Hot Hadronic Matter Research Articles

Axion Emission from Strange Matter in Core-Collapse SNe.

The duration of the neutrino burst from the supernova event SN 1987A is known to be sensitive to exotic sources of cooling, such as axions radiated from the dense and hot hadronic matter thought to constitute the inner core of the supernova. We perform the first quantitative study of the role of hadronic matter beyond the first generation--in particular strange matter. We do so by consistently including the full baryon and meson octets, and computing axion emissivity induced from baryon-meson to baryon-axion scatterings as well as from baryon decays. We consider a range of supernova thermodynamic conditions, as well as equation-of-state models with different strangeness content. We obtain the first bound on the axial axion-strange-strange coupling, as well as the strongest existing bound on the axion-down-strange counterpart. Our bound on the latter coupling can be as small as O(10^{-2}) for f_{a}=10^{9} GeV.

Effect of time-varying electromagnetic field on Wiedemann-Franz law in a hot hadronic matter

Effect of time-varying electromagnetic field on Wiedemann-Franz law in a hot hadronic matter

Electric conductivity of hot pion matter

The determination of transport coefficients plays a central role in characterizing hot and dense nuclear matter. Currently, there are significant discrepancies between various calculations of the electric conductivity of hot hadronic matter. In the present work we calculate the electric conductivity of hot pion matter by extracting it from the electromagnetic spectral function, via its zero energy limit at vanishing 3-momentum, within the Vector Dominance Model (VDM). Since within the VDM the photon couples to the hadronic currents primarily through the ρ meson, we use hadronic many-body theory to calculate the ρ-meson's self-energy in hot pion matter, by dressing its pion cloud with thermal π-ρ and π-σ loops including vertex corrections to maintain gauge invariance. In particular, we analyze the low-energy transport peak of the spectral function, extract its behavior with temperature and compare to (the results of) existing approaches in the literature.

Interplay between chiral dynamics and repulsive interactions in hot hadronic matter

We investigate fluctuations of the net-baryon number density in hot hadronic matter. We discuss the interplay between chiral dynamics and repulsive interactions and their influence on the properties of these fluctuations near the chiral crossover. The chiral dynamics is modeled by the parity doublet Lagrangian that incorporates the attractive and repulsive interactions mediated via the exchange of scalar and vector mesons, respectively. The mean-field approximation is employed to account for chiral criticality. We focus on the properties and systematics of the cumulants of the net-baryon number density up to the sixth order. It is shown that the higher-order cumulants exhibit a substantial suppression in the vicinity of the chiral phase transition due to the presence of repulsive interactions. We find, however, that the characteristic properties of cumulants near the chiral crossover observed in lattice QCD results are entirely linked to the critical chiral dynamics and, in general, cannot be reproduced in phenomenological models, which account only for effective repulsive interactions via excluded-volume corrections or van-der-Waals type interactions. Consequently, a description of the higher-order cumulants of the net-baryon density in the chiral crossover requires a self-consistent treatment of the chiral in-medium effects and repulsive interactions.

NLD Equation of State for compressed, hot and relativistic nuclear matter

We investigate the properties of compressed and hot hadronic matter within the Non-Linear Derivative (NLD) formalism. The novel feature of the NLD model is an explicit momentum dependence of the mean-fields, which is regulated by cut-off’s of natural hadronic scale. It is covariantly and thermodynamical-consistently formulated at the basis of a field-theoretical level. We show that the NLD model describes adequately all the empirical information of cold nuclear matter as function of density (equation of state) and, in particular, as function of particle momenta (optical potential). Finally, we present predictions of the NLD approach for hot and compressed hadronic matter in terms of the Equation of state as function of density and temperature. These studies are relevant for the forthcoming experiments at FAIR@GSI. They are also important for astrophysical purposes, e.g., static neutron stars and dynamic neutron star binary systems.

Υ suppression in a hadron gas

In this work, we study the interactions of bottom mesons which lead to $\mathrm{\ensuremath{\Upsilon}}$ production and absorption in hot hadronic matter. We use effective Lagrangians to calculate the $\mathrm{\ensuremath{\Upsilon}}$ production cross section in processes such as ${\overline{B}}^{(*)}+{B}^{(*)}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Upsilon}}+(\ensuremath{\pi},\ensuremath{\rho})$ and also the $\mathrm{\ensuremath{\Upsilon}}$ absorption cross section in the corresponding inverse processes. We update and extend previous calculations by Lin and Ko, introducing anomalous interactions. The obtained cross sections are used as input to solve the rate equation which allows us to follow the time evolution of the $\mathrm{\ensuremath{\Upsilon}}$ multiplicity. In contrast to previous conjectures, our results suggest that the interactions in the hadron gas phase reduce the $\mathrm{\ensuremath{\Upsilon}}$ abundance.

