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.The production of a new state of matter, the Quark-Gluon Plasma (QGP), can be obtained through ultrarelativistic heavy ion collision (RHIC) at CERN and at Brookhaven [1]. QGP can be formed in the first stages of the collisions, and can be studied through the secondary particles produced.Some features of the quark matter can be revealed by studying the properties of hadrons in a dense medium. The particle J/Ψ is a good candidate because the formation of the QGP might lead to its suppression[2]. Here we want to show that in reality informations about the QGP are carried by the charm quarks. These quarks interact strongly with the surrounding matter and as a result we have a suppression of the J/Ψ, but also large fluctuations of the charm quarks kinetic energies which could be revealed by the D mesons distributions or other charmed mesons or baryons. To see this, we elaborate on a semiclassical model which has an EOS resembling the well known properties of nuclear matter and its transition to the QGP at zero temperature and finite baryon densities already discussed in [3]. We simulate the nuclear matter which is composed of nucleons (which are by themselves composite three-quark objects) and its dissolution into quark matter. In addition, for our system of colored quarks, we will show how the color screening is related to the lifetime of the particle J/Ψ in the medium. In particular, we will see that the lifetime of the J/Ψ as a function of density behaves as an order parameter. On exactly the same ground we show that the variances of the charm quarks are large and they display a jump at the critical point for a first order phase transition. Thus this quantity, similarly to the lifetime of the J/Ψ, behaves * Email:terranova@lns.infn.it; zhou@lns.infn.it; bonasera@lns.infn.it exactly as an order parameter and could give important informations about not only the transition to the QGP but also to the order of the phase transition, i.e. first, second order or simply crossover to the QGP. Of course since D particles are the lighest charmed meson they are most easily produced in heavy ion collisions thus they are the best probes for the phase transition.An i...
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. *
A transport model based on the mean free path approach to describe pp collisions is proposed. We assume that hadrons can be treated as bags of partons similarly to the MIT bag model. When the energy density in the collision is higher than a critical value, the bags break and partons are liberated. The partons expand and can coalesce to form new hadrons. The results obtained compare very well with available data, and some predictions for higher energies collisions are discussed. Based on the model we suggest that a QGP could already be formed in pp collisions at high energies.
Some thermodynamical properties of the interacting meson system and QGP at finite temperature are discussed. For a pure meson gas the Hagedorn limiting temperature is reproduced when the experimentally observed resonances are included. For QGP our results for different numbers of flavors Nf compare very well to the theoretical ones. A transport model based on the mean free path approach is used to simulate the evolution of the system. During the evolution we use the MIT bag model to perform the transition between meson gas and QGP.
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