Properties Of Quark-gluon Plasma Research Articles

Measurement of azimuthal flow of soft and high-pT charged particles in 5.02 TeV Pb+Pb collisions with the ATLAS detector

The experimental data collected by the ATLAS experiment during the 2015 heavy ion LHC run offers new opportunities to study properties of Quark-Gluon Plasma at unprecedented high temperatures and densities. Study of the azimuthal anisotropy of produced particles not only constrains our understanding of initial conditions of nuclear collisions and soft particle collective dynamics, but also sheds light on jet-quenching phenomena via measurement of flow harmonics at high transverse momenta. A new ATLAS measurement of elliptic flow and higher-order Fourier harmonics of charged particles in Pb+Pb collisions at sNN=5.02 TeV in a wide range of transverse momenta, pseudorapidity (|η|<2.5) and collision centrality is presented. These measurements are based on the Scalar Product and Two Particle Correlation methods. The results obtained are compared with experimental results at lower collision energies.

Phenomenological Review on Quark–Gluon Plasma: Concepts vs. Observations

In this review, we present an up-to-date phenomenological summary of research developments in the physics of the Quark–Gluon Plasma (QGP). A short historical perspective and theoretical motivation for this rapidly developing field of contemporary particle physics is provided. In addition, we introduce and discuss the role of the quantum chromodynamics (QCD) ground state, non-perturbative and lattice QCD results on the QGP properties, as well as the transport models used to make a connection between theory and experiment. The experimental part presents the selected results on bulk observables, hard and penetrating probes obtained in the ultra-relativistic heavy-ion experiments carried out at the Brookhaven National Laboratory Relativistic Heavy Ion Collider (BNL RHIC) and CERN Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) accelerators. We also give a brief overview of new developments related to the ongoing searches of the QCD critical point and to the collectivity in small (p + p and p + A) systems.

Hadrons anti-hadrons production in reaction planes in relativistic heavy ion collisions on two common event generators: HIJING and HYDJET++

The study of hadron production in heavy ion collisions provides the researcher with valuable techniques to investigate the properties of quark gluon plasma (QGP). The hadron and anti-hadron production in the reaction plane, at relativistic heavy ion collisions are studied for the energy per nucleon available at the RHIC-STAR experiment of ∘ _(sNN) = 200 GeV. In order to test the models used for hadron and anti-hadron production, two common event generators (HIJING1.35 and HYDJET+ +2.0.2), established on Monte Carlo techniques, are discussed for hadron and anti-hadron production in the reaction plane for heavy ions 197Au79 −197Au79 collisions at √ ___SNN = 200 GeV. We find that, HYDJET+ + 2.0.2 is more realistic in comparing the results of simulations with those of the experimental data published by the STAR-Collaboration.

Hadrons anti-hadrons production in reaction planes in relativistic heavy ion collisions on two common event generators: HIJING and HYDJET++

The study of hadron production in heavy ion collisions provides the researcher with valuable techniques to investigate the properties of quark gluon plasma (QGP). The hadron and anti-hadron production in the reaction plane, at relativistic heavy ion collisions are studied for the energy per nucleon available at the RHIC-STAR experiment of ∘ _( s NN ) = 200 GeV. In order to test the models used for hadron and anti-hadron production, two common event generators ( HIJING 1.35 and HYDJET + +2.0.2), established on Monte Carlo techniques, are discussed for hadron and anti-hadron production in the reaction plane for heavy ions 197 Au 79 − 197 Au 79 collisions at √ ___ S NN = 200 GeV. We find that, HYDJET + + 2.0.2 is more realistic in comparing the results of simulations with those of the experimental data published by the STAR-Collaboration.

Meson production in Au+Au collisions at in STAR

In this article, we report the measurements of the nuclear modification factor (RAA) and elliptic flow (v2) for in Au+Au collisions at from the STAR experiment. These results are compared with the results of other open charm mesons to study the hadronization mechanism of the charm quarks and disentangle the transport properties of quark-gluon plasma and hadronic phase [1]. We found that the nuclear modification factor for Ds are systematically higher than unity and D0 RAA. The ratio of Ds/D0 for 10-40% central Au+Au collisions is also higher than that in p+p collisions as predicted by PYTHIA. The Ds/D0 ratio is also compared to that in Pb+Pb collisions at measured by the ALICE experiment. Our results indicate an enhancement of Ds meson production in Au+Au collisions.

