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Nuclear Physics Monday HK 4.9 Mon 18:00 C Experimental Investigations of Advanced Cold Moderators and Comparison with MCNPX Simulations — •K. Nuenighoff for the JESSICA collaboration — Forschungszentrum Jülich GmbH, 52425 Jülich The aim of the JESSICA experiment at the Jülich proton accelerator COSY is the investigation of the characteristics of advanced cold moderators for spallation neutron sources. In this contribution we will present the neutron energy spectra for methane hydrate and mesitylene and discuss the advantages and disadvantages of both materials. We will furhter show first comparisons of the measured energy spectra of an ice moderator at different temperatures with Monte-Carlo simulations performed with MCNPX applying new developed neutron scattering kernels. Further we will show the wavelength dependent time-of-flight spectra for selected materials, like ice, methane-hydrate, and mesitylene. HK 4.10 Mon 18:15 C Determination of RBE of low-energy X-rays at ELBE — •Anna Panteleeva 1 , Wolfgang Enghardt 1 , Elisabeth Lessmann 1 , Jörg Pawelke 1 , Wolfgang Wagner 1 , and Wolfgang Dörr 2 — 1 Forschungszentrum Rossendorf — 2 Technical University of Dresden The precise determination of the relative biological effectiveness (RBE) of low-energy X-rays is important because of their wide application in diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of both 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was found to be in the range from 1.0 to 1.4, depending on the used radiation quality, cell line and the biological endpoint. In order to study in detail the RBE dependence on photon energy, the investigations will be continued at a monochromatic X-ray source. The installation of an intensive, tunable, quasi-monochromatic source in the energy range 10 - 100 keV is currently under progress at HK 5 Theory I the ELBE accelerator at Forschungszentrum Rossendorf. X-rays are produced by channeling of a relativistic electron beam in a diamond crystal. The status of the commissioning of the radiation source will be presented, such as the experimental verification of the theoretical calculation of the spatial energy and intensity distribution. Furthermore, a monochromator, designed to minimize the contribution of the background radiation to the dose in the cell target, will be presented. HK 4.11 Mon 18:30 C Upgrade of the 30 ◦ forward cone of the Crystal-Barrel-Detector — •Christian Funke for the CBELSA collaboration — Helmholtz- Institut für Strahlen- und Kernphysik der RFWU Bonn, 53115 Bonn The Crystal-Barrel experiment at ELSA is used to investigate the structure of hadrons by electromagnetic probes. The 4π-geometry of this electromagnetic calorimeter especially predestines this experiment for the research on multi-photon final states. Due to it’s setup as a ”fixed target” experiment an efficient trigger for particles (photons and protons in our case) and their energy determination under small forward angles is a subject of great importance. The TAPS detector covering the 30 ◦ forward angle provided this functionality until December 2003. To maintain this ability a new forward-detector based on the 90 CsI-(Tl) crystals of the original Crystal-Barrel configuration is under development. The existing photodiode based readout is replaced by fast photomultipliers and matching back-end electronics. Additionally the front of the crystals facing the reaction target will be outfitted with 2 additional layers of plastic-scintillators which allow to trigger on and separate charged particles. In order to provide (pre-)trigger signals for the data acquisition system a fast SRAM-based cluster-finder-logic is being developed. This talk summarizes the current status and capabilities of this new forwarddetector. This project is supported by the DFG. Time: Monday 15:45–18:45 Room: D Group Report HK 5.1 Mon 15:45 D Novel approach to nuclear forces from effective field theory — •Ulf-G. Meißner 1,2 , Evgeny Epelbaum 3 , and Walter Glöckle 4 — 1 HISKP (Th), Universität Bonn, Bonn, Germany — 2 IKP (Th), FZ Jülich, Jülich, Germany — 3 Jefferson Lab, TH Div, Newport News, USA — 4 RUB, TP II, Bochum, Germany We report on a new formulation to calculate the forces between two, three, . . . nucleon from chiral effective field theory. We