arXiv subjects

A. Bonasera

Publications and source records attributed to A. Bonasera.

At least 91 records · Page 5Linked to original sources

arXiv2006

Mean Field Effects In The Quark-Gluon Plasma

A transport model based on the mean free path approach for an interacting meson system at finite temperatures is discussed. A transition to a quark gluon plasma is included within the framework of the MIT bag model. The results obtained compare very well with Lattice QCD calculations when we include a mean field in the QGP phase due to the Debye color screening. In particular the cross over to the QGP at about 175 MeV temperature is nicely reproduced. We also discuss a possible scenario for hadronization which is especially important for temperatures below the QGP phase transition.

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arXiv2006

Kinetic Description of a Finite Temperature Meson Gas

A transport model based on the mean free path approach for an interacting meson system at finite temperatures is discussed. A transition to a quark gluon plasma is included within the framework of the bag model. We discuss some calculations for a pure meson gas where the Hagedorn limiting temperature is reproduced when including the experimentally observed resonances. Next we include the possibility for a QGP formation based on the MIT bag model. The results obtained compare very well with Lattice QCD calculations. In particular the cross over to the QGP at about 175 MeV temperature is nicely reproduced.

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arXiv2005

A Novel Dynamical Approach To Relativistic Heavy Ion Collisions

A transport model for ultra-relativistic nucleus-nucleus collisions based on the mean free path approach is proposed. The method is manifestly Lorentz invariant. We discuss some calculations for pp and AA collisions and compare to a previously proposed transport model and to data. We demonstrate that our approach gives a different impact parameter distribution already in pp collisions as compared to the previous one. The role of hadronization times is discussed. Comparison to data is reasonable and the model can be easily modified to take into account genuine many body effects and quantum statistics similarly to low energy heavy ion collisions.

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arXiv2005

Influence of Chaos on the fusion enhancement by electron screening

We study the effect of screening by bound electrons in low energy nuclear reactions. We use molecular dynamics to simulate the reactions involving many electrons: D+$d$, D+D, $^3$He+$d$, $^3$He+D, $^6$Li+$d$, $^6$Li+D, $^7$Li+$p$, $^7$Li+H. Quantum effects corresponding to the Pauli and Heisenberg principles are enforced by constraints in terms of the phase space occupancy. In addition to the well known adiabatic and sudden limits, we propose a new "dissipative limit" which is expected to be important not only at high energies but in the extremely low energy region. The dissipative limit is associated with the chaotic behavior of the electronic motion. It affects also the magnitude of the enhancement factor. We discuss also numerical experiments using polarized targets. The derived enhancement factors in our simulation are in agreement with those extracted within the $R$-matrix approach.

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arXiv2005

Constrained Molecular Dynamics II: a N-body approach to nuclear systems

In this work we illustrate the basic development of the constrained molecular dynamics applied to the N-body problem in nuclear physics. The heavy computational taskes related to quantum effects, to the presence of the "hard core" repulsive interaction have been worked out by defining a set of transformations based on the concept of impulsive forces. In particular in the implemented version II of the Constrained Molecular Dynamics model the problem related to the non conservation of the total angular momentum has been solved. This problem can affect others semiclassical microscopic approaches as due to the "hard core" repulsive interaction or to the use of stochastic forces. The effect of the restored conservation law on the fusion cross section for 40Ca+40Ca system is also briefly discussed.

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arXiv2004

Large Momenta Fluctuations Of Charm Quarks In The Quark-Gluon Plasma

We show that large fluctuations of D mesons kinetic energy (or momentum) distributions might be a signature of a phase transition to the quark gluon plasma (QGP). In particular, a jump in the variance of the momenta or kinetic energy, as a function of a control parameter (temperature or Fermi energy at finite baryon densities) might be a signature for a first order phase transition to the QGP. This behaviour is completely consistent with the order parameter defined for a system of interacting quarks at zero temperature and finite baryon densities which shows a jump in correspondance to a first order phase transition to the QGP. The $J/Ψ$ shows exactly the same behavior of the order parameter and of the variance of the D mesons. We discuss implications for relativistic heavy ion collisions within the framework of a transport model and possible hints for experimental data.

