Assuming that in the hot dense matter produced in relativistic heavy-ion collisions, the energy density, entropy density, and pressure as well as the azimuthal and space-time rapidity components of the shear tensor are uniform in the direction transversal to the reaction plane, we derive a set of schematic equations from the Isreal-Stewart causal viscous hydrodynamics. These equations are then used to describe the evolution dynamics of relativistic heavy-ion collisions by taking the shear viscosity to entropy density ratio of $1/4π$ for the initial quark-gluon plasma (QGP) phase and of ten times this value for the later hadron-gas (HG) phase. Using the production rate evaluated with particle distributions that take into account the viscous effect, we study dilepton production in central heavy-ion collisions. Compared with results from the ideal hydrodynamics, we find that although the dilepton invariant mass spectra from the two approaches are similar, the transverse momentum spectra are significantly enhanced at high transverse momenta by the viscous effect. We also study the transverse momentum dependence of dileptons produced from QGP for a fixed transverse mass which is essentially absent in the ideal hydrodynamics, and find that this so-called transverse mass scaling is violated in the viscous hydrodynamics, particularly at high transverse momenta.
We present a first calculation of the dilepton yield and elliptic flow done with 3+1D viscous hydrodynamical simulations of relativistic heavy ion collisions at the top RHIC energy. A comparison with recent experimental data from the STAR collaboration is made.
The invariant mass spectrum and the elliptic flow of lepton pairs produced in relativistic heavy-ion collisions at RHIC are studied with viscous hydrodynamics. The effects of viscous corrections on dilepton observables are explored. The lepton pairs originating from charm quarks evolving in the viscous background are seen to be a good probe of quark energy loss and gain, as quantified by the dilepton spectrum and by the dilepton elliptic flow.
Starting from IP-Glasma initial conditions, we investigate the effects of bulk pressure on low mass dilepton production at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) energies. Though thermal dilepton $v_2$ is affected by the presence of both bulk and shear viscosity, whether or not these effects can be measured depends on the dilepton "cocktail" contribution to the the low mass dilepton $v_2$. Combining the thermal and "cocktail" dileptons, the effects of bulk viscosity on total dilepton $v_2$ is investigated.
A simple schematic model anchored on the notion of hadronic freedom inferred from hidden local symmetry in the vector manifestation, the infinite tower of vector mesons in holographic QCD and "stickiness" of $ππ$ interactions inferred from dispersion relations is used to describe the dileptons produced in relativistic heavy ion collisions at PHENIX/RHIC. It is shown that due to the near "blindness" of dileptons to Brown-Rho scaling, those dileptons with invariant mass less than $m_ρ=770$ MeV come mostly from pion-composites that we interpret as "transient $ρ$'s."
This work calculates the first correction to the leading order qq dilepton production rates due to shear viscosity in an expanding gas. The modified rates are integrated over the space-time history of a viscous hydrodynamic simulation of RHIC collisions. The net result is a {\em hardening} of $q_\perp$ spectrum with the magnitude of the correction increasing with invariant mass. We argue that a thermal description is reliable for invariant masses less than $M_{max}\approx(2τ_0 T_0^2)/(η/s)$. For reasonable values of the shear viscosity and thermalization time $M_{max}\approx 4.5$ GeV. Finally,…
Viscous modifications to the thermal distributions of quark-antiquarks and gluons have been studied in a quasi-particle description of the quark-gluon-plasma medium created in relativistic heavy-ion collision experiments. The model is described in terms of quasi-partons that encode the hot QCD medium effects in their respective effective fugacities. Both shear and bulk viscosities have been taken in to account in the analysis and the modifications to thermal distributions have been obtained by modifying the the energy momentum tensor in view of the non-trivial dispersion relations for the gluo…
We have analysed the invariant mass distribution of dileptons in S+W collisions at 200A GeV as measured by the HELIOS-3 collaboration at CERN SPS. Three scenarios were considered where the collision lead to formation of (i) the quark-gluon plasma, (ii) the ideal hot hadron gas and (iii) the viscous hot hadron gas. The space-time evolution was governed by the minimal extension of the Bjorken hydrodynamics. All the three scenarios indicate excess dileptons in the experiment.
Recently lots of efforts have been made to obtain the next to leading order and Landau-Pomeranchuk-Migdal corrections to the thermal dilepton emission rate in perturbative QCD. Here we apply these results to the plasma created in heavy ion collisions and see wether these corrections improve the comparison between theoretical calculations and experimental results for the invariant mass dependence of the dilepton emission rate. In particular, we simulate the quark-gluon plasma produced at RHIC and LHC using a 2+1-dimensional viscous hydro model. We compare our results to STAR experiment and comm…
In this contribution we study the effects of three transport coefficients of dissipative hydrodynamics on thermal dilepton anisotropic flow observables. The first two transport coefficients investigated influence the overall size and growth rate of shear viscous pressure, while the last transport coefficient governs the magnitude of net baryon number diffusion in relativistic dissipative fluid dynamics. All calculations are done using state-of-the-art 3+1D hydrodynamical simulations. We show that thermal dileptons are sensitive probes of the transport coefficients of dissipative hydrodynamics.
