Production Of Quark-gluon Plasma Research Articles

Analysis of Midrapidity pT Distributions of Identified Charged Particles in Pb + Pb Collisions at snn = 5.02 TeV Using Tsallis Distribution with Embedded Transverse Flow

The midrapidity transverse momentum distributions of the charged pions, kaons, protons, and antiprotons, measured by ALICE Collaboration at ten centrality classes of Pb + Pb collisions at snn = 5.02 TeV in the Large Hadron Collider (LHC, CERN, Switzerland), are successfully analyzed using combined minimum χ2 fits with a thermodynamically non-consistent, as well as thermodynamically consistent, Tsallis function with transverse flow. The extracted non-extensivity parameter q decreases systematically for all considered particle species with increasing Pb + Pb collision centrality, suggesting an increase in the degree of system thermalization with an increase in collision centrality. The results for q suggest quite a large degree of thermalization of quark–gluon plasma (QGP) created in central Pb + Pb collisions at snn = 5.02 TeV with the average number of participant nucleons ⟨Npart⟩ > 160. The obtained significantly different growth rates of transverse flow velocity, ⟨βT⟩, in regions ⟨Npart⟩ < 71 ± 7 and ⟨Npart⟩ > 71 ± 7 with the temperature parameter T0 remaining constant within uncertainties in region ⟨Npart⟩ > 71 ± 7 probably indicates that ⟨Npart⟩ ≈ 71 ± 7 (corresponding to ⟨dNch/dη⟩ ≈ 251 ± 20) is a threshold border value for a crossover transition from a dense hadronic state to the QGP phase (or mixed phase of QGP and hadrons) in Pb + Pb collisions at snn = 5.02 TeV. The threshold border value for transverse flow velocity ⟨βT⟩ ≈ 0.46 ± 0.03 (corresponding to ⟨Npart⟩ ≈ 71 ± 7), estimated by us in Pb + Pb collisions at snn = 5.02 TeV, agrees well with the corresponding border value ⟨βT⟩ ≈ 0.44 ± 0.02, recently obtained in Xe + Xe collisions at snn = 5.44 TeV, and with almost constant ⟨βT⟩ values extracted earlier in the Beam Energy Scan (BES) program of the Relativistic Heavy-Ion Collider (RHIC, Brookhaven, GA, USA) in central Au + Au collisions in the snn = 7.7 − 39 GeV energy range, where the threshold for QGP production is achieved. The correlations between extracted T0 and ⟨βT⟩ parameters are found to be greatly different in regions ⟨βT⟩ < 0.46 and ⟨βT⟩ > 0.46, which further supports our result obtained for the threshold border value in Pb + Pb collisions at snn = 5.02 TeV.

Flavor-dependent photoproduction in heavy-ion collisions

Strong electromagnetic fields produced in the non-central heavy-ion collisions can induce vector meson photoproduction. In this paper, we study the photoproduction J/ψ and ϕ mesons in the relativistic heavy-ion collision from ultra-peripheral nuclear collisions to peripheral hadronic heavy ion collisions. And then include both initial hadronic production and thermal production in quark-gluon plasma (QGP). We find, for the charm anti-charm bound state J/ψ, the photoproduced J/ψs are mainly in the very low momentum region and clearly exceed the hadronic production. However, considering the thermal production of strange quark anti-quark pairs in QGP produced in relativistic heavy-ion collisions, the photoproduced ϕ is usually smaller than the thermal production and only evident at very peripheral collisions as even their photoproduction is much larger than J/ψ.

Recent results of strong interaction program from NA61/SHINE experiment at CERN SPS

The NA61/SHINE experiment at the CERN SPS pursues a rich program of strong interactions. The main physics goals of this program are the study of properties of the onset of deconfinement and search for the signatures of the critical point of strongly interacting matter by performing the two-dimensional scan in a broad region of energy (beam momentum 13A-158A GeV/c) and system size (p+p, Be+Be, Ar+Sc and Xe+La). Recent NA61/SHINE results on particle spectra and event-by-event fluctuations in p+p, Be+Be and Ar+Sc collisions are shown with emphasis on the measurements of particle ratios, namely of pion a strangeness production, multiplicity fluctuations versus energy and the system size of colliding nuclei. It will be shown that the hadron production properties in heavy ion collisions which change rapidly in the low SPS energy domain and are interpreted as the beginning of quark-gluon plasma production – onset of deconfinement could be also the case in inelastic p+p interactions and probably in Be+Be collisions. The paper presents a selection of NA61/SHINE results on particle production properties discussed together with existing data from the NA49 collaboration. The evolution of non-monotonic structures in the pion and strangeness production as a function of the system size and energy is addressed. The rapid change of hadron production properties from p+p and Be+Be up to Ar+Sc and Pb+Pb collisions can be interpreted as the beginning of the large clusters formation of strongly interacting matter - the onset of fireball. The NA61/SHINE strong interaction programme is presented including the recent status on proton intermittency analysis and strongly intensive fluctuation observables of particle multiplicity and transverse momentum.

