Evidence for psi' regeneration in heavy ion collisions

The study of hidden charm production is an important part of the heavy ion program. The standard approach to this problem [1] assumes that c¯c bound states are created only at the initial stage of the reaction and then partially destroyed at later stages due to interactions with the medium [2, 3, 4]

Group theory of Wannier functions providing the basis for a deeper understanding of magnetism and superconductivity

The paper presents the group theory of best localized and symmetry-adapted Wannier functions in a crystal of any given space group G or magnetic group M. Provided that the calculated band structure of the considered material is given and that the symmetry of the Bloch functions at all the points of symmetry in the Brillouin zone is known, the paper details whether or not the Bloch functions of particular energy bands can be unitarily transformed into best localized Wannier functions symmetry-adapted to the space group G, to the magnetic group M, or to a subgroup of G or M. In this context, the paper considers usual as well as spin-dependent Wannier functions, the latter representing the most general definition of Wannier functions. The presented group theory is a review of the theory published by one of the authors in several former papers and is independent of any physical model of magnetism or superconductivity. However, it is suggested to interpret the special symmetry of the best localized Wannier functions in the framework of a nonadiabatic extension of the Heisenberg model, the nonadiabatic Heisenberg model. On the basis of the symmetry of the Wannier functions, this model of strongly correlated localized electrons makes clear predictions whether or not the system can possess superconducting or magnetic eigenstates

Comment to 'The Dependence of the anomalous J / psi suppression on the number of participant nucleons'

The recently published experimental dependence of the J/psi suppression pattern in Pb+Pb collisions at the CERN SPS on the energy of zero degree calorimeter EZDC are analyzed. It is found that the data obtained within the minimum bias analysis (using theoretical Drell-Yan ) are at variance with the previously published experimental dependence of the same quantity on the transversal energy of neutral hadrons ET . The discrepancy is related to the moderate centrality region: 100 << Np << 200 (Np is the number of nucleon participants). This could result from systematic experimental errors in the minimum bias sample. A possible source of the errors may be contamination of the minimum bias sample by o -target interactions. The data obtained within the standard analysis (using measured Drell-Yan multiplicity) are found to be much less sensitive to the contamination

Federalism, Decentralization, and Economic Growth

The distribution of competencies between the different levels of a federal system may have remarkable effects on economic growth, because mainly the regions of a country contribute to national economic development. Thus, a government’s economic policy is reasonably shaped along regional lines. The theoretical discussion in economics focuses however on the efficiency aspects of a decentralized provision and financing of public services; rarely the argument is raised that decentralization or federalism increases growth through a higher ability of the political system to innovate and to carry out reforms. After a discussion of the theoretical arguments on federalism and growth, we address the empirical question in this paper how important the assignment of decision making competencies and the design of fiscal federalism are for economic development. Finally, on the basis of existing theoretical and empirical studies on economic growth and federalism, open questions and possible ways of answering them are presented.

Charm coalescence at relativistic energies

The J/psi yield at midrapidity at the top RHIC (relativistic heavy ion collider) energy is calculated within the statistical coalescence model, which assumes charmonium formation at the late stage of the reaction from the charm quarks and antiquarks created earlier in hard parton collisions. The results are compared to the new PHENIX data and to predictions of the standard models, which assume formation of charmonia exclusively at the initial stage of the reaction and their subsequent suppression. Two versions of the suppression scenario are considered. One of them assumes gradual charmonium suppression by comovers, while the other one supposes that the suppression sets in abruptly due to quark-gluon plasma formation. Surprisingly, both versions give very similar results. In contrast, the statistical coalescence model predicts a few times larger J/psi yield in the most central collisions

Statistical coalescence model analysis of J / psi production in Pb + Pb collisions at 158 A GeV

Production of J/psi mesons in heavy ion collisions is considered within the statistical coalescence model. The model is in agreement with the experi- mental data of the NA50 Collaboration for Pb+Pb collisions at 158 A·GeV in a wide centrality range, including the so called anomalous suppression domain. The model description of the J/ psi data requires, however, strong enhancement of the open charm production in central Pb+Pb collisions. This model prediction may be checked in the future SPS runs

Second cluster integral and excluded volume effects for the pion gas

The quantum mechanical formula for Mayer s second cluster integral for the gas of relativistic particles with hard-core interaction is derived. The proper pion volume calculated with quantum mechanical formula is found to be an order of magnitude larger than its classical evaluation. The second cluster integral for the pion gas is calculated in quantum mechanical approach with account for both attractive and hard-core repulsive interactions. It is shown that, in the second cluster approximation, the repulsive -interactions as well as the finite width of resonances give important but almost canceling contributions. In contrast, an appreciable deviation from the ideal gas of pions and pion resonances is observed beyond the second clus- ter approximation in the framework of the Van der Waals excluded-volume model

Open charm enhancement in Pb + Pb collisions at SPS

The statistical coalescence model for the production of open and hidden charm is considered within the canonical ensemble formulation. The data for the J/psi multiplicity in Pb+Pb collisions at 158 A·GeV are used for the model prediction of the open charm yield. We find a strong enhancement of the open charm production, by a factor of about 2 4, over the standard hard-collision model extrapolation from nucleon-nucleon to nucleus-nucleus collisions. A possible mechanism of the open charm enhancement in A+A collisions at the SPS energies is proposed