Yogiro Hama

Topology studies of hydrodynamics using two-particle correlation analysis.

The effects of fluctuating initial conditions are studied in the context of relativistic heavy ion collisions where a rapidly evolving system is formed. Two-particle correlation analysis is applied to events generated with the NEXSPHERIO hydrodynamic code, starting with fluctuating nonsmooth initial conditions (IC). The results show that the nonsmoothness in the IC survives the hydroevolution and can be seen as topological features of the angular correlation function of the particles emerging from the evolving system. A long range correlation is observed in the longitudinal direction and in the azimuthal direction a double peak structure is observed in the opposite direction to the trigger particle. This analysis provides clear evidence that these are signatures of the combined effect of tubular structures present in the IC and the proceeding collective dynamics of the hot and dense medium.

Examining the necessity to include event-by-event fluctuations in experimental evaluations of elliptical flow

Elliptic flow at RHIC is computed event-by-event with NeXSPheRIO. We show that when symmetry of the particle distribution in relation to the reaction plane is assumed, as usually done in the experimental extraction of elliptic flow, there is a disagreement between the true and reconstructed elliptic flows (15-30% for

Freeze-out problem in hydrokinetic approach to A + A collisions.

\eta

Topics on Hydrodynamic Model of Nucleus-Nucleus Collisions

=0, 30% for

Fluctuations of the initial conditions and the continuous emission in the hydrodynamical description of two-pion interferometry

p_\perp

Smoothed particle hydrodynamics for relativistic heavy-ion collisions

=0.5 GeV). We suggest a possible way to take into account the asymmetry and get good agreement between these elliptic flows.

Freeze-out in hydrodynamical models

A new method for evaluating spectra and correlations in the hydrodynamic approach is proposed. It is based on an analysis of the Boltzmann equations (BE) in terms of probabilities for constituent particles to escape from the interacting system. The conditions of applicability of the Cooper-Frye freeze-out prescription are considered within the method. The results are illustrated with a nonrelativistic exact solution of BE for an expanding spherical fireball as well as with approximate solutions for ellipsoidally expanding ones.

Simple solutions of relativistic hydrodynamics for systems with ellipsoidal symmetry

A survey is given on the applications of hydrodynamic model of nucleus-nucleus collisons, focusing especially on i) the resolution of hydrodynamic equations for arbitrary configurations, by using the smoothed-particle hydrodynamic approach; ii) effects of the event-by-event fluctuation of the initial conditions on the observables; iii) decoupling criteria; iv) analytical solutions; and others.

Incident-energy dependence of the effective temperature in heavy-ion collisions

Within the hydrodynamical approach, we study the Bose-Einstein correlation of identical pions by taking into account both event-by-event fluctuating initial conditions and continuous pion emission during the whole development of the hot and dense matter formed in high-energy collisions. Important deviations occur, compared to the usual hydrocalculations with smooth initial conditions and a sudden freeze-out on a well defined hypersurface. Comparison with data at the BNL Relativistic Heavy Ion Collider (RHIC) shows that, despite the rather rough approximation we used here, this description can account for the m(T) dependence of R(L) and R(s), and produces a significant improvement for R(o) with respect to the usual version.

Continuous particle emission: a probe of thermalized matter evolution?

A smoothed particle hydrodynamics (SPH) method is developed for the study of relativistic heavy-ion collisions. In order to describe the flow of a high-energy but low baryon number density fluid, entropy is taken as the SPH base. The method is formulated in terms of a variational principle, and the SPH equations for an arbitrary curvilinear coordinate system are obtained. Several examples show that SPH is a promising tool for the study of hadronic flow in relativistic heavy-ion processes.