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arXiv2004

Constrained Molecular Dynamics simulation of the Quark-Gluon Plasma

We calculate the Equation of State of a quark system interacting through a phenomenological potential: the Richardson's potential, at finite baryon density and zero temperature. In particular we study three different cases with different quark masses($u$ and $d$), and different assumptions for the potential at large distances. We solve molecular dynamics with a constraint due to Pauli blocking and find evidencies of a phase transition from "nuclear" to "quark matter", which is analyzed also through the behaviour of the $J/Ψ$ embedded in the quark system. We show that the $J/Ψ$ particle behaves as an order parameter.

hep-ph↗

arXiv2004

Ambiguities in statistical calculations of nuclear fragmentation

The concept of freeze out volume used in many statistical approaches for disassembly of hot nuclei leads to ambiguities. The fragmentation pattern and the momentum distribution (temperature) of the emanated fragments are determined by the phase space at the freeze-out volume where the interaction among the fragments is supposedly frozen out. However, to get coherence with the experimental momentum distribution of the charged particles, one introduces Coulomb acceleration beyond this freeze-out. To be consistent, we investigate the effect of the attractive nuclear force beyond this volume and find that the possible recombination of the fragments alters the physical observables significantly casting doubt on the consistency of the statistical model.

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arXiv2003

Influence of the Pauli principle on the dynamics of the Quark-Gluon Plasma

A simple parton cascade model for the ultra-relativistic nucleus-nucleus collisions is proposed to investigate the Pauli blocking at the transition from hadronic to partonic state, i.e. QGP. A boost invariant study of the Pauli blocking is implemented in the Monte Carlo simulation for the first time. It turns out that the higher reaction energy the stronger the partonic Pauli effect is. It amounts to about ten percent at SPS and RHIC energies but nearly reaches twenty percent at LHC energy. Thus the effect is relevant to the formation and evolution of the quark-gluon plasma.

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arXiv2002

Charged multiplicity density and number of participant nucleons in relativistic nuclear collisions

The energy and centrality dependences of charged particle pseudorapidity density in relativistic nuclear collisions were studied using a hadron and string cascade model, JPCIAE. Both the relativistic $p+\bar p$ experimental data and the PHOBOS and PHENIX $Au+Au$ data at RHIC energy could be fairly reproduced within the framework of JPCIAE model and without retuning the model parameters. The predictions for $Pb+Pb$ collisions at the LHC energy were also given. We computed the participant nucleon distributions using different methods. It was found that the number of participant nucleons is not a well defined variable both experimentally and theoretically. Thus it may be inappropriate to use the charged particle pseudorapidity density per participant pair as a function of the number of participant nucleons for distinguishing various theoretical models. A discussion for the effect of different definitions in nuclear radius (diffused or sharp) was given.

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arXiv2002

Dynamical properties of constrained drops

In this communication we analyze the behavior of excited drops contained in spherical volumes. We study different properties of the dynamical systems i.e. the maximum Lyapunov exponent MLE, the asymptotic distance in momentum space $d_{\infty}$ andthe normalized variance of the maximum fragment NVM. It is shown that the constrained systems behaves as undergoing a first order phase transition at low densities while as a second order one at high densities. The transition from liquid-like to vapor-like behavior is signaled both by the caloric curves, thermal response functions and the MLE. The relationship between $MLE,d_{\infty}$, and the CC is explored.

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arXiv2001

Energy and centrality dependences of charged multiplicity density in relativistic nuclear collisions

Using a hadron and string cascade model, JPCIAE, the energy and centrality dependences of charged particle pseudorapidity density in relativistic nuclear collisions were studied. Within the framework of this model, both the relativistic $p+\bar p$ experimental data and the PHOBOS and PHENIX $Au+Au$ data at $\sqrt s_{nn}$=130 GeV could be reproduced fairly well without retuning the model parameters. The predictions for full RHIC energy $Au+Au$ collisions and for $Pb+Pb$ collisions at the ALICE energy were given. Participant nucleon distributions were calculated based on different methods. It was found that the number of participant nucleons, $ $, is not a well defined variable both experimentally and theoretically. Therefore, it is inappropriate to use charged particle pseudorapidity density per participant pair as a function of $ $ for distinguishing various theoretical models.

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arXiv2000

Constraint Molecular Dynamics approach to Fermionic systems

We propose a Constraint Molecular Dynamics model for Fermionic system. In this approach the equations of motion of wave packets for the nuclear many-body problem are solved by imposing that the one-body occupation probability $\bar{f}(r,p,t)$ can assume only values less or equal to 1. This condition reflects the Fermionic nature of the studied systems and it is implemented with a fast algorithm which allows also the study of the heaviest colliding system. The parameters of the model have been chosen to reproduce the average binding energy and radii of nuclei in the mass region $A=30\sim 208$. Some comparison to data is given.

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arXiv2000

Critical Phenomena in Finite Systems

We discuss the dynamics of finite systems within molecular dynamics models. Signatures of a critical behavior are analyzed and compared to experimental data both in nucleus-nucleus and metallic cluster collisions. We suggest the possibility to explore the instability region via tunneling. In this way we can obtain fragments at very low temperatures and densities. We call these fragments quantum drops.

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arXiv2000

Color Dynamics In Phase Space: The Balescu-Lenard-Vlasov Approach

We propose to use the Balescu-Lenard-Vlasov (BLV) equation to describe relativistic heavy ion collisions. We use an inter-quark Richardson's potential consistent with the indications of Lattice QCD calculations. The color degrees of freedom are explicitly taken into account. We explicitly demonstrate that the Vlasov approach alone is insufficient in the hadronization region. In order to overcome this problem we prepare the initial condition for many events using molecular dynamics with frictional cooling and a Thomas-Fermi approximation to the Fermi motion. These events are averaged and propagated in time using the Vlasov approach. The fluctuations are used to evaluate the collision term and in turn the number of q-$\bar q$ created.

hep-ph↗

arXiv2000

Color Dynamics On Phase Space

We describe the properties of quark matter at zero temperature and finite baryon densities within microscopic Vlasov/molecular dynamics approaches. We use an inter-quark Richardson's potential consistent with the indications of Lattice QCD calculations. The color degrees of freedom are explicitly taken into account. We explicitly demonstrate that the Vlasov approach alone is insufficient in the hadronization region. In order to overcome this problem we prepare the initial condition for many events using molecular dynamics with frictional cooling and a Thomas-Fermi approximation to the Fermi motion. These events are averaged and propagated in time using the Vlasov approach. We find some evidence for a second order phase transition from nuclear to quark matter at high baryon densities. An order parameter suitable to describe the phase transition is discussed. At low densities the quark condensate into approximately color white clusters (nucleon).

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arXiv1999

Lyapunov Exponent, Generalized Entropies and Fractal Dimensions Of Hot Drops

We calculate the maximal Lyapunov exponent, the generalized entropies, the asymptotic distance between nearby trajectories and the fractal dimensions for a finite two dimensional system at different initial excitation energies. We show that these quantities have a maximum at about the same excitation energy. The presence of this maximum indicates the transition from a chaotic regime to a more regular one. In the chaotic regime the system is composed mainly of a liquid drop while the regular one corresponds to almost freely flowing particles and small clusters. At the transitional excitation energy the fractal dimensions are similar to those estimated from the Fisher model for a liquid gas phase transition at the critical point.

chao-dyn↗

arXiv1999

Vlasov Description Of Dense Quark Matter

We discuss properties of quark matter at finite baryon densities and zero temperature in a Vlasov approach. We use a screened interquark Richardson's potential consistent with the indications of Lattice QCD calculations. We analyze the choices of the quark masses and the parameters entering the potential which reproduce the binding energy (B.E.) of infinite nuclear matter. There is a transition from nuclear to quark matter at densities 5 times above normal nuclear matter density. The transition could be revealed from the determination of the position of the shifted meson masses in dense baryonic matter. A scaling form of the meson masses in dense matter is given.

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