arXiv subjects
Publications and source records attributed to P. B. Gossiaux.
Charmed hadron observables from the RHIC to LHC energies have been very successfully described with the recently advanced EPOS4HQ event generator. Here we extend this investigation to the production of beauty hadrons in proton-proton (pp) and heavy ion (HI) collisions
This document summarizes the efforts of the EMMI Rapid Reaction Task Force on "Suppression and (re)generation of quarkonium in heavy-ion collisions at the LHC", centered around their 2019 and 2022 meetings. It provides a review of existing experimental results and theoretical approaches, including lattice QCD calculations and semiclassical and quantum approaches for the dynamical evolution of quarkonia in the quark-gluon plasma as probed in high-energy heavy-ion collisions. The key ingredients of the transport models are itemized to facilitate comparisons of calculated quantities such as reaction rates, binding energies, and nuclear modification factors. A diagnostic assessment of the various results is attempted and coupled with an outlook for the future.
The future opportunities for high-density QCD studies with ion and proton beams at the LHC are presented. Four major scientific goals are identified: the characterisation of the macroscopic long wavelength Quark-Gluon Plasma (QGP) properties with unprecedented precision, the investigation of the microscopic parton dynamics underlying QGP properties, the development of a unified picture of particle production and QCD dynamics from small (pp) to large (nucleus--nucleus) systems, the exploration of parton densities in nuclei in a broad ($x$, $Q^2$) kinematic range and the search for the possible onset of parton saturation. In order to address these scientific goals, high-luminosity Pb-Pb and p-Pb programmes are considered as priorities for Runs 3 and 4, complemented by high-multiplicity studies in pp collisions and a short run with oxygen ions. High-luminosity runs with intermediate-mass nuclei, for example Ar or Kr, are considered as an appealing case for extending the heavy-ion programme at the LHC beyond Run 4. The potential of the High-Energy LHC to probe QCD matter with newly-available observables, at twice larger center-of-mass energies than the LHC, is investigated.
We report on broadly based systematic investigations of the modeling components for open heavy-flavor diffusion and energy loss in strongly interacting matter in their application to heavy-flavor observables in high-energy heavy-ion collisions, conducted within an EMMI Rapid Reaction Task Force framework. Initial spectra including cold-nuclear-matter effects, a wide variety of space-time evolution models, heavy-flavor transport coefficients, and hadronization mechanisms are scrutinized in an effort to quantify pertinent uncertainties in the calculations of nuclear modification factors and elliptic flow of open heavy-flavor particles in nuclear collisions. We develop procedures for error assessments and criteria for common model components to improve quantitative estimates for the (low-momentum) heavy-flavor diffusion coefficient as a long-wavelength characteristic of QCD matter as a function of temperature, and for energy loss coefficients of high-momentum heavy-flavor particles.
We pursue the study of event by event correlations between low-mass particles and heavy mesons flow harmonics in ultrarelativistic heavy ion collisions and clarify some ambiguities found in one of our previous work.
The influence of final-state radiation (FSR) of heavy quarks on observables in high-energy proton-proton collisions is studied. The transverse momentum correlation of D and Dbar mesons, which have been emitted with an azimuthal difference angle close to 180 degrees, is identified as an observable which is sensitive to the FSR process. We demonstrate this by performing calculations with the EPOS3+HQ model and with the event generator Pythia 6. The initial symmetric pT = pT' correlation for back-to-back pairs does not completely vanish in EPOS3+HQ, neither for the final DDbar pairs nor for the ccbar pairs before hadronisation. Also a significant difference in the shape of the correlation distribution for EPOS3+HQ and Pythia 6 is observed. Therefore, particle correlations in pp data offer the possibility to study several aspects of energy loss in heavy-ion collisions.