have developed a cut-off scheme for pion loop integrals, in particular the two-pion exchange, based on spectral function regularization [1]. This scheme allows for a consistent implementation of the constraints from pion-nucleon scattering. It leads to a much improved description of the partial waves with l ≥ 2 compared to the calculation utilizing dimensional regularization. We have also studied the low partial waves and deuteron properties at next-to-leading order [2] and find an overall good description of the twonucleon force. We also show that the numerical values of the coupling constants of the four-nucleon contact operators, that are determined from a fit to the low partial waves, can be understood in terms of resonance saturation. This allows for a connection with more conventional boson exchange phenomenology. At this meeting, we present results for the partial waves and deuteron properties obtained at N 3 LO [3], which are of the same precision as one obtains when employing the so–called high precision potentials. [1] E. Epelbaum et al., arXiv:nucl-th/0304037, Eur. Phys. J. A, in print [2] E. Epelbaum et al., arXiv:nucl-th/0308010, Eur. Phys. J. A, in print [3] E. Epelbaum, W. Glöckle and U.-G. Meißner, in preparation HK 5.2 Mon 16:15 D Can the D∗ sJ(2317) be explained as a DK molecule? — •Felix Sassen — IKP Theorie Forschungzentrum-Jülich, 52425 Jülich Applying the Blankenbecler Sugar scattering equation in the case of coupled DK- and D + s π-channels we find that a dynamically generated pole arises close to 2317 MeV, when we assume SU(4)-symmetry to relate the coupling parameters to the well known coupling parameters in the case of ππ-K ¯ K scattering. Our model relates in a natural way the contributions of D + s π scattering originating from this pole to the contributions from the opening iso vector DK-channel, if we assume that isospin breaking only happens via the mass differences and ρω- as well as πη-mixing. We use the constrains coming from the BaBar, Cleo and Belle observations of the D ∗ sJ(2317) to give an estimate for the non molecular iso scalar contribution to the observed state. HK 5.3 Mon 16:30 D Glueball mixing in an effective field theoretical approach — •Francesco Giacosa, Thomas Gutsche, Valery Lyubovitskij, and Amand Faessler — Institut fuer Theoretische Physik, Auf der Morgenstelle 14, Geb. D, 72076 Tuebingen The search and the identification of the glueball is an open problem both from experimental and theoretical point of view. It is believed that the pure glueball mixes with its ”neigbouhrs”, scalar quark-antiquark states, giving rise to three resonances: f0(1310), f0(1500) and f0(1710); each of them is formed by gluon-gluon and quark-antiquark. The system is analyzed within an effective field theoretical approach in order to find the relation between the masses ”before” the mixing and those ”after” the mixing (which are the masses of the physicl states); also the composition of the resonances in terms of their gluon-gluon and quark-antiquark admixtures is evaluated. The goal is the calculation of the strong and the radiative deays of the physical resonances. HK 5.4 Mon 16:45 D Three-body spin-orbit forces from chiral two-pion exchange — •Norbert Kaiser — Physik Department T39, Technische Universität München, D-85747 Garching, Germany Using chiral perturbation theory, we calculate the density-dependent spin-orbit coupling generated by the two-pion exchange three-nucleon interaction involving virtual ∆-isobar excitation. From the corresponding three-loop Hartree and Fock diagrams we obtain an isoscalar spin-orbit strength Fso(kf) which amounts at nuclear matter saturation density to about half of the empirical value of 90 MeVfm 5 . The associated isovector spin-orbit strength Gso(kf) comes out about a factor of 20 smaller. Interestingly, this three-body spin-orbit coupling is not a relativistic effect but independent of the nucleon mass M. Furthermore, we calculate the threebody spin-orbit coupling generated by two-pion exchange on the basis of the most general chiral ππNN-contact interaction. We find similar (numerical) results for the isoscalar and isovector spin-orbit strengths Fso(kf)
