title":"Achenbachet al., The present and future of QCD, Nucl","work_id":"38a58b24-f871-428a-9759-276d19fda2b5","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":1998,"title":"Methods for analyzing anisotropic flow in relativistic nuclear collisions","work_id":"efb01f48-109c-4308-beb3-a3d5aa42ccdd","ref_index":3,"cited_arxiv_id":"nucl-ex/9805001","is_internal_anchor":true},{"doi":"","year":2011,"title":"Torqued fireballs in relativistic heavy-ion collisions","work_id":"0ce7abde-9190-4e7e-815a-963488bd7cee","ref_index":4,"cited_arxiv_id":"1011.3354","is_internal_anchor":true},{"doi":"","year":2014,"title":"Forward-backward eccentricity and participant-plane angle fluctuations and their influences on longitudinal dynamics of collective flow","work_id":"6c66c206-9817-4d34-bf14-8e3771baf9b7","ref_index":5,"cited_arxiv_id":"1403.6077","is_internal_anchor":true}],"resolved_work":65,"snapshot_sha256":"2d6506effd463b967be575a077b8bcd6152dee6c413f496096ddc6bc75b4b1bf","internal_anchors":34},"formal_canon":{"evidence_count":2,"snapshot_sha256":"d683398862f8227b19fd8c9e9cb8f2b46726682fa4a22050609c87d00ae07b25"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}