Formation Of QGP Research Articles

From high p⊥ theory and data to inferring anisotropy of Quark-Gluon Plasma

High p⊥ theory and data are commonly used to study high p⊥ parton interactions with QGP, while low p⊥ data and corresponding models are employed to infer QGP bulk properties. On the other hand, with a proper description of high p⊥ parton-medium interactions, high p⊥ probes become also powerful tomography tools, since they are sensitive to global QGP features, such as different temperature profiles or initial conditions. This tomographic role of high p⊥ probes can be utilized to assess the spatial anisotropy of the QCD matter. With our dynamical energy loss formalism, we show that a (modified) ratio of RAA and ν2 presents a reliable and robust observable for straightforward extraction of initial state anisotropy. We analytically estimated the proportionality between the ν2/(1−RAA) and anisotropy coefficient ϵ2L, and found surprisingly good agreement with full-fledged numerical calculations. Within the current error bars, the extraction of the anisotropy from the existing data using this approach is still inaccessible. However, with the expected accuracy improvement in the upcoming LHC runs, the anisotropy of the QGP formed in heavy ion collisions can be straightforwardly derived from the data. Such a data-based anisotropy parameter would present an important test to models describing the initial stages of heavy-ion collision and formation of QGP, and demonstrate the usefulness of high p⊥ theory and data in obtaining QGP properties.

The surprising heavy hadrons production in pp and AA collisions: hadronization within coalescence and fragmentation

The hadronization process of heavy hadrons with bottom and charm quarks, especially for baryons Λ c and Λ b , in a dense QGP medium is largely not understood. We present within a coalescence plus fragmentation model the predictions for D 0, Ds, Λ c , B and Λ b spectra and the related baryon to meson ratios at RHIC and LHC in a wide range of transverse momentum region up to 10 GeV, moreover we show the effect of the hadronization mechanism which plays a fundamental role to describe simultaneously the experimental data for the nuclear suppression factor RAA and the elliptic flow υ 2(pT) of heavy hadrons from RHIC to LHC energies. In particular, we show the considerable change of the Nuclear modification factor of D mesons due to the large Ac production, explaining the RAA (pT) < 1 observed by STAR at low momenta. We will discuss how our model can naturally predict values of the order of O(1) for Λ c /D 0 as recently measured at both RHIC and LHC, and we present the novel predictions for Λ b /B not yet measured, which are much larger than the expectations from fragmentation. Moreover assuming that ar the LHC top energies there can be the formation of QGP, we show that in the same scheme due to considerable volume effect a still large Λ c /D 0 ≈ 0.5 is predicted as seen by ALICE in pp and pA collisions Furthermore in the same scheme can be predicted a baryon to meson ratio Λ c /D 0 in pp collisions assuming that at the LHC top energies there can be the formation of QGP matter. The results show a considerable volume effects that significantly reduce the ratios, but still predict quite larger values with respect to fragmentation, in agreement with recent data from ALICE in pp collisions.

Semiholography for heavy ion collisions

The formation of QGP in heavy ion collisions gives us a great opportunity for learning about nonperturbative dynamics of QCD. Semiholography provides a new consistent framework to combine perturbative and non-perturbative effects in a coherent way and can be applied to obtain an effective description for heavy ion collisions. In particular, it allows us to include nonperturbative effects in existing glasma effective theory and QCD kinetic theory for the weakly coupled saturated degrees of freedom liberated by the collisions in the initial stages in a consistent manner. We argue why the full framework should be able to confront experiments with only a few phenomenological parameters and present feasibility tests for the necessary numerical computations. Furthermore, we discuss that semiholography leads to a new description of collective flow in the form of a generalised non-Newtonian fluid. We discuss some open questions which we hope to answer in the near future.

Two component model with collective flow for hadroproduction in heavy-ion collisions

The spectra shape of produced charged hadrons on the size of a colliding system is discussed using a two component model. The hierarchy by the system-size in the spectra shape is observed. Next, the hydrodynamic extension of the model is suggested to describe the spectra of charged particles produced in heavy-ion collisions in the full range of transverse momenta, pT. Data from heavy-ion collisions measured at RHIC and LHC are analyzed and combined in terms of energy density.The observed regularities might be explained by the formation of QGP during the collision.

Multiplicity and theremalization time in heavy-ions collisions

We present a concise review of quark-gluon plasma formation in heavy-ions collisions within the holographic approach. In particular, we discuss how to get the total multiplicity in heavy ions collision to fit the recent experimental data. We also discuss theoretical estimations of time formation of QGP in heavy ions collision and show that different observables can give the different times of QGP formation.

