Plasma In Heavy-ion Collisions Research Articles

Effect of the magnetic field on the photon radiation from quark–gluon plasma in heavy ion collisions

We develop a formalism for the photon emission from the quark-gluon plasma with an external electromagnetic field. We then use it to investigate the effect of magnetic field on the photon emission from the quark-gluon plasma created in $AA$ collisions. We find that even for very optimistic assumption on the magnitude of the magnetic field generated in $AA$ collisions its effect on the photon emission rate is practically negligible. For this reason the magnetic field cannot generate a significant azimuthal asymmetry in the photon spectrum.

Chiral vortical wave and induced flavor charge transport in a rotating quark-gluon plasma

We show the existence of a new gapless collective excitation in a rotating fluid system with chiral fermions, named as the Chiral Vortical Wave (CVW). The CVW has its microscopic origin at the quantum anomaly and macroscopically arises from interplay between vector and axial charge fluctuations induced by vortical effects. The wave equation is obtained both from hydrodynamic current equations and from chiral kinetic theory and its solutions show nontrivial CVW-induced charge transport from different initial conditions. Using the rotating quark-gluon plasma in heavy ion collisions as a concrete example, we show the formation of induced flavor quadrupole in QGP and estimate the elliptic flow splitting effect for Lambda baryons that may be experimentally measured.

Formation time of quark–gluon plasma in heavy-ion collisions in the holographic shock wave model

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 decreases the thermalization time as well as an anisotropy accelerates the thermalization.

Electromagnetic response of quark–gluon plasma in heavy-ion collisions

We study the electromagnetic response of the quark–gluon plasma in AA-collisions at RHIC and LHC energies for a realistic space–time evolution of the plasma fireball. We demonstrate that for a realistic electric conductivity the electromagnetic response of the plasma is in a quantum regime when the induced electric current does not generate a classical electromagnetic field, and can only lead to a rare emission of single photons.

Time-dependent flow from an AdS Schwarzschild black hole

I discuss two examples of time-dependent flow which can be described in terms of an AdS Schwarzschild black hole via holography. The first example involves Bjorken hydrodynamics which should be applicable to the formation of the quark gluon plasma in heavy ion collisions. The second example is the cosmological evolution of our Universe.

Muon Physics in ALICE: The MFT Upgrade Project

The ALICE experiment is dedicated to the study of the quark gluon plasma in heavy-ion collisions at the CERN LHC. The Muon Forward Tracker (MFT) is under consideration by the ALICE experiment to be part of its program of detector upgrades to be installed during the LHC Long Shutdown 2 (LS2) planned for 2018. Designed as a silicon pixel detector added in the Muon Spectrometer acceptance (−4.0 < η < −2.5) upstream of the hadron absorber, the MFT will allow a drastic improvement of the measurements that are presently done with the Muon Spectrometer and, in addition, will give access to new measurements that are not possible with the present Muon Spectrometer setup. Motivations and preliminary results are discussed here, concerning the measurement of prompt and displaced charmonia, open heavy flavors, and low mass dimuons in central Pb–Pb collisions at = 5.5 TeV.

J/ψ elliptic flow measurement in Pb–Pb collisions at sNN=2.76 TeV at forward rapidity with the ALICE experiment

J/ψ suppression induced by color screening of its constituent quarks was proposed 26 years ago as a signature of the formation of a quark gluon plasma in heavy-ion collisions. Recent results from ALICE in Pb–Pb collisions exhibit a smaller suppression with respect to previous measurements at the SPS and RHIC. The study of azimuthal anisotropy in particle production gives information on the collective hydrodynamic expansion at the early stage of the fireball, where the matter created in high-energy nuclear collisions is expected to be in a deconfined state. In particular, J/ψ elliptic flow v2 is important to test the degree of thermalization of heavy quarks. Together with the production yields, the elliptic flow is a powerful observable to address the question of suppression and regeneration of J/ψ in QGP. We present the first inclusive J/ψ elliptic flow measurement performed with the muon spectrometer of ALICE, in Pb–Pb collisions, at forward rapidity. Integrated and pT-differential v2 results are presented and a comparison with recent STAR results and with a parton transport model is also performed.

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.