Evidences of quark-gluon plasma formation in central nuclear collisions

Due to the absence of clear and unambiguous theoretical signals of the deconfinement transition from hadron matter to quark-gluon plasma (QGP) the experimental searches of QGP formation are based the analysis of various irregularities in the collision energy dependence of thermodynamic and hydrodynamic quantities. Here we present several remarkable irregularities at chemical freeze-out (CFO) of hadrons which are found using an advanced version of the hadron resonance gas model (HRGM). Among them are the sharp peaks of the trace anomaly and baryonic density which are seen at the center of mass energies √sNN = 4.9 GeV and √sNN = 9.2 GeV, and the two sets of highly correlated quasi-plateaus in the collision energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon which we found at the center of mass energies 3.8-4.9 GeV and 7.6-10 GeV. In addition we found a significant change of slope of the hadron yield ratios and , when the center of mass collision energy increases from 4.3 GeV to 4.9 GeV and from 7.6 GeV to 9.2 GeV [1]. The increase of slopes of these ratios at the collision energy interval 4.3-4.9 GeV is accompanied by a dramatic growth of resonance decays at CFO. We argue that such a strong correlation between the previously found irregularities and an enhancement of strangeness production can serve as the quark-gluon plasma formation signature. Hence, we conclude that a dramatic change of the system properties seen in the narrow collision energy range √sNN = 4.3-4.9 GeV may open entirely new possibilities for experimental studies of QGP properties at NICA JINR and FAIR GSI accelerators.

Toward an understanding of the RAA and v2 puzzle for heavy quarks

One of the primary aims of the ongoing nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies is to create a Quark Gluon Plasma (QGP). The Heavy Quarks (HQ) constitutes a unique probe of the QGP properties. Both at RHIC and LHC energies a puzzling relation between the nuclear modification factor RAA(pT) and the elliptic flow v2(pT) related to heavy quark has been observed which challenged all the existing models.We discuss how the temperature dependence of the heavy quark drag coefficient can address for a large part of such a puzzle. We have considered four different models to evaluate the temperature dependence of drag and diffusion coefficients propagating through a quark gluon plasma (QGP). All the four different models are set to reproduce the same RAA(pT) experimentally observed at RHIC energy. We have found that for the same RAA(pT) one can generate 2–3 times more v2 depending on the temperature dependence of the heavy quark drag coefficient.

STAR Overview of Hard Probe Observables

Parton energy loss, quarkonium sequential melting and particle production from electromagnetic interactions are tools to study Quark Gluon Plasma properties. The STAR detector, with large acceptance at mid-rapidity, excellent particle identification and wide transverse momentum coverage, is able to study these probes in details. In Hard Probes 2015, the STAR collaboration reported measurements of reconstructed jets, heavy-flavor physics, di-lepton production and the performance of new detectors in seven presentations and one poster. Given the rich results from STAR, this overview report will focus on a few selected results on jets and ϒ measurements in Au+Au collisions at sNN=200 GeV, J/ψ production in p+p collisions at sNN=500 GeV, and the di-electron spectrum in the low mass region from the Beam Energy Scan – Phase I.

Electrical conductivity of (an-)isotropic quark gluon plasma

In this article, we have calculated one of the transport coefficient viz. electrical conductivity of the quark gluon plasma (QGP) phase which exhibits an anisotropy in the momentum space. Relativistic Boltzmann's kinetic equation has been solved in the relaxation-time approximation to obtain the electrical conductivity. We have used the quasiparticle description to define the basic properties of QGP through the distribution functions of partons.

