Monday, March 11, 2002 - DPG-Tagungen

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Nuclear Physics Monday Sessions – Invited and Contributed Lectures, Posters – HK1 Plenary Session Time: Monday 13:45–15:45 Room: Plenarsaal Plenary Talk HK 1.1 Mon 13:45 Plenarsaal Instantons and Confinement in QCD — •Gerard ’t Hooft — Utrecht University and Spinoza Institute Quantum Chromodynamics, a theory that describes in great detail the dynamics of the strong forces among the subatomic particles, is a non-Abelian gauge theory, and it has a delicate topological structure. The nature of the forces that keep the quarks permanently confined into pairs or triplets can be understood in terms of this topology: we find that Bose-Einstein condensation takes place in the colour-magnetic sector. The theory allows for a very special kind of transitions, or events, called ”instantons”. It turns out that these explain the special way in which the chiral symmetry of the system is manifested, such as the entirely different mixing angles between the vector particles on the one hand and the isoscalars on the other. Plenary Talk HK 1.2 Mon 14:30 Plenarsaal A Perspective on Nuclear Structure Physics in the Context of the U.S. Long Range Planning Process — •Richard F. Casten — Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520-8124, U.S.A. Nuclear physics in the USis entering a crucial phase in which two major facilities – CEBAF at Jefferson Laboratory and RHIC at Brookhaven National Laboratory – are now running and obtaining significant new results, and in which a third facility, the exotic beam laboratory Rare Isotope Accelerator (RIA), is being recommended as the highest priority for major new construction in the current Long Range Planning Pro- HK2 Theory I cess. These initiatives reflect the three major pillars on which nuclear physics research stands, namely, the interactions of quarks and gluons, the quark-gluon structure of hadronic matter, and of the structure of nuclei themselves. Each of these has wider ramifications, especially in regard to astrophysics and the Standard Model. This talk will focus on the recent Long Range planning effort in the US– both the nature of the process itself and on the Recommendations resulting from it. It will then go on to discuss in more specificity the major accomplishments in nuclear structure in recent years and the exciting prospects for future discoveries in this field. Especially important in this regard is the discovery potential inherent in the RIA facility. This work was supported by U.S. DOE under Grant No. DE-FG02-91ER-40609. Plenary Talk HK 1.3 Mon 15:15 Plenarsaal Heavy Ion Physics in the RHIC Era — •Thomas Peitzmann — Universität Münster, 48149 Münster, Germany The first year of running of the Relativistic Heavy Ion Collider in Brookhaven at a beam energy of √ sNN = 130 GeV has brought the study of strongly interacting matter into a new era and has already provided a large number of exciting results by the four heavy ion experiments. Highlights of these early results will be presented and discussed in comparison with previous results from lower energy heavy ion experiments and from measurements in pp (p¯p) collisions and with theoretical expectations. The status of the measurements at the full RHIC energy of √ sNN = 200 GeV in 2001 and the future prospects will also be discussed. Time: Monday 16:15–19:00 Room: A Group Report HK 2.1 Mon 16:15 A New soft pion theorems for hard reactions — •M.V. Polyakov 1,2 , P.V. Pobylitsa 1,2 ,andM.I. Strikman 1,3 — 1 Petersburg Nuclear Physics Institute, 188350 Gatchina, Russia — 2 Institute for Theoretical Physics II, Ruhr University Bochum, 44780 Bochum, Germany — 3 Pennsylvania State University, University Park, PA16802,USA We prove a new soft pion theorem for the near threshold pion production by a hard electromagnetic probe. This theorem relates various near threshold pion production amplitudes to the nucleon form factors at large momentum transfer. The new soft pion theorem exploits the kinematic domain Q 2 ≫ Λ 3 /mπ (Λ ∼ 1 GeV is a typical hadronic scale, Q 2 is a virtuality of the incident photon). The new soft pion theorem is in a good agreement with the SLAC data for the structure function F p 2 (W, Q 2 ) for W 2 ≤ 1.4 GeV 2 and 9 ≤ Q 2 ≤ 30.7 GeV 2 . Group Report HK 2.2 Mon 16:45 A Relativistic chiral SU(3) symmetry, large Nc sum rules and meson-baryon scattering — •Matthias F.M. Lutz 1 and Evgeni E. Kolomeitsev 2 — 1 GSI, Planck Str. 1, D-64291 Darmstadt and Institut für Kernphysik, TU Darmstadt, D-64289 Darmstadt — 2 ECT*, Villa Tambosi, I-38050 Villazzano (Trento) The relativistic chiral SU(3) Lagrangian is used to describe kaonnucleon scattering imposing constraints from the pion-nucleon sector and the axial-vector coupling constants of the baryon octet states. We solve the covariant coupled-channel Bethe-Salpeter equation with the interaction kernel truncated at chiral order Q 3 where we include only those terms which are leading in the large Nc limit of QCD. The baryon decuplet states are an important explicit ingredient in our scheme, because together with the baryon octet states they form the large