Dilepton production as a measure of QGP thermalization time
Mauricio Martinez, Michael Strickland
备注：
4 pages, 3 figures, talk given at the 20th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM 2008), Jaipur, India, 4-10 Feb 2008
We discuss dilepton production from a quark-gluon plasma which has a time-dependent anisotropy in momentum space. A phenomenological model for the hard momentum scale, p_hard(tau) and the plasma anisotropy parameter, xi(tau), is presented. The model interpolates between early-time 1+1 free streaming behavior (tau << tau_iso) and late-time ideal 1+1 hydrodynamical behavior (tau >> tau_iso). Using this model, we find that the dilepton rate arising from electromagnetic annihilations of quarks in the kinematic range 3 <p_T< 8 GeV is sensitive to the assumed isotropization time of the system, tau_iso. Therefore high-energy dilepton production can be used to probe the degree of momentum-space isotropy of a quark-gluon plasma produced in relativistic heavy ion collisions and the time of onset of hydrodynamic expansion of the QGP.
The rate of the emission of the high energy low-mass dileptons from the QGP is found in the first nonvanishing order with respect to strong coupling. We base on the real-time kinetic approach [2] without an explicit assumption about a complete thermal equilibrium in the emitting system. For the class of the partons distributions which may simulate that of the "hot glue scenario"[1] the rate of emission is found analytically . ( Figures can be obtained from the author )
The rate of emission of heavy dileptons from QGP is found without an assumption of its complete thermal equilibrium. We base on the real-time quantum field kinetic approach [1] and use the expansion up to the second order with respect to strong coupling constant $g$. The final answer is not free from the collinear singularities and we show that this is the actual issue. As a result the main contribution to the rate of the heavy dileptons production at $M/T \sim 10$ comes from the process $q\bar{q}g\rightarrow γ^{*}$. ( Figures can be obtained from the author )
We study the \textit{non-ideal} effects arising due to viscosity (both bulk and shear), equation of state ($ε\neq 3P$) and cavitation on thermal dilepton production from QGP at RHIC energies. We calculate the first order corrections to the dilepton production rates due to shear and bulk viscosities. Ignoring the cavitation can lead to a wrong estimation of dilepton spectra. We show that the shear viscosity can enhance the thermal dilepton spectra whereas the bulk viscosity can suppress it. We present the combined effect of bulk and shear viscosities on the dilepton spectra.
A fireball of QGP is evoluted at temperature dependent chemical potential by a statistical model in the pionic medium. We study the dilepton emission rate at temperature dependent chemical potential (TDCP) from such a fireball of QGP. In this model, we take the dynamical quark mass as a finite value dependence on temparature and parametrization factor of the QGP evolution. The temperature and factor in quark mass enhance in the growth of the droplets as well as in the dilepton emission rates. The emission rate from the plasma shows dilepton spectrum in the intermediate mass region (IMR) of (1.…
Relativistic heavy-ion collisions produce a hot and dense thermalized medium, that is expected to emit thermal radiation in form of dileptons. These dileptons are not affected by the strong force and are therefore a clean probe for the possible creation of a Quark Gluon Plasma (QGP). However, electroweak decays of open-charm mesons are expected to induce a substantial background in the invariant mass region between the $ϕ$ and $J/Ψ$ peak ($1\,\text{GeV} \lesssim M_{\ell^+ \ell^-} \lesssim 3 \,\text{GeV}$) of the thermal QGP radiation. To evaluate this background radiation we apply a Langevin a…
We study the thermalization process of charm quarks in hot and dense matter. The diffusion of heavy quarks is calculated via a Langevin equation, both for a static medium as well as a QGP medium generated by a (3+1)D hydrodynamic model. We define two criteria for the thermalization of the heavy quarks, and observe thermalization times that are longer than the lifetime of the QGP phase for reasonable values of the diffusion constant.
