Quark Matter Formation Research Articles

A method for probing the formation of quark matter

Based on a multi-phase transport model for relativistic heavy-ion collisions, effects of the parton scatterings on the production of strangeness in relativistic heavy-ion collisions are studied. It is found that the distributions of strange quark and strange baryon, especially for the double strangeness Ξ−, are significantly affected by the parton scatterings in heavy-ion collisions below sNN∼ 10 GeV. Given parton scatterings as a signal of the formation of quark matter, the transverse momentum distribution of the ratio of single and double strangeness (Λ+Σ0)/Ξ− produced in heavy-ion collisions may serve as a potential probe of the emergence of quark matter, or equivalently, the occurrence of hadron-quark phase transition in relativistic heavy-ion collisions.

Exploring the Phase Diagram of V-QCD with Neutron Star Merger Simulations

Determining the phase structure of Quantum Chromodynamics (QCD) and its Equation of State (EOS) at densities and temperatures realized inside neutron stars and their mergers is a long-standing open problem. The holographic V-QCD framework provides a model for the EOS of dense and hot QCD, which describes the deconfinement phase transition between a dense baryonic and a quark matter phase. We use this model in fully general relativistic hydrodynamic (GRHD) simulations to study the formation of quark matter and the emitted gravitational wave signal of binary systems that are similar to the first ever observed neutron star merger event GW170817.

Role of the conserved charges in the chiral symmetry restoration phase transition

The effect of conserved baryon, isospin and strangeness charges on the behavior of phase transitions in dense matter is studied. Baryonic matter is described within the three-flavor Polyakov$-$Nambu$-$Jona-Lasinio model and several charge fractions $Y_Q$ are considered. The role of the vector interaction, which can be important to describe dense systems, is discussed. Special attention is given to the case with charge fraction $Y_Q=0.4$, due to its importance in heavy-ion collisions and core-collapse supernova matter. It is shown that the possible formation of chiral-symmetric quark matter in the laboratory will be favored in asymmetric matter. Besides, the inclusion of the vector interaction reinforces the formation of quark matter at lower densities.

Understanding the "CENTAURO" cosmic ray events in terms of a transition to quark matter

We have developed a phenomenological model, based on the \Iavailable\i and accepted information for the Centauro events. Our model attempts to explain the observed features of the average event and to estimate characteristic thermodynamic quantities, such as ε, μ, Τ, whose knowledge is necessary for an educated suggestion of a possible phase transition to quark matter in a highly dense nuclear system. The model we presented makes certain plausible assumptions and arguments, which do not conflict with any known theory nor contradict any existing experimental data. The important assumptions are: the collision of a medium-14 mass cosmic ray nucleus with an Ν nucleus and the small changes cf the fireball entropy, volume and temperature during the phase transition. The justification of these assumptions is given by the self- consistency of the model and the estimated auantities and the reasonable and plausible values of these quantities, which are also within the range considered to be necessary for the phase transition. Our "Centauro" model is (to our knowledge) the only one capable of being tested at RHIC and the LHC. In view of the highly interesting and still puzzling Centauro events, we believe that every effort should be made to implement appropriate measurements of particle multiplicity, ID, energy content and <p > Τ in the fragmentation rapidity region. It may give a direct and undoubted indication of quark matter formation in a highly dense nuclear system and solve the mystery of the Centauro and other exotic cosmic ray events. At the same time, the possibility of observing "strangelets" adds a new dimension of excitement to these measurements.

Rotation-Driven Phase Transitions in the Cores of Pulsars

In this paper, we discuss the impact of rotation on the particle composition of rotating neutron stars (pulsars). Particular emphasis is put on the formation of quark matter during stellar spin-down, driven by continuous gravitational compression. Our study is based on modern models for the nuclear equation of state whose parameters are tightly constrained by nuclear data, neutron star masses, and the latest estimates of neutron star radii.