Violation of Wiedemann-Franz Law for hot hadronic matter created at NICA, FAIR and RHIC energies using non-extensive statistics

We present here the computation of electrical and thermal conductivity by solving the Boltzmann transport equation in relaxation time approximation. We use the $q$-generalized Boltzmann distribution function to incorporate the effects of non-extensivity. The behaviour of these quantities with changing temperature and baryochemical potential has been studied as the system slowly moves towards thermodynamic equilibrium. We have estimated the Lorenz number at NICA, FAIR and the top RHIC energies and studied as a function of temperature, baryochemical potential and the non-extensive parameter, $q$. We have observed that Wiedemann-Franz law is violated for a non-extensive hadronic phase as well as for an equilibrated hadron gas at high temperatures.

Parity doubling of baryons in QCD thermodynamics

Motivated by the recent lattice study, thermal masses of the baryon parity-doublers are explored for various pion masses. A general trend of the nucleon and delta parity-doublers is consistent with the lattice QCD results, whereas hyperon masses exhibit a qualitatively different behavior, traced back to the lattice set-up with mπ/mK∼1.We further investigate the fluctuations and correlations involving baryon number in hot hadronic matter with modified masses of negative-parity baryons, in the context of the hadron resonance gas. Confronting the baryon number susceptibility, baryon-charge correlation, and baryon-strangeness correlation and their ratios with the lattice QCD data, we show that the strong downward mass shift in the hyperons can accidentally reproduce some correlation ratios, however it also tends to overshoot the individual fluctuations and correlations. This indicates that in order to correctly account for the influence of the chiral symmetry restoration on the fluctuation observables, a consistent framework of in-medium effects beyond hadron mass shifts is required.

Direct photon production in pp, p-Pb and Pb-Pb collisions: results from ALICE

Direct photon measurements provide a tool for testing QCD predictions in pp collisions and valuable information about properties of the quarkgluon matter created in nucleus-nucleus collisions. Comparing direct photon production in pp, p-Pb and Pb-Pb collisions, one can check the scaling with the number of binary collisions expected at high transverse momentum and get insight into the hot and cold hadronic matter properties with soft photons. The elliptic flow of direct photons is another unique possibility to trace the collective flow formation and space-time evolution of the fireball. We present the latest measurements of direct photon production in pp, p-Pb and Pb-Pb collisions and of the elliptic flow in Pb-Pb collisions at the LHC energies. Comparison to recent theory predictions will be also discussed.

NA61/SHINE Experiment—Program beyond 2020

The fixed-target NA61/SHINE experiment (SPS CERN) looks for the critical point (CP) of strongly interacting matter and the properties of the onset of deconfinement. It is a scan of measurements of particle spectra and fluctuations in proton–proton, proton–nucleus, and nucleus–nucleus interactions as a function of collision energy and system size. This gives unique possibilities to researching critical properties of the dense hot hadronic matter created in the collision process. New measurements and their objectives, related to the third stage of the experiment after 2020, are presented and discussed here.

Overlap between Lattice QCD and HRG with in-medium effects and parity doubling

We investigate the fluctuations and correlations involving baryon number in hot hadronic matter with modified masses of negative-parity baryons, in the context of the hadron resonance gas. Temperature-dependent masses are adopted from the recent lattice QCD results and from a chiral effective model which implements the parity doubling structure with respect to the chiral symmetry. Confronting the baryon number susceptibility, baryon-charge correlation, and baryon-strangeness correlation and their ratios with the lattice QCD data, we show that the strong downward mass shift in hyperons can accidentally reproduce some correlation ratios, however it also tends to overshoot the individual fluctuations and correlations. This indicates, that in order to correctly account for the influence of the chiral symmetry restoration on the fluctuation observables, a consistent framework of in-medium effects beyond hadron mass shifts is required.

Production of Σ(1385)± and Ξ(1530)0 in p–Pb collisions at measured by ALICE at the LHC

In order to study the hot hadronic matter created in heavy-ion collisions, it is important to compare particle production in large systems to that in smaller systems, such as proton-proton (pp) and proton-lead (p–Pb) collisions. In particular, resonances with different lifetimes are good candidates to probe the interplay of particle re-scattering and regeneration in the hadronic phase. The yields of the strange and double-strange hyperon resonances Σ(1385)± and Ξ(1530)0 are measured in the rapidity range −0.5 < yCMS < 0 in p–Pb collisions at with the ALICE detector at the LHC. We report on the transverse momentum distributions and mean transverse momentum as a function of the charged-particle multiplicity. These results complement the information derived from the measurements of other resonances such as K*(892)0 and ˚(1020). The multiplicity dependence of the integrated yield ratios of excited hyperons to longer-lived particles is discussed and compared to model predictions from pQCD-inspired models such as PYTHIA8 as well as statistical hadronization models.

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.

Quasiparticle theory of transport coefficients for hadronic matter at finite temperature and baryon density

We develop a flexible quasiparticle theory of transport coefficients of hot hadronic matter at finite baryon density. We begin with a hadronic quasiparticle model which includes a scalar and a vector mean field. Quasiparticle energies and the mean fields depend on temperature and baryon chemical potential. Starting with the quasiparticle dispersion relation, we derive the Boltzmann equation and use the Chapman-Enskog expansion to derive formulas for the shear and bulk viscosities and thermal conductivity. We obtain both relaxation time approximation formulas and more general integral equations. Throughout the work, we explicitly enforce the Landau-Lifshitz conditions of fit and ensure the theory is thermodynamically self-consistent. The derived formulas should be useful for predicting the transport coefficients of the hadronic phase of matter produced in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and at other accelerators.

