arXiv subjects

Mate Csanad

Publications and source records attributed to Mate Csanad.

At least 37 records · Page 2Linked to original sources

arXiv2018

Perturbative accelerating solutions of relativistic hydrodynamics

In ultra-relativistic collisions of heavy ions, the strongly interacting Quark Gluon Plasma (sQGP) is created. The fluid nature of the sQGP was one of the important discoveries of high energy heavy ion physics in the last decades. Henceforth the explosion of this matter may be described by hydrodynamical models. Besides numerical simulations, it is important to study the analytic solutions of the equations of hydrodynamics, as these enable us to understand the connection of the final and initial states better. In this paper we present a perturbative, accelerating solution of relativistic hydrodynamics, on top of a known class of solutions describing Hubble-expansion. We describe the properties of this class of perturbative solutions, and investigate a few selected solutions in detail.

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arXiv2017

Accelerating hydrodynamic description of pseudorapidity density and the initial energy density in p+p, Cu+Cu, Au+Au, and Pb+Pb collisions at RHIC and LHC

A known class of analytic, exact, accelerating solutions of prefect relativistic hydrodynamics with longitudinal acceleration is utilized to describe results on the pseudorapidity distributions for different collision systems. These results include $dN/dη$ measured in p+p, Cu+Cu, Au+Au, and Pb+Pb collisions at RHIC and LHC, in a broad centrality range. Going beyond the traditional Bjorken model, from the accelerating hydrodynamic description we determine the initial energy density and other thermodynamic quantities in those collisions.

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arXiv2017

Femtoscopy via Levy sources with PHENIX at RHIC

Charged pion two-particle correlation functions were measured in 0-30% centrality 200 GeV Au+Au collisions with the PHENIX experiment at RHIC. The measured correlation functions can be statistically well described based on the assumption of Levy-shaped source distributions. In this proceedings paper we present the Levy parameters of the measured correlation functions: correlation strength parameter lambda, Levy index alpha and Levy scale parameter R as a function of pair transverse mass mT, in 31 bins from 228 to 871 MeV, separately for positive and negative pion pairs. We discuss the physical interpretation of the mT dependence of the parameters.

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arXiv2017

Lévy femtoscopy with PHENIX at RHIC

In this paper we present the measurement of charged pion two-particle femtoscopic correlation functions in 200 GeV Au+Au collisions, in 31 average transverse mass bins, separately for positive and negative pion pairs. Lévy-shaped source distributions yield a statistically acceptable description of the measured correlation functions, with three physical parameters: correlation strength parameter lambda, Lévy index alpha and Lévy scale parameter R. The transverse mass dependence of these Lévy parameters is then investigated and their physical interpretation is also discussed, and the appearance of a new scaling variable is observed.

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arXiv2017

Initial energy density of p+p collisions at the LHC

Accelerating, exact, explicit and simple solutions of relativistic hydrodynamics allow for a simple description of highly relativistic p+p collisions. These solutions yield a finite rapidity distribution, thus they lead to an advanced estimate of the initial energy density of high energy collisions. We show that such an advanced estimate yields an initial energy density in $\sqrt{s}=7$ and 8 TeV p+p collisions at LHC around or above the critical energy density from lattice QCD, and a corresponding initial temperature above the critical temperature from QCD and the Hagedorn temperature. We also show, that several times the critical energy density may have been reached in high multiplicity events, hinting at a non-hadronic medium created in high multiplicity $\sqrt{s}=7$ and 8 TeV p+p collisions.

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arXiv2017

Higher-order anisotropies in the Blast-Wave Model - disentangling flow and density field anisotropies

We formulate a generalisation of the blast-wave model which is suitable for the description of higher order azimuthal anisotropies of the hadron production. The model includes anisotropy in the density profile as well as an anisotropy in the transverse expansion velocity field. We then study how these two kinds of anisotropies influence the single-particle distributions and the correlation radii of two-particle correlation functions. Particularly we focus on the third-order anisotropy and consideration is given to the averaging over different orientation of the event plane.

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arXiv2017

Initial energy density of $\sqrt{s}=$ 7 and 8 TeV p+p collisions at the LHC

Results from the RHIC and LHC experiments show, that in relativistic heavy ion collisions, a new state of matter, a strongly interacting perfect fluid is created. Accelerating, exact and explicit solutions of relativistic hydrodynamics allow for a simple and natural description of this medium. A finite rapidity distribution arises from these solutions, leading to an advanced estimate of the initial energy density of high energy collisions. These solutions can be utilized to describe various aspects of proton-proton collisions, as originally suggested by Landau. We show that an advanced estimate based on hydrodynamics yields an initial energy density in $\sqrt{s}=7$ and 8 TeV p+p collisions at LHC on the same order as the critical energy density from lattice QCD, and a corresponding initial temperature around the critical temperature from QCD and the Hagedorn temperature. The multiplicity dependence of the estimated initial energy density suggests that in high multiplicity pp collisions at the LHC, there is large enough initial energy density to create a non-hadronic perfect fluid.

