Hot Nuclear Matter Research Articles

Skyrme-RPA study of charged-current neutrino opacity in hot and dense supernova matter

Neutrino emission and their transport of energy to the supernova shock region are sensitive to the physics of hot and dense nuclear matter, which is a complex problem due to the strong correlations induced by nuclear forces. We derive charged-current opacities for electron neutrinos and antineutrinos in supernova matter using a self-consistent approach based on the Skyrme effective interaction. We include a mean field energy shift due to nuclear interaction and corrections due to RPA correlations. A complete treatment of the full Skyrme interaction, including a spin-orbit term, is given. To test the effect of RPA corrections, neutrino and antineutrino opacities are computed using different Skyrme parameterisations consistent with a number of infinite matter constraints.

Heavy-ion Physics (ATLAS)

The ATLAS experiment at the Large Hadron Collider has undertaken a broad physics program to probe and characterize the hot nuclear matter created in relativistic heavy-ion collisions. This talk presents recent results on production of electroweak bosons and quarkonium, charged particles and jets, bulk particle collectivity and electromagnetic processes in ultra-peripheral collisions, from Pb+Pb and p+Pb systems.

Mean free path and shear viscosity in centralXe129+Sn119collisions below 100 MeV/nucleon

Thermal and transport properties of hot nuclear matter formed in central $^{129}$Xe + $^{119}$Sn collisions at the Fermi energy are investigated using the isospin-dependent quantum molecular dynamical (IQMD) model. Temperature ($T$), average density ($\rho$), chemical potential ($\mu$), mean momentum ($P$), shear viscosity ($\eta$) and entropy density ($s$) are obtained from the phase-space information. The mean free path ($\lambda_{nn}$) and the in-medium nucleon-nucleon cross section ($\sigma_{nn}$) in the highest compressible stage at different incident energies are deduced and compared with the experimental results from Phys. Rev. C $\bf{90}$ (2014) 064602. The result shows that $\lambda_{nn}$ and $\sigma_{nn}$ have the same trend and similar values as the experimental results when the beam energy is greater than 40 MeV/u at maximum compressed state. Furthermore, the derived shear viscosity over entropy density ($\eta/s$) shows a decreasing behaviour to a saturated value around $\frac{3}{4\pi}$ as a function of incident energy.

Effect of intense magnetic fields on reduced-magnetohydrodynamics evolution in sNN=200 GeV Au + Au collisions

We investigate the effect of large magnetic fields on the $2+1$ dimensional reduced-magnetohydrodynamical expansion of hot and dense nuclear matter produced in $\sqrt{s_{\rm NN}}$ = 200 GeV Au+Au collisions. For the sake of simplicity, we consider the case where the magnetic field points in the direction perpendicular to the reaction plane. We also consider this field to be external, with energy density parametrized as a two-dimensional Gaussian. The width of the Gaussian along the directions orthogonal to the beam axis varies with the centrality of the collision. The dependence of the magnetic field on proper time ($\tau$) for the case of zero electrical conductivity of the QGP is parametrized following [Deng 2012], and for finite electrical conductivity following [Tuchin 2013]. We solve the equations of motion of ideal hydrodynamics for such an external magnetic field. For collisions with non-zero impact parameter we observe considerable changes in the evolution of the momentum eccentricities of the fireball when comparing the case when the magnetic field decays in a conducting QGP medium and when no magnetic field is present. The elliptic-flow coefficient $v_2$ of $\pi^{-}$ is shown to increase in the presence of an external magnetic field and the increment in $v_2$ is found to depend on the evolution and the initial magnitude of the magnetic field.

