Minijet deformation and charge-independent angular correlations on momentum subspace(η,ϕ)in Au-Au collisions atsNN<

Abstract

Measurements of two-particle correlations on angular difference variables η 1 − η 2 (pseudorapidity) and φ 1 − φ 2 (azimuth) are presented for all primary charged hadrons with transverse momentum 0.15 p t 2 GeV/c and |η| 1.3 from Au-Au collisions at √ s NN = 130 GeV. Large-amplitude correlations are observed over a broad range in relative angles where distinct structures appear on the same-side and away-side (i.e., relative azimuth less than π/2 or greater than π/2). The principal correlation structures include that associated with elliptic flow plus a strong, same-side peak. It is hypothesized that the latter results from correlated hadrons associated with semi-hard parton scattering in the early stage of the heavy-ion collision which produces a jet-like correlation peak at small relative angles. The width of the jet-like peak on η 1 − η 2 increases by a factor 2.3 from peripheral to central collisions, suggesting strong coupling of semi-hard scattered partons to a longitudinally-expanding medium. The new methods of jet analysis introduced here provide access to scattered partons at low transverse momentum well below the kinematic range where perturbative quantum chromodynamics and standard fragmentation models are applicable.

Azimuthal di-hadron correlations ind+Au and Au + Au collisions atsNN

“…It has also been argued recently that this long-range correlation in η could be caused by long-range structures in the medium, due to density fluctuations in the medium [29] or color flux tubes [30][31][32]. The "ridge"-like correlation structure in η is further explored in other STAR publications [26,[33][34][35].…”

Energy and system-size dependence of two- and four-particlev2measurements in heavy-ion collisions atsNN=62.4and 200

“…This is a robust upper limit since larger values of σ v 2 /v 2 would require negative values of nonflow contrary to expectations and to measurements of two-particle correlations [20]. We present model comparisons of eccentricity fluctuations to the upper limit of σ v 2 /v 2 .…”

“…The δ 2 derived in this way can be compared to measurements of two-particle correlations [20] to check the validity of the models. Finally, we present the ratio of v 2 to the initial eccentricity from the models.…”

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

“…Those structures provide a complementary approach to medium studies. Inference of jet structure (minijets) from minimum-bias (all particles in the p t acceptance) angular correlations [21][22][23][24] differs qualitatively from high-p t jet methods in that the minijet analysis does not depend on an a priori jet model. No "trigger particle" (parton proxy) is required and no "associated-particle" p t cuts are imposed.…”