Anomalous centrality evolution of two-particle angular correlations from Au-Au collisions at √sNN=62 and 200 GeV

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dc.citation.firstpage64902en_US
dc.citation.issueNumber6en_US
dc.citation.journalTitlePhysical Review Cen_US
dc.citation.volumeNumber86en_US
dc.contributor.authorSTAR Collaborationen_US
dc.date.accessioned2015-05-11T15:16:43Zen_US
dc.date.available2015-05-11T15:16:43Zen_US
dc.date.issued2012en_US
dc.description.abstractWe present two-dimensional (2D) two-particle angular correlations measured with the STAR detector on relative pseudorapidity η and azimuth ϕ for charged particles from Au-Au collisions at √sNN=62 and 200 GeV with transverse momentum pt≥0.15 GeV/c, |η|≤1, and 2π in azimuth. Observed correlations include a same-side (relative azimuth <π/2) 2D peak, a closely related away-side azimuth dipole, and an azimuth quadrupole conventionally associated with elliptic flow. The same-side 2D peak and away-side dipole are explained by semihard parton scattering and fragmentation (minijets) in proton-proton and peripheral nucleus-nucleus collisions. Those structures follow N-N binary-collision scaling in Au-Au collisions until midcentrality, where a transition to a qualitatively different centrality trend occurs within one 10% centrality bin. Above the transition point the number of same-side and away-side correlated pairs increases rapidly relative to binary-collision scaling, the η width of the same-side 2D peak also increases rapidly (η elongation), and the ϕ width actually decreases significantly. Those centrality trends are in marked contrast with conventional expectations for jet quenching in a dense medium. The observed centrality trends are compared to perturbative QCD predictions computed in hijing, which serve as a theoretical baseline, and to the expected trends for semihard parton scattering and fragmentation in a thermalized opaque medium predicted by theoretical calculations and phenomenological models. We are unable to reconcile a semihard parton scattering and fragmentation origin for the observed correlation structure and centrality trends with heavy-ion collision scenarios that invoke rapid parton thermalization. If the collision system turns out to be effectively opaque to few-GeV partons the present observations would be inconsistent with the minijet picture discussed here.en_US
dc.identifier.citationSTAR Collaboration. "Anomalous centrality evolution of two-particle angular correlations from Au-Au collisions at √sNN=62 and 200 GeV." <i>Physical Review C,</i> 86, no. 6 (2012) American Physical Society: 64902. http://dx.doi.org/10.1103/PhysRevC.86.064902.en_US
dc.identifier.doihttp://dx.doi.org/10.1103/PhysRevC.86.064902en_US
dc.identifier.urihttps://hdl.handle.net/1911/80195en_US
dc.language.isoengen_US
dc.publisherAmerican Physical Societyen_US
dc.rightsArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.en_US
dc.titleAnomalous centrality evolution of two-particle angular correlations from Au-Au collisions at √sNN=62 and 200 GeVen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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