We calculate the production of dileptons and photons in the presence of a nontrivial Polyakov loop in QCD. This is applicable to the semi-Quark Gluon Plasma (QGP), at temperatures above but near the critical temperature for deconfinement. The Polyakov loop is small in the semi-QGP, and near unity in the perturbative QGP. Working to leading order in the coupling constant of QCD, we find that there is a mild enhancement, ~ 20%, for dilepton production in the semi-QGP over that in the perturbative QGP. In contrast, we find that photon production is strongly suppressed in the semi-QGP, by about an…
We consider the thermal production of dileptons and photons at temperatures above the critical temperature in QCD. We use a model where color excitations are suppressed by a small value of the Polyakov loop, the semi Quark-Gluon Plasma (QGP). Comparing the semi-QGP to the perturbative QGP, we find a mild enhancement of thermal dileptons. In contrast, to leading logarithmic order in weak coupling there are far fewer hard photons from the semi-QGP than the usual QGP. To illustrate the possible effects on photon and dileptons production in heavy ion collisions, we integrate the rate with a realis…
I discuss how the initial conditions for QGP-production in ultrarelativistic heavy ion collisions at the LHC and RHIC can be computed from perturbative QCD.
The QGP that might be created in ultrarelativistic heavy-ion collisions is expected to radiate thermal dilepton radiation. However, this thermal dilepton radiation interferes with dileptons originating from hadron decays. In the invariant mass region between the $ϕ$ and $J/Ψ$ peak ($1\,$GeV$\lesssim M_{\ell^+ \ell^-} \lesssim 3 \,$GeV) the most substantial background of hadron decays originates from correlated D$\bar{\mathrm{D}}$-meson decays. We evaluate this background using a Langevin simulation for charm quarks. As background medium we utilize the well-tested UrQMD-hybrid model. The requir…
Production rates of dileptons and photons from the quark-gluon (QGP) phase are calculated taking into account effects of confinement and spontaneous chiral symmetry breaking (χSB) not far from the transition temperature $T_c$. We find that the production rates of dileptons with large momenta and of photons originating from the QGP around $T_c$ are suppressed by the χSB effect. We also discuss to what extent information about details of the chiral transition, such as its characteristic temperature range and the steepness of the crossover, are reflected in these quantities.
We study the lightlike and timelike R-current correlators in the AdS-Vaidya spacetime, which are associated with the production of prompt photons and dileptons from a nonequilibrium, rapidly thermalizing, and strongly coupled plasma in the AdS/CFT correspondence. In particular, we focus on the photon production. We find that the amplitude of the photon-emission spectrum increases during the thermalization of the medium. Also, the time-dependent emission rate for hard photons has an oscillatory pattern and thermalizes faster than soft photons.
In this paper we propose to use the measurement of the thermal Quark-Gluon Plasma (QGP) dilepton spectra in the Intermediate Mass Region (IMR) of heavy-ion collisions, as a new method to search for GeV-scale dark gauge bosons (gamma' or Z'). Such light mediators are a common feature of light (i.e. low mass) dark matter scenarios, which have been invoked to explain puzzling signals in dark matter indirect and direct detection experiments. First we show that a light gamma' or Z' will generate a resonant enhancement of the dilepton spectrum produced thermally by the QGP, at an energy correspondin…
Dileptons are considered as one of the cleanest signals of the quark-gluon plasma (QGP), however, the QGP radiation is masked by many 'background' sources from either hadronic decays or semileptonic decays from correlated charm pairs. In this study we investigate the relative contribution of these channels in heavy-ion collisions from $\sqrt{s_{\rm NN}}=$ 8 GeV to 5 TeV with a focus on the competition between the thermal QGP radiation and the semileptonic decays from correlated $D-$meson pairs. As a 'tool' we employ the parton-hadron-string dynamics (PHSD) transport approach to study dilepton …
I review our current understanding of the processes driving the thermalization and isotropization of the quark gluon plasma (QGP) created in ultrarelativistic heavy ion collisions (URHICs). I begin by discussing the phenomenological evidence in favor of the creation of a thermal but momentum-space anisotropic QGP in URHICs. I then discuss the degree of isotropization using viscous (dissipative) hydrodynamics, weak-coupling approaches to QGP dynamics, and strong-coupling approaches to QGP dynamics. Finally, I report on recent progress in the area of real-time non-abelian gauge field simulations…
Dilepton production from the quark-gluon plasma (QGP) phase of ultra-relativistic heavy-ion collisions is computed using the leading-order (3+1)-dimensional anisotropic hydrodynamics. It is shown that high-energy dilepton spectrum is sensitive to the initial local-rest-frame momentum-space anisotropy of the QGP. Our findings suggest that it may be possible to constrain the early-time momentum-space anisotropy in relativistic heavy-ion collisions using high-energy dilepton yields.
