1,590 research outputs found
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 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 pair, in a
hydrodynamically cooling fireball, to evaluate the total suppression
at both RHIC and LHC energies. Although its limitation is observed, this
approach results to a 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
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
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
Azimuthal correlations of heavy quarks in Pb+Pb collisions at LHC ( TeV)
In this paper we study the azimuthal correlations of heavy quarks in Pb+Pb
collisions with 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
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
Heavy-flavor observables at RHIC and LHC
We investigate the charm-quark propagation in the QGP media produced in
ultrarelativistic heavy-ion collisions at RHIC and the LHC. Purely collisional
and radiative processes lead to a significant suppression of final -meson
spectra at high transverse momentum and a finite flow of heavy quarks inside
the fluid dynamical evolution of the light partons. The -meson nuclear
modification factor and the elliptic flow are studied at two collision
energies. We further propose to measure the triangular flow of mesons,
which we find to be nonzero in non-central collisions.Comment: Proceedings of the 24th Quark Matter conference, 19-24 May 2014,
Darmstadt, Germany. 4 p
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