The in-medium spectral functions of $ρ$ and $ω$ mesons and the broadening of the nucleon resonances at finite baryon density are calculated self-consistently by combining a resonance dominance model for the vector meson production with an extended vector meson dominance model. The influence of the in-medium modifications of the vector meson properties on the dilepton spectrum in heavy-ion collisions is investigated. The dilepton spectrum is generated for the C+C reaction at 2.0$A$ GeV and compared with recent HADES Collaboration data. The collision dynamics is then described by the Tübingen re…
The first part of this thesis focuses on the production of thermal dileptons from a hadronic gas at finite temperature. The rates are calculated by an expansion in Pion density and constrained by broken chiral symmetry and vacuum correlation functions, many of which have been measured by experiment. We focus on emission processes having two Pions in the final state. Next, follows a separate discussion on viscous hydrodynamics and its effect on $p_\perp$ spectra and elliptic flow. A non-central hydrodynamic model of Au-Au collisions in 2+1 dimensions is simulated.Off-equilibrium corrections to …
Dileptons, as an electromagnetic probe, are crucial to study the properties of a Quark-Gluon Plasma (QGP) created in heavy ion collisions. We calculated the invariant mass spectra and the anisotropic emission of thermal dielectrons from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) energy $\sqrt{s_{NN}}=200$~GeV based on EPOS3. This approach provides a realistic (3+1)-dimensional event-by-event viscous hydrodynamic description of the expanding hot and dense matter with a very particular initial condition, and a large set of hadron data and direct photons (besides $v_{2}$ and $…
Dissipative spin hydrodynamics in Bjorken flow and thermal dilepton production
Birla Institute of Technology and Science Pilani（比拉理工学院皮拉尼分校）；National Institute of Science Education and Research（国家科学教育与研究机构）；Institute of Physics（物理研究所）
We study the thermal dilepton and photon production from relativistic heavy ion collisions in presence of viscosities by employing the recently developed second order dissipative hydrodynamic formulation estimated within a quasiparticle description of thermal QCD (Quantum Chromo-Dynamics) medium. The sensitivity of shear and bulk viscous pressures to the temperature dependence of relaxation time is analyzed within one dimensional boost invariant expansion of quark gluon plasma (QGP).The dissipative corrections to the phase-space distribution functions upto first order in gradients are obtained…
We derive relativistic viscous hydrodynamic equations invoking the generalized second law of thermodynamics for two different forms of the non-equilibrium single-particle distribution function. We find that the relaxation times in these two derivations are identical for shear viscosity but different for bulk viscosity. These equations are used to study thermal dilepton and hadron spectra within longitudinal scaling expansion of the matter formed in relativistic heavy-ion collisions. For consistency, the same non-equilibrium distribution function is used in the particle production prescription …
Study of thermal particle production is crucial to understand the space-time evolution of the fireball produced in high energy heavy-ion collisions. We consider thermal particle production within the framework of relativistic viscous hydrodynamics and employ recently obtained analytical solutions of higher-order viscous hydrodynamics with longitudinal Bjorken expansion to calculate the spectra of dileptons and photons. Using these analytical solutions, we constrain the allowed initial states by demanding positivity and reality of energy density throughout the evolution. Further, we compute the…
In simulations of high energy heavy ion collisions that employ viscous hydrodynamics, single particle distributions are distorted from their thermal equilibrium form due to gradients in the flow velocity. These are closely related to the formulas for the shear and bulk viscosities in the quasi-particle approximation. Distorted single particle distributions are now commonly used to calculate the emission of photons and dilepton pairs, and in the late stage to calculate the conversion of a continuous fluid to individual particles. We show how distortions of the single particle distribution funct…
Using the two-component model that includes charmonium production from initial nucleon-nucleon hard scattering and regeneration in the produced quark-gluon plasma, we study $J/ψ$ production in heavy ion collisions at SPS, RHIC and LHC. For the expansion dynamics of produced hot dense matter, we use a schematic viscous hydrodynamic model with the specific shear viscosity taken, respectively, to be twice and ten times the lower bound of $1/4π$ suggested by the Ads/CFT correspondence in the quark-gluon plasma and in the hadron gas. For the initial dissociation and the subsequent thermal decay of …
Relativistic fluid dynamics finds application in astrophysics, cosmology and the physics of high-energy heavy-ion collisions. In this thesis, we present our work on the formulation of relativistic dissipative fluid dynamics within the framework of relativistic kinetic theory. We employ the second law of thermodynamics as well as the relativistic Boltzmann equation to obtain the dissipative evolution equations. We present a new derivation of the dissipative hydrodynamic equations using the second law of thermodynamics wherein all the second-order transport coefficients get determined uniquely w…