Nc baryon ground states of QCD. Part of our technical developments is a minimal chiral subtraction scheme within dimensional regularization, which leads to a manifest realization of the covariant chiral counting rules. All SU(3) symmetry-breaking effects are well controlled by the combined chiral and large Nc expansion, but still found to play a crucial role in understanding the empirical data. We achieve an excellent description of the data set typically up to laboratory momenta of plab � 500 MeV. Group Report HK 2.3 Mon 17:15 A Determination of vector meson properties by matching resonance saturation to a constituent quark model — •Stefan Leupold — Institut für Theoretische Physik, Universität Giessen, Germany We calculate the low-energy coefficients of chiral perturbation theory in two different ways, namely (i) by assuming resonance saturation and (ii) within a constituent quark model derived as the low energy effective theory of the instanton model. By matching the expressions of the two models we determine mass and coupling constants for vector and axialvector mesons. We recover in this way the KSFR relation as well as the universality of the vector meson coupling. The latter is found to be g =2π. For the ρ-meson mass we get mρ = √ 8 πFπ ≈ 826 MeV where Fπ denotes the pion decay constant. HK 2.4 Mon 17:45 A Electromagnetic transition form factors and dilepton decay rates of nucleon resonances — •Mikhail Krivoruchenko, Christian Fuchs, Boris Martemyanov, andAmand Faessler —Institut fuer Theoretische Physik, Universitaet Tuebingen, Auf der Morgenstelle 14, D-72076 Tuebingen, Germany Relativistic, kinematically complete phenomenological expressions for the dilepton decay rates of nucleon resonances with arbitrary spin and parity are derived in terms of the magnetic, electric, and Coulomb tran-
Nuclear Physics Monday sition form factors. The dilepton decay rates of the nucleon resonances with masses below 2 GeV are estimated using the extended vector meson dominance model for the transition form factors. The model provides a unified description of the photo- and electroproduction data, the vector meson decays, and the dilepton decays. The constraints on the transition form factors from the quark counting rules are taken into account. The parameters of the model are fixed by fitting the available photo- and electroproduction data and using results of the multichannel partial-wave analysis of the πN scattering. The vector meson coupling constants of the magnetic, electric, and Coulomb types are determined. The dilepton widths and the dilepton spectra from decays of nucleon resonances with masses below 2 GeV are calculated [1,2]. The results are used to model the dilepton spectra in proton-proton, proton-deuteron, and heavy-ion collisions. [1] M.I. Krivoruchenko, Amand Faessler: Phys.Rev. D 65, 017502 (2002). [2] M.I. Krivoruchenko, B.V. Martemyanov, Amand Faessler, C. Fuchs: submitted to Ann.Phys. (N.Y.), nucl-th/0110066. HK 2.5 Mon 18:00 A Color-Flavor Unlocking and Phase Structure of Strongly Interacting Matter — •Michael Buballa 1,2 , Jǐri Hǒsek 3 ,andMicaela Oertel 4 — 1 IKP, TU Darmstadt, Darmstadt, Germany — 2 GSI, Darmstadt, Germany — 3 Dept. Theor. Phys., ˇ Reˇz (Prague), Czech Republik — 4 IPN-Lyon, Villeurbanne, France At low temperatures and high densities strongly interacting matter is expected to be a color superconductor. One can distinguish at least two different superconducting phases, the two-flavor color superconductor (2SC) and the so-called color-flavor locked (CFL) phase, which incorporates three quark flavors. We calculate the phase diagram within a 3-flavor NJL-type quark model with realistic quark masses. The model exhibits spontaneous chiral symmetry breaking as well as diquark condensation in the 2SC phase and in the CFL phase. We investigate the colorflavor unlocking phase transition, taking into account self-consistently calculated effective quark masses. We find that it is mainly triggered by a first-order phase transition with respect to the strange quark mass. It takes place at a relatively high value of the chemical potential such that we find a large region where the 2SC phase is the most favored state. We also investigate the possible existence of more “exotic” phases, like unisotropic condensates. It turns out that the relevance of such condensates is strongly parameter dependent. This leaves room for surprises. HK 2.6 Mon 18:15 A Dispersion relations in real and virtual Compton scattering — •Marc Vanderhaeghen 1 , Dieter Drechsel 1 , Michael Gorchtein 1 , Andreas Metz 2 , and Barbara Pasquini 3 — 1 Johannes Gutenberg University Mainz — 2 Vrije Universteit Amsterdam — 3 ECT* Trento A unified presentation is given of the use of dispersion relations in the real and virtual Compton scattering processes off the nucleon. It is reviewed how for Compton scattering, dispersion relations establish a connection between low energy nucleon structure quantities such as its HK3 Nuclear Physics / Spectroscopy I polarizabilities on the one hand and the nucleon excitation spectrum on the other hand. Various types of dispersion relations are subsequently discussed for