Signature Of Quark-gluon Plasma Research Articles

Searching for QGP droplets with high- pT hadrons and heavy flavor

The search for the smallest quark-gluon plasma (QGP) droplets in nature has motivated recent small collisions system programs at RHIC and LHC. Unambiguous identification of jet quenching due to final-state interactions is key to confirming QGP formation in these reactions. We compute the nuclear modification factors $R_{AA}$ and $R_{p(d)A}$ of charged hadrons and heavy flavor mesons in large (Au-Au, Xe-Xe, Pb-Pb) and small ($d$-Au, $p$-Pb, O-O) colliding systems, respectively. Our results include the Cronin effect and initial-state parton energy loss in cold nuclear matter. In the final state, hard partons undergo collisional energy loss and branching that was recently derived using Soft-Collinear-Effective-Theory with Glauber Gluon (SCET$_{\rm G}$). In large colliding systems, medium-modified QCD evolution of the fragmentation functions dominates the nuclear correction. As the system size decreases, we find that cold nuclear matter effects, collisional energy loss, and QGP-induced radiations can become equally important. A systematic scan over the medium size and mass/flavor dependence of $R_{AA}$ provides the opportunity to separate these individual contributions and identify QGP signatures in small systems. Predictions for $R_{AA}^{h}$, $R_{AA}^{D}$, $R_{AA}^{B}$ in O-O collisions at $\sqrt{s}=7$ TeV are presented with and without the formation of a QGP and contrasted with the corresponding $R_{p(d)A}$ calculations. Upcoming single-hadron measurements at the LHC will not only test the O-O predictions for both light and heavy flavor production, but will shed light on the possibly very different dynamics of $p$-A and A-A reactions at similar soft particle production multiplicities.

Prehydrodynamic evolution and its impact on quark-gluon plasma signatures

State-of-the-art hydrodynamic models of heavy-ion collisions have considerable theoretical model uncertainties in the description of the very early pre-hydrodynamic stage. We add a new computational module, K$_\mathrm{T}$Iso, that describes the pre-hydrodynamic evolution kinetically, based on the relativistic Boltzmann equation with collisions treated in the Isotropization Time Approximation. As a novelty, K$_\mathrm{T}$Iso allows for the inclusion and evolution of initial-state momentum anisotropies. To maintain computational efficiency K$_\mathrm{T}$Iso assumes strict longitudinal boost invariance and allows collisions to isotropize only the transverse momenta. We use it to explore the sensitivity of hadronic observables measured in relativistic heavy-ion collisions to initial-state momentum anisotropies and microscopic scattering during the pre-hydrodynamic stage.

Diphoton production rate in relativistic nuclear collisions

In this study, we have made an effort to reveal some information about the space-time evolution of quark gluon plasma (QGP). We deal with one of the important signature of quark gluon plasma from the analysis of the experimental results on electromagnetic probes which are measured at relativistic heavy-ion collider (RHIC) and large hadron collider (LHC). Electromagnetic radiations as diphotons emitted from hot and dense matter are investigated using a phenomenological model with quasiparticle approach at temperatures above critical temperature. In this, we use thermodynamically consistent quasiparticle model composed of quarks and gluons. Due to interactions among the quarks, mass of these particles is generated in highly dense and hot matter of QGP. The mass of these particles is temperature dependent and it is found that the model works well at temperatures above the critical temperature. Thus, this work is carried out using a phenomenological model in heavy-ion collisions in the limit of high temperature and zero chemical potential. The rate of diphoton production is calculated by suitably fitted parametrization factors in quark mass. We found an appreciable enhancement using thermal quark mass as compared to dynamical quark mass in the current results of two photon production rate. The results are compared with earlier estimated diphoton production rates from QGP and hadronic matter. Our results are therefore enhanced in comparison to the other theoretical results. The estimation of diphoton emission anticipates useful insights in the relevant range of mass. So these insights on diphotons can be advantageous tool for spectroscopy and thermometry in high energy heavy-ion collisions at RHIC and LHC.

