Higher-order anisotropic flows and dihadron correlations in Pb-Pb collisions at<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msqrt><mml:msub><mml:mi>s</mml:mi><mml:mrow><mml:mi>N</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:msub></mml:msqrt><mml:mo>=</mml:mo><mml:mn>2.76</mml:mn></mml:mrow></mml:math>TeV in a multiphase transport model

175

188

A measurement of event-plane correlations involving two or three event planes of different order is presented as a function of centrality for 7 μb −1 Pb + Pb collision data at √ s NN = 2.76 TeV, recorded by the ATLAS experiment at the Large Hadron Collider. Fourteen correlators are measured using a standard event-plane method and a scalar-product method, and the latter method is found to give a systematically larger correlation signal. Several different trends in the centrality dependence of these correlators are observed. These trends are not reproduced by predictions based on the Glauber model, which includes only the correlations from the collision geometry in the initial state. Calculations that include the final-state collective dynamics are able to describe qualitatively, and in some cases also quantitatively, the centrality dependence of the measured correlators. These observations suggest that both the fluctuations in the initial geometry and the nonlinear mixing between different harmonics in the final state are important for creating these correlations in momentum space.

Section: Resultsmentioning

confidence: 98%

Measurement of event-plane correlations insNN=2.76TeV lead-lead collisions with the ATLAS detector

Agustoni¹,

Beck²,

Albert³

et al. 2014

175

188

“…[81,82], respectively. Both papers include "string melting," or a parton cascade, as well as fluctuating initial conditions and pQCD jets described by HIJING.…”

Section: J Centrality Trends For Other Conventional Modelsmentioning

confidence: 99%

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

Agakishiev¹,

Aggarwal²,

Ahammed³

et al. 2012

We 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 √ s NN = 62 and 200 GeV with transverse momentum p t 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 064902-2 ANOMALOUS CENTRALITY EVOLUTION OF TWO-. . .PHYSICAL REVIEW C 86, 064902 (2012) 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.

“…The dynamics of the subsequent hadronic rescattering is then described by a relativistic transport (ART) model [20]. In this work, the AMPT model with the newly fitted parameters is used to simulate Pb + Pb collisions at √ s NN = 2.76 TeV, which has shown good descriptions for many experimental observables at LHC energy, such as pseudorapidity and p T distributions [21] and harmonic flows [22,23]. Two sets of Pb + Pb simulations are performed by setting the partonic interaction cross sections as 1.5 and 0 mb, which correspond to two different physical scenarios for partonic + hadronic interactions and hadronic interactions only, respectively.…”

Section: The Ampt Modelmentioning

confidence: 99%

Dijet asymmetry in Pb+Pb collisions atsNN=2.76TeV within a multiphase transport model

2013

Within a multiphase transport (AMPT) model, dijet asymmetry is studied in Pb + Pb collisions at √ s NN = 2.76 TeV. It is found that a large dijet asymmetry (A J ) is produced by strong interactions between jets and partonic matter. It is demonstrated that hadronization and final-state hadronic rescatterings have little effect on A J . The final A J is found to be driven by both initial A J and partonic jet energy loss, which is consistent with an increasing jet energy loss in a hot and strongly interacting partonic medium in more central Pb + Pb collisions.