Recent PHENIX results on high-pT light hadron production

Production of Quark Gluon Plasma (QGP) has been established in central heavy ion collisions (Au+Au, Cu+Cu) at RHIC energies. Observation of strong suppression of hadron yields at high transverse momentum served as one of the most important evidences in favor of production of a new state of matter in such collisions. Recent RHIC run with asymmetric collision system (Cu+Au) provides the means to systematically study suppression pattern of hadrons in different nuclear overlap geometry needed to improve theoretical description of parton energy loss in QGP. Non-zero elliptic flow and a hint of suppression of high pT hadrons suggests that mini-QGP can be formed in collisions of light and heavy nuclei characterized by high charged particle multiplicities. To address the question of collective behavior in small systems RHIC provided series of geometry controlled experiments with highly asymmetric systems (p+Al, p+Au, 3He+Au). The recent results from the PHENIX experiment at RHIC on π0 and η mesons production in asymmetric systems will be presented and discussed.

CGC/saturation approach for high energy soft interactions:v2in proton-proton collisions

In this paper we continue our program to construct a model for high energy soft interactions, based on the CGC/saturation approach. We demonstrate that in our model which describes diffractive physics as well as multi-particle production at high energy, the density variation mechanism leads to the value of $v_2$ which is about $60\% \div 70\%$ of the measured $v_2$. Bearing in mind that in CGC/saturation approach there are two other mechanisms present: Bose enhancement in the wave function and local anisotropy, we believe that the azimuthal long range rapidity correlations in proton-proton collisions stem from the CGC/saturation physics, and not from quark-gluon plasma production.

Flavor dependence of jet quenching in pp collisions and its effect on R AA for heavy mesons

We study the flavor dependence of the medium modification factor $R_{pp}$ for $pp$ collisions for scenario with formation of a small-size quark-gluon plasma (QGP) for RHIC ($\sqrt{s}=0.2$ TeV) and LHC ($\sqrt{s}=2.76$ TeV) energies. We find that at $p_T\sim 10$ GeV the pion spectrum is suppressed by $\sim 20-30\,(25-35)$\% for RHIC (LHC), for $D$~($B$) mesons the suppression effect is smaller by a factor of $\sim 0.7-0.8$ ($0.5$). The flavor hierarchy $R_{pp}^\pi<R_{pp}^D<R_{pp}^B$ is held at $p_T\lesssim 20$ GeV for RHIC and at $p_T\lesssim 70$ GeV for LHC. This gives a sizeable reduction of the heavy-to-light ratios of the nuclear modification factors $R_{AA}$ as compared to that in the standard scenario without the QGP production in $pp$ collisions.

Thermal charm and charmonium production in quark gluon plasma

We study the effect of thermal charm production on charmonium regeneration in high energy nuclear collisions. By solving the kinetic equations for charm quark and charmonium distributions in Pb+Pb collisions, we calculate the global and differential nuclear modification factors $R_{AA}(N_{part})$ and $R{AA}(p_t)$ for $J/\Psi$s. Due to the thermal charm production in hot medium, the charmonium production source changes from the initially created charm quarks at SPS, RHIC and LHC to the thermally produced charm quarks at Future Circular Collider (FCC), and the $J/\Psi$ suppression ($R_{AA}<1$) observed so far will be replaced by a strong enhancement ($R_{AA}>1$) at FCC at low transverse momentum.