Geometrically confined thermal field theory: Finite size corrections and phase transitions

Motivated by evidence for quark-gluon plasma signatures in small systems, we study a simple model of a massless, noninteracting scalar field confined with Dirichlet boundary conditions. We use this system to investigate the finite size corrections to thermal field--theoretically derived quantities compared to the usual Stefan-Boltzmann limit of an ideal gas not confined in any direction. Two equivalent expressions with different numerical convergence properties are found for the free energy in $D$ rectilinear spacetime dimensions with $c\ensuremath{\le}D\ensuremath{-}1$ spatial dimensions of finite extent. We find that the first law of thermodynamics generalizes such that the pressure depends on direction. For systems with finite dimension(s) but infinite volumes, such as a field constrained between two parallel plates or a rectangular tube, the relative fluctuations in energy are zero, and hence the canonical and microcanonical ensembles are equivalent. We present precise numerical results for the free energy, total internal energy, pressure, entropy, and heat capacity of our field between parallel plates, in a tube, and in finite volume boxes of various sizes in four spacetime dimensions. For temperatures and system sizes relevant for heavy ion phenomenology, we find large deviations from the Stefan-Boltzmann limit for these quantities, especially for the pressure. Our main result is the discovery that an isolated system of fields constrained between parallel plates reveals a divergent isoenergetic compressibility at a critical length ${L}_{c}\ensuremath{\sim}1/T$. This divergence constitutes a novel phase transition, which, unlike the usual temperature-driven phase transition, is driven solely by the size of the system.

Exploring potential signatures of QGP in UHECR ground profiles

In this work we explore the possibility that the formation of Quark Gluon Plasma (QGP) during the first interactions of Ultra High Energy Cosmic Rays (UHECRs) may result in observable signatures in ground profile and shower particle composition that could conceivably be detectable by an air shower array experiment such as the Pierre Auger Observatory. Knowledge of whether QGP formation affects the properties of UHECR development will further the understanding of both UHECR behavior and high energy hadronic interaction behavior. We find that for the vast majority of showers signals of QGP do not manifest themselves in ways that are observable, but on rare occasion, such as within deeply penetrating showers, observable signals can be seen. Results show potential for QGP detection at 100 PeV initial energy at an initial interaction event height of 12 km through a μ± excess at 10 GeV between 100–300 m from the shower core favoring QGP forming events. In contrast, higher initial interaction heights of 24 and 36 km at 100 PeV initial energy show no significant potential for QGP detection. Unfortunately at present, the 12 km observable signals cannot be seen with current detectors, such as the Pierre Auger Observatory [1]; however, there may be potential for detection in future experiments.

Charting the Future Frontier(s) of Particle Production

This short note describes the long collaborative effort between Arizona and Krak\'ow, showing some of the key strangeness signatures of quark-gluon plasma. It further presents an annotated catalog of foundational questions defining the research frontiers which I believe can be addressed in the foreseeable future in the context of relativistic heavy ion collision experiments. The list includes topics that are specific to the field, and ventures towards the known-to-be-unknown that may have a better chance with ions as compared to elementary interactions.

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.

Experimental studies of the quantum chromodynamics phase diagram at the STAR experiment

We review the STAR experiment’s results to date from the Beam Energy Scan (BES) at Brookhaven’s Relativistic Heavy Ion Collider, and outline future plans and prospects in this area. BES Phase-I is based on Au + Au data taken in 2010 and 2011 at \(\sqrt {s_{NN}}= 7.7\), 11.5, 19.6, 27 and 39 GeV, and when interpreted in conjunction with the large datasets available at 62.4 and 200 GeV, permits an initial exploration of the phase diagram of quantum chromodynamics (QCD) matter. The three goals of BES Phase-I are as follows: (1) a search for turn-off of the promising signatures of quark gluon plasma (QGP) already reported at the top RHIC energies; (2) a search for evidence of a possible first-order phase transition such as a signature of softening of the QCD equation of state (EoS); (3) a search for a critical end point as expected in a scenario where there is a cross-over transition from hadronic matter to QGP at the highest RHIC energies, but a first-order phase transition at lower energies with finite net-baryon density. We summarize several analyses of BES data from 2010 and 2011 that are either published or submitted, as well as several more that have been reported at meetings in preliminary forms. The physics interpretation of BES Phase-I measurements is frequently limited by the increasing statistical error bars as the beam energy decreases, and the planned BES Phase-II will have much improved capabilities in this regard.

