W. M. Alberico

Heavy quark bound states above T c

A comprehensive parametrization of the color-singlet heavy quark free energy above T{sub c} is given, using the lattice data in quenched (N{sub f}=0) and unquenched (N{sub f}=2 and N{sub f}=3) QCD. The corresponding (temperature dependent) potentials thus obtained are then inserted into the Schroedinger equation for charmonium and bottomonium in the deconfined phase of QCD. The solution of the equation provides an estimate of the melting temperature and of the radii for the different cc and bb bound states.

Quarkonia in the deconfined phase: Effective potentials and lattice correlators

The Schroedinger equation for the charmonium and bottomonium states at finite temperature is solved by employing an effective temperature-dependent potential given by a linear combination of the color-singlet free and internal energies obtained on the lattice from the Polyakov loop correlation functions. The melting temperatures and other properties of the quarkonium states are evaluated. The consistency of the potential model approach with the available lattice data on the quarkonium temporal correlators and spectral functions is explored.

The 2p–2h electromagnetic response in the quasielastic peak and beyond

Abstract The contribution to the nuclear transverse response function R T arising from two particle–two hole (2p–2h) states excited through the action of electromagnetic meson exchange currents (MEC) is computed in a fully relativistic framework. The MEC considered are those carried by the pion and by Δ degrees of freedom, the latter being viewed as a virtual nucleonic resonance. The calculation is performed in the relativistic Fermi gas model in which Lorentz covariance can be maintained. All 2p–2h many-body diagrams containing two pionic lines that contribute to R T are taken into account and the relative impact of the various components of the MEC on R T is addressed. The non-relativistic limit of the MEC contributions is also discussed and compared with the relativistic results to explore the role played by relativity in obtaining the 2p–2h nuclear response.

Potential models and lattice correlators for quarkonia at finite temperature

We update our recent calculation of quarkonium Euclidean correlators at finite temperatures in a potential model by including the effect of zero modes in the lattice spectral functions. These contributions cure most of the previously observed discrepancies with lattice calculations, supporting the use of potential models at finite temperature as an important tool to complement lattice studies.

Meson Screening Masses in the Interacting QCD Plasma

Abstract The meson screening mass in the pseudoscalar channel is calculated from the momentum dependent meson spectral function, using HTL fermionic propagators. A careful subtraction procedure is required to get an UV finite result. It is shown that in the whole range of temperatures explored here the HTL screening mass stays above the non-interacting result, slowly approaching the value m scr = 2 π 2 T 2 + m ∞ 2 , where m ∞ 2 is the HTL asymptotic thermal quark mass. Our analysis leads to a better understanding of the excitations of QGP at sufficiently large temperatures and may be of relevance for interpreting lattice results.

Meson correlation functions in a QCD plasma

Abstract The temporal pseudoscalar meson correlation function in a QCD plasma is investigated in a range of temperatures exceeding T c and yet of experimental interest. Only the flavour-singlet channel is considered and the imaginary time formalism is employed for the finite temperature calculations. The behaviour of the meson spectral function and of the temporal correlator is first studied in the HTL approximation, where one replaces the free thermal quark propagators with the HTL resummed ones. This procedure satisfactory describes the soft fermionic modes, but its application to the propagation of hard quarks is not reliable. An improved version of the so-called NLA scheme, which allows a better treatment of the hard fermionic modes, is then proposed. The impact of the improved NLA on the pseudoscalar temporal correlator is investigated.

Finite momentum meson correlation functions in a QCD plasma

Abstract The finite momentum meson spectral function (MSF) in the pseudoscalar channel is evaluated, adopting for the fermionic propagators HTL expressions. The different contributions to the meson spectral functions are clearly displayed. Our analysis may be of relevance for lattice studies of MSF based so far on the maximum entropy method. As a further step the correlation function along the (imaginary-) temporal direction is evaluated.

Role of 2p–2h MEC excitations in superscaling

Abstract Following recent studies of inclusive electron scattering from nuclei at high energies which focused on two-nucleon emission mediated by meson-exchange currents, in this work the superscaling behavior of such contributions is investigated. Comparisons are made with existing data below the quasielastic peak where at high momentum transfers scaling of the second kind is known to be excellent and scaling of the first kind is good, in the proximity of the peak where both 1p–1h and 2p–2h contributions come into play, and above the peak where inelasticity becomes important and one finds scaling violations of the two kinds.

Heavy quark dynamics in the QGP: RAA and v2 from RHIC to LHC

We study the stochastic dynamics of c and b quarks in the hot plasma produced in nucleus-nucleus collisions at RHIC and LHC, providing results for the nuclear modification factor RAA and the elliptic flow coefficient v2 of the single-electron spectra arising from their semi-leptonic decays. The initial QQˆ pairs are generated using the POWHEG code, implementing pQCD at NLO. For the propagation in the plasma we develop a relativistic Langevin equation (solved in a medium described by hydrodynamics) whose transport coefficients are evaluated through a first-principle calculation. Finally, at Tc, the heavy quarks are made to hadronize and decay into electrons: the resulting spectra are then compared with RHIC results. Predictions for LHC are also attempted.

Screening masses of scalar and pseudo-scalar excitations in quark–gluon plasma

Abstract The Quark–Gluon Plasma (QGP) excitations, corresponding to the scalar and pseudo-scalar meson quantum numbers, for different temperatures are calculated. Analysis is performed in the Hard Thermal Loop (HTL) Approximation and leads to a better understanding of the excitations of QGP in the deconfined phase and is also of relevance for lattice studies.