We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, p_hard(tau), and plasma anisotropy parameter, xi(tau), is constructed which interpolates between free streaming behavior at early times (tau << tau_iso) and ideal hydrodynamic behavior at late times (tau >> tau_iso). We show that high-energy dilepton production is sensitive to the assumed plasma isotropization time, tau_iso, and can therefore be used to experimentally determine the time of onset for hydrodynamic expan…
We estimate the thermalization time in two colliding shock waves holographic model of heavy-ion collisions. For this purpose we model the process by the Vaidya metric with a horizon defined by the trapped surface location. We consider two bottom-up AdS/QCD models that give, within the colliding shock waves approach, the dependence of multiplicity on the energy compatible with RHIC and LHC results. One model is a bottom-up AdS/QCD confining model and the other is related to an anisotropic thermalization. We estimate the thermalization time and show that increasing the confining potential decrea…
We obtain the thermal photon and dilepton production rates in a strongly coupled quark-gluon plasma (QGP) at both zero and nonzero baryon chemical potential using a bottom-up Einstein-Maxwell-Dilaton (EMD) holographic model that is in good quantitative agreement with the thermodynamics of $(2+1)$-flavor lattice QCD around the crossover transition for baryon chemical potentials up to 400 MeV, which may be reached in the beam energy scan (BES) at RHIC. We find that increasing the temperature $T$ and the baryon chemical potential $μ_B$ enhances the peak present in both spectra. We also obtain the…
We investigate the temperature dependence of the thermal dilepton rate and the electrical conductivity of the gluon plasma at temperatures of $1.1T_c$, $1.3T_c$ and $1.5T_c$ in quenched QCD. Making use of non-perturbatively clover-improved Wilson valence quarks allows for a clean extrapolation of the vector meson correlation function to the continuum limit. We found that the vector correlation function divided by $T^3$ is almost temperature independent in the current temperature window. The spectral functions are obtained by $χ^2$ fitting of phenomenologically inspired Ansätze for the spectral…
Specific results of the computer simulation of dilepton production from expanding pion gas created in Pb+Pb 160 GeV/n collisions are presented. Azimuthal asymmetry of dilepton pairs in non-central collisions and interesting shape of the rapidity distribution of dilepton pairs are predicted. These results are understood on theoretical level as a consequence of momentum and space asymmetries in the initial state of pion gas without any assumption of thermalization. Implication on the production of dileptons in pre-hadronic phase of HIC is drawn.
Electromagnetic radiation from the quark-gluon plasma (QGP) is an important observable to be considered in heavy ion collision experiments. I will provide an update on recent advancements from perturbation theory and quenched lattice simulations. The resummed next-to-leading order (NLO) emission rate has recently been decomposed into transverse and longitudinal components, and extended to non-zero baryon chemical potential. The associated spectral function has also been tested against the Euclidean correlator, for continuum-extrapolated lattice data (at $μ_{\rm B}=0$).