Nuclear Physics Monday and Gso(kf) with a strong dominance of the p-wave part of the ππNNcontact interaction and the Hartree contribution. We consider also the effect of iterated pion-photon exchange on the Coulomb energy of nuclei. It leads to an additional binding of each proton by about 0.2MeV. We propose as a mechanism to resolve the Nolen-Schiffer anomaly the iteration of one-photon exchange with a short-range pp-interaction. The corresponding energy per proton reads: Ē[ρp] = (2/15π 2 )(π 2 −3+6 ln2)App k 2 p with ρp = k 3 p /3π2 the proton density. N. Kaiser, Phys. Rev. C68 (2003) 054001. Work supported in part by BMBF, GSI and DFG. HK 5.5 Mon 17:00 D Chiral Perturbation Theory for Heavy Nuclei — •Akaki Rusetsky 1 , Luca Girlanda 2 , and Wolfram Weise 2,3 — 1 HISKP (Th), Universität Bonn, Bonn, Germany — 2 ECT*, Trento, Italy — 3 Physik- Department, TU München, Garching, Germany We propose a novel formulation of Chiral Perturbation Theory in a nuclear background, characterized by a static, non-uniform distribution of the baryon number that describes the finite nucleus[1]. The proposed approach is directly applicable to study of the deeply bound (1s) states of pionic atoms formed with Pb and Sn isotopes, whose spectrum has been measured at GSI[2]. The results of this high-precision experiment have recently triggered a discussion about the possibility of observation of the “fingerprints of chiral restoration” in nuclear medium. This issue, however, can only be resolved, provided a systematic theoretical framework is available for the description of pionic atoms within Chiral Perturbation Theory, taking into account the effects of the finite nuclear size. The proposed approach intends to fill this gap. In addition, it opens perspectives for many applications of ChPT in nuclear physics – especially for the problems in which the finite boundaries of the system are crucial. In the limiting case of a uniform distribution, the proposed framework[1] reduces to the well-known zero-temperature in-medium ChPT. We further use the approach to calculate the self-energy of the charged pion in the background of the heavy nucleus at O(p 5 ) in the chiral expansion, and to derive the leading terms of the pion-nucleus optical potential. [1] L. Girlanda, A. Rusetsky and W. Weise, arXiv:hep-ph/0311128. [2] K. Suzuki et al., arXiv:nucl-ex/0211023. HK 5.6 Mon 17:15 D Separating long- and short-distance physics in chiral effective field theory — •T.R. Hemmert 1 , V. Bernard 2 , and U.-G. Meißner 3 — 1 Physik Department T39, TU München — 2 LPT, U. Louis Pasteur, Strasbourg — 3 HISKP (Th), U. Bonn We discuss the use of cutoff regularization methods in chiral perturbation theory [1]. We develop a cutoff scheme based on the operator structure of the chiral effective field theory that allows to suppress high momentum contributions in Goldstone boson loop integrals and— by construction—is free of the problems traditional cutoff schemes have with gauge invariance or chiral symmetries. In this scheme momentum modes above the scale of chiral symmetry breaking are effectively transfered into local operators of the effective theory parameterizing short distance physics. As examples we discuss the quark mass dependence of the nucleon mass and of the polarizabilities of the nucleon [2]. [1] V.Bernard, T.R. Hemmert and U.-G. Meißner, [hep-ph/0307115]. [2] T.R. Hemmert and B.R. Holstein, forthcoming. This work has been supported in part by BMBF and DFG. HK 5.7 Mon 17:30 D Low energy double-pion photoproduction and pion absorption in nuclei — •Luis Alvarez-Ruso, Oliver Buss, Ulrich Mosel, and Pascal Mühlich — Institut für Theoretische Physik, Universität Giessen, 35392 Giessen, Germany We investigate π 0 π 0 and π ± π 0 photoproduction off nuclei at incident beam energies of 400-460 MeV. For the pion-pair production on the nucleons we use a theoretical model developed in Valencia (Nacher et al.). A full coupled-channel treatment of final state interactions is performed by means of the semi-classical BUU transport model. We observe that quasi-elastic and charge-exchange scatterings of the final state pions with the nucleons of the surrounding medium cause a downward shift of the ππ invariant mass distributions. In the π 0 π 0 channel, our results agree well with the data on 12 C and 208 Pb obtained recently at MAMI-B without introducing any additional in-medium modification. In the π ± π 0 channel, however, we overestimate the total