The Schr\"odinger-Langevin equation with and without thermal fluctuations

The Schr\"odinger-Langevin (SL) equation is considered as an effective open quantum system formalism suitable for phenomenological applications involving a quantum subsystem interacting with a thermal bath. We focus on two open issues relative to its solutions: the stationarity of the excited states of the non-interacting subsystem when one considers the dissipation only and the thermal relaxation toward asymptotic distributions with the additional stochastic term. We first show that a proper application of the Madelung/polar transformation of the wave function leads to a non zero damping of the excited states of the quantum subsystem. We then study analytically and numerically the SL equation ability to bring a quantum subsystem to the thermal equilibrium of statistical mechanics. To do so, concepts about statistical mixed states and quantum noises are discussed and a detailed analysis is carried with two kinds of noise and potential. We show that within our assumptions the use of the SL equation as an effective open quantum system formalism is possible and discuss some of its limitations.Comment: 38 pages, 31 figure

Semi-classical approach to J/ψJ/\psi suppression in high energy heavy-ion collisions

We study the heavy quark/antiquark pair dynamics in strongly-coupled quark gluon plasma. A semi-classical approach, based on the Wigner distribution and Langevin dynamics, is applied to a color screened $c{\bar c}$ pair, in a hydrodynamically cooling fireball, to evaluate the total $J/\psi$ suppression at both RHIC and LHC energies. Although its limitation is observed, this approach results to a $J/\psi$ suppression of around 0.30 at RHIC and 0.25 at LHC.Comment: 4 pages, 6 figures, Proceeding for International Conference on Strangeness in Quark Matter 2013 (SQM 2013) at Birmingha

Radiative energy loss reduction in an absorptive plasma

The influence of the damping of radiation on the radiative energy loss spectrum of a relativistic charge in an infinite, absorptive plasma is studied. We find increasing reduction of the spectrum with increasing damping. Our studies, which represent an Abelian approximation for the colour charge dynamics in the quark-gluon plasma, may influence the analysis of jet quenching phenomena observed in high-energy nuclear collisions. Here, we focus on a formal discussion of the limiting behaviour with increasing radiation frequency. In an absorptive (and polarizable) medium, this is determined by the behaviour of the exponential damping factor entering the spectrum and the formation time of radiation.Comment: Jan 2012. 4pp. Talk given at Quark Matter 2011, 23-28 May 2011, Annecy, Franc

Recent results on heavy quark quenching in ultrarelativistic heavy ion collisions: the impact of coherent gluon radiation

We present a model for radiative energy loss of heavy quarks in quark gluon plasma which incorporates coherence effects. We then study its consequences on the radiation spectra as well as on the nuclear modification factor of open heavy mesons produced in ultrarelativistic heavy ion collisions.Comment: Proceedings of Hard Probes 2012 conferenc

Gluon radiation by heavy quarks at intermediate energies

Employing scalar QCD we study the gluon emission of heavy quarks created by the interaction with light quarks considered as dynamical scattering centers. We develop approximation formulas for the high energy limit and study when the full calculation reaches this high energy limit. For zero quark masses and in the high energy limit our model reproduces the Gunion-Bertsch results. We justify why scalar QCD represents a good approximation to the full QCD approach for the energy loss of heavy quarks. In the regime of accessible phenomenology we observe that the emission at small transverse momentum (dead cone effect) is less suppressed than originally suggested. We also investigate the influence of a finite gluon mass on the discussed results

Azimuthal correlations of heavy quarks in Pb+Pb collisions at LHC (s=2.76\sqrt{s}=2.76 TeV)

In this paper we study the azimuthal correlations of heavy quarks in Pb+Pb collisions with $\sqrt{s}=2.76$ TeV at LHC. Due to the interaction with the medium heavy quarks and antiquarks are deflected from their original direction and the initial correlation of the pair is broadened. We investigate this effect for different transverse momentum classes. Low-momentum heavy-quark pairs lose their leading order back-to-back initial correlation, while a significant residual correlation survives at large momenta. Due to the larger acquired average deflection from their original directions the azimuthal correlations of heavy-quark pairs are broadened more efficiently in a purely collisional energy loss mechanism compared to including radiative corrections. This discriminatory feature survives when next-to-leading order production processes are included.Comment: final, published versio

Heavy-flavor azimuthal correlations of D mesons

Observables of heavy-quark azimuthal correlations in heavy-ion collisions are a new and promising tool for the investigation of the in-medium energy loss. We explore the potential of these observables to discriminate the collisional and radiative contributions within a hybrid EPOS+MC@sHQ transport approach.Comment: final version of proceedings for SQM 2013, C13-07-22.

Toward a consistent evolution of the quark-gluon plasma and heavy quarks

Heavy-quark observables in ultrarelativistic heavy-ion collisions, like the nuclear modification factor and the elliptic flow, give insight into the mechanisms of high-momentum suppression and low-momentum thermalization of heavy quarks. Here, we present a global study of these two observables within a coupled approach of the heavy-quark propagation in a realistic fluid dynamical medium, MC@sHQ+EPOS2, and compare to experimental data from RHIC and LHC experiments. The heavy quarks scatter elastically and inelastically with the quasiparticles of the quark-gluon plasma (QGP), which are represented consistently with the underlying equation of state. We examine two scenarios: first, we interpret the lattice QCD equation of state as a sum of partonic and hadronic contributions, and second, as a gas of massive partonic quasiparticles. It is observed that independent of their momentum the energy loss of heavy quarks depends strongly on how the lattice QCD equation of state is translated into degrees of freedom of the QGP

Radiative energy loss in the absorptive QGP: taming the long formation lengths in coherent emission

In an absorptive plasma, damping of radiation mechanisms can influence the bremsstrahlung formation in case of large radiation formation lengths. We study qualitatively the influence of this effect on the gluon bremsstrahlung spectrum off heavy quarks in the quark-gluon plasma. Independent of the heavy-quark mass, the spectrum is found to be strongly suppressed in an intermediate gluon energy region which grows with increasing gluon damping rate and increasing energy of the heavy quark. Thus, just as polarization effects in the plasma render the bremsstrahlung spectra independent of the quark mass in the soft gluon regime, damping effects tend to have a similar impact for larger gluon energies.Comment: contribution to the International Meeting "Excited QCD", Peniche, Portugal, 06 - 12 May 201