Hydrodynamical modeling of heavy ion collisions at RHIC suggests that the quark-gluon plasma (QGP) "thermalizes" in a remarkably short time scale, about 0.6 fm/c. We argue that this should be viewed as indicating fast isotropization, but not necessarily complete thermalization, of the non-equilibrium QGP. Non-Abelian plasma instabilities can drive local isotropization of an anisotropic QGP on a time scale which is faster than ordinary perturbative scattering processes. As a result, we argue that theoretical expectations based on weak coupling analysis are not necessarily in conflict with hydro…
The vacuum parton creation in quickly varying external fields is studied at the time scale of order 1 fm/$c$ typical for the quark-gluon plasma formation and thermalization. To describe the pre-equilibrium evolution of the system the transport kinetic equation is employed. It is shown that the dynamics of production process at times comparable with particle inverse masses can deviate considerably from that based on classical Schwinger-like estimates for homogeneous and constant fields. One of the effects caused by non-stationary chromoelectric fields is the enhancement of the yield of $s\bar{s…
We study the dynamics of open charm production and the dilepton radiation of the semi-leptonic decays of correlated $D\bar D$ pairs versus the quark-gluon plasma (QGP) radiation and hadronic sources in relativistic heavy-ion collisions. Our study is based on the Parton-Hadron-String Dynamics (PHSD) transport approach employing a non-perturbative QCD description of the strongly interacting quark-gluon plasma (sQGP) in terms of dynamical quasiparticles and the EoS based on lattice QCD. We compare the PHSD results for charm observables with the calculations from BAMPS (Boltzmann Approach to Multi…
The collective behavior of hadrons and of electromagnetic radiation in heavy-ion collisions has been widely used to study the properties of the the Quark-Gluon Plasma (QGP). Indeed this collectivity, as measured by anisotropic flow coefficients, can be used to constrain the transport properties of QGP. The goal of this contribution is to investigate the influence of the specific bulk viscosity ($ζ/s$) on dilepton production, both at Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. We explore the sensitivity of dileptons to dynamical features that bulk viscosity …
We propose a novel relation between the low-mass enhancement of dielectrons observed at PHENIX and transport coefficients of QGP such as the charge diffusion constant $D$ and the relaxation time $τ_{\rm J}$. We parameterize the transport peak in the spectral function using the second-order relativistic dissipative hydrodynamics by Israel and Stewart. Combining the spectral function and the full (3+1)-dimensional hydrodynamical evolution with the lattice EoS, theoretical dielectron spectra and the experimental data are compared. Detailed analysis suggests that the low-mass dilepton enhancement …
We perform SU(3) Lattice Gauge Theory simulations of the deconfinement transition attempting to mimic conditions encountered in heavy ion collisions. Specifically, we perform a sudden temperature quench across the deconfinement temperature, and follow the response of the system in successive simulation sweeps under spatial lattice expansion and temperature fall-off. In measurements of the Polyakov loop and structure functions a robust strong signal of global instability response is observed through the exponential growth of low momentum modes. Development of these long range modes isotropizes …
Charm- and bottom-quark rescattering in a Quark-Gluon Plasma (QGP) is investigated with the objective of assessing the approach towards thermalization. Employing a Fokker-Planck equation to approximate the collision integral of the Boltzmann equation we augment earlier studies based on perturbative parton cross sections by introducing resonant heavy-light quark interactions. The latter are motivated by recent QCD lattice calculations which indicate the presence of "hadronic" states in the QGP. We model these states by colorless (pseudo-) scalar and (axial-) vector D- and B-mesons within a heav…
We determine the out-of-equilibrium production rate of dileptons at rest in strongly coupled N=4 Super Yang-Mills plasma using the AdS/CFT correspondence. Thermalization is achieved via the gravitational collapse of a thin shell of matter in AdS_5 space and the subsequent formation of a black hole, which we describe in a quasistatic approximation. Prior to thermalization, the dilepton spectral function is observed to oscillate as a function of frequency, but the amplitude of the oscillations decreases when thermal equilibrium is approached. At the same time, we follow the flow of the quasinorm…
We calculate the yield of lepton pair production from jet-plasma interaction where the plasma is anisotropic in momentum space. We compare both the $M$ and $p_T$ distributions from such process with the Drell-Yan contribution. It is observed that the invariant mass distribution of lepton pair from such process dominate over the Drell-Yan up to $3$ GeV at RHIC and up to $10$ GeV at LHC. Moreover, it is found that the contribution from anistropic quark gluon plasma (AQGP) increases marginally compared to the isotropic QGP. In case of $p_T$-distribution we observe an increase by a factor of $3-4$…
