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Nuclear Physics Monday ing, thus extending earlier work [1]. We present compact formulae that can be used for the chiral extrapolation of lattice simulations, that usually work at higher quark (meson) masses [2]. As a by-product, we also construct the complete fourth order meson-baryon Lagrangian for three HK 6 Theory II flavors with all possibel external sources. [1] B. Borasoy and U.-G. Meißner, Ann. Phys. 254 (1997 )192-232 [2] M. Frink and U.-G. Meißner, in preparation Time: Monday 15:45–18:45 Room: E Group Report HK 6.1 Mon 15:45 E Fermi-liquid theory of quark matter at high densities — •Kai Hebeler and Bengt Friman — Gesellschaft für Schwerionenforschung, 64291 Darmstadt, Planckstr. 1 We explore the Fermi-liquid properties of ultrarelavistic electron and quark systems at zero temperature and high baryon densities. Contributions to the effective interaction due to the polarisation of the medium are computed in the random-phase-approximation. As is well known, the lack of screening for transverse gauge bosons implies that the quasiparticle strength vanishes for states at the Fermi surface, and consequently that such a system formally is not a normal Fermi liquid. However, since the corresponding singularity is logarithmic, the normal Fermi-liquid behaviour is restored at minimal temperatures. The corresponding Fermiliquid parameters, including spin, flavour and colour degrees of freedom are presented. An appropriately modified Fermi-liquid approach could be relevant for the description of a possible colour-superconducting phase. Group Report HK 6.2 Mon 16:15 E Point-Form Dynamics of Relativistic Few-Body Sytems — •Wolfgang Schweiger 1 , Marcus Lechner 1 , William H. Klink 2 , and Andreas Krassnigg 3 — 1 Inst. Theor. Physik, Univ. Graz, Graz, Austria — 2 Dept. Physics and Astr., Univ. of Iowa, Iowa City, USA — 3 Argonne National Lab., Argonne, USA The general problem of formulating relativistic quantum mechanics for a fixed number of particles goes back to the pioneering work of Dirac in which he suggested three different forms of relativistic dynamics, i.e. the instant form, the front form, and the point form. These forms differ by the set of Poincarè generators which are interaction dependent. Although it has a number of advantages, the point form has been the least used and is the most unfamiliar of the three forms. Our contribution deals with a point-form formulation of relativistic few-body systems. We present a relativistic, Poincarè invariant coupled-channel formalism for few-body systems interacting via one-particle exchange. Our approach takes the exchange particle explicitly into account and relates the coupling of the exchange particle to an underlying quantum field theory. As illustrative examples we will present vector mesons within the chiral constituent quark model and electromagnetically bound systems like hydrogen and positronium. The vector-meson system allows us to study the effect of retardation in the Goldstone-boson exchange. The investigation of hydrogen and positronium serves as a test of the point-form approach for well studied QED systems and reveals the relation between point-form and instant-form dynamics. HK 6.3 Mon 16:45 E Particle production in space-time dependent fields — •Dennis Dietrich — Laboratoire de Physique Théorique, Bâtiment 210, Université Paris XI, 91405 Orsay Cedex, France The exact retarded propagators of particles in classical space-time dependent gauge fields is derived by solving the equations of motion for the Green’s functions with corresponding boundary conditions. From the retarded propagators obtained in this way, the momentum spectrum for pairs produced by vacuum polarisation is calculated. Different approximations and the exact solution for the Green’s functions and the momentum spectra are presented. HK 6.4 Mon 17:00 E Fermionic Casimir Effect: Cavities Interact in the Fermi Sea — •Andreas Wirzba 1 and Aurel Bulgac 2 — 1 Universität Bonn, HISKP(Theorie), Nussallee 14-16, 53115 Bonn — 2 Department of Physics, University of Washington, Seattle WA 98195-1560, USA We report about a new force that acts on cavities (literally empty regions of space) when they are immersed in a background of noninteracting fermionic matter fields. The interaction follows from the obstructions to the (quantum mechanical) motions of the fermions in the Fermi sea caused by the presence of bubbles or other (heavy) particles immersed in the latter, as e.g. nuclei in the neutron sea in the crust of a neutron star. This effect resembles the traditional Casimir effect which describes the attraction between two parallel metallic mirrors in vacuum. Here, however, the fluctuating (bosonic) electromagnetic fields are replaced by real fermionic fields, the Casimir energy is inferred from the geometrydependent part of the density of states, and its sign is not fixed, but varies according to the relative arrangement and distances of the cavities. This topic is relevant to the physics of neutron star crusts (nuclei embedded in a neutron gas), to inhomogeneous phases in the quark-gluon plasma, to dilute Bose-Einstein-condensate bubbles inside the background of a