Heavy quarks (charm and bottoms) are one of the few probes which are sensitive to the degrees of freedom of a Quark Gluon Plasma (QGP), which cannot be revealed by lattice gauge calculations in equilibrium. Due to the rapid expansion of the QGP energetic heavy quarks do not come to an equilibrium with the QGP. Their energy loss during the propagation through the QGP medium depends strongly on the modelling of the interaction of the heavy quarks with the QGP quarks and gluons, i.e. on the assuption of the degrees of freedom of the plasma. Here we compare the results of different models, the pQCD based Monte-Carlo (MC@sHQ), the Dynamical Quasi Particle Model (DQPM) and the effective mass approach, for the drag force in a thermalized QGP and discuss the sensitivity of heavy quark energy loss on the properties of the QGP as well as on non-equilibrium dynamics
This report reviews the study of open heavy-flavour and quarkonium production in high-energy hadronic collisions, as tools to investigate fundamental aspects of Quantum Chromodynamics, from the proton and nucleus structure at high energy to deconfinement and the properties of the Quark-Gluon Plasma. Emphasis is given to the lessons learnt from LHC Run 1 results, which are reviewed in a global picture with the results from SPS and RHIC at lower energies, as well as to the questions to be addressed in the future. The report covers heavy flavour and quarkonium production in proton-proton, proton-nucleus and nucleus-nucleus collisions. This includes discussion of the effects of hot and cold strongly interacting matter, quarkonium photo-production in nucleus-nucleus collisions and perspectives on the study of heavy flavour and quarkonium with upgrades of existing experiments and new experiments. The report results from the activity of the SaporeGravis network of the I3 Hadron Physics programme of the European Union 7th Framework Programme.
The heavy quark collisional scattering on partons of the quark gluon plasma (QGP) is studied in a QCD medium at finite temperature and chemical potential. We evaluate the effects of finite parton masses and widths, finite temperature $T$ and quark chemical potential $μ_q$ on the different elastic cross sections for dynamical quasi-particles (on- and off-shell particles in the QGP medium as described by the dynamical quasi-particles model "DQPM") using the leading order Born diagrams. Our results show clearly the decrease of the $qQ$ and $gQ$ total elastic cross sections when the temperature and the quark chemical potential increase. These effects are amplified for finite $μ_q$ at temperatures lower than the corresponding critical temperature $T_c (μ_q)$. Using these cross sections we, furthermore, estimate the energy loss and longitudinal and transverse momentum transfers of a heavy quark propagating in a finite temperature and chemical potential medium. Accordingly, we have shown that the transport properties of heavy quarks are sensitive to the temperature and chemical potential variations. Our results provide some basic ingredients for the study of charm physics in heavy-ion collisions at Beam Energy Scan (BES) at RHIC and CBM experiment at FAIR.
Within the aim of a dynamical study of on- and off-shell heavy quarks Q in the quark gluon plasma (QGP) - as produced in relativistic nucleus-nucleus collisions - we study the heavy quark collisional scattering on partons of the QGP. The elastic cross sections $σ_{q,g-Q}$ are evaluated for perturbative partons (massless on-shell particles) and for dynamical quasi-particles (massive off-shell particles as described by the dynamical quasi-particles model "DQPM") using the leading order Born diagrams. We demonstrate that the finite width of the quasi-particles in the DQPM has little influence on the cross sections $σ_{q,g-Q}$ except close to thresholds. We, furthermore, calculate the heavy quark relaxation time as a function of temperature T within the different approaches using these cross sections.
The interactions of heavy quarks with the partonic environment at finite temperature $T$ and finite quark chemical potential $μ_q$ are investigated in terms of transport coefficients within the Dynamical Quasi-Particle model (DQPM) designed to reproduce the lattice-QCD results (including the partonic equation of state) in thermodynamic equilibrium. These results are confronted with those of nuclear many-body calculations close to the critical temperature $T_c$. The hadronic and partonic spatial diffusion coefficients join smoothly and show a pronounced minimum around $T_c$, at $μ_q=0$ as well as at finite $μ_q$. Close and above $T_c$ its absolute value matches the lQCD calculations for $μ_q=0$. The smooth transition of the heavy quark transport coefficients from the hadronic to the partonic medium corresponds to a cross over in line with lattice calculations, and differs substantially from perturbative QCD (pQCD) calculations which show a large discontinuity at $T_c$. This indicates that in the vicinity of $T_c$ dynamically dressed massive partons and not massless pQCD partons are the effective degrees-of-freedom in the quark-gluon plasma.