We calculate the rapidity dependence of leading-order medium dilepton yields resulting from a quark-gluon plasma which has a local time-dependent anisotropy in momentum space. We present a phenomenological model which includes temporal evolution of the plasma anisotropy parameter, xi, and the hard momentum scale, p_hard. Our model interpolates between 1+1 dimensional collisionally-broadened expansion at early times and 1+1 dimensional ideal hydrodynamic expansion at late times. Using our model, we find that at LHC energies, forward high-energy medium dilepton production would be suppressed by …
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 tim…
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 $…
Heavy-ion colliders have revealed the process of "fast thermalization". This experimental breakthrough has led to new theoretical tools to study the thermalization process at both weak and strong coupling. We apply this to the reheating epoch of inflationary cosmology, and the formation of a cosmological quark gluon plasma (QGP). We compute the thermalization time of the QGP at reheating, and find it is determined by the energy scale of inflation and the shear viscosity to entropy ratio $η/s$; or equivalently, the tensor-to-scalar ratio and the strong coupling constant at the epoch of thermali…
The properties of thermal dilepton production from heavy-ion collisions in the RHIC energy regime are evaluated for invariant masses ranging from 0.5 to 3 GeV. Using an expanding thermal fireball to model the evolution through both quark-gluon and hadronic phases various features of the spectra are addressed. In the low-mass region, due to an expected large background, the focus is on possible medium modifications of the narrow resonance structures from $ω$ and $ϕ$ mesons, whereas in the intermediate-mass region the old idea of identifying QGP radiation is reiterated including effects of chemi…
In ultrarelativistic nuclear collisions heavy quarks are produced out of thermal equilibrium in the very early stage of the reaction and their thermalization time was expected to be considerably larger than that of light quarks. On the other hand, a strongly-interacting QGP can be envisaged in the heavy quark sector due to the presence of heavy-light hadron-like resonances in the QGP for temperatures up to $\sim$$2 T_{C}$. We investigate the consequences of such states employing a relativistic Langevin simulation. Hadronization is modeled by a coalescence-fragmentation scheme. We present the p…
We discuss the latest theoretical results on direct photon and dilepton production from relativistic heavy-ion collisions. While the dilepton spectra at low invariant mass show in-medium effects like a collisional broadening of the vector meson spectral functions, the dilepton yield at high invariant masses (above 1.1 GeV) is dominated by QGP contributions for central heavy-ion collisions at relativistic energies. The present status of the photon $v_2$ "puzzle" - a large elliptic flow $v_2$ of the direct photons experimentally observed at RHIC and LHC energies - is also addressed. The role of …
Electromagnetic tomography of radial flow in the quark-gluon plasma
Department of Physics, University of California, Berkeley（加州大学伯克利分校物理系）；Nuclear Science Division, Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室核科学部）；Department of Physics, The Ohio State University（俄亥俄州立大学物理系）
The production of charmonium in heavy-ion collisions is investigated based on Boltzmann-type transport model for charmonium evolution and langevin equation for charm quark evolution. Charmonium suppression and regeneration in both quark-gluon plasma (QGP) and hadron phase are considered. Charm quarks are far from thermalization, and regeneration of charmonium in QGP and hadron gas is neglectable at SPS and FAIR. At peripheral collisions, charmonium suppression with hadron gas explains the experimental data well. But at central collisions, additional suppression from deconfined matter (QGP) is …
We calculate leading-order dilepton yields from a quark-gluon plasma which has a time-dependent anisotropy in momentum space. Such anisotropies can arise during the earliest stages of quark-gluon plasma evolution due to the rapid longitudinal expansion of the created matter. A phenomenological model for the proper time dependence of the parton hard momentum scale, p_hard, and the plasma anisotropy parameter, xi, is proposed. The model describes the transition of the plasma from a 0+1 dimensional collisionally-broadened expansion at early times to a 0+1 dimensional ideal hydrodynamic expansion …