Fermi-Dirac condensate, to buckyballs in liquid mercury, to superconducting droplets in a Fermi liquid, etc. This work is supported under Contract 41445400 (COSY-067) of the Forschungszentrum Jülich GmbH. HK 6.5 Mon 17:15 E Semileptonic Decays of Baryons in a Covariant Quark Model — •Sascha Migura, Dirk Merten, Bernard Metsch, and Herbert-R. Petry — Helmholtz-Institut für Strahlen- und Kernphyik, Abteilung Theorie, Nußallee 14-16, D-53115 Bonn We are calculating semileptonic decays of baryons in a relativistic covariant constituent-quark model which is based on the Bethe-Salpeterequation in instantaneous approximation. This model generates mass spectra for mesons and baryons up to the highest observable energies. Without introducing additional free parameters we compute on this basis helicity amplitudes of semileptonic decays. We thus obtain decay widths for semileptonic decays in good agreement with experiment. HK 6.6 Mon 17:30 E Static properties of baryons in the Bethe-Salpter framework — •Christian Haupt, Ulrich Löring, Bernard Metsch, and Herbert-R. Petry — Helmholtz-Institut für Strahlen- und Kernphysik, Abteilung Theorie, Nußallee 14-16, D-53115 Bonn We derive a method, to compute static properties (e. g. magnetic moments and charge radii) of baryons from the Bethe-Salpeter equation in the instantaneous approximation. This is usually done by taking the limit of some form factor. We develop instead a new approach, which expresses the static moments as expectation values of appropriate operators with respect to Salpeter amplitudes. We discuss the analytic derivation of these expecation values, show the numerical results and compare them to experiment. HK 6.7 Mon 17:45 E Hyperon-nucleon Dirac-Brueckner calculations — •Christoph Keil and Horst Lenske — Institut für Theoretische Physik, Universität Giessen, 35392 Giessen, Germany We present a model for the calculation of relativistic effective inmedium interactions for NN and YN scattering. The model is based on the covariant meson exchange formalism of the Bonn potentials which are extended to also include the octet hyperons as well as the lowest three meson octets, accounting for pseudoscalar, vector and scalar interactions. The decomposition of the G-matrix, for which we have to use an enlarged set of invariants, is discussed. For the decomposition also the half off-shell amplitudes are utilized which removes the ambiguities in this process. We will present first results for the application of our effective Λ-N interaction to single Λ hypernuclei calculated in the density dependent relativistic hadron field theory DDRH. Work supported by the European graduate school Giessen–Copenhagen.
Nuclear Physics Monday HK 6.8 Mon 18:00 E Nuclear structure of light nuclei in an extended FMD approach — •Thomas Neff 1 , Hans Feldmeier 1 , and Robert Roth 2 — 1 Gesellschaft für Schwerionenforschung, Darmstadt — 2 Institut für Kernphysik, TU Darmstadt The internal structure of light nuclei up to the drip lines is studied using FMD many-body states. The calculations make no a priori assumptions about a core or single particle-states and energies. The same correlated two-body interaction is used for all nulei. Continuum effects are included. Energies, mass and charge radii, as well as electromagnetic transitions are calculated without using effective charges. The FMD representation provides not only a very intuitive and descriptive picture but also quantitative predictions. Both, variaton after projection on total angular-momentum eigenstates and configuration mixing are important to understand the changes in structure with increasing neutron number. For example, the binding energies and radii near the driplines can only be reproduced when the halo neutrons are swaying collectively against the rest of the nucleus. Intrinsic clusterization is essential for a quantitative description of low lying states (e.g. C, Ne isotopes). HK 6.9 Mon 18:15 E Photons and the Triton at Very Low Energies — •Harald W. Griesshammer — Institut für Theoretische Physik (T39), TU München, Germany Recently, the Effective Field Theory of the three-nucleon system in which pions are integrated out as heavy was systematised to all orders in the low-energy expansion [1]. In this consistent and modelindependent approach, calculations involving external electro-weak currents can be performed straightforwardly, and the theoretical error can be estimated systematically. They are relevant e.g. for big-bang nucleosynthesis and the extraction of neutron properties from experiments on HK 7 Heavy Ions I light nuclei. Often, three-body forces are irrelevant, but in the doublet- S-wave (triton/ 3 He) channel, three-body forces are stronger than naïvely expected. Using the requirement that physical low-energy observables are insensitive to details of the short distance treatment, two simple observables like the triton binding energy and scattering length suffice to determine the three-body forces for wave functions accurate to ∼ 1%. We present a calculation of the triton and 3 He form factors and an investigation into charge symmetry breaking in the triton/ 3 He-system. Our result for triton photo-disintegration resolves a 15% discrepancy