Monday, March 11, 2002 - DPG-Tagungen

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Nuclear Physics Monday =38±4 ms)to 56 Ni [1], (ii) the accurate determination of the branching ratio for the 58 Cu(1 + )→