State Of Nuclear Matter Research Articles

Overview of quarkonium production in ALICE

ALICE is an experiment mainly dedicated to the study of the quark-gluon plasma (QGP), a state of nuclear matter where quarks and gluons are deconfined, due to high temperature and density. The production of quarkonia, bound states of either a charm and anti-charm quark pair for charmonia or a bottom and anti-bottom quark pair for bottomonia, is a very useful probe of this state of matter. Indeed, the presence of the QGP modifies their production yields, due to a competition between medium-induced suppression and, at least for charmonia, a recombination mechanism in medium or at hadronization. The measurement of quarkonium production in proton-proton (pp) collisions is also essential to investigate its production mechanism as well as to test quantum chromodynamics (QCD) models. It also provides a reference for the investigation of the properties of the QGP in nucleus–nucleus collisions. Measurements in proton–nucleus collisions allow one to study the cold nuclear matter effects. In addition, high multiplicity pp collisions are useful to investigate multiparton interactions and to search for collectivity in small systems. In this contribution, we will report on the latest quarkonium production results, obtained with the ALICE detector in pp collisions, for different center-of-mass energies, at midrapidity and forward rapidity. We will also present the measurements of the quarkonium nuclear modification factor in p–Pb collisions at sNN=8.16TeV. Finally, in Pb–Pb collisions at sNN=5.02TeV, we will report on the new ψ(2S) measurement, the nuclear modification factor of the prompt and non-prompt J/ψ, as well as the first measurement of quarkonium polarization, the latter carried out also as a function of the event plane. All the measurements will be compared to theoretical predictions.

Probing the nuclear equation of state using the neutron star observables within the Bayesian inference approach

The constraint on nuclear matter's equation of state has been a shared goal in nuclear physics and astrophysics. The most difficult one to constrain the equation of state is the constraint on the symmetry energy in nuclear matter. In this study, we adopt a theoretical framework that combines an isospin-dependent parametric equation of state for neutron star cores with a Bayesian inference approach to calculate the posterior probability distribution functions of the parameters of the equation of state in the nuclear matter based on mass and radius data reported by the LIGO/Virgo and NICER Collaborations, and thus constrain both the equation of state in symmetric nuclear matter and the equation of state in non-symmetric nuclear matter. It is found that a stiffer equation of state is supported by the data from the NICER Collaboration, and the improvement in the equation of state is not observed. The 68% credible intervals for the parameters are $L~=~45^{+15}_{-9}$ MeV for the slope, $K_{\mathrm{sym}}$ = $-100_{-110}^{+50}$ MeV for the curvature parameters of the symmetry energy and $J_0~=~-180_{-40}^{+60}$ MeV for the skewness parameter of the equation of state of symmetric nuclear matter. The symmetry energy values at two and three times normal density are, respectively, $E_{\mathrm{sym}}(2\rho_0)~=~48.9_{-16}^{+7.8}$ MeV and $E_{\mathrm{sym}}(3\rho_0)~=~81.8_{-57.2}^{+21.1}$ MeV.

Equation of state for holographic nuclear matter as instanton gas

In a holographic model, which was used to investigate the color superconducting phase of QCD, a dilute gas of instantons is introduced to study the nuclear matter. The free energy of the nuclear matter is computed as a function of the baryon chemical potential in the probe approximation. Then the equation of state is obtained at low temperature. Using the equation of state for the nuclear matter, the Tolman-Oppenheimer-Volkov equations for a cold compact star are solved. We find the mass-radius relation of the star, which is similar to the one for quark star. This similarity implies that the instanton gas given here is a kind of self-bound matter.