Resonance-like QGP signals displayed in general charge balance functions

Experiment and lattice simulation show that the quark–gluon plasma (QGP) system displays strong interaction between constituents at temperature a few times the critical temperature Tc. This QGP picture can be explained by assuming that the QGP matter above Tc is rich in different kinds of bound states, namely resonance-like QGP (RQGP). The chemical composition of the QGP system produced in ultra-relativistic heavy-ion collisions can be investigated through a general charge balance function which describes two-wave quark production during expansion afterward. In this paper, we investigate the signals of this RQGP through general charge balance functions. We find that the quasiparticles in QGP contribute a little to the balance functions because of their heavy masses. The balance functions reduce to the situation discussed before where only one-wave charge production is involved if only the quasiparticles in QGP are considered. However, the baryonic bound states in QGP have a significant effect on the balance function [Formula: see text], causing a dip in the [Formula: see text] balance function at small Δy. The existence of the binary and baryonic bound states amplify the negative dip of the balance function BpK-(Δy) at Δy ∽ 1.

Study of J/ψ production and cold nuclear matter effects in pPb collisions at $ \sqrt{{{s_{NN }}}} $ = 5 TeV

The production of $J/\psi$ mesons with rapidity $1.5<y<4.0$ or $-5.0<y<-2.5$ and transverse momentum $p_\mathrm{T}<14 \mathrm{GeV}/c$ is studied with the LHCb detector in proton-lead collisions at a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}=5 \mathrm{TeV}$. The analysis is based on a data sample corresponding to an integrated luminosity of about $1.6 \mathrm{nb}^{-1}$. For the first time the nuclear modification factor and forward-backward production ratio are determined separately for prompt $J/\psi$ mesons and $J/\psi$ from $b$-hadron decays. Clear suppression of prompt $J/\psi$ production with respect to proton-proton collisions at large rapidity is observed, while the production of $J/\psi$ from $b$-hadron decays is less suppressed. These results show good agreement with available theoretical predictions. The measurement shows that cold nuclear matter effects are important for interpretations of the related quark-gluon plasma signatures in heavy-ion collisions.

Strangeness in QGP: Hadronization Pressure

We review strangeness as signature of quark gluon plasma (QGP) and the hadronization process of a QGP fireball formed in relativistic heavy-ion collisions in the entire range of today accessible reaction energies. We discuss energy dependence of the statistical hadronization parameters within the context of fast QGP hadronization. We find that QGP breakup occurs for all energies at the universal hadronization pressure $P = 80\pm 3\,\mathrm{MeV/fm}^3 $.

Physics of Quark Gluon Plasma: An Update and the Status Report

The microsecond old universe was too hot for the nucleons to survive as bound states of quarks. When the temperature of the universe fell below ∼10 K as a result of cooling due to expansion, the quarks got confined inside the nucleons to reside there ever after—making them inaccessible to any direct observation in isolation. Natural objects like the core of the compact astrophysical objects may also contain deconfined quark matter. Therefore, creation of a deconfined phase of thermal quarks and gluons will be very important for understanding the evolution of the early universe and the physics of compact astrophysical objects like neutron star. Calculations based on lattice QCD indicate that hadronic matter at high temperatures and densities undergoes a phase transition to a thermalized system of deconfined quarks and gluons, called quark gluon plasma (QGP). It is expected that such high densities and temperatures may be achieved by colliding two nuclei at RHIC, LHC, or FAIR energies. The present volume addresses some of the experimental and theoretical issues related to quark-hadron phase transition in the relativistic heavy ion collisions by the world experts in the field. On the experimental sides it contains results from CERN’s Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) and Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC). Comparison of experimental results from RHIC and LHC is extremely useful to gain insights into the properties of the matter formed in these experiments. The present volume offers a review on this subject. On the theoretical side the present volume contains papers on the space-time evolution of the system formed in heavy ion collisions including the effects of viscosities through hydrodynamic equations, issues of equilibration, electromagnetic and heavy quark probes of QGP, quarkonia suppression in QGP, ridge, and transverse correlations. Recent progress in the femtoscopy and particle production in strong electromagnetic fields in heavy ion collisions is also addressed adequately. In summary, the present volume brings out recent developments on almost all the relevant issues of heavy ion collisions like creation, evolution, and signals of QGP. We are sure that the volume will be useful for the current practitioners and young new entrants to this exciting field of research.