Effect of inelastic scattering process of gluons on dilepton productions of quark-gluon plasma

Dileptons have large mean free paths due to their small cross sections for electromagnetic interaction in plasma. Therefore they are considered to be an important probe for the formation and evolution of the quark matter. In this work, we calculate the dilepton production of quark-gluon plasma (QGP) produced in Au197+ Au197 central collisions at relativistic heavy ion collider (RHIC) energy based on the evolution model of a chemically equilibrating viscous QGP. The evolution of the QGP system is described by a set of coupled relaxation equations containing the master equations of partons, the equation of baryon number conservation and equation of energy-momentum conservation. Solving the set of evolution equations, one can obtain the evolution of temperature T, quark chemical potential q, fugacities q for quarks and g for gluons. To discuss the shear viscosity of QGP, the contributions of the elastic scattering of quarks qqqqand gluons gggg, as well as the inelastic scattering process of gluons ggggg are included. Based on the evolution model including the viscosity, we perform a complete calculation of the dilepton production, including the processes of quark-antiquark annihilation qqll, next-order annihilation qqgll, Compton-like scattering qg qll, qg qll, multiple scattering of quarks, as well as gluon fusion gg cc, annihilation qqcc. It is found that the spectra from the quark-antiquark annihilations qqll and qqgll are dominated. The contributions from multiple scattering cannot be neglected. We also find that the dilepton yields remarkably decrease with considering an additional gluon inelastic process in the calculation compared with the results with considering only elastic scatterings of quarks and gluons. This indicates that the evolution of QGP system is accelerated and the evolution time is shortened by the inelastic scatterings of gluons.

Verification of the model of a collision of a 800-GeV proton with an emulsion-nucleus tube

The production of quark-gluon plasma is discussed within the hydrodynamic theory of multiparticle hadron production in head-on collisions of nucleons with nucleons and nuclei. In searches for collisions of a proton with a tube of a track-emulsion nucleus, the use of parametrically invariant quantities is proposed. An experimental verification of statistical models involving qualitatively different pseudorapidity distributions of weakly ionizing secondary particles is performed. The results of this verification are discussed.

Heavy-quark-state production inA-Acollisions atspp=200GeV

We estimate differential rapidity cross sections for $J/\ensuremath{\Psi}$ and $\ensuremath{\Upsilon}(1S)$ production via Cu-Cu and Au-Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC), and the relative probabilities of ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ to $J/\ensuremath{\Psi}$ production via $p$-$p$ collisions using our recent theory of mixed heavy-quark hybrids, in which the ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ mesons have approximately equal normal $q\overline{q}$ and hybrid $q\overline{q}g$ components. We also estimate the relative probabilities of ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ to $J/\ensuremath{\Psi}$ production via Cu-Cu and Au-Au collisions, which will be measured in future RHIC experiments. We also review production ratios of $\ensuremath{\Upsilon}(2S)$ and $\ensuremath{\Upsilon}(3S)$ to $\ensuremath{\Upsilon}(1S)$ in comparison to recent experimental results.This is an extension of our recent work on $p$-$p$ collisions for possible tests of the production of quark-gluon plasma via $A$-$A$ collisions at RHIC.

Elliptic flow from thermal photons with magnetic field in holography

We compute the elliptic flow ${v}_{2}$ of thermal photons in a strongly coupled plasma with constant magnetic field via gauge/gravity duality. The D3/D7 embedding is applied to generate the contributions from massive quarks. By considering the cases in $2+1$ flavor super Yang-Mills analogous to the photon production in quark gluon plasma, we obtain the thermal photon ${v}_{2}$, which is qualitatively consistent with the direct photon ${v}_{2}$ measured at the relativistic heavy ion collider at intermediate energy. However, due to the simplified setup, the thermal photon ${v}_{2}$ in our model should be regarded as the upper bound for the ${v}_{2}$ generated by solely a magnetic field in the strongly coupled scenario.

The Numerical Analysis of Beta Decay Stimulation by the High Thermal Spike Single Photon Incidence to Valence Nucleons

The Numerical Analysis of Beta Decay Stimulation by the High Thermal Spike Single Photon Incidence to Valence Nucleons Since, at RHIC and LHC heavy-ion colliders the classical color field play an important role to study production of quark-gluon plasma, we propose a theory to describe strong-field inside the nucleons based on Dual Ginzburg-Landau-Pitaevski (DGL) theory.

Strangeness in high multiplicity proton–proton collisions in the ALICE experiment

The ALICE experiment at CERN is primarily focused on quark–gluon plasma production in heavy ion (Pb–Pb) collisions. In addition, high multiplicity events from the LHC pp programme will provide an interesting field of study. As with A–A collisions, high multiplicity could suggest high underlying energy density of the system, possibly exceeding that required for deconfinement. Bjorken first suggested that deconfinement might occur in pp collisions, and evidence for this was sought by the E-735 experiment at Fermilab but no clear signature was seen. The LHC will offer new possibilities for examining this idea owing to the much greater multiplicity reach available at higher energy. The ALICE experiment has powerful triggering tools and particle identification (PID), which place it in a strong position to analyse these events and to measure the observable signatures of deconfinement that may arise. Signatures particularly related to strangeness production will be outlined and the capabilities for such studies at ALICE will be discussed.