We study the heavy quark scattering on partons of the quark gluon plasma (QGP) being especially interested in the collisional (elastic) scattering processes of heavy quarks on quarks and gluons. We calculate the different cross sections for perturbative partons (massless on-shell particles in the vacuum) and for dynamical quasi-particles (off-shell particles in the QGP medium as described by the dynamical quasi-particles model "DQPM") using the leading order Born diagrams. Our results show clearly the effect of a finite parton mass and width on the perturbative elastic $(q(g) Q \rightarrow q (g) Q)$ cross sections which depend on temperature $T$, energy density $ε$, the invariant energy $\sqrt{s}$ and the scattering angle $θ$. Our detailed comparisons demonstrate that the finite width of the quasi-particles in the DQPM - which encodes the multiple partonic scattering - has little influence on the cross section for $q Q \rightarrow q Q$ as well as $g Q \rightarrow g Q$ scattering except close to thresholds. Thus when studying the dynamics of energetic heavy quarks in a QGP medium the spectral width of the degrees-of-freedom may be discarded. We have, furthermore, compared the cross sections from the DQPM with corresponding results from hard-thermal-loop (HTL) approaches. The HTL inspired models - essentially fixing the regulators by elementary vacuum cross sections and decay amplitudes instead of properties of the QGP at finite temperature - provide quite different results especially w.r.t. the temperature dependence of the $qQ$ and $gQ$ cross sections (in all settings). Accordingly, the transport properties of heavy quarks will be very different as a function of temperature when compared to DQPM results.
In this conference contribution, we discuss the influence of gluon-bremsstrahlung damping in hot, absorptive QCD matter on the heavy-quark radiation spectra. Within our Monte-Carlo implementation for the description of the heavy-quark in-medium propagation we demonstrate that as a consequence of gluon damping the quenching of heavy quarks becomes significantly affected at higher transverse momenta.
We determine the energy loss spectrum per time-interval of a relativistic charge traversing a dispersive medium. Polarization and absorption effects in the medium are modelled via a complex index of refraction. We find that the spectrum amplitude becomes exponentially damped due to absorption mechanisms. Taking explicitly the effect of multiple scatterings on the charge trajectory into account, we confirm results obtained in a previous work.
We study e^+e^- pair production in proton-proton and central Pb+Pb collisions at sqrt(s_NN)=2.76 TeV within two models: an extended statistical hadronization model (SHM) and the Parton-Hadron-String Dynamics (PHSD) transport approach. We find that the PHSD calculations roughly agree with the dilepton spectrum from hadronic sources with the 'cocktail' estimates from the statistical hadronization model matched to available data at LHC energies. The dynamical simulations within the PHSD show a moderate increase of the low mass dilepton yield essentially due to the in-medium modification of the rho-meson. Furthermore, pronounced traces of the partonic degrees of freedom are found in the PHSD results in the intermediate mass regime. The dilepton production from the strongly interacting quark-gluon plasma (sQGP) exceeds that from the semi-leptonic decays of open charm and bottom mesons. Additionally, we observe that a transverse momentum cut of 1 GeV/c further suppresses the relative contribution of the heavy meson decays to the dilepton yield, such that the sQGP radiation strongly dominates the spectrum for masses from 1 to 3 GeV, allowing a closer look at the electromagnetic emissivity of the partonic plasma in the early phase of Pb+Pb collisions.
We extend our recently advanced model on collisional energy loss of heavy quarks in a quark gluon plasma (QGP) by including radiative energy loss. We discuss the approach and present calculations for PbPb collisions at $\sqrt{s}=2.76 TeV$. The transverse momentum spectra, RAA, and the elliptic flow $v_2$ of heavy quarks have been obtained using the model of Kolb and Heinz for the hydrodynamical expansion of the plasma.
We extend our recently advanced model on collisional energy loss of heavy quarks in a quark gluon plasma (QGP) by including radiative energy loss. We discuss the approach and present first preliminary results. We show that present data on nuclear modification factor of non photonic single electrons hardly permit to distinguish between those 2 energy loss mechanisms.
Using the recently published model for the collisional energy loss of heavy quarks (Q) in a Quark Gluon Plasma (QGP), based on perturbative QCD (pQCD) with a running coupling constant, we study the interaction between heavy quarks and plasma particles in detail. We discuss correlations between the simultaneously produced $c$ and $\bar{c}$ quarks, study how central collisions can be experimentally selected, predict observable correlations and extend our model to the energy domain of the large hadron collider (LHC). We finally compare the predictions of our model with that of other approaches like AdS/CFT.