Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userViscosity in the excluded volume hadron gas model
114
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The shear viscosity $eta$ in the van der Waals excluded volume hadron-resonance gas model is considered. For the shear viscosity the result of the non-relativistic gas of hard-core particles is extended to the mixture of particles with different masses, but equal values of hard-core radius r. The relativistic corrections to hadron average momenta in thermal equilibrium are also taken into account. The ratio of the viscosity $eta$ to the entropy density s is studied. It monotonously decreases along the chemical freeze-out line in nucleus-nucleus collisions with increasing collision energy. As a function of hard-core radius r, a broad minimum of the ratio $eta/sapprox 0.3$ near $r approx 0.5$ fm is found at high collision energies. For the charge-neutral system at $T=T_c=180$ MeV, a minimum of the ratio $eta/scong 0.24$ is reached for $rcong 0.53$ fm. To justify a hydrodynamic approach to nucleus-nucleus collisions within the hadron phase the restriction from below, $r~ ge ~0.2$ fm, on the hard-core hadron radius should be fulfilled in the excluded volume hadron-resonance gas.
rate research
Read More
The multiplicity fluctuations are studied in the van der Waals excluded volume hadron-resonance gas model. The calculations are done in the grand canonical ensemble within the Boltzmann statistics approximation. The scaled variances for positive, negative and all charged hadrons are calculated along the chemical freeze-out line of nucleus-nucleus collisions at different collision energies. The multiplicity fluctuations are found to be suppressed in the van der Waals gas. The numerical calculations are presented for two values of hard-core hadron radius, $r=0.3$ fm and 0.5 fm, as well as for the upper limit of the excluded volume suppression effects.
In this work we discuss a modified version of Excluded Volume Hadron Resonance Gas model and also study the effect of Lorentz contraction of the excluded volume on scaled pressure and susceptibilities of conserved charges. We find that the Lorentz contraction, coupled with the variety of excluded volume parameters reproduce the lattice QCD data quite satisfactorily.
In this work we study the interactions of bottom mesons which lead to $Upsilon$ production and absorption in hot hadronic matter. We use effective Lagrangians to calculate the $Upsilon$ production cross section in processes such as $ bar{B}^{(*)} + B^{(*)} to Upsilon + (pi, rho)$ and also the $Upsilon$ 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 $Upsilon$ multiplicity. In contrast to previous conjectures, our results suggest that the interactions in the hadron gas phase strongly reduce the $Upsilon$ abundance.
The suppression of high momentum particles in heavy-ion collisions in comparison to elementary reactions is one of the main indications for the formation of a quark-gluon plasma. In recent studies, full jets are being reconstructed and substructure observables are gaining importance in assessing the medium modifications of hard probes. In this work, the effect of the late stage hadronic interactions are explored within the hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). High momentum particles are incorporated in a radially expanding hadron gas to analyse the corresponding angular distributions, also refered to as `jet shape observables. We find that the full hadron gas can be approximated with a pion gas with constant elastic cross-sections of 100 mb. In addition, the temperature and probe energy dependence of diffusion coefficients $tilde{q}$ and $tilde{e}$ quantifying the transverse and parallel momentum transfers are extracted. The species dependence and the importance of different interaction types are investigated. Parametrizations are presented that can be employed in future jet quenching calculations to include the effect of the hadronic phase.
The two-Equation of State (Two-EoS) model is used to describe the hadron-quark phase transition in dense-hot matter formed in heavy-ion collisions. The non-linear Walecka model is used to describe the hadronic phase. For the quark phase, the Nambu--Jona-Lasinio model coupled to Polyakov-Loop fields (PNJL) is used to include both the chiral and (de)confinement dynamics. The phase diagrams are derived from the Gibbs conditions and compared with the results obtained in the Hadron-NJL model without confinement. As in the Hadron-NJL case a first order transition is observed, but with a Critical-End-Point at much higher temperature, consequence of the confinement mechanism that reduces the degrees of freedom of the quark matter in proximity of the phase transition. Particular attention is devoted to the phase transition in isospin asymmetric matter. Interesting isospin effects are found at high baryon density and reduced temperatures, in fact common also to other quark models, like MIT-Bag and NJL model. Some possible observation signals are suggested to probe in Heavy-Ion Collision (HIC) experiments at intermediate energies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