The hot Hagedorn Universe. Presented at the ICFNP2015 meeting, August 2015

In the context of the half-centenary of Hagedorn temperature and the statistical bootstrap model (SBM) we present a short account of how these insights coincided with the establishment of the hot big-bang model (BBM) and helped resolve some of the early philosophical difficulties. We then turn attention to the present day context and show the dominance of strong interaction quark and gluon degrees of freedom in the early stage, helping to characterize the properties of the hot Universe. We focus attention on the current experimental insights about cosmic microwave background (CMB) temperature fluctuation, and develop a much improved understanding of the neutrino freeze-out, in this way paving the path to the opening of a direct connection of quark-gluon plasma (QGP) physics in the early Universe with the QCD-lattice, and the study of the properties of QGP formed in the laboratory.

STAR heavy-ion highlights

Parton energy loss, quarkonium sequential melting and particle production from electromagnetic interactions are tools to study Quark Gluon Plasma properties. The STAR detector, with large acceptance at mid-rapidity, excellent particle identification and wide transverse momentum coverage, is able to study these probes in details. Di-electron spectra form Beam Energy Scan, measurements of reconstructed jets in Au+Au collisions and quarkonium measurements in p+p and heavy ion collisions are reported in this paper.

Production of non-photonic electrons in U+U collisions at √sNN= 193 GeV at the STAR experiment

Heavy quarks are suitable probes to study the properties of Quark-Gluon Plasma (QGP), a strongly interacting medium, which can be created in ultrarelativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC). Non-photonic electrons (NPE) that originate from semileptonic decays of D and B mesons can serve as a good proxy for heavy flavor quarks. Nuclear modification factor RAA of NPE is measured in heavy-ion collisions, which is sensitive to the effect of QGP on heavy quarks.Measurements of NPE RAA in Au+Au collisions at √sNN = 200 GeV reveal that NPE production is strongly suppressed. In year 2012 STAR collected data from U+U collisions at √sNN = 193 GeV. In most central collisions higher energy density can be achieved in comparison to collisions of gold nuclei. In this proceedings the preliminary results on NPE in 0-5% most central U+U collisions at a transverse momentum range 1.2 are presented. The nuclear modification factor in U+U collisions is compared to that in Au+Au collisions and theoretical models.

Effects of hadronic rescattering on multistrange hadrons in high-energy nuclear collisions

We study the effects of hadronic rescattering on hadron distributions in high-energy nuclear collisions by using an integrated dynamical approach. This approach is based on a hybrid model combining (3+1)-dimensional ideal hydrodynamics for the quark gluon plasma (QGP), and a transport model for the hadron resonance gas. Since the hadron distributions are the result of the entire expansion history of the system, understanding the QGP properties requires investigating how rescattering during the hadronic stage affects the final distributions of hadrons. We include multistrange hadrons in our study, and quantify the effects of hadronic rescattering on their mean transverse momenta and elliptic flow. We find that multistrange hadrons scatter less during the hadronic stage than nonstrange particles, and thus their distributions reflect the properties of the system in an earlier stage than the distributions of nonstrange particles.

Melting hadrons, boiling quarks

In the context of the Hagedorn temperature half-centenary I describe our understanding of the hot phases of hadronic matter both below and above the Hagedorn temperature. The first part of the review addresses many frequently posed questions about properties of hadronic matter in different phases, phase transition and the exploration of quark-gluon plasma (QGP). The historical context of the discovery of QGP is shown and the role of strangeness and strange antibaryon signature of QGP illustrated. In the second part I discuss the corresponding theoretical ideas and show how experimental results can be used to describe the properties of QGP at hadronization. The material of this review is complemented by two early and unpublished reports containing the prediction of the different forms of hadron matter, and of the formation of QGP in relativistic heavy ion collisions, including the discussion of strangeness, and in particular strange antibaryon signature of QGP.