Jet energy loss and high [formula omitted] photon production in hot quark-gluon plasma

Jet-quenching and photon production at high transverse momentum are studied at RHIC energies, together with the correlation between jets and photons. The energy loss of hard partons traversing the hot QGP is evaluated in the AMY formalism, consistently taking into account both induced gluon emission and elastic collisions. The production of high p T photons in Au+Au collisions is calculated, incorporating a complete set of photon-production channels. Putting all these ingredients together with a (3+1)-dimensional ideal relativistic hydrodynamical description of the thermal medium, we achieve a good description of the current experimental data. Our results illustrate that the interaction between hard jets and the soft medium is important for a complete understanding of jet quenching, photon production, and photon-hadron correlations in relativistic nuclear collisions.

Static quark-antiquark interactions in zero and finite temperature QCD: I. Heavy quark free energies, running coupling, and quarkonium binding

We analyze heavy quark free energies in 2-flavor QCD at finite temperature and the corresponding heavy quark potential at zero temperature. Static quark anti-quark sources in color singlet, octet and color averaged channels are used to probe thermal modifications of the medium. The temperature dependence of the running coupling, $\alpha_{qq}(r,T)$, is analyzed at short and large distances and is compared to zero temperature as well as quenched calculations. In parts we also compare our results to recent findings in 3-flavor QCD. We find that the characteristic length scale below which the running coupling shows almost no temperature dependence is almost twice as large as the Debye screening radius. Our analysis supports recent findings which suggest that $\chi_c$ and $\psi\prime$ are suppressed already at the (pseudo-) critical temperature and thus give a probe for quark gluon plasma production in heavy ion collision experiments, while $J/\psi$ may survive the transition and will dissolve at higher temperatures.

Quark number susceptibilities and the Wróblewski parameter

The Wroblewski parameter is a convenient indicator of strangeness production and can be employed to monitor a signal of quark-gluon plasma production : enhancement of strangeness production. It has been shown to be about a factor two higher in heavy ion collisions than in hadronic collisions. Using a method proposed by us earlier, we obtained lattice QCD results for the Wroblewski parameter from our simulations of QCD with two light quarks both below and above the chiral transition. Our first principles based and parameter free result compare well with the A-A data from SPS and RHIC.

The Wroblewski parameter from lattice QCD

Enhancement of strangeness production has for long been proposed as a promising signal of quark–gluon plasma production. A convenient indicator for it is the Wroblewski parameter which has been shown to be about a factor of 2 higher in heavy-ion collisions. Using a method proposed by us earlier, we obtained lattice QCD results for the Wroblewski parameter from our simulations of QCD with two light quarks both below and above the chiral transition. Our first principles based and parameter-free result compares well with the A–A data.

Latest results from RHIC

Some of the most recent results from the Relativistic Heavy Ion Collider (RHIC) are reported. Exciting new experimental features have been observed in data from all four experiments. These new observations indicate the creation of a new form of ‘hot dense matter’ at RHIC energies, the properties of which are now beginning to be determined. PACS: 25.75.-q Relativistic heavy-ion collisions – 25.75.Nq Quark-gluon plasma production

Phase space description of the production of quark gluon plasma in heavy-ion collisions

A new source term is proposed to describe the production of quark gloun plasma in heavy-ion collisions.

Charmonium cross-sections and the QGP

In this short review we summarize experimental information and theoretical results for the low-energy dissociation cross sections of charmonia by light hadrons. These cross sections are required for the simulation of charmonium absorption through collisions with comovers in heavy ion collisions, which competes with quark-gluon plasma production as a charmonium-suppression mechanism. If the cross sections are sufficiently large these dissociation reactions may be misinterpreted as an effect of quark-gluon plasma production. Theoretical predictions for these RHIC-related processes have used various methods, including a color-dipole scattering model, meson exchange models, constituent interchange models and QCD sum rules. As the results have been largely unconstrained by experiment, some of the predictions differ by orders of magnitude, notably in the near-threshold regime that is most relevant to QGP searches.