Enhanced dilepton radiation at RHIC

Recently, there is growing evidence that a new state of matter is formed in  Au+Au collisions at RHIC: a strongly coupled Quark Gluon Plasma of partonic degrees of freedom which develops a collective motion. Dilepton spectra are not affected by strong interaction and can therefore probe the whole time evolution of the collision. Thus they may be sensitive to the onset of deconfinement, chiral symmetry restoration, as well as the production of thermal photons. The PHENIX experiment measured the production of e⁺e⁻ pairs in p+p and Au+Au collisions at . An enhanced dilepton yield in the mass range is measured. The excess increases faster with centrality than the number of participating nucleons, and is concentrated at . At higher p_T the excess below 300 MeV/c² has been related to an enhanced production of direct photons, possibly of thermal origin.     

Status and plans of the NA61/SHINE physics program

One of the NA61/SHINE experiment??s goals is to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. This is to be achieved by performing a two-dimensional phase diagram (T-?? _B ) scan??measuring hadron production in collisions of various beam particles and targets at various beam energies. NA61/SHINE also collects data for the T2K experiment, which are just about to be published.     

The horn, kink and step, dale: from few GeV to few TeV

Rich experimental data have been collected in heavy-ion collisions at high energies to study the properties of strongly interacting matter. As the theory of strong interactions, QCD, predicts asymptotic freedom, the created matter at sufficiently high temperature and density will be dominated by a state of quasi-free quarks and gluons referred to as the Quark-Qluon Plasma (QGP). Experimental signals for the onset of the QGP creation (the onset of the deconfinement) have been predicted within the statistical model for the early stage of nucleus-nucleus collisions. In this model the existence of two different phases is assumed: confined mater and the QGP, as well as a first order phase transition between them. Until recently, these predictions were confirmed only by the NA49 experiment at the CERN SPS. In this report recent results from STAR at RHIC/BNL and from ALICE at LHC/CERN, related to the onset of deconfinement, will be compared to published results from NA49.     

Nonextensive effects on the phase structure of quantum hadrodynamics

In this Letter, we investigate nonextensive effects on phase transition in nuclear matter in the context Walecka many-body field theory. A difference is observed when the results calculated for the nuclear matter at vanishing baryon density is compared to those obtained through the standard Fermi-Dirac distribution. It is observed a dependence between the nonextensive parameter q and the coupling constants of the phase transition. A numerical relation for this thermodynamical dependence is also proposed.     

Probing dense matter with strangeness production in nuclear collisions

Experiments on strangeness production in nucleus–nucleus collisions at SIS energies address fundamental questions of modern nuclear physics: the determination of the nuclear equation-of-state at high baryon densities and the properties of hadrons in dense nuclear matter. From the yields of K⁺ mesons measured in heavy-ion collisions a value for the nuclear compressibility of is extracted for nuclear densities around twice saturation density using different microscopic transport models. Both the yield of K⁺ mesons and their anisotropic azimuthal angular distribution (elliptic flow) exhibit strong evidence for a repulsive K⁺N potential. The yields of K⁺ and K⁻ mesons measured in proton–nucleus collisions can be reproduced by transport calculations assuming at saturation density a repulsive K⁺N potential of and an attractive K⁻N potential of .     

Charm and bottom production at RHIC

The current status of charm and bottom production measurements at RHIC is summarized. Heavy-flavor data from p+p collisions at provide a crucial testing ground for perturbative QCD calculations and serve as a baseline for measurements in nucleus-nucleus collisions. Due to their large mass heavy quarks are produced in hard parton scattering processes in the earliest phase of a nucleus-nucleus collisions such that they can be used to probe the hot and dense medium that is formed in the course of Au+Au collisions at RHIC.     

Status and plans of the ion program of NA61 at the CERN SPS

The NA61/SHINE at the CERN SPS is a new experiment to study hadron production in p+p, p+A, h+A and A+A interactions. The main goal of the NA61 ion program is to explore the phase diagram (T ? ?? _B ) of strongly interacting matter. In particular, we plan to study the properties of the onset of deconfinement and to search for the signatures of the critical point. A two-dimensional scan of the phase diagram will be performed by varying the energy (13A?C158A GeV) and system size (p+p, Be+Be, Ar+Ca, Xe+La) of collisions. This paper summarizes the status and plans of the NA61/SHINE ion program. In particular the detector upgrades, data taking schedule and the first results on spectra and correlations are discussed.     

Identification of a rotator phase of octamethyl ferrocene and correlations between its structural and dynamical properties

The low- and high-temperature phases of octamethyl ferrocene were studied in detail, using high-resolution X-ray powder diffraction, differential scanning calorimetry and nuclear resonant scattering, in particular the novel technique of synchrotron radiation perturbed angular correlations (SRPAC). Much as in the case of an analogous but more unsymmetrical molecule, octamethyl ethinyl ferrocene, the high-temperature phase possesses the space group with lattice parameters , , which in the rhombohedral setting correspond to , α=104.79^°. An increase of the volume per formula unit of about 12% across the phase transition is observed.The rotation of the electric field gradient, which can be identified with the rotation of the entire molecule within the lattice, follows Arrhenius behaviour with a high activation energy of . Whereas precursor effects and a change in activation energy were observed for octamethyl ethinyl ferrocene, no such effects are observed for octamethyl ferrocene. We relate this difference to the absence of the ethinyl substituent in octamethyl ferrocene.     

Scattering problem with nonlocal separable potential of rank-two: Application to statistical mechanics

In this paper, we present a formulation of statistical mechanics of a thermodynamic system consisting of free particles and independent correlated pairs interacting via nonlocal potential in terms of the scattering properties. Some quantum statistical properties such as energy, heat capacity, second virial coefficient, virial pressure and quantum correction of kinetic energy are described analytically. The difference between the resolvents of the interacting and free Hamiltonians, represented as , that is associated with particle correlations is used for the evaluation of the properties. The statistical properties are related to correlated states, when making a pole expansion of the analytically continued momentum matrix element of . The present work illustrates these relations for a three-dimensional nonlocal separable potential of rank-two.