QCD in Stars

We discuss cold dense QCD by examining constraints from neutron stars, nuclear experiments, and QCD calculations at low and high baryon density. The two solar mass constraint and suggestive small radii (10~13 km) of neutron stars constrain the strength of hadron-quark matter phase transitions. Assuming the adiabatic continuity from hadronic to quark matter, we use a schematic quark model for hadron physics and examine the size of medium coupling constants. We find that to baryon density nB ~ 10n0 (n0: nuclear saturation density), the model coupling constants should be as large as in the vacuum, indicating that gluons remain non- perturbative even after the quark matter formation.

Phenomenological QCD equations of state for neutron stars

We delineate the properties of QCD matter at baryon density nB=1−10n0 (n0: nuclear saturation density), through the construction of neutron star equations of state that satisfy the neutron star mass-radius constraints as well as physical conditions on the speed of sound. The QCD matter is described in the 3-window modeling: at nB≲2n0 purely nuclear matter; at nB≳5n0 percolated quark matter; and at 2n0≲nB≲5n0 matter intermediate between these two which are constructed by interpolation. Using a schematic quark model with effective interactions inspired from hadron and nuclear physics, we analyze the strength of interactions necessary to describe observed neutron star properties. Our finding is that the interactions should remain as strong as in the QCD vacuum, indicating that gluons at nB=1−10n0 remain non-perturbative even after quark matter formation.

Core collapse supernovae in the QCD phase diagram

We compare two classes of hybrid equations of state with a hadron-to-quark matter phase transition in their application to core collapse supernova simulations. The first one uses the quark bag model and describes the transition to three-flavor quark matter at low critical densities. The second one employs a Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model with parameters describing a phase transition to two-flavor quark matter at higher critical densities. These models possess a distinctly different temperature dependence of their transition densities which turns out to be crucial for the possible appearance of quark matter in supernova cores. During the early post bounce accretion phase quark matter is found only if the phase transition takes place at sufficiently low densities as in the study based on the bag model. The increase critical density with increasing temperature, as obtained for our PNJL parametrization, prevents the formation of quark matter. The further evolution of the core collapse supernova as obtained applying the quark bag model leads to a structural reconfiguration of the central proto-neutron star where, in addition to a massive pure quark matter core, a strong hydrodynamic shock wave forms and a second neutrino burst is released during the shock propagation across the neutrinospheres. We discuss the severe constraints in the freedom of choice of quark matter models and their parametrization due to the recently observed 2 solar mass pulsar and their implications for further studies of core collapse supernovae in the QCD phase diagram.

QCD critical point in the strong coupling lattice QCD and during black hole formation

We discuss the QCD phase diagram from two different point of view. We first investigate the phase diagram structure in the strong coupling lattice QCD with Polyakov loop effects, and show that the the chiral and ZNc deconfinement transition boundaries deviate at finite μ as suggested from large Nc arguments. Next we discuss the possibility to probe the QCD critical point during prompt black hole formation processes. The thermodynamical evolution during the black hole formation would result in quark matter formation, and the critical point in isospin asymmetric matter may be swept. (T, μB) region probed in heavy-ion collisions and the black hole formation processes covers most of the critical point locations predicted in recent lattice Monte-Carlo simulations and chiral effective models.

Entropy development in ideal relativistic fluid dynamics with the Bag Model equation of state

We consider an idealized situation where the Quark–Gluon Plasma (QGP) is described by a perfect, (3+1)-dimensional fluid dynamic model starting from an initial state and expanding until a final state where freeze-out and/or hadronization takes place. We study the entropy production with attention to effects of (i) numerical viscosity, (ii) late stages of flow where the Bag Constant and the partonic pressure are becoming similar, (iii) and the consequences of final freeze-out and constituent quark matter formation.

10.1007/s11450-008-2017-4

The arguments are presented showing that crossover, fluctuation phenomena, and possible Anderson transition are the precursors of quark matter formation.

The strange prospects for astrophysics

The implications of the formation of strange quark matter in neutron stars and in core-collapse supernovae are discussed with special emphasis on the possibility of having a strong first-order QCD phase transition at high baryon densities. If strange quark matter is formed in core-collapse supernovae shortly after the bounce, it causes the launch of a second outgoing shock which is energetic enough to lead to an explosion. A signal for the formation of strange quark matter can be read off from the neutrino spectrum, as a second peak in antineutrinos is released when the second shock runs over the neutrinosphere.