Study of cold and hot nuclear matter effects on jets with direct photon triggered correlations from PHENIX

Direct photons, being colorless objects, provide an unmodified control particle that can be used in conjunction with jets to probe the quark-gluon plasma. To leading order the direct photon momentum balances the momentum of opposing jets and can therefore provide a clean handle on the jet energy. Therefore, angular correlations with direct photons provide a mechanism to study the fragmentation of the opposing jet without performing jet reconstruction. Jet fragmentation modification has been measured previously in PHENIX in central Au+Au collisions. Recent RHIC runs offer the potential to study these observables in heavy ion collisions with greater statistics and over different collision systems including asymmetric collision geometries. In this talk we present results of isolated direct photon-triggered correlations in d+Au collisions and discuss the constraints of cold nuclear matter effects on the fragmentation functions. We also present the latest results with higher statistics on direct photon-triggered correlations in Au+Au collisions including differential measurements of fragmentation function modification. Finally, we present the status of the centrality and collision species dependence of these observables, including comparisons to related dihadron correlations. Together these results can give a view of jet modification going from small to large system size.

Magnetic moments of octet baryons in hot and dense nuclear matter

We have calculated the in-medium magnetic moments of octet baryons in the presence of hot and dense symmetric nuclear matter. Effective magnetic moments of baryons have been derived from medium modified quark masses within the chiral SU(3) quark mean field model. Further, for better insight into the medium modification of baryonic magnetic moments, we have considered the explicit contributions from the valence quarks, sea quarks and the sea orbital angular momentum of sea quarks. These effects have been successful in giving the description of baryonic magnetic moments in vacuum. The magnetic moments of baryons are found to vary significantly as a function of density of nuclear medium.

Nuclear modification of light flavour and strangeness at LHC energies with ALICE

Thanks to its unique particle identification capabilities the ALICE detector is able to identify light-flavour, strange and multi-strange hadrons, including π, K, p, , Λ, Ξ and Ω, over a wide range of transverse momentum, from pp and p–Pb interactions up to central Pb–Pb collisions. The latest results on the nuclear modification factor, RAA, as a function of the Pb–Pb collision centrality, is shown for various particle specie at centre-of-mass energy. For each particle specie, the RAA is compared with the nuclear modification factors RpA in p-Pb collisions to asses the presence of hot nuclear matter effects affecting the high-pΤ particle production in Pb–Pb collisions. The results on the RAA of charged hadrons at , the highest energy ever reached in the laboratory for heavy-ion collisions, is also shown.

Warm unstable asymmetric nuclear matter: Critical properties and the density dependence of the symmetry energy

The spinodal instabilities in hot asymmetric nuclear matter and some important critical parameters derived thereof are studied using six different families of relativistic mean-field (RMF) models. The slopes of the symmetry energy coefficient vary over a wide range within each family. The critical densities and proton fractions are more sensitive to the symmetry energy slope parameter at temperatures much below its critical value ($T_c\sim$14-16 MeV). The spread in the critical proton fraction at a given symmetry energy slope parameter is noticeably larger near $T_c$, indicating that the warm equation of state of asymmetric nuclear matter at sub-saturation densities is not sufficiently constrained. The distillation effects are sensitive to the density dependence of the symmetry energy at low temperatures which tend to wash out with increasing temperature.

Bulk and isospin instabilities in hot nuclear matter

The instability of hot asymmetric nuclear matter with respect to bulk density distortions is considered. The equation of state of the extended Thomas-Fermi approximation is used. The origin of the anomalous dispersion and the influence of the Fermi-surface distortion effects on the bulk and isospin instabilities in homogenous nuclear matter are investigated. It is shown that the development of both instabilities is reduced significantly due to the Fermi-surface distortion effects. The dependence of the bulk instability on the temperature and on the multipolarity of the particle density distortions are shown for the nucleus of $^{208}\mathrm{Pb}$. The dependence of the formation of the decay modes (fission or multifragmentation) of the nuclei on the temperature and the Fermi-surface distortion effects are demonstrated. It is shown that in the case of low temperatures the preferable mode for the bulk instability is binary fission. For higher temperatures, the preferred modes are the multifragmentations for small clusters. The number of clusters increases with increasing temperature.