Toward a solution to the RAA and v2 puzzle for heavy quarks

The heavy quarks constitute a unique probe of the quark–gluon plasma properties. A puzzling relation between the nuclear modification factor RAA(pT) and the elliptic flow v2(pT) has been observed both at RHIC and LHC energies. Predicting correctly both observables has been a challenge to all existing models, especially for D mesons. We discuss how the temperature dependence of the heavy quark drag coefficient is responsible for a large part of such a puzzle. In particular, we have considered four different models to evaluate the temperature dependence of drag and diffusion coefficients propagating through a quark gluon plasma (QGP). All the four different models are set to reproduce the same RAA(pT) observed in experiments at RHIC and LHC energy. We point out that for the same RAA(pT) one can generate 2–3 times more v2 depending on the temperature dependence of the heavy quark drag coefficient. A non-decreasing drag coefficient as T→Tc is a major ingredient for a simultaneous description of RAA(pT) and v2(pT).

Quantifying properties of hot and dense QCD matter through systematic model-to-data comparison

We systematically compare an event-by-event heavy-ion collision model to data from the Large Hadron Collider. Using a general Bayesian method, we probe multiple model parameters including fundamental quark-gluon plasma properties such as the specific shear viscosity $\eta/s$, calibrate the model to optimally reproduce experimental data, and extract quantitative constraints for all parameters simultaneously. The method is universal and easily extensible to other data and collision models.

Physics performance with the ALICE silicon tracker

The detailed characterization of the quark gluon plasma (QGP) produced in heavy-ion collisions is the main goal of the ALICE experiment at the CERN LHC . The analysis of heavy quarks via the decays of the corresponding short-lived hadrons is among the prominent measurements to address the properties of QGP . To efficiently reconstruct these decays, the ALICE apparatus comprises a precise Inner Tracking System (ITS) made out of six layers of silicon detectors based on three different technologies, namely two layers of pixels, two of drifts and two of double-sided microstrip, listed in the order they are crossed by particles produced in the beam collision. In this paper, the contribution of the ITS to some of the main physics measurements that have been accomplished with proton and lead beams by the ALICE experiment will be discussed.

Electrical conductivity of an anisotropic quark gluon plasma: A quasiparticle approach

The study of transport coefficients of strongly interacting matter got impetus after the discovery of perfect fluid ever created at ultrarelativistic heavy ion collision experiments. In this article, we have calculated one such coefficient viz. electrical conductivity of the quark gluon plasma (QGP) phase which exhibits a momentum anisotropy. Relativistic Boltzmann's kinetic equation has been solved in the relaxation-time approximation to obtain the electrical conductivity. We have used the quasiparticle description to define the basic properties of QGP. We have compared our model results with the corresponding results obtained in different lattice as well as other model calculations. Furthermore, we extend our model to calculate the electrical conductivity at finite chemical potential.

Anisotropic flow and jet quenching in relativistic nuclear collisions

The exploration of the strong-interaction matter under extreme conditions is one of the main goals of relativistic heavy-ion collisions. We provide some of the main results on the novel properties of quark-gluon plasma, with particular focus given to the strong collectivity and the color opaqueness exhibited by such hot and dense matter produced in high-energy nuclear collisions at RHIC and the LHC.

Quarkonium production in ALICE at the LHC

In heavy-ion collisions at the LHC, the ALICE Collaboration is studying Quantum Chromodynamics (QCD) matter at very high energy density where the formation of a Quark Gluon Plasma (QGP) is expected. Quarkonium production is an important probe to characterize the QGP properties. High precision data in pp collisions provide the baseline of Pb-Pb measurements and p-Pb collisions serve to quantify the amount of initial and/or final state effects, related to cold nuclear matter, that are largely unknown at the LHC energy. Since 2010, the LHC provided Pb-Pb collisions at sqrt{s_{NN}} = 2.76 TeV, pp collisions at various energies and in 2013 p-Pb collisions at sqrt{s_{NN}} = 5.02 TeV. In ALICE, quarkonia can be reconstructed at forward rapidity in the dimuon channel and at mid-rapidity in the dielectron channel, and, for both channels, down to zero transverse momentum. New measurements on inclusive production of J/psi, psi (2S) and Upsilon performed in p-Pb collisions and on the p_T dependence of inclusive J/psi in Pb-Pb collisions are presented. The contribution of J/psi from B hadrons to the inclusive production in Pb-Pb is also discussed. Finally, an estimation of the cold nuclear matter effect in Pb-Pb, extrapolated from p-Pb measurements, is given.