What have we learned about the quark–gluon plasma with the ATLAS detector at the LHC?

Abstract

Recent results from lead-lead and proton-lead collisions, measured by the ATLAS experiment at the LHC, are presented. In leadlead collisions, electroweak bosons are found to be produced proportionally to the number of binary nucleon-nucleon collisions, and to have rapidity distributions compatible with perturbative QCD calculations, suggesting no need for large nuclear PDF effects. Conversely the large suppression of inclusive jets, the elliptic flow of hadrons at high p T and the direct measurements of jet v 2 support the need for a path-length dependent energy loss in the hot, dense medium. Proton-lead measurements provide new insights on particle production in small, longitudinally asymmetric systems, but require further insights into the fluctuating nature of proton-proton collisions. The modification factors for charged hadrons show a non-trivial dependence on centrality and rapidity, with a "Cronin" peak appearing only in the most central events, and in the lead-going direction. Finally the measurements of inclusive jets in proton-lead show a striking scaling in the R CP suppression variable that is only a function of the jet momentum, while the suppression factor relative to PYTHIA jet cross sections show an enhanced yield in peripheral events, and a suppressed yield in central events.

Collective bulk excitations in the QGP: From the weakly non‐ideal case to the strong correlation limit

“…Also, the experiments at CERN have such energy to reach this high temperatures. [ 28 ] Keeping in mind statements written above, we describe two different experiments with different energies, or we describe different time phases of the same experiment, where we have the highest temperature at the beginning and the following freezing out of fireball.…”

Forward-Backward Multiplicity Correlations in Relativistic Heavy-Ion Collisions

“…In the most recent past, experimental studies at the RHIC [3] and LHC [4] have had convincing evidence in support of the formation of a deconfined phase of quarks and gluons. Although the theoretical physics community has proposed a great deal of insight into the possible occurrence of the deconfined phase [5], for an experimentalist, it is also important to (2039) have an understanding of the observables which could actually be tested on a theoretical model to establish the physical phenomena taking place during the process and to have an understanding of the evolution of the processes. One such approach is to investigate the correlations amongst the particles emitted at the freeze-out of QGP which could actually shed light on the earlier stages of the heavy-ion collisions too.…”

Computational Challenges in the Measurement of Heavy-Ion Collision Event Characteristics With the Atlas Experiment at the LHC

“…For a recent review of ATLAS results, see [10,19]. In the domain of HI physics, the research program of the experiment aims to elucidate the properties of the QGP [28].…”