D. Strottman

Dynamically generated open and hidden charm meson systems

We will study open and hidden charm scalar meson resonances within two different models. The first one is a direct application of a chiral Lagrangian already used to study flavor symmetry breaking in Skyrme models. In another approach to the problem a SU(4) symmetric Lagrangian is built and the symmetry is broken down to SU(3) by identifying currents where heavy mesons are exchanged and suppressing those. Unitarization in coupled channels leads to dynamical generation of resonances in both models, in particular, a new hidden charm resonance with mass 3.7 GeV is predicted. The small differences between these models and with previous works is discussed. We also perform an error analysis of the results, checking their stability and determining the uncertainties in masses and couplings of the heavy resonances.

Pion-nucleus elastic scattering in a local approximation to the delta-hole model☆

Abstract Differential elastic cross sections for pion-nucleus scattering are calculated by means of a handy and useful local approximation to a Δh model based on a many-body expansion which provides a good description of the different pion-nuclear reaction cross sections. Good agreement with the experimental results is obtained in a wide range of energies around resonance and for different nuclei. The model is particularly useful for the study of heavy nuclei where the original Δh model in its different versions becomes technically prohibitive.

Folded diagrams and 1s-Od effective interactions derived from Reid and Paris nucleon-nucleon potentials

Abstract The sd-shell effective-interaction matrix elements are derived from the Paris and Reid potentials using a microscopic folded-diagram effective-interaction theory. A comparison of these matrix elements is carried out by calculating spectra and energy centroids for nuclei of mass 18 to 24. The folded diagrams were included by both solving for the energy-dependent effective interaction self-consistently and by including the folded diagrams explicitly. In the latter case the folded diagrams were grouped either according to the number of folds or as prescribed by the Lee and Suzuki iteration technique; the Lee-Suzuki method was found to converge better and yield the more reliable results. Special attention was given to the proper treatment of one-body connected diagrams in the calculation of the two-body effective interaction. We first calculate the (energy-dependent) G-matrix appropriate for the sd-shell for both potentials using a momentum-space matrix-inversion method which treats the Pauli exclusion operator essentially exactly. This G-matrix interaction is then used to calculate the irreducible and non- folded diagrams contained in the Q - box . The effective-interaction matrix elements are obtained by evaluating a Q - box folded diagram series. We considered four approximations for the basic Q - box . These were (C1) the inclusion of diagrams up to 2nd order in G, (C2) 2nd order plus hole-hole phonons, (C3) 2nd order plus (bare TDA) particle-hole phonons, and (C4) 2nd order plus both hole-hole and particle-hole phonons. The contribution of the folded diagrams was found to be quite large, typically about 30%, and to weaken the interaction. Also, due to the greater energy dependence of higher-order diagrams, the effect of folded diagrams was much greater in higher orders. That is, the contribution from higher-order diagrams for most cases was greatly reduced by the folded diagrams. The convergence of the folded-diagram series deteriorates with the inclusion of higher-order Q - box processes in the method which groups diagrams by the number of folds, but remains excellent in the Lee-Suzuki method. Whereas the inclusion of the particle-hole phonon was essential to obtain agreement with experiment in earlier work, when the folded diagrams are included the effect of the particle-hole phonon is to reduce the amount of binding. All four approximations to both potentials produce interactions which badly underbind nuclei. The excitation spectra given by these interactions are, however, all rather similar to each other. The Paris interaction produces more binding than does the Reid, but differences between results obtained with the two interactions were often less than differences obtained in the four approximations. Essentially no difference was found between the effective non-central interactions from the Reid and Paris potentials after including the folded diagrams, although these two potentials themselves are quite different, especially in the strength of the tensor force. Comparisons between.calculated spectra and experiment were done for 18O, 18F, 19F, 20O, 20Ne, 22Ne, 22Na and 24Mg.