Viscosity, wave damping, and shock-wave formation in cold hadronic matter

We study linear and nonlinear wave propagation in a dense and cold hadron gas and also in a cold quark-gluon plasma, taking viscosity into account and using the Navier-Stokes equation. The equation of state of the hadronic phase is derived from the nonlinear Walecka model in the mean-field approximation. The quark-gluon plasma phase is described by the MIT equation of state. We show that in a hadron gas viscosity strongly damps wave propagation and also hinders shock-wave formation. This marked difference between the two phases may have phenomenological consequences and lead to new quark-gluon plasma signatures.

Electromagnetic and hadron signatures of quark-gluon plasma in heavy-ion collisions at 62.4 GeV in the PHOENIX experiment on the RHIC

The motivation for quark-gluon plasma studies at beam energies of 20–100 GeV are the detailed exploration of the phase diagram of QCD matter and the search for the critical point of deconfinement transition. The PHOENIX experiment on the RHIC measures nuclear modification factors for protons, π0 and φ mesons in heavy-ion collisions at \(\sqrt s\) 6 = 2.4 GeV. The possibility of obtaining the electromagnetic signatures of quark-gluon plasma measurements with an innovative HBD detector is discussed.

Measurements of Υ Production and Nuclear Modification Factor at STAR

Thermal suppression of quarkonium production in heavy-ion collisions, due to Debye screening of the quark-antiquark potential, has been proposed as a clear signature of quark-gluon plasma (QGP) formation. At RHIC energies, the Υ meson is a clean probe of the early system thanks to negligible levels of enhancement from bb̄ recombination and non-thermal suppression from co-mover absorption. We report on our measurement of the Υ → e+e− cross section in Au+Au collisions at =200 GeV. We compute the Nuclear Modification Factor by comparing these results to p+p collisions. In order to have a complete assessment of both hot and cold nuclear matter effects on Upsilon production we also report on results from d+Au collisions.

On QGP formation in pp collisions at 7 TeV

The mechanism of quark–gluon plasma (QGP) formation in pp collisions is discussed in the framework of the EPOS model. The enhancement of direct photons at low pt is predicted as a sensitive QGP signal in pp collisions at 7 TeV. Experimental measurements to test this prediction and to cross-check from other QGP signals are advocated.

Radial flow from electromagnetic probes and signal of quark gluon plasma

A first attempt has been made to extract the evolution of radial flow from the analysis of the experimental data on electromagnetic probes experimentally measured at SPS and RHIC energies. The $p_T$ spectra of photons and dileptons measured by WA98 and NA60 collaborations respectively at CERN-SPS and the photon spectra obtained by PHENIX collaboration at BNL-RHIC have been used to constrain the theoretical models, rendering the outcome of the analysis largely model independent. We argue that the variation of the radial velocity with invariant mass is indicative of a phase transition from initially produced partons to hadrons at SPS and RHIC energies.

ϒ Production in p+p, d+Au, Au+Au collisions at in STAR

The properties of the quark-gluon Plasma (QGP) produced in heavy-ion collisions can be investigated by studying its effect on quarkonia production. Suppression of quarkonia is theorized to be a QGP signature due to the Debye color screening of the potential between the heavy quarks. In particular, the ϒ states are of interest because effects due to co-movers and feed down are smaller than for J/ψ. Lattice studies show that a sequential suppression of quarkonia states in heavy-ion collisions when compared to production in p+p collisions can provide us with a thermometer for the matter produced in relativistic heavy-ion collisions. This requires a detailed understanding of ϒ production in p+p collisions which gives a baseline needed to calculate RAA. It is also necessary to understand ϒ production in d+Au collisions in order to properly account for cold nuclear matter effects. We present our preliminary results for mid-rapidity ϒ production in p+p, d+Au and Au+Au at in the STAR experiment. We compare these results with models based on QCD calculations.

Quark-gluon plasma signals in CBM experiment

Quark-gluon plasma signals in CBM experiment

ΛcEnhancement from Strongly Coupled Quark-Gluon Plasma

We propose the enhancement of Lambdac as a novel quark-gluon plasma signal in heavy ion collisions at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider. Assuming a stable bound diquark state in the strongly coupled quark-gluon plasma near the critical temperature, we argue that the direct two-body collision between a c quark and a [ud] diquark would lead to an enhanced Lambdac production in comparison with the normal three-body collision among independent c, u, and d quarks. In the coalescence model, we find that the Lambdac/D yield ratio is enhanced substantially due to the diquark correlation.