Violation of the Holographic Viscosity Bound in a Strongly Coupled Anisotropic Plasma

We study the conductivity and shear viscosity tensors of a strongly coupled N=4 super-Yang-Mills plasma which is kept anisotropic by a θ parameter that depends linearly on one of the spatial dimensions. Its holographic dual is given by an anisotropic axion-dilaton-gravity background and has recently been proposed by Mateos and Trancanelli as a model for the preequilibrium stage of quark-gluon plasma in heavy-ion collisions. By applying the membrane paradigm which we also check by numerical evaluation of Kubo formula and lowest lying quasinormal modes, we find that the shear viscosity purely transverse to the direction of anisotropy saturates the holographic viscosity bound, whereas longitudinal shear viscosities are smaller, providing the first such example not involving higher-derivative theories of gravity and, more importantly, with fully known gauge-gravity correspondence.

Evolution of collectivity as a signal of quark gluon plasma formation in heavy ion collisions

A measurement for studying the mass dependence of the dilepton interferometry in relativistic heavy-ion collision experiments as a tool to characterize the quark-gluon phase is proposed. In calculations involving dileptons, we show that the mass dependence of radii extracted from the virtual photon (dilepton) interferometry provide access to the development of collective flow with time. It is argued that the non-monotonic variation of HBT radii with invariant mass of the lepton pairs signals the formation of quark gluon plasma in heavy ion collisions. Our proposal of experimentally measuring the ratio, $R_{\mathrm out}/R_{\mathrm side}$ for dileptons can be used to estimate the average life times of the partonic as well as the hadronic phases.

PROSPECTS OF SEARCHING FOR (UN)PARTICLES FROM HIDDEN SECTORS USING RAPIDITY CORRELATIONS IN MULTIPARTICLE PRODUCTION AT THE LHC

Most signatures of new physics have been studied on the transverse plane with respect to the beam direction at the LHC where background is much reduced. In this paper we propose the analysis of inclusive longitudinal (pseudo)rapidity correlations among final-state (charged) particles in order to search for (un)particles belonging to a hidden sector beyond the Standard Model, using a selected sample of p–p minimum bias events (applying appropriate off-line cuts on events based on, e.g. minijets, high-multiplicity, event shape variables, high-p⊥ leptons and photons, etc.) collected at the early running of the LHC. To this aim, we examine inclusive and semi-inclusive two-particle correlation functions, forward–backward correlations, and factorial moments of the multiplicity distribution, without resorting to any particular model but under very general (though simplifying) assumptions. Finally, motivated by some analysis techniques employed in the search for quark–gluon plasma in heavy-ion collisions, we investigate the impact of such intermediate (un)particle stuff on the (multi)fractality of parton cascades in p–p collisions, by means of a Lévy stable law description and a Ginzburg–Landau model of phase transitions. Results from our preliminary study seem encouraging for possible dedicated analyses at LHC and Tevatron experiments.

Quasi-particle model for lattice QCD: quark–gluon plasma in heavy ion collisions

We propose a quasi-particle model to describe the lattice QCD equation of state for pure SU(3) gauge theory in its deconfined state, for T≥1.5T c. The method involves mapping the interaction part of the equation of state to an effective fugacity of otherwise non-interacting quasi-gluons. We find that this mapping is exact. Using the quasi-gluon distribution function, we determine the energy density and the modified dispersion relation for the single particle energy, in which the trace anomaly is manifest. As an application, we first determine the Debye mass, and then the important transport parameters, viz., the shear viscosity, η, and the shear viscosity to entropy density ratio, $\eta/{\mathcal{S}}$ . We find that both η and $\eta/{\mathcal{S}}$ are sensitive to the interactions, and that the interactions significantly lower both η and $\eta/\mathcal{S}$ .

Gauge-gravity duality and high energy collisions

We propose an overview on the Gauge/Gravity correspondence applied to the dynamics of high-energy collisions, such as the properties and formation of the quark-gluon plasma in heavy-ion collisions. Some recent applications to other high-energy scattering processes are also discussed.

From glasma to quark–gluon plasma in heavy-ion collisions

When two sheets of color glass condensate collide in a high-energy heavy-ion collision, they form matter with very high energy densities called the glasma. We describe how this matter is formed, its remarkable properties and its relevance for understanding the thermalization of the quark–gluon plasma in heavy-ion collisions. Long-range rapidity correlations contained in the near-side ridge measured in heavy-ion collisions may allow one to directly infer the properties of the glasma.

