Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead–lead collisions at sNN=2.76 TeV with the ATLAS detector

Constraints on the Jet-Medium Coupling from Measurements at RHIC and LHC

“…In addition, the figure exhibits the so-called highp T v 2 -problem [5]: The high-p T elliptic flow below p T ∼ 20 GeV is about a factor of two below the measured data [1,2,3,4]. This effect has been discussed in literature [5,12,13] and recently it has been suggested by CUJET3.0 [14] that a temperature and energydependent jet-medium coupling κ = κ(E 2 , T ), which includes non-perturbative effects around the phase transition of T c ∼ 160 MeV, can overcome this problem.…”

“…It includes a running coupling α S (E 2 ) = 1/(c + 9/4π log(E 2 /T 2 c )) with c = 1.05, the Polyakov-loop suppression of the color-electric scattering [15] via χ T = c q L + c g L 2 with pre-factors c q , c g for quarks and gluons, and the Polyakov loop L < 1 as parametrized from lattice QCD, as well as an enhancement of scattering due to the magnetic monopoles near the critical temperature [1,2,3,4] is compared to a pQCD-based energy loss dE/dτ = κ(E 2 , T )E 0 τ 1 e 3/4 ζ 0 v f , including jet-energy loss fluctuations (ζ 0 ) and transverse flow fields (v f ), for a jet-medium coupling that depends on the energy of the jet, the temperature of the medium, and non-equilibrium effects around the phase transition (κ = κ(E 2 , T )) applying the hydrodynamic backgrounds of VISH2+1 [6] (solid lines) and the parton cascade BAMPS [7] (dashed-dotted lines). For comparison, we include the results of CUJET3.0 [14] (dotted lines).…”

“…Below, we study the influence of the details of the jet-medium coupling and the medium background on the simultaneous description of the nuclear modification factor (R AA ) and the high-p T elliptic flow (v 2 ) measured at RHIC and LHC [1,2,3,4] for a radiative pQCD energy-loss ansatz [5]. We contrast media determined via the viscous hydrodynamic approach VISH2+1 [6] with the parton-cascade BAMPS [7] as well as a jet-medium coupling depending on the collision energy with a jet-medium coupling influenced by the energy of the jet, the temperature of the medium and non-equilibrium effects around the phase transition.…”

“…On the other hand, the jet-energy loss of the Hybrid AdS energy-loss ansatz [8] is based on falling strings [1,2,3,4] is compared to a pQCD-based energy loss dE/dτ = κ( √ s NN )E 0 τ 1 e 3/4 ζ 0 v f , including jet-energy loss fluctuations (ζ 0 ) and transverse flow fields (v f ), for a jet-medium coupling that depends on the collision energy (κ = κ( √ s NN )) applying the hydrodynamic backgrounds of VISH2+1 [6] (solid lines) and the parton cascade BAMPS [7] (dashed-dotted lines).…”

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

“…Also, the inclusive yields of jets are suppressed by a factor of about two in the 0-10% centrality interval, relative to the peripheral 60-80% interval. ATLAS has studied the path length dependence of jet suppression both by looking at the charged particle v 2 at high transverse momentum (p T > 10 GeV) [6], and by the v 2 of fully-reconstructed jets with p T,jet > 45 GeV [7], as seen in the left and right panels, respectively, of Fig. 2.…”