A theoretical approach to pion nuclear reactions in the resonance region

Abstract A local version of the microscopic isobar-hole model for pion-nucleus reactions is developed which provides a unified description of the different pion-nuclear reactions. In order to separate the total reaction cross section into the different channels it is necessary to split the imaginary part of the Δ selfenergy into the contributions from the different analytical cuts of the corresponding many-body Feynman diagrams. When this is done the results obtained with this theory agree remarkably well with experiment for the elastic cross section and the inclusive inelastic, single- and double-charge exchange and absorption reactions for different nuclei and a wide range of energies around resonance.

Fluid dynamics and quark gluon string model: What we can expect for Au + Au collisions at 11.6-A/GeV/c

Abstract Central Au + Au collisions at 11.6 AGeV c are examined within the Quark Gluon String Model (QGSM) and one-Fluid Dynamical Model (FDM). QGSM is used to study baryon stopping and production of Δ — matter. FDM allows to extract measurable signatures of the transition of hadronic matter to Quark Gluon Plasma (QGP).

Global analysis of relativistic heavy-ion collisions☆

Abstract A global analysis of relativistic heavy-ion collisions is proposed which entails a measurement of the momentum of all emitted particles. The resultant thrust is a measure of final-state momentum flow and provides information on the global dynamics governing the collisions. This proposal is tested with a relativistic hydrodynamic model for collisions of equal-mass nuclei. The angle at which the thrust, or maximal directed momentum flow, occurs is O° CM for grazing collisions and increases monotonically to 90° CM for central collisions. Experimental observation of this dramatic behaviour would imply a mean free path much less than the size of the colliding nuclei.

Resonances in quantum mechanical tunneling

Abstract In asymmetric double-well potentials, it can be tacitly assumed that a wave function in the higher-energy well (false vacuum) will always tunnel to the lower well, given enough time. However, in general this is not true. Whether a state can significantly tunnel to the true vacuum is a very sensitive function of the shape of the potential. We illustrate this with analytic and numerical examples. Thus, if there is not dissipation or coupling to other modes, a wave function may not tunnel.

Initial state of ultrarelativistic heavy ion collisions

A model for energy, pressure, and flow velocity distributions at the beginning of ultrarelativistic heavy ion collisions is presented, which can be used as an initial condition for hydrodynamic calculations. Our model takes into account baryon recoil for both target and projectile, arising from the acceleration of partons in an effective field F mn produced in the collision. The typical field strength ~string tension! for RHIC energies is about 5‐12 GeV/fm, which allows us to talk about ‘‘string ropes.’’ The results show that a quark-gluon plasma forms a tilted disk, such that the direction of the largest pressure gradient stays in the reaction plane, but deviates from both the beam and the usual transverse flow directions. Such initial conditions may lead to the

Clues to the nature of the Δ∗(1700) resonance from pion- and photon-induced reactions

Abstract We make a study of the π − p → K 0 π 0 Λ , π + p → K + π + Λ , K + K ¯ 0 p , K + π + Σ 0 , K + π 0 Σ + , and η π + p reactions, in which the basic dynamics is given by the excitation of the Δ ∗ ( 1700 ) resonance which subsequently decays into K Σ ∗ ( 1385 ) or Δ ( 1232 ) η . In a similar way we also study the γ p → K 0 π + Λ , K + π − Σ + , K + π + Σ − , K 0 π 0 Σ + , and η π 0 p related reactions. The cross sections are proportional to the square of the coupling of Δ ∗ ( 1700 ) to Σ ∗ K ( Δη ) for which there is no experimental information but which is provided in the context of coupled channels chiral unitary theory where the Δ ∗ ( 1700 ) is dynamically generated. Within present theoretical and experimental uncertainties one can claim a global qualitative agreement between theory and experiment. We provide a list of items which need to be improved in order to make further progress along these lines.

High nuclear temperatures by antimatter-matter annihilation

Abstract Using two rather different approaches the temperature of nuclear matter has been calculated as a function of the momentum of incident antiprotons and antideuterons. The results of this study show that a high temperature can be achieved by raising the beam momentum above 2 GeV c . For incident momentum of the order of 6 GeV c , temperatures of the magnitude necessary to study the possible quark-gluon plasma phase transition are reached.