Anomalous centrality evolution of two-particle angular correlations from Au-Au collisions at root s(NN)=62 and 200 GeV

0388197 - ÚJF 2013 RIV US eng J - Journal Article
Agakishiev, G. - Aggarwal, M. M. - Ahammed, Z. - Alakhverdyants, A. V. - Alekseev, I. - Alford, J. - Anderson, B. D. - Anson, C. - Arkhipkin, D. - Averichev, G. S. - Balewski, J. - Bielčíková, Jana - Chaloupka, Petr - Chung, Paul - Hajková, O. - Kapitán, Jan - Pachr, M. - Rusňák, Jan - Šumbera, Michal - Tlustý, David … Total 353 authors
Anomalous centrality evolution of two-particle angular correlations from Au-Au collisions at root s(NN)=62 and 200 GeV.
Physical Review. C. Roč. 86, č. 6 (2012), s. 064902. ISSN 0556-2813
R&D Projects: GA MŠMT LA09013
Institutional support: RVO:61389005
Keywords : heavy ion collisions * QCD matter * STAR
Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders
Impact factor: 3.715, year: 2012

We present two-dimensional (2D) two-particle angular correlations measured with the STAR detector on relative pseudorapidity eta and azimuth phi for charged particles from Au-Au collisions at root s(NN) = 62 and 200 GeV with transverse momentum p(t) >= 0.15 GeV/c, vertical bar eta vertical bar <= 1, and 2 pi in azimuth. Observed correlations include a same-side (relative azimuth <pi/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 eta width of the same-side 2D peak also increases rapidly (eta elongation), and the phi 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.
Permanent Link: http://hdl.handle.net/11104/0217029