arXiv subjects

F. Grassi

Publications and source records attributed to F. Grassi.

26 records · Page 2Linked to original sources

arXiv2001

An attempt to incorporate separate chemical and thermal freeze outs in hydrodynamics

From an analysis of various types of data obtained in relativistic nuclear collisions, the following picture has emerged in thermal and hydrodynamical descriptions: as the fluid expands and cools, particles first undergo a chemical freeze out at T_ch.~160-200 MeV then a thermal freeze out at T_th~100-140 MeV. In this paper we show how to incorporate these separate freeze outs consistently in a hydrodynamical code via a modified equation of state (general case) or via a modified Cooper-Frye formula (particular case of T_ch. close to T_th. or few particle species undergoing early chemical freeze-out). The modified equation of state causes faster cooling and may have sizable impact on the predicted values of observables.

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arXiv2000

Freeze-out in hydrodynamical models in relativistic heavy ion collisions

Freeze-out of particles across 3-dimensional space-time hypersurface with space-like normal is discussed in a simple kinetic model. The final momentum distribution of emitted particles shows a non-exponential transverse momentum spectrum, which is in quantitative agreement with recently measured SPS pion and $h^-$ spectra.

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arXiv2000

Pion abundance and entropy in the hydrodynamical description of relativistic nuclear collisions

We show that a hydrodynamical model with continuous particle emission instead of sudden freeze out can explain both the strange particle abundances and pion abundance from NA35 without extra assumption (e.g., sequential freeze out, modified equation of state, sudden plasma hadronization,...). In this scenario, the observation of a larger pion abundance is natural and does not imply a higher initial entropy and early plasma phase.

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arXiv1999

Large $p_t$ enhancement from freeze out

Freeze out of particles across three dimensional space-time hypersurface is discussed in a simple kinetic model. The final momentum distribution of emitted particles, for freeze out surfaces with space-like normal, shows a non-exponential transverse momentum spectrum. The slope parameter of the $p_t$ distribution increases with increasing $p_t$, in agreement with recently measured SPS pion and $h^-$ spectra.

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arXiv1999

Kinetic freeze out

Freeze out of particles across a space-time hypersurface is discussed in kinetic models. The calculation of final momentum distribution of emitted particles is described for freeze out surfaces, with spacelike normals. The resulting non-equilibrium distribution does not resemble, the previously proposed, cut Juttner distribution, and shows non-exponential p_t-spectra similar to the ones observed in experiments.

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arXiv1999

Freeze out in hydrodynamical models

We study the effects of strict conservation laws and the problem of negative contributions to final momentum distribution during the freeze out through 3-dimensional hypersurfaces with space-like normal. We study some suggested solutions for this problem, and demonstrate it on one example.

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arXiv1997

Can we see the hadron-quark transition happening in neutron stars?

In order to actually see the hadron-quark transition happening in a neutron star, we point out and study two static conditions (the transition hadronic density must be lower than the neutron star maximum hadronic density; the neutron star mass at the transition hadronic density must be in the observed range, of order 1.4 solar mass) and one dynamical condition (nucleation must occur during the star lifetime). We find that the mini-colapse acompanying the transition from metastable hadronic matter to quark matter may be relevant to explain macro-glitches and gamma ray bursts, but that the mecanism increasing the star density must be relatively fast, e.g. accretion but not slowing down. This rules out a scenario for gamma ray bursts proposed recently.

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arXiv1997

Confronting particle emission scenarios with strangeness data

We show that a hadron gas model with continuous particle emission instead of freeze out may solve some of the problems (high values of the freeze out density and specific net charge) that one encounters in the latter case when studying strange particle ratios such as those by WA85. This underlines the necessity to understand better particle emission in hydrodynamics to be able to analyze data. It also re-opens the possibility of a quark-hadron transition occuring with phase equilibrium instead of explosively.

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