We present the complete physical picture for the evolution of a high-energy jet propagating through a weakly-coupled quark-gluon plasma (QGP) by analytical and numerical investigation of thermalization of the soft components of the jet. Our results support the following physical picture: the leading particle emits a significant number of mini-jets which promptly evolve via multiple branching and thus degrade into a myriad of soft gluons, with energies of the order of the medium temperature $T$. Via elastic collisions with the medium constituents, these soft gluons relax to local thermal equili…
We discuss the emission of high momentum lepton pairs (p_T>4 GeV) with low invariant masses (M << p_T) in central Au+Au collisions at RHIC (\sqrt{s_{NN}}=200 GeV). The spectra of dileptons produced through interactions of quark and antiquark jets with the quark-gluon plasma (QGP) have been calculated. Annihilation and Compton scattering processes, as well as processes benefitting from collinear enhancement, including Landau-Pomeranchuk-Migdal (LPM) effects, are calculated and convolved with a one dimensional hydrodynamic expansion. The jet-induced contributions are compared to thermal dilepton…
After the discovery of the Quantum Chromodynamics (QCD), many experimental and theoretical efforts have been made to investigate physics issues involved in ultra relativistic heavy-ion collisions. The fundamental goal of this work is to present a short guide of the underlying theory of strong interactions with emphasis on the light vector mesons based on the exceptional work of R.Rapp and J.Wambach. Today widely believed that deconfinement and chiral symmetry restoration probably takes place in a hot and dense hadronic medium as this produced at these collisions. We focus at the place where th…
While it is commonly believed that there is a {\it direct} transition from the hadronic to a quark gluon phase at high temperature, it would be prejudicial to rule out a sequence of dynamically generated intermediate scales. Using as guide, an effective lagrangian with unconfined gluons and constituent quarks, interacting with a chiral multiplet, we examine a scenario in which the system undergoes first-order transitions at $ T_{comp}$, the compositeness scale of the pions, at $T_χ$, the scale for spontaneous chiral symmetry breaking, and at $T_c$, the confinement temperature. We find that at …
Dilepton production in In+In collisions at 158 AGeV is studied within the microscopic parton-hadron-string dynamics (PHSD) transport approach that incorporates explicit partonic degrees-of-freedom, dynamical hadronization as well as the more familiar hadronic dynamics in the final reaction stages. A comparison to the data of the NA60 Collaboration shows that the measured dilepton yield is well described by including the collisional broadening of vector mesons, while simultaneously accounting for the electromagnetic radiation of the strongly coupled quark-gluon plasma (sQGP) via off-shell quark…
Thermalization and collective flow of charm (c) and bottom (b) quarks are evaluated from elastic parton scattering via "D"- and "B"-meson resonances in an expanding, strongly interacting quark-gluon plasma at RHIC. Pertinent drag and diffusion coefficients are implemented into a relativistic Langevin simulation to compute transverse-momentum spectra and azimuthal flow asymmetries (v_2) of c- and b-quarks. Upon hadronization (including coalescence and fragmentation) and semileptonic D- and B-decays, the resulting electron spectra (R_{AA} and v_2) are compared to recent RHIC data.
At high temperatures and densities the nuclear matter undergoes a phase transition to a new state of matter called quark gluon plasma (QGP). This new state of matter which existed in the universe after a few microsecond of the big bang can be created in the laboratory by colliding two nuclei at relativistic energies. In this presentation we will discuss how the the properties of QGP can be extracted by analyzing the spectra of photons, dileptons and heavy flavours produced in nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies.
We attempt to understand the low-mass dielectron enhancement observed by PHENIX Collaboration at Relativistic Heavy Ion Collider (RHIC) by transport peak in the spectral function. On the basis of the second-order formalism of relativistic dissipative hydrodynamics, we parameterize the spectral function in low-frequency and long-wavelength region by two transport coefficients, electric diffusion coefficient $D$ and relaxation time $τ_{\rm J}$, and compared our theoretical dielectron spectra with the experimental data. We study spectrum of dielectrons produced in relativistic heavy ion collision…
We study the variation of elliptic flow of thermal dileptons with transverse momentum and invariant mass of the pairs for Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The dilepton productions from quark gluon plasma (QGP) and hot hadrons have been considered including the spectral change of light vector mesons in the thermal bath. The space time evolution has been carried out within the frame work of 2+1 dimensional ideal hydrodynamics with lattice+hadron resonance gas equation of state. We find that a judicious selection of invariant mass(M) and transverse momentum (p_T) windows can be use…