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arXiv2016

Time evolution of the anisotropies of the hydrodynamically expanding sQGP

In high energy heavy ion collisions of RHIC and LHC, a strongly interacting quark gluon plasma (sQGP) is created. This medium undergoes a hydrodynamic evolution, before it freezes out to form a hadronic matter. The initial state of the sQGP is determined by the initial distribution of the participating nucleons and their interactions. Due to the finite number of nucleons, the initial distribution fluctuates on an event-by-event basis. The transverse plane anisotropy of the initial state can be translated into a series of anisotropy coefficients or eccentricities: second, third, fourth-order anisotropy etc. These anisotropies then evolve in time, and result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we investigate the time evolution of the anisotropies. With a numerical hydrodynamic code, we analyze how the speed of sound and viscosity influence this evolution.

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arXiv2015

Recent results on Bose-Einstein correlations by the PHENIX Experiment

Bose-Einstein momentum correlation functions of identical bosons reveal the shape and size of the (soft) particle emitting source of the given particle. The widths of these correlation functions are called HBT radii, named after Brown and Twiss who studied the angular diameter of stars via intensity correlations in their radio telescopes. Today, high energy physics experiments measure the HBT radii as a function of many parameters: particle type, transverse momentum, azimuthal angle, collision energy, collision geometry. In this paper we present results from the RHIC PHENIX experiment. These include the observation of strong azimuthal-angle dependence of the extracted Gaussian HBT radii, the similarities and differences between kaon and pion HBT radii. The key point of this paper is the application of Bose-Einstein correlations to the search for the critical point: how HBT radii would show the appearance of a first order phase transition, and what the non-monotonic collision energy dependence of the pion source tells us about the critical point; and how the non-Gaussian shape of correlation functions is related to one of the critical exponents.

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arXiv2014

Multipole solution of hydrodynamics and higher order harmonics

The time evolution of the medium created in heavy ion collisions can be described by hydrodynamical models. After expansion and cooling, the hadrons are created in a freeze-out. Their distribution describes the final state of this medium. In particular their azimuthal asymmetry, characterized by the elliptic flow coefficient $v_2$, is one of the most important observables in heavy ion physics. In recent years it has been revealed that if measuring relative to higher order event planes $Ψ_n$, higher order flow coefficients $v_n$ for $n>2$ can be measured. This is due to initial state fluctuations, previously not described by analytic solutions of relativistic hydrodynamics. In this paper we show the first solutions that utilize higher order asymmetries and thus yield realistic $v_n$ flow coefficients. It is a clear consequence of this that different flow patterns may lead to the same observed flow coefficients. We also compare our results to PHENIX measurements and determine a possible parameter set corresponding to these data.

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arXiv2013

Dilepton creation based on an analytic hydrodynamic solution

High-energy collisions of various nuclei, so called ``Little Bangs'' are observed at various experiments of heavy ion colliders. The time evolution of the strongly interacting quark-gluon plasma created in heavy ion collisions can be described by hydrodynamical models. After expansion and cooling, the hadrons are created in a freeze-out. Their distribution describes the final state of this medium. To investigate the time evolution one needs to analyze penetrating probes, such as direct photon or dilepton observables, as these particles are created throughout the evolution of the medium. In this paper we analyze an 1+3 dimensional analytic solution of relativistic hydrodynamics, and we calculate dilepton transverse momentum and invariant mass distributions. We investigate the dependence of dilepton production on time evolution parameters, such as emission duration and equation of state. Using parameters from earlier fits of this model to photon and hadron spectra, we compare our calculations to measurements as well. The most important feature of this work is that dilepton observables are calculated from an exact, analytic, 1+3D solution of relativistic hydrodynamics that is also compatible with hadronic and direct photon observables.

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arXiv2012

Equation of state and initial temperature of quark gluon plasma at RHIC

In gold-gold collisions of the Relativistic Heavy Ion Collider (RHIC) a perfect fluid of quarks, sometimes called the strongly interacting quark gluon plasma (sQGP) is created for an extremely short time. The time evolution of this fluid can be described by hydrodynamical models. After expansion and cooling, the freeze-out happens and hadrons are created. Their distribution reveals information about the final state of the fluid. To investigate the time evolution one needs to analyze penetrating probes, such as direct photon observables. Transverse momentum distributions of low energy direct photons were mesured in 2010 by PHENIX, while azimuthal asymmetry in 2011. These measurements can be compared to hydrodynamics to determine the equation of state and the initial temperature of sQGP. In this paper we analyze an 1+3 dimensional solution of relativistic hydrodynamics. We calculate momentum distribution, azimuthal asymmetry and momentum correlations of direct photons. Based on earlier fits to hadronic spectra, we compare photon calculations to measurements to determine the equation of state and the initial temperature of sQGP. We find that the initial temperature in the center of the fireball is 507+-12 MeV, while for the sound speed we get a speed of sound of 0.36+-0.02. We also estimate a systematic error of these results. We find that the measured azimuthal asymmetry is also not incompatible with this model, and predict a photon source that is significantly larger in the out direction than in the side direction.