cross-section. Furthermore, we study the role of the real part of the pion optical potential in the pion propagation inside nuclei within our semi-classical model. The aim is to describe simultaneously low-energy pion absorption and double-pion photoproduction in nuclei. Work supported by the Humboldt foundation and the European graduate school Giessen–Copenhagen. HK 5.8 Mon 17:45 D Ground-state energy of pionic hydrogen to one loop — •E. Lipartia 1 , J. Gasser 2 , M.A. Ivanov 3 , M. Mojzis 4 , and A. Rusetsky 5 — 1 Institute for Theoretical Physics (T39), TU München, Germany — 2 ITP, Univesity of Bern, Bern Switzerland — 3 BLTP, JINR, Dubna, Russia — 4 Departmet of Physics, Univesity of Massachusetts, Amherst, USA — 5 HISKP, Bonn Univesity, Bonn, Germany We investigate the ground-state energy of the π − N atom (pionic hydrogen) in the framework of QCD and QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at next-toleading order in the low-energy expansion in the framework of infrared regularized effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths - evaluated in pure QCD - at next-to-leading order in isospin breaking and in the low-energy expansion. We compare our result with available model calculations. Work supported by Swiss National Science Foundation. [1] J. Gasser, M.A. Ivanov, E. Lipartia, M. Mojzis, A. Rusetsky, Eur.Phys.J.C26:13-34,2002. HK 5.9 Mon 18:00 D Quantum Chaos in Baryon Spectra — •Harald Markum 1 , Willibald Plessas 2 , Rainer Pullirsch 1 , Bianka Sengl 2 , and Robert F. Wagenbrunn 2 — 1 Atominstitut, TU Wien — 2 Inst. f. Theoretische Physik, Univ. Graz The Bohigas-Giannoni-Schmit conjecture for quantum chaos is formulated and evaluated within random-matrix theory. We discuss randommatrix theory as a tool to study the spectral behaviour of an analytically solvable Hamiltonian, of a model Hamiltonian, and of experimental data. As a particular case we consider the spectroscopy of baryons. Within the framework of a relativistic constituent quark model we investigate the excitation spectra of the nucleon and the delta with regard to a possible chaotic behaviour for the cases when a hyperfine interaction of either Goldstone-boson-exchange or one-gluon-exchange type is added to the confinement interaction. HK 5.10 Mon 18:15 D The nuclear many-body problem in the context of low-energy QCD — •Paolo Finelli 1,2 , Norbert Kaiser 3 , Dario Vretenar 4 , and Wolfram Weise 2,3 — 1 Physics Department, University of Bologna, Italy — 2 ECT*, Villazzano (Trento), Italy — 3 Physik Department, Technische Universität München — 4 Physics Department, University of Zagreb A microscopic relativistic point-coupling model of nuclear many-body dynamics constrained by in-medium QCD sum rules and chiral symmetry is derived and applied to nuclear matter and finite nuclei. The effective Lagrangian is characterized by density-dependent coupling strengths, determined by chiral one- and two-pion exchange and by QCD sum rule constraints for the large isoscalar nucleon self-energies that arise through changes of the quark condensate and the quark density at finite baryon density. This approach is tested in the analysis of the equations of state for symmetric and asymmetric nuclear matter, and of bulk and single-nucleon properties of finite nuclei. In comparison with purely phenomenological mean-field approaches, the built-in QCD constraints and the explicit treatment of pion exchange restrict the freedom in adjusting parameters and functional forms of density dependent couplings. It is shown that nuclear binding and saturation are almost completely generated by chiral (two-pion exchange) fluctuations, whereas strong scalar and vector fields of about equal magnitude and opposite sign, induced by changes of the QCD vacuum in the presence of baryonic matter, generate the large effective spin-orbit potential in finite nuclei. HK 5.11 Mon 18:30 D Analysis of baryon masses to second order in the quark masses — •Matthias Frink and Ulf-G. Meißner — IKP, FZ Jülich, Jülich, Germany and HISKP (Th), Universität Bonn, Bonn, Germany We analyse the masses of the ground state baryon octet to second order in the quark masses in the framework of a lorentz-invariant formulation of baryon chiral perturbation theory. We also include strong isospin break-
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