between potential-model calculations and the measured total cross section at thermal neutron energies [2]. Work supported in part by DFG and BMBF. [1.] Bedaque, Grießhammer, Hammer and Rupak: Nucl. Phys.A714 (2003), 589 [nucl-th/0207034]. [2.] Bedaque, Grießhammer, Hammer and Rupak: in preparation. HK 6.10 Mon 18:30 E P-shell nuclei within the modified J-matrix approach to scattering — •Arina Sytcheva 1 , Frans Arickx 1 , Jan Broeckhove 1 , and Viktor Vasilevsky 2 — 1 Groupe Computational Modeling and Programming, University of Antwerpen, Middelheimlaan, 1, 2020, Antwerpen, Belgium — 2 Bogoliubov Institute for Theoretical Physics, Metrolohichna str., 14-b, Kiev, 03143, Ukraine We will discuss coupled-channel calculations in two-cluster systems with the possibility of collective excitations. We present a number of results for such nuclei as 5 He, 5 Li and 8 Be. We use the modified J-matrix method with the ”frozen” clusters. We take into account three possible channels - cluster, monopole and quadrupole. Our focus is on the energy region where only the cluster channel is open and the quadrupole and monopole channels are closed. We calculate the phase shifts and derive energies and widths of resonances within coupled and uncoupled channel calculations. We can provide a clear-cut analysis of the resonances which appear in the two-cluster continuum in terms of individual channel contributions. Time: Monday 15:45–18:45 Room: F Group Report HK 7.1 Mon 15:45 F Heavy-flavor measurements with the PHENIX experiment at RHIC — •Ralf Averbeck for the PHENIX Collaboration collaboration — State University of New York at Stony Brook The production of heavy flavor, i.e. charm or beauty quarks, is an important probe of the hot and dense medium created in high energy nuclear collisions. Once produced, heavy quark-antiquark pairs form either bound quarkonia or hadronize into separate particles carrying open heavy flavor. The total yield is sensitive to the parton density in the incoming nuclei and, as such, also reflects initial state nuclear effects like shadowing. Medium effects from the hot and dense phase are expected to leave their footprint on heavy-flavor observables in later stages of the collision. The yield of heavy quarkonia might be reduced due to screening of the QCD potential in a deconfined medium or even enhanced due to coalescence. The issue of quark energy loss in the nuclear medium constitutes a critical test of our understanding of these reactions as well. One approach to study heavy-flavor physics in nuclear reactions is to investigate the leptonic decay channels of particles carrying heavy flavor. At RHIC, PHENIX is the only experiment specifically designed for the measurement of electromagnetic probes and, therefore, is ideally suited for such studies. Present results from p-p, d-Au, and Au-Au collisions at √ sNN = 200 GeV are discussed. Group Report HK 7.2 Mon 16:15 F Anisotropic Flow and Global Observables in the Forward Directions at RHIC — •Jörn Putschke for the STAR collaboration — Max-Planck-Institut für Physik, Föhringer Ring 6, 80805 München We present the first observation of directed flow (v1) in Au+Au collisions at 200 GeV at RHIC. Measured by three particle correlations, v1 is found to be independent of pseudorapidity near mid rapidity (η = 0) and a peak value of 1.5% around η = 4. This analysis also gives us the first direct indication of in-plane elliptic flow at RHIC. First results of the centrality and η dependence of particle multiplicity density and mean transverse momenta in this forward region at the STAR experiment will be reported for Au+Au collisions at √ sNN = 200 GeV and discussed in connection with the anisotropic flow measurements in the limiting fragmentation picture. The measurements of the centrality dependence of dN/dη and transverse momentum spectra from mid-rapidity to forward rapidity in d+Au collisions at 200 GeV provide a sensitive tool to understand the dynamics of multi-particle production in the high parton density regime. Comparsion with theoretical predictions of parton saturation in the Color Glass Condensate [1] and a perturbative QCD parton model [2] will be discussed. [1] Dmitri Kharzeev, arXiv:hep-ph/0212316 v2 16 Jan 2003 [2] Xin-Nian Wang, arXiv:nucl-th/0303004 v1 3 Mar 2003 HK 7.3 Mon 16:45 F Lambda production at high rapidity in d+Au and p+p collisions at √ SNN = 200 GeV — •Frank Simon for the STAR collaboration — Max–Planck–Institut für Physik, München, Germany We present first studies of Lambda and Anti-Lambda production in the pseudorapidity region 2.5 < |η| < 4, covered by the forward radial-drift TPCs (FTPCs) at STAR. The FTPCs provide momentum and charge determination but no particle identification, making the use of combinatorial methods and background subtraction necessary for Lambda identification. The Anti-Lambda/Lambda ratio measured at high rapidity will be compared to the ratio obtained at mid-rapidity with the STAR TPC. Differences in the ratio for different collision systems and a possible asymmetry in d+Au collisions will give indications of what mechanisms drive the antibaryon to baryon ratio at high rapidities.
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