A critical review of RHIC experimental results

The relativistic heavy-ion collider (RHIC) was constructed to achieve an asymptotic state of nuclear matter in heavy-ion collisions, a near-ideal gas of deconfined quarks and gluons denoted quark–gluon plasma or QGP. RHIC collisions are indeed very different from the hadronic processes observed at the Bevalac and AGS, but high-energy elementary-collision mechanisms are also non-hadronic. The two-component model (TCM) combines measured properties of elementary collisions with the Glauber eikonal model to provide an alternative asymptotic limit for A–A collisions. RHIC data have been interpreted to indicate formation of a strongly-coupled QGP (sQGP) or "perfect liquid". In this review, I consider the experimental evidence that seems to support such conclusions and alternative evidence that may conflict with those conclusions and suggest different interpretations.

Search for Tetraquarks in Relativistic Heavy-IonCollisions

Tetraquarks can be produced in relativistic heavy-ion collision.The yield of this kind of tetraquarks can increase significantlysoon as the formation of QGP after the collision. If there is nophase transition after collision, the upper bound of theproduction of this four-quark states can be estimated from thefree hadronic gas model for nuclear matter. The relative yieldratio of tetraquark css̄s̄ to Ω is less than 0.0164.

Strange stars at finite temperature

We calculate strange star properties, using large Nc approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock meanfield approximation method, using a modified Richardson potential with two scale parameters Λ and Λ′, to find a new set of equation of state (EOS) for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom (AF) and CSM.

CRITICAL PARAMETERS OF PHASE TRANSITION IN DUAL QCD

Color confinement is studied in dual version of SU (2) color gauge theory using its topological structure and the dynamical breaking of the magnetic symmetry which has been shown to effectively trigger the QCD monopole condensation in a dynamical way. The resulting flux tube structure of the QCD vacuum is explored which has been shown to lead to the perfect dual superconducting nature to the QCD vacuum in its dynamically broken phase. The analysis of the flux tube energy at different hadronic length scales has been shown to lead to the appearance of the strong confinement forces in QCD vacuum at large hadronic distances and an indication for the deconfinement phase at small scales. The analysis of the flux tube energy is then used to compute numerically the critical radius and the critical flux tube density of the phase transition from the flux tube phase to deconfined one inside hadrons. The numerical estimates are shown to be in fairly good agreement with the analytical values. The possible implications of these critical parameters on the formation of QGP as a result of the flux tubes fusion in intermediate energy regime are also discussed.

Search for Exotic Strange Dibaryon in Relativistic Heavy Ion Collisions**The project supported in part by National Natural Science Foundation of China under Grant No. 90103019, the Doctoral Program Foundation of Institution of Higher Education, and the State Education Commission of China under Grant No. 2000000147

The exotic strange dibaryon particle with S=-6 can be produced in relativistic heavy ion collisions. The yields of this kind of exotic strange dibaryon particles can increase significantly soon as the formation of QGP does exhibit after the collision. If there is no phase transition after the collision, the upper bound of the production of this diomega can be estimated from the free hadronic gas model for nuclear matter. The relative yield ratio of diomega to deuteron is less than 0.000205, this means that if there is no QGP creation it is difficult to observe the production of diomega in relativistic heavy ion collisions.

Hadronic entropy enhancement and low density QGP

Recent studies show that for central collisions the rise in the incident energy from AGS to RHIC decreases the value of the chemical potential in the hadron-QGP phase diagram. Thus, the formation of QGP at RHIC energies in central collisions may be expected to occur at very small values of the chemical potential. Using many different relativistic mean-field hadronic models (RMF) at this regime we show that the critical temperature for the hadron-QGP transition is hadronic model independent. We have traced back the reason for this and conclude that it comes from the fact that the QGP entropy is much larger than the hadronic entropy obtained in all the RMF models. We also find that almost all of these models present a strong entropy enhancement in the hadronic sector coming from the baryonic phase transition to a nucleon–antinucleon plasma. This result is in agreement with the recent data obtained in the STAR collaboration at RHIC where a rich proton–antiproton matter was found.

Photon emission in heavy ion collisions at the CERN SPS

We compute the thermal photon spectrum in the Pb+Pb collisions at the CERN SPS energy using thermal emission rates and a hydrodynamic description for the evolution of produced hot matter and compare our results with the measurements of the excess photons by the WA98 Collaboration. Our results show that the measured photon spectrum can be reproduced with realistic initial conditions which take properly into account also the finite longitudinal size of the initial collision zone and which simultaneously describe well both the transverse and longitudinal hadron spectra. In the scenario with initial formation of QGP the recently calculated emission rate, complete to order α s , reproduces the measured spectrum. However, the experimental spectrum can also be reproduced in a purely hadronic scenario without transition to QGP state, but a high initial temperature, much over the values predicted for the phase transition temperature T c , is required.

Ω Production and Corresponding Ratio of Antiparticle to Particle in Relativistic Nucleus-Nucleus Collisions11The project supported by National Natural Science Foundation of China

We use the event generator LUCIAE to analyze the WA85 data of ratio of Ω- to Ω- in reaction (200A GeV/c)S + W. The result indicates that the reproduction of WA85 data might be achieved in hadronic rescattering regime of LUCIAE and might need not to rely on the formation of QGP.