Thermal photon emission from the πρω system

We investigate thermal photon emission rates in hot hadronic matter from a system consisting of π, ρ, and ω mesons. The rates are calculated using both relativistic kinetic theory with Born diagrams as well as thermal field theory at the two-loop level. This enables us to cross-check our calculations and to manage a pole contribution that arises in the Born approximation corresponding to the ω→π0γ radiative decay. After implementing hadronic form factors to account for finite-size corrections, we find that the resulting photo-emission rates are comparable to existing results from πρ→πγ processes in the energy regime of 1–3 GeV. We expect that our new sources will provide a non-negligible contribution to the total hadronic rates, thereby enhancing calculated thermal photon spectra from heavy-ion collisions, which could improve the description of current direct-photon data from experiment.

Strangeness and phase changes in hot hadronic matter - 1983

Two phases of hot hadronic matter are described with emphasis put on their distinction. Here the role of strange particles as a characteristic observable of the quark-gluon plasma phase is particularly explored.

Identified light-flavour particle production measured with ALICE at the LHC as a probe of soft QCD and hot hadronic matter

ALICE is a general-purpose heavy-ion experiment able to identify particles over a wide momentum range thanks to excellent vertexing and tracking performance, low material budget and different Particle IDentification (PID) techniques. In this paper the measurement of the production of identified light flavour particles in pp, p-Pb and Pb-Pb collisions is reported. It is of fundamental importance to study the particle production mechanisms playing a role in the different momentum ranges and probe the hot medium formed in heavy-ion collisions. Information on the effects of the medium produced in Pb-Pb collisions on particle production can be obtained comparing the particle ratios in pp and Pb-Pb events and studying the nuclear modification factor (RAA). The transverse momentum (pT) integrated yields and ratios are then discussed in terms of thermal models to extract the properties of the medium produced in Pb-Pb collisions at the chemical freeze-out.

Bottomonium states in hot asymmetric strange hadronic matter

We calculate the in-medium masses of the bottomonium states $[\ensuremath{\Upsilon}(1S),\ensuremath{\Upsilon}(2S),\ensuremath{\Upsilon}(3S)$, and $\ensuremath{\Upsilon}(4S)]$ in isospin asymmetric strange hadronic matter at finite temperatures. The medium modifications of the masses arise due to the interaction of these heavy quarkonium states with the gluon condensates of QCD. The gluon condensates in the hot hadronic matter are computed from the medium modification of a scalar dilaton field within a chiral SU(3) model, introduced in the hadronic model to incorporate the broken scale invariance of QCD. There is seen to be a drop in the masses of the bottomonium states and mass shifts are observed to be quite considerable at high densities for the excited states. The effects of density, isospin asymmetry, strangeness, as well as temperature of the medium on the masses of the $\ensuremath{\Upsilon}$ states are investigated. The effects of the isospin asymmetry as well as strangeness fraction of the medium are seen to be appreciable at high densities and small temperatures. The density effects are the most dominant medium effects which should have observable consequences in the compressed baryonic matter (CBM) in the heavy ion collision experiments in the future facility at FAIR, GSI. The study of the $\ensuremath{\Upsilon}$ states will, however, require access to energies higher than the energy regime planned at CBM experiment. The density effects on the bottomonium masses should also show up in the dilepton spectra at the Super Proton Synchrotron (SPS) energies, especially for the excited states for which the mass drop is observed to quite appreciable.

Hadronic resonance production measured with the ALICE detector at the LHC

Hadronic resonance production has been studied with the ALICE detector in different collision systems at LHC energies. The aim is to disentangle initial-state effects from genuine medium-induced effects, which may occur in the hot and dense hadronic matter after the chemical freeze-out in Pb-Pb collisions. In these proceedings, transverse- momentum spectra of φ(1020) and K ∗ (892) 0 and the ratio of their yield to long-lived particles are discussed in this light.

Hadron mass spectrum and the shear viscosity to entropy density ratio of hot hadronic matter

Lattice calculations of the QCD trace anomaly at temperatures $T<160$ MeV have been shown to match hadron resonance gas model calculations, which include an exponentially rising hadron mass spectrum. In this paper we perform a more detailed comparison of the model calculations to lattice data that confirms the need for an exponentially increasing density of hadronic states. Also, we find that the lattice data is compatible with a hadron density of states that goes as $\rho(m) \sim m^{-a}\exp(m/T_H) $ at large $m$ with $a> 5/2$ (where $T_H \sim 167$ MeV). With this specific subleading contribution to the density of states, heavy resonances are most likely undergo 2-body decay (instead of multi-particle decay), which facilitates their inclusion into hadron transport codes. Moreover, estimates for the shear viscosity and the shear relaxation time coefficient of the hadron resonance model computed within the excluded volume approximation suggest that these transport coefficients are sensitive to the parameters that define the hadron mass spectrum.