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arXiv2012

Direct photon observables from hydrodynamics and implications on the initial temperature and EoS

The expansion of the strongly interacting quark gluon plasma (sQGP) created in Au+Au collisions at RHIC can be described by hydrodynamical models. Hadrons are created after a freeze-out, thus their distribution describes the final state of the evolution. The earlier stages can be analyzed via penetrating probes like photon observables. These were measured in 2010 and 2011 by the PHENIX experiment. Here we analyze an analytic, 1+3 dimensional perfect relativistic hydrodynamic solution and calculate hadron and photon observables, such as transverse momentum spectra, elliptic flow and correlation (HBT) radii. We find that our model is not incompatible with the data, not even with the direct photon elliptic flow. From fitting the data, we find that early temperatures of the sQGP were well above the quark-hadron transition temperature, in the hottest point, the center of the fireball the temperature may have reached 507+-12 MeV. The equation of state of this quark matter can be described by an average sound speed of 0.36+-0.02. We also predict a photon source that is significantly larger in the out direction than in the side direction.

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arXiv2011

Ultra-peripheral Au+Au collisions at PHENIX

Ultra-peripheral collisions (UPC) of heavy-ions involve long range electromagnetic interactions at impact parameters twice larger than the nuclear radius, where no nucleon-nucleon collisions occur. The first measurement of photoproduction of $J/ψ$ and of two-photon production of high-mass $e^+ e^-$ pairs in ultra-peripheral nucleus-nucleus interactions will be presented, using Au+Au data at $\sqrt{s_{_{NN}}}$ = 200 GeV. The measured cross sections at midrapidity are consistent with various theoretical predictions.

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arXiv2011

Femtoscopic results in Au+Au and p+p from PHENIX at RHIC

Ultra-relativistic gold-gold and proton-proton collisions are investigated in the experiments of the Relativistic Heavy Ion Collider (RHIC). In the last several years large amount of results were revealed about the matter created in these collisions. The latest PHENIX results for femtoscopy and correlations are reviewed in this paper. Bose-Einstein correlations of charged kaons in 200 GeV Au+Au collisions and of charged pions in 200 GeV p+p collisions are shown. They are both compatible with previous measurements of charged pions in gold-gold collisions, with respect to transverse mass or number of participants scaling.

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arXiv2011

A method of eta' decay product selection to study partial chiral symmetry restoration

In case of chiral U_A(1) symmetry restoration the mass of the eta' boson (the ninth, would-be Goldstone boson) is decreased, thus its production cross section is heavily enhanced. The eta' decays (through one of its decay channels) into five pions. These pions will not be correlated in terms of Bose-Einsten correlations, thus the production enhancement changes the strength of two-pion correlation functions at low momentum. Preliminary results strongly support the mass decrease of the eta' boson. In this paper we propose a method to select pions coming from eta' decays. We investigate the efficiency of the proposed kinematical cut in several collision systems and energies with several simulators. We prove that our method can be used in all investigeted collision systems.

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arXiv2011

Initial temperature and EoS of quark matter from direct photons

The time evolution of the quark gluon plasma created in gold-gold collisions of the Relativistic Heavy Ion Collider (RHIC) can be described by hydrodynamical models. Distribution of hadrons reflects the freeze-out state of the matter. To investigate the time evolution one needs to analyze penetrating probes, such as direct photon spectra. Distributions of low energy photons was published in 2010 by PHENIX. In this paper we analyze a 3+1 dimensional solution of relativistic hydrodynamics and calculate momentum distribution of direct photons. Using earlier fits of this model to hadronic spectra, we compare photon calculations to measurements and find that the initial temperature of the center of the fireball is at least 519+-12 MeV, while for the equation of state we get c_s= 0.36+-0.02.

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arXiv2011

Observables from a solution of 1+3 dimensional relativistic hydrodynamics

In this paper we analyze a 1+3 dimensional solution of relativistic hydrodynamics. We calculate momentum distribution and other observables from the solution and compare them to measurements from the Relativistic Heavy Ion Collider (RHIC). We find that the solution we analyze is compatible with the data. In the last several years many numerical models were tested, but it is the first time that an exact, parametric, 1+3 dimensional relativistic solution is compared to data.

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