Strange hadron yields and ratios in heavy ion collisions at RHIC energy

Recent experimental data support the presence of quark coalescence in heavy ion collisions at RHIC energies. Hadronization of quark matter and hadron formation in heavy ion collisions can be described by the coalescence process, and measured data are reproduced successfully. On the other hand, the theoretical coalescence calculations are based on a non-relativistic description. Here we investigate the robustness of the coalescence description, using different wavefunction overlap during hadron formation.

The robustness of quasiparticle coalescence in quark matter

Experimental data collected in heavy ion collisions at RHIC energies strongly support quark matter formation and the presence of quark coalescence at these energies. Hadronization of quark matter and hadron formation in heavy ion collisions can be described by the coalescence process, and measured data could have been reproduced successfully. Theoretical calculations are based on a quantum mechanical description of coalescence. Here we investigate the robustness of the coalescence description, using different wave-function overlap during hadron formation.

Toward the understanding of quark matter formation

The arguments are presented showing that crossover, fluctuation phenomena, and possible Anderson transition are the precursors of quark matter formation.

Formation of quark phases in compact stars and their connection to gamma-ray-bursts

We analyze the occurrence of quiescent times in the temporal structure of the gamma-ray-bursts (GRBs) light curves. We show that if a long quiescent time is present, it is possible to divide the total duration of GRBs into three periods: the pre-quiescence emission, the quiescent time and the post-quiescence emission. We then discuss a model of the GRBs inner engine based on the formation of quark phases during the life of a hadronic star. Within this model the pre-quiescence emission is interpreted as due to the deconfinement of a quark inside a hadronic star and the formation of 2SC quark matter. The post-quiescence emission is due to the conversion of 2SC into the color-flavor-locking (CFL) phase. The temporal delay between these two processes is connected with the nucleation time of the CFL phase in the 2SC phase and it can be associated with the observed quiescent times in the GRBs light curves. The stability of CFL cores in compact stars is also discussed.

Magnetic catalysis of stability of quark matter in the Nambu-Jona-Lasinio model

The effect of an external magnetic field H on the stability of quark matter is studied on the basis of the Nambu-Jona-Lasinio model. It is shown that, at H = 0, droplets of quark matter are stable only in the case where the coupling constant G is greater than some value Gbag. If H ≠ 0, stable multiquark formations may exist even for G ≤ Gbag (magnetic catalysis of stability). For G > Gbag, a magnetic field facilitates the formation of stable quark matter.

Current Status of Quark –Gluon Plasma Signals

Compelling evidence for the creation of a new form of matter has been claimed to be found in Pb+Pb collisions at SPS. We discuss the uniqueness of often proposed experimental signatures for quark matter formation in relativistic heavy ion collisions. It is demonstrated that so far none of the proposed signals like J/ϕ meson production/suppression, strangeness enhancement, dileptons, and directed flow unambiguously show that a phase of deconfined matter has been formed in SPS Pb+Pb collisions. We emphasize the need for systematic future measurements to search for simultaneous irregularities in the excitation functions of several observables in order to come close to pinning the properties of hot, dense QCD matter from data.

Simple predictions from ALCOR c for rehadronization of charmed quark matter

We study the production of charmed hadrons with the help of ALCOR c , the algebraic coalescence model for rehadronization of charmed quark matter. Mesonic ratios are introduced as factors connecting various anti-baryon to baryon ratios. The resulting simple relations could serve as tests of quark matter formation and coalescence type rehadronization in heavy ion collisions.

Electromagnetic signals of quark gluon plasma

Successive equilibration of quark degrees of freedom and its effects on electromagnetic signals of quark gluon plasma are discussed. The effects of the variation of vector meson masses and decay widths on photon production from hot strongly interacting matter formed after Pb + Pb and S + Au collisions at CERN SPS energies are considered. It has been shown that the present photon spectra measured by WA80 and WA98 Collaborations can not distinguish between the formation of quark matter and hadronic matter in the initial state.