Fluctuations driven isotropization of the quark-gluon plasma in heavy ion collisions

Averaged over ensemble of initial conditions kinetic transport equations of weakly coupled systems of quarks and gluons are derived. These equations account for the correlators of fluctuations of particles and classical gluon fields. The isotropization of particle momenta by field fluctuations at the early prethermal stage of matter evolution in ultrarelativistic heavy ion collisions is discussed. Our results can be useful for understanding under what conditions isotropization of the quark-gluon plasma in ultrarelativistic heavy ion collisions can be reached within phenomenologically observed time scales.

Soft physics in ALICE

The ALICE experiment has been designed to study the properties of strongly interacting matter and characterize the quark gluon plasma in heavy-ion collisions at Large Hadron Collider (LHC). The programme and performance of ALICE in the soft physics domain are described, emphasizing the novel aspects offered by the LHC. This overview is thus focused on the ‘bulk’ observables (from low to intermediate hadron measurements): global event properties, chemical composition, hadronization mechanisms, expansion dynamics (flow and particle correlations) and event-by-event fluctuations. ALICE will start with proton–proton (pp) collisions which will serve as a reference for nucleus–nucleus collisions but will also bring genuine pp physics in a new energy regime. The ALICE capabilities for this first physics are also briefly described.

The ALICE experiment at LHC

The ALICE experiment is designed to study the physics of strongly interacting matter and the Quark Gluon Plasma in heavy-ion collisions at LHC. After a short survey of the tracking and particle indentification capabilities provided by the instrumental ensemble, the physics programme and performance of ALICE are described, starting with the “bulk” observables (from low and intermediate pT hadron measurements). The novel opportunities offered at the LHC regime by hard probes (jets and photons, open heavy flavors and quarkonia) are then examined.

Silicon-tungsten calorimeter for the forward direction in the PHENIX experiment at RHIC

The PHENIX detector at RHIC has been designed to study hadronic and leptonic signatures of the Quark Gluon Plasma in heavy ion collisions and spin dependent structure functions in polarized proton collisions. The baseline detector measures muons in two muon spectrometers located forward and backward of mid-rapidity, and measures hadrons, electrons, and photons in two central spectrometer arms, each of which covers 90. in azimuth and 0.35 units of rapidity. Further progress requires extending rapidity coverage for hadronic and electromagnetic signatures by upgrading the functionality of the PHENIX muon spectrometers to include photon and jet measurement capabilities. Tungsten calorimeters with silicon pixel readout and fine transverse and longitudinal segmentation are proposed to attain this goal. The use of such a design provides the highest density and finest granularity possible in a calorimeter.

Silicon-tungsten calorimeter for the forward direction in the PHENIX experiment at RHIC

The PHENIX detector at RHIC has been designed to study hadronic and leptonic signatures of the Quark Gluon Plasma in heavy ion collisions and spin dependent structure functions in polarized proton collisions. The baseline detector measures muons in two muon spectrometers located forward and backward of mid-rapidity, and measures hadrons, electrons, and photons in two central spectrometer arms, each of which covers 90/spl deg/ in azimuth and 0.35 units of rapidity. Further progress requires extending rapidity coverage for hadronic and electromagnetic signatures by upgrading the functionality of the PHENIX muon spectrometers to include photon and jet measurement capabilities. Tungsten calorimeters with silicon pixel readout and fine transverse and longitudinal segmentation are proposed to attain this goal. The use of such a design provides the highest density and finest granularity possible in a calorimeter.

Silicon vertex tracker for PHENIX detector at the central rapidity region

We present the status of the silicon vertex tracker for the PHENIX experiment. The purpose of the PHENIX detector is to investigate very high-density and high-temperature matter, so called Quark Gluon Plasma in heavy ion collisions upto 100 GeV/nucleon and spin structure of the nucleon with polarized proton beam up to 250 GeV/beam. We plan to build the silicon vertex tracker to identify the charm and bottom quark decay by using displaced decay vertex, with two inner pixel layers and two outer stripixel layers. The design goal of the displaced vertex resolution is at the level of 30–50 μm in high charged multiplicity environment with minimum material budget requirement to avoid generating background for outer detectors in the PHENIX.