the real Compton scattering (RCS) process as a tool to extract nucleon polarizabilities from RCSdata and the present knowledge on the nucleon polarizabilities obtained in this way is reviewed [1]. Subsequently, we present the extension of the dispersion relation formalism to the virtual Compton scattering (VCS) process as a tool to extract generalized polarizabilities of the nucleon [2]. The information on generalized nucleon polarizabilities as extracted in this way from recent VCS experiments is reviewed in particular in view of new JLab VCSdata for photon virtualities Q 2 in the range 1 - 2 GeV 2 . [1] D. Drechsel, B. Pasquini and M. Vanderhaeghen, in preparation [2] B. Pasquini et al., Eur.Phys.J.A 11 (2001) 185. HK 2.7 Mon 18:30 A Thermodynamics of the chiral condensate — •Thomas M. Schwarz, Norbert Kaiser, and Wolfram Weise — Physik-Department, Technische Universität München. We study the temperature and density dependence of the scalar quark condensate 〈¯qq〉 using effective field theory methods. Nucleons interact via perturbative chiral pion exchange and scalar plus vector four-point interactions. The latter are treated in relativistic mean field approximation giving rise to an effective nucleon mass M ∗ and an effective chemical potential µ ∗ . Contributions from pion fluctuations at two-loop level are included in the self consistency equations for M ∗ and µ ∗ . The strengths of the contact interactions are adjusted to the empirical nuclear matter saturation point and compressibility κ. From this we predict an effective nucleon mass of M ∗ (ρ0) � 0.8M. At a temperature T � 17 MeV a liquid-gas phase transition is observed. The dependence of the equation of state P (T,µ,mπ) on the pion mass allows to calculate deviations from the leading linear decrease in density of the quark condensate. We find that these are small below normal nuclear matter density, but substantial at higher densities. In a further step we include three-loop contributions from 2π-exchange. Supported in part by BMBF and GSI. HK 2.8 Mon 18:45 A Renormalon Model of Twist-4 Corrections to Meson Wave Functions — •Stefan Gottwald — Institut für Theoretische Physik, Universität Regensburg, D-93040 Regensburg, Germany In this talk I present a renormalon-inspired model of twist-4 power corrections to the light-cone wave functions of the pion and the rhomeson, and compare it to the results obtained using the conformal wave expansion. This renormalon approach allows one to get some insight in the convergence properties of the conformal expansion and the basic result is that global features of the higher-twist wave functions calculated in the renormalon approach turn out to be surprisingly close to simple models based on the truncated conformal expansion. At the same time, the renormalon calculation indicates a “soft” divergence of the conformal expansion close to the kinematic boundaries. Time: Monday 16:15–19:00 Room: B Group Report HK 3.1 Mon 16:15 B New interpretation of the O(6) limit of the interacting boson model. — •J. Jolie 1 , P. von Brentano 1 , V. Werner 1 ,andR.F. Casten 2 — 1 Institut fuer Kernphysik, Universitaet zu Koeln — 2 Yale University, New Haven, USA It is shown that the O(6) limit of the IBM, can be interpreted as a critical point of a phase transition inbetween oblate and prolate rotational nuclei[1]. This quantum phase transition relates to the shape of the nucleus and can be described exactly for any number of interacting bosons N at the critical point. It will be shown that an important tool to theoretically study such finite-N quantum phase transitions is provided by the determination of the wavefunction entropy [2]. Besides this also other signatures of phase transitional character are discussed [3]. [1] J.Jolie, R.F. Casten, P. von Brentano, V. Werner, Phys. Rev. Lett.87 (2001) 162501. [2] P. Cejnar, J.Jolie Phys. Rev. E 61 (2000) 6237. [3] V. Werner, P. von Brentano, R.F. Casten, J. Jolie, acc. for publ. in Phys. Lett. B. Work supported by DFG under project No Br 799/10-1 of US- DOE under grant N0 DE-FG02-91ER40609 and NATO under grant No SA 5-2-05 (CRG 950668). Group Report HK 3.2 Mon 16:45 B Decay properties of N� nuclei: A status report from the ISOL facility of GSI — •J. Döring for the GSI-ISOL collaboration — GSI, Darmstadt, Germany Nuclei with N�Z between the double shell closures 56 Ni and 100 Snare of great interest due to their special nuclear-structure features, including shape coexistence, the influence of the proton drip-line, tests of the Standard Model of Weak Interaction by means of precision data on superallowed 0 + →0 + β-decays, and the relevance to the astrophysical rp process. These motivations form the basis of the research program pursued at the ISOL facility of GSI Darmstadt. After describing the fusion-evaporation reactions, used for producing the neutron-deficient isotopes of interest, and the detectors for decay measurements, we present examples of recent experiments, i.e. (i) the β-delayed proton emission from 57 Zn (T1/2
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Monday, March 11, 2002 - DPG-Tagungen

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