Measurements of open charm hadrons at the STAR experiment

Because of their large masses, charm quarks are predominantly produced in the early stages of the heavy-ion collisions via hard scatterings. Therefore, they experience the entire evolution of the Quark-Gluon Plasma created in such collisions. Compared to light quarks, charm quarks thermalize more slowly. Therefore, the open charm hadrons present a unique probe to the properties of the hot and dense nuclear matter by measuring their energy loss and degree of thermalization in the medium. Furthermore, with the combined measurements of D0 and Ds mesons, we can study multiple modes of coalescence of charm quarks with light quarks in heavy-ion collisions. Heavy Flavor Tracker at the STAR experiment enables full topological reconstruction of open charm hadrons which greatly improves measurements of D0 mesons and opens the door to reconstructing the Ds mesons for the first time at RHIC. In this paper, we present the nuclear modification factor and azimuthal anisotropy for the D0 and Ds mesons as well as the ratio of Ds/D0 in Au+Au collisions at the center-of-mass energy .

Hot magnetized nuclear matter: Thermodynamic and saturation properties

We have used a realistic nuclear potential, AV18, and a many body technique, the lowest order constraint variational (LOCV) approach, to calculate the properties of hot magnetized nuclear matter. By investigating the free energy, spin polarization parameter, and symmetry energy, we have studied the temperature and magnetic field dependence of the saturation properties of magnetized nuclear matter. In addition, we have calculated the equation of state of magnetized nuclear matter at different temperatures and magnetic fields. It was found that the flashing temperature of nuclear matter decreases by increasing the magnetic field. In addition, we have studied the effect of the magnetic field on liquid gas phase transition of nuclear matter. The liquid gas coexistence curves, the order parameter of the liquid gas phase transition, and the properties of critical point at different magnetic fields have been calculated.

The electric conductivity of a pion gas

The determination of transport coefficients plays a central role in characterizing hot and dense nuclear matter. In the present work we calculate the electric conductivity of hot hadronic matter by extracting it from the ρ meson spectral function, as its zero-energy limit at vanishing momentum. Using hadronic many-body theory, we calculate the ρ meson self-energy in a pion gas. This requires the dressing of the pion propagators in the ρ self-energy with π-ρ loops, and the inclusion of vertex corrections to maintain gauge invariance. The resulting spectral function is used to calculate the electric conductivity of hot hadronic matter. In particular, we analyze the transport peak of the spectral function and extract its behavior with temperature and coupling strength. Our results suggest that, while obeying lower bounds proposed by conformal field theories in the strong-coupling limit, hot pion matter is a strongly-coupled medium.

Measurement of inclusive jet spectra in pp, p–Pb, and Pb–Pb collisions with the ALICE detector

Highly energetic jets are sensitive probes of the kinematic properties and the topology of high energy hadron collisions. Jets are collimated sprays of charged and neutral particles, which are produced in fragmentation of hard scattered partons from an early stage of the collision. In ALICE, jets have been measured in pp, p–Pb, and Pb–Pb collisions at several collision energies. While analyses of Pb–Pb events unveil properties of the hot and dense medium formed in heavy-ion collisions, pp and p–Pb collisions can shed light on hadronization and cold nuclear matter effects in jet production. Additionally, pp and p–Pb collisions serve as a baseline for disentangling hot and cold nuclear matter effects. A possible modification of the initial state is tested in p–Pb analyses. For the extraction of a jet signal, the exact evaluation of the background from the underlying event is an especially important ingredient. Due to the different nature of underlying events, each collision system requires a different analysis technique for removing the effect of the background on the jet sample. The focus of this publication is on the ALICE measurements of nuclear modification factors connecting p–Pb and Pb–Pb events to pp collisions. Furthermore, the radial jet structure is explored by comparing jet spectra reconstructed with different resolution parameters.

Λ production in p+p collisions at 40 and 158 GeV/c

The research programme of the NA61 collaboration covers a wide range of hadronic physics in the CERN SPS energy range. It encompasses measurements of hadron-hadron, hadron-nucleus as well as nucleus-nucleus collisions. The latter are analyzed to better understand the properties of hot and dense nuclear matter. In this contribution we present results on production in proton-proton interactions at beam energies of 40 and 158 GeV/c.

Digamma diagnostics for the mixed-phase generation at NICA

A novel type of diagnostics for dense and/or hot nuclear matter produced in heavy-ion collisions at NICA and similar future colliders (FAIR, etc.) is suggested. The diagnostics is based on an assumption (confirmed in many experiments worldwide) about intensive generation of light scalar mesons (σ ) the consequent decay of which produces γγ pairs with the mass and width dependent upon density and temperature of the fireball produced in the collision process. Thus, measurements of the absolute yield, mass and width of the γγ signal carry valuable information about the state of fireball generated during the high-energy nuclear collision.

Track reconstruction and particle identification developments for a study of event-by-event fluctuations in heavy ion collisions at NICA

A Monte Carlo simulation of heavy ion collisions (Au+Au) has been performed at MPD (Multi Purpose Detector) at NICA (Dubna) for a study of the possible critical point in the phase diagram of the hot nuclear matter. The simulation took into account real detector effects with as many details as possible to properly describe the apparatus response. Particle identification (PID) has been tuned to account for modifications in track reconstruction. Some results on hadron identification in the TPC and TOF (Time Of Flight) detectors with realistically simulated response have been also obtained.

Recent heavy ion results from the ATLAS experiment

The ATLAS experiment at the LHC has undertaken a broad physics program to probe and characterize the hot nuclear matter created in relativistic lead-lead collisions. This overview presents recent results on production of electroweak bosons, charmonia, charged-particles, jets, and bulk particle collectivity from Pb+Pb and p +Pb collisions at 2.76 TeV and 5.02 TeV, respectively, as well as on electromagnetic processes in ultra-peripheral Pb+Pb collisions at 5.02 TeV.

Cold and hot nuclear matter effects on charmonium production in p+Pb collisions at LHC energy

We study cold and hot nuclear matter effects on charmonium production in p+Pb collisions at $\sqrt{s_\text{NN}}=5.02$ TeV in a transport approach. At the forward rapidity, the cold medium effect on all the $c\bar c$ states and the hot medium effect on the excited $c\bar c$ states only can explain well the $J/\psi$ and $\psi'$ yield and transverse momentum distribution measured by the ALICE collaboration, and we predict a significantly larger $\psi'$ $p_\text{T}$ broadening in comparison with $J/\psi$. However, we can not reproduce the $J/\psi$ and $\psi'$ data at the backward rapidity with reasonable cold and hot medium effects.

Production of quarkonia at RHIC

The production of different quarkonium states provides unique insight to the hot and cold nuclear matter effects in the strongly interacting medium that is formed in high energy heavy ion collisions. While LHC explores the energy frontier, RHIC has a broad physics program to explore the nuclear modification at different energies in a wide range of systems. Some of the most interesting recent results on [Formula: see text] and [Formula: see text]production in p+p, d+Au and A+A collisions from PHENIX and STAR are summarized in this work.

Indications for a critical point in the phase diagram for hot and dense nuclear matter

Two-pion interferometry measurements are studied for a broad range of collision centralities in Au+Au (sNN=7.7–200 GeV) and Pb+Pb (sNN=2.76 TeV) collisions. They indicate non-monotonic excitation functions for the Gaussian emission source radii difference (Rout−Rside), suggestive of reaction trajectories which spend a fair amount of time near a soft point in the equation of state (EOS) that coincides with the critical end point (CEP). A Finite-Size Scaling (FSS) analysis of these excitation functions, provides further validation tests for the CEP. It also indicates a second order phase transition at the CEP, and the values Tcep∼165 MeV and μBcep∼95 MeV for its location in the (T,μB)-plane of the phase diagram. The static critical exponents (ν≈0.66 and γ≈1.2) extracted via the same FSS analysis, place this CEP in the 3D Ising model (static) universality class. A Dynamic Finite-Size Scaling analysis of the excitation functions, gives the estimate z∼0.87 for the dynamic critical exponent, suggesting that the associated critical expansion dynamics is dominated by the hydrodynamic sound mode.