arXiv subjects
Publications and source records attributed to Denes Molnar.
Puzzling discrepancies between recent pion interferometry data on Au+Au reactions at s^1/2 = 130 and 200 AGeV from RHIC and predictions based on ideal hydrodynamics are analyzed in terms of covariant parton transport theory. The discrepancies of out and longitudinal radii are significantly reduced when the finite opacity of the gluon plasma is taken into account.
We investigate whether it is possible to dynamically generate from classical transport theory the observed surprising Rout ~ Rside in Au+Au at s^1/2 = 130A GeV at RHIC. We obtained covariant solutions to the Boltzmann transport equation via the MPC technique, for a wide range of partonic initial conditions and opacities. We demonstrate that there exist transport solutions that yield a freezeout distribution with Rout < Rside for Kperp > ~ 1.5 GeV. These solutions correspond to continuous evaporation-like freezeout, where the emission duration is comparable to the source size. Naively this would mean Rout > Rside. Nevertheless, our sources exhibit Rout < Rside because they are narrower in the 'out' than in the 'side' direction and, in addition, a positive x_out-t correlation develops reducing Rout further.
Differential elliptic flow and particle spectra are calculated from covariant Boltzmann transport theory taking into account the finite transport opacity of the gluon plasma produced in Au+Au at $E_{cm}\sim 130$ $A$ GeV at RHIC. The solutions are shown to depend mainly on the transport opacity, $χ=\int dz σ_tρ_g$. The elliptic flow saturation pattern reported by STAR indicates that $χ_{b=0} \sim 25$, i.e., the gluon plasma is $\sim 80$ times more opaque than the pQCD estimate based on HIJING. Such large opacities are also consistent with the measured charged hadron spectra.
The effect of scattering with non-zero impact parameters between consituents in relativistic heavy ion collisions is investigated. In solving the relativistic Boltzmann equation, the characteristic range of the collision kernel is varied from approximately one fm to zero while leaving the mean-free path unchanged. Modifying this range is shown to significantly affect spectra and flow observables. The finite range is shown to provide effective viscosities, shear, bulk viscosity and heat conductivity, with the viscous coefficients being proportional to the square of the interaction range.
Differential elliptic flow out to p_T ~ 5 GeV/c and particle spectra are calculated using the MPC elastic parton cascade model for Au+Au at Ecm ~ 130A GeV. The evolution is computed from parton transport theory, followed by hadronization either via independent fragmentation or by imposing parton-hadron duality. With pQCD elastic cross sections, very large initial gluon densities dN/deta > 7000 are required to reproduce the data measured by the STAR collaboration. In addition, elliptic flow and the p_T spectra are shown to be very sensit ive to particle subdivision.
Differential elliptic flow out to p_t ~ 5 GeV/c is calculated using the MPC elastic parton cascade model for Au+Au at Ecm ~ 130A GeV. The results are compared to recent STAR/RHIC elliptic flow data. An elliptic flow pattern comparable to the data seems to require initial parton densities at least twice higher than predicted by the HIJING model. Elliptic flow is also shown to be sensitive to the hadronization procedure.
New solutions of 3+1D covariant kinetic theory are presented for nuclear collisions in the energy domain Ecm ~ 200 AGeV. They are obtained using MPC, a new Monte-Carlo parton transport technique that employs very high parton subdivision that is necessary to preserve covariance. The transport results are compared with ideal hydrodynamics solutions. We show that the transport evolution differs significantly from hydrodynamics. In addition, we compare the transport freeze-out distributions to those obtained from ideal hydrodynamics with the Cooper-Frye isotherm freeze-out prescription. The transport freeze-out four-volume is shown to be sensitive to the reaction rates and deviates from both time-like and space-like freeze-out 3D hypersurfaces commonly assumed. In particular, we find that there does not exist a universal freeze-out temperature. Finally, the transverse momentum distributions are found to deviate by up to an order of magnitude from (Cooper-Frye frozen) hydrodynamics for a wide range of possible initial conditions and reaction rates at RHIC energies.
In energetic heavy ion collisions, if quark-gluon plasma is formed, its hadronization may lead to observable critical fluctuations, i.e., DCC formation. The strength and observability of these fluctuations depend on the initial state. Here we study the canonical ensemble of initial states of chiral fluctuations in heavy ion collisions and the probability to obtain observable domains of chiral condensates.
Possibility to detect DCC fluctuations is discussed. It is shown that interactions with quark background and dissipative effects due to interactions in the chiral field may result in damping of fluctuations. Since the magnitude of fluctuations depends strongly on the initial state and speed of chiral phase transition accurate evaluation of all modifying processes is required to predict observability of DCCs.