OBTAINING NEUTRON MATTER AND HYPERHEAVY NUCLEI: POSSIBLE QUANTUM-TECHNOLOGICAL INSTRUMENTAL APPROACHES

Possible mechanisms of creation of both hyperheavy nuclei by electron-nuclear collapse and neutron matter by condensation of ultracold neutrons are discussed. The fundamental possibility of the existence of such objects was previously substantiated by A.B.Migdal, who suggested that the known set of proton-neutron nuclei with mass numbers from 0 to 300 and a maximum specific binding energy of about 8 MeV / nucleon at A≈60 corresponds to the first region, beyond which (starting from about the charge Z≈ ( hc/e2 )3/2 ≈1600 ) there is an additional region describing a possible state of nuclear matter, stabilized by a pion condensate. In this region, the maximum specific energy corresponds to ≈15 MeV / nucleon at A ≈ 100000. It is shown that neutron matter can be obtained under certain conditions, and its systematization can be realized as an addition to the Periodic Table. When solving such problems, it becomes quite real to study not only physical, but also chemical, and possibly engineering and technical properties. Analysis shows that the stability of neutron matter at the microlevel is ensured by the Tamm interaction and the Hund beta equilibrium. Such matter can be quite stable not only on the mega-level (neutron stars) due to gravitational interaction, as was a priori assumed earlier, but also on the scale of "ordinary" matter. The process of neutronization is possible not only with critical gravitational interaction, but also by other mechanisms (supercritical increase in the atomic number of elements due to electron-nuclear collapse and condensation of ultracold neutrons), which opens the way to the fundamental possibility of obtaining both neutron matter in laboratory conditions and superheavy nuclei. Based on the works of Migdal, Tamm and Hund, the possibility of the existence of stable neutron matter (with Z >> 175, N >> Z, A> 10 3 -10 5 and a size of 200-300 femtometers and more) is argued at the microlevel, and not only at the mega-level, as is now considered in astrophysics. A critical analysis of the well-established concept of the minimum possible mass of neutron stars is carried out. The following quantum technological approaches to the realization of UCN condensation are proposed: 1. Slow isothermal compression; 2. Refrigerator for dissolving helium-3 and helium-4; 3. Use of a conical concentrator for UCN focusing (Vysotskii cone); 4. Magnetic trap; 5. Additional UCN laser cooling. Neutron matter is considered as a potential cosmological candidate for dark matter. One should take into account the possibility of the formation of fragments of neutron matter as dark matter (neutral, femto-, pico- and nanoscale, the cooling of relics makes it difficult to detect them by now) already at the initial origin of the Universe, which is the dominant process. The observable part of the Universe is formed by the residual part of protons, and then by decayed single neutrons and unstable fragments of neutron matter (with Z> 175, N >> Z, but A <10 3 -10 5 ).

Thermal properties of hot and dense matter: Influence of rapid rotation on protoneutron stars, hot neutron stars, and neutron star merger remnants

The knowledge of the equation of state is a key ingredient for many dynamical phenomena that depend sensitively on the hot and dense nuclear matter, such as the formation of protoneutron stars and hot neutron stars. In order to accurately describe them, we construct equations of state at FInite temperature and entropy per baryon for matter with varying proton fractions. This procedure is based on the momentum dependent interaction model and state-of-the-art microscopic data. In addition, we investigate the role of thermal and rotation effects on microscopic and macroscopic properties of neutron stars, including the mass and radius, the frequency, the Kerr parameter, the central baryon density, etc. The latter is also connected to the hot and rapidly rotating remnant after neutron star merger. The interplay between these quantities and data from late observations of neutron stars, both isolated and in matter of merging, could provide useful insight and robust constraints on the equation of state of nuclear matter.

Observation of a Liquid–Gas Phase Transition upon Antiproton Annihilation in a Nuclear Emulsion

Five hundred events of antiproton stopping and annihilation in nuclear emulsion were observed. A description of the equation of state for nuclear matter in terms of the van de Waals equation made it possible to determine the temperature dependence of the pressure and density and to obtain an estimate for the boundary of the spinodal region in which a uniform state undergoes an instantaneous transition from to a uniform state to a mixture of two phases—fragments and a nuclear gas of nucleons observed experimentally.

Horizon radiation reaction forces

Using Effective Field Theory (EFT) methods, we compute the effects of horizon dissipation on the gravitational interactions of relativistic binary black hole systems. We assume that the dynamics is perturbative, i.e it admits an expansion in powers of Newton’s constant (post-Minkowskian, or PM, approximation). As applications, we compute corrections to the scattering angle in a black hole collision due to dissipative effects to leading PM order, as well as the post-Newtonian (PN) corrections to the equations of motion of binary black holes in non-relativistic orbits, which represents the leading order finite size effect in the equations of motion. The methods developed here are also applicable to the case of more general compact objects, eg. neutron stars, where the magnitude of the dissipative effects depends on non-gravitational physics (e.g, the equation of state for nuclear matter).

Binding Energy of Nuclear Matter in Terms of QCD Condensates

We calculate the nucleon parameters – the effective mass $$m{\text{*}}$$ , vector self energy $${{\Sigma }_{V}}$$ and the binding energy per nucleon $$\mathfrak{P}$$ in terms of QCD condensates. We study the equilibrium states of the matter. We employ the QCD sum rules approach. Including the condensates with d = 6 we find equilibrium states of nuclear matter for $${{{\sigma }}_{N}} > 41$$ MeV. The equilibrium is due to influence of the relativistic motion of nucleons on the scalar quark condensate.

Optimal Neutron-star Mass Ranges to Constrain the Equation of State of Nuclear Matter with Electromagnetic and Gravitational-wave Observations

Abstract Exploiting a very large library of physically plausible equations of state (EOSs) containing more than 107 members and yielding more than 109 stellar models, we conduct a survey of the impact that a neutron-star radius measurement via electromagnetic observations can have on the EOS of nuclear matter. Such measurements are soon to be expected from the ongoing Neutron Star Interior Composition Explorer mission and will complement the constraints on the EOS from gravitational-wave detections. Thanks to the large statistical range of our EOS library, we can obtain a first quantitative estimate of the commonly made assumption that the high-density part of the EOS is best constrained when measuring the radius of the most massive, albeit rare, neutron stars with masses M ≳ 2.1 M ⊙. At the same time, we find that radius measurements of neutron stars with masses M ≃ 1.7–1.85 M ⊙ can provide the strongest constraints on the low-density part of the EOS. Finally, we quantify how radius measurements by future missions can further improve our understanding of the EOS of matter at nuclear densities.

Nuclear modification factors of light mesons in Cu+Au collisions

Strongly interacting quark-gluon plasma (sQGP) is a state of nuclear matter at extremely high values of temperature with quarks and gluons as degrees of freedom. Jet-quenching is one of the evidences for sQGP formation in relativistic heavy ion collisions (A+A) and is manifested by suppression of particle yields at high transverse momentum relative to yields of the same particles measured at elementary proton-proton collisions at the same collision energy. Systematic experimental research of jet-quenching is provided by the measurement of nuclear modification factors of light mesons (π0, η, , ω etc.) in different A+A systems. Asymmetric system of Cu+Au collisions at GeV is characterised by similar energy density but different collision geometry when compared to symmetric systems (Au+Au or Cu+Cu). This paper presents measurements of π0 and η mesons nuclear modification factors in Cu+Au collisions. Results are compared with ones measured in Au+Au and Cu+Cu collisions at the same collision energy.

Heavy flavor measurements at the STAR experiment

In ultra-relativistic heavy-ion collisions at RHIC, a new state of nuclear matter with extreme properties is produced — the strongly interacting quark-gluon plasma. Heavy quarks, predominantly produced at early stages of collisions owing to their large masses, provide an exceptional probe for exploring the hot and dense medium created in such collisions. The Heavy Flavor Tracker and Muon Telescope Detector have been fully operational since 2014 and have significantly improved STAR’s capabilities in measuring both open and hidden heavy flavor hadrons in heavy-ion collisions. We present an overview of recent heavy flavor results obtained at the STAR experiment.

Negative-parity nucleon excited state in nuclear matter

Spectral functions of the nucleon and its negative parity excited state in nuclear matter are studied using QCD sum rules and the maximum entropy method (MEM). It is found that in-medium modifications of the spectral functions are attributed mainly to density dependencies of the $\langle \bar{q}q \rangle $ and $\langle q^{\dagger}q \rangle $ condensates. The MEM reproduces the lowest-energy peaks of both the positive and negative parity nucleon states at finite density up to $\rho \sim \rho_N$ (normal nuclear matter density). As the density grows, the residue of the nucleon ground state decreases gradually while the residue of the lowest negative parity excited state increases slightly. On the other hand, the positions of the peaks, which correspond to the total energies of these states, are almost density independent for both parity states. The density dependencies of the effective masses and vector self-energies are also extracted by assuming the mean-field green functions for the peak states. We find that, as the density increases, the nucleon effective mass decreases while the vector self-energy increases. The density dependence of these quantities for the negative parity state on the other hand turns out to be relatively weak.

New state of nuclear matter: Nearly perfect fluid of quarks and gluons in heavy-ion collisions at RHIC energies

This article reviews several important results from RHIC experiments and discusses their implications. They were obtained in a unique environment for studying QCD matter at temperatures and densities that exceed the limits wherein hadrons can exist as individual entities and raises to prominence the quark-gluon degrees of freedom. These findings are supported by major experimental observations via measuring of the bulk properties of particle production, particle ratios and chemical freeze-out conditions, and elliptic flow; followed by hard probe measurements. The results reveal that a dense, strongly-interacting medium is created in central Au+Au collisions at 200 GeV at RHIC. This revelation of a new state of nuclear matter has also been observed in measurements at the LHC. Further, the IP-Glasma model coupled with viscous hydrodynamic models, which assumes the formation of a QGP, reproduces well the experimental flow results from Au+Au at 200 GeV. This implies that the fluctuations in the initial geometry state are important and the created medium behaves as a nearly perfect liquid of nuclear matter because it has an extraordinarily low ratio of shear viscosity to entropy density. However, these discoveries are far from being fully understood. Furthermore, recent experimental results from RHIC and LHC in small p+A, d+Au and He+A collision systems provide brand new insight into the role of initial and final state effects. These have proven to be interesting and more surprising than originally anticipated; and could conceivably shed new light in our understanding of collective behavior in heavy-ion physics. Accordingly, the focus of the experiments at both facilities RHIC and the LHC is on detailed exploration of the properties of this new state of nuclear matter, the QGP.

Extreme states of nuclear matter - 1980

The theory of hot nuclear fireballs consisting of all possible finite-size hadronic constituents in chemical and thermal equilibrium is presented. As a complement of this hadronic gas phase characterized by maximal temperature and energy density, the quark bag description of the hadronic fireball is considered. Preliminary calculations of temperatures and mean transverse momenta of particles emitted in high multiplicity relativistic nuclear collisions together with some considerations on the observability of quark matter are offered.

Behavior of relativistic shock waves in nuclear matter

An equation of state of nuclear matter describing the quark–hadron phase transition is derived within a variant of the MIT bag model. This equation of state is analyzed in order to test the criteria of instability and neutral stability of relativistic shock waves. It is shown that Taub adiabats passing through the phase transition region contain segments with an ambiguous representation of the shock-wave discontinuity, which means the possibility of splitting a shock wave with the formation of a combined compression wave. Isentropes passing through the mixed phase region have bends and are not completely convex (in the p–T plane, where T is the generalized specific volume); as a result, shock and combined rarefaction waves can appear. Numerical simulation has confirmed the appearance of these singularities of wave processes in nuclear matter in the region of the phase transition from the hadronic state to the quark–gluon plasma.

English

Proton-proton collision is a simple system to investigate nuclear matter and it is considered to be a guide for more sophisticated processes in the proton-nucleus and the nucleus-nucleus collisions. In this article, the authors present a phenomological study of how the mechanism of particle production in pp interaction changes over a wide range of interaction energy. This study is done on data of charged particle produced in pp experiments at different values of energy. Some of these data give the created particles classified as hadrons, baryons and mesons, which help us compare between production of different particles. This might probe some changes in the state of nuclear matter and identify the mechanism of interaction. Key words: String, gluon fragmentation, jet production.

LOCV approach and core-crust transition in neutron stars

In this paper, we have calculated the core-crust transition parameters and the location of inner edge for crust in the neutron stars. We have also investigated the structural properties of neutron stars, such as mass and radius for the core and crust, the moment of inertia, and its crustal fraction. Here we have employed the lowest-order constrained variational approach and used the UV14 + TNI and AV18 potentials to compute the equation of state of nuclear matter. Finally, we have compared our results with those of other techniques.

Nuclear-chemical processes under the conditions of laser ablation of metals in aqueous media (problems of “cold fusion”)

A brief review of results on initiation of nuclear transformations under conditions of the laser ablation of metals in aqueous media upon exposure to picosecond laser impulses with peak intensity JE ∼ 1010–1013 W/cm2, which is orders of magnitude less than required for the direct initiation of nuclear processes, JE ∼ 1018–1019 W/cm2, is presented. It is shown that the decay rate of radioactive nuclei (using the example of uranium 238) increases significantly (by orders of magnitude), nucleus transmutation processes are initiated (using the example of the transmutation of mercury 196 nuclei into gold 197), and the nuclear fusion of light elements occurs (using the example of tritium nuclei) under such conditions. Concepts regarding the processes of inelastic (with the generation of neutrino-antineutrino pair) interactions between electrons of high (on the chemical scale) energies (∼5–10 eV) and nuclei are developed in order to understand the totality of the current experimental data on the initiation of such processes under conditions of the laser ablation of metals in solutions of ordinary and heavy water. This is reflected in the definition of such processes as nuclear-chemical. It is suggested that the state of nuclear matter in nuclei formed during such interactions is in an unbalanced in-shake-up state, and cannot be pictured in the standard manner, as an ensemble of a certain number of nucleons. Such states are reactive for a wide class of nuclear transformations.

Superfluid states in β-stable nuclear matter

Two superfluid states of nuclear matter, which are supposed to play an important role in neutron stars, are discussed: the first one due to the proton-proton 1S0 pairing in β-equilibrium nuclear matter; the second one due to the anisotropic neutron-neutron 3PF2 pairing in neutron matter. Since the two phases appear at high density of nuclear matter, the three-body forces were added to the pairing interaction and the strong correlation effects in the single-paricle spectrum. The energy gaps, obtained solving the extended BCS equations, significantly deviate from the values without medium effects so as to limit the role of these two superfluid states in the interpretation of phenomena occurring in the neutron-star core.

The Equation of State of Nuclear Matter and Neutron Stars Properties

The equation of state (EOS) of symmetric nuclear and pure neutron matter has been investigated extensively by adopting the non-relativistic Brueckner-Hartree-Fock (BHF). For more comparison, the extended BHF approaches using the self-consistent Green’s function approach or by including a three-body force will be done. The EOS will be studied for different approaches at zero temperature. We can calculate the total mass and radius of neutron stars using various equations of state. A comparison with relativistic BHF calculations will be done. Relativistic effects are known to be important at high densities, giving an increased repulsion. This leads to a stiffer EOS compared to the EOS derived with a non-relativistic approach.