Participants

Dipartimento di Fisica Teorica - Università degli Studi di Torino

via P. Giuria, 1 - 10125 Torino - Italy

Politecnico di Torino - Dipartimento di Fisica

Corso Duca degli Abruzzi, 24 - 10129 Torino - Italy

Research activity

The research activity is focussed on several items: 

• High-energy QCD and saturation: The concept of parton saturation in the framework of the colour glass condensate model, which entails the onset of collective phenomena in a strongly interacting system, has been applied to the calculation of the multiplicity of charged particles emitted in a nucleus-nucleus collisions at high energies and to their distribution as a function of the collision centrality and rapidity. A successfull comparison with the experimental data of RHIC (Brookhaven) for Au-Au collisions at three different energies has been obtained. Recently the same model has been used to predict the outcome of the collision D-Au and the high energy collisions foreseen to be carried out at LHC.

• Quarkonia in a deconfined medium: J/psi and, in general, charmonium suppression due to the Debye screening of the color interaction in the deconfined medium is one of the first observables proposed (by Matsui and Satz) as deconfinement signatures . The experimental data obtained at SPS (CERN) since the middle of '90s immediately aroused a great interest, although their interpretation was not easy at all. Thanks to the subsequent data, more and more complete and precise, the almost unanimous conclusion that the "anomalous suppression" seen in central Pb-Pb collisions is caused by the formation of deconfined matter. From a more detailed analysis of the most recent data (both from SPS and RHIC) it can be argued that the anomalous suppression is due to the break up of the charmonium excited states (which would normally decay into J/psi) rather than to J/psi itself . This conclusion is supported by theoretical studies of the dissociation temperatures of charmonium states in QGP. Further studies are concerned with the free energy of heavy QQbar pairs, meson spectral functions, mesonic correlators in the imaginary time formalism.

• Light mesons in a deconfined medium: In QCD the deconfinement phase transitions appears to coincide with the chiral phase transition: chiral symmetry is broken at ordinary energy densities (indeed scalar/pseudoscalar mesons and vector/axial mesons have different masses). It is interesting to investigate the behaviour of the pseudoscalar pions and of the scalar sigma mesonor of other chiral partners as the temperature and baryonic density vary in the proximity of the phase transition. Above T_c the spectral functions of these mesons become degenerate and show a peak, which signals a strongly correlated state, surviving within some temperature range. This studies have been performed within the PNJL model, based on an effective Lagrangian which allows to describe both phase transitions (chiral and deconfinement). For temperatires well above the phase transition, instead, studies are performed starting from the QCD Lagrangian, within the so-called HTL approximation. Mesonic correlation functions have been calculated both at zero and at finite momentum, as well as the spatial correlators, from which one can extract the screening masses and perform a comparison with lattice QCD.

• Shear viscosity and transport coefficients: in ultrarelativistic heavy-ion collisions a new phenomenon has been observed with respect to proton-proton collisions: the produced particles show a collective flow which, surprisingly, is well described within models assuming the conditions of a fluid with zero viscosity. This indication, however, contrasts the description (supported by lattice QCD calculations) of the QGP as an ideal fluid of quasi-particles, namely a highly viscous fluid. We are thus performing calculation of the shear viscosity within different effective models.

• Non-extensive statistics: To study anomalous physical processes in the relativistic heavy-ion collisions, we consider methods based on a generalized statistics, which describes non-linear many-body systems. We aim at a connection between long-range interactions and/or long-time tail memory functions in the systems and the unusual feature of the non-extensive Tsallis statistics. Future developments will also include the analysis of the RHIC data on transverse momentum spectra and multiplicities, at various rapidity intervals, in the framework of the generalized Tsallis statistics.

• Dense hadronic matter and astrophysical applications: Within a many-body theory which employs the Boson Loop Expansion (BLE) we are  investigating the static properties of nuclear matter. The work utilizes a functional method and an interaction Lagrangian based on quantum hadrodynamics (QHD). The suggested approximation scheme has been examined formally up to the two-loop order. Numerical results suggest a weak convergence of the BLE. Our ultimate intention is to apply this approach to hyperonic matter and neutron stars.

Schools

In addition to an intense activity research, our Group organizes, since a few years, an important International School, which is directed to PhD students and young researchers  

International School on QGP and Heavy Ions Collisions

which will be in  its fourth Edition this year.

Publications

Our pubblications  (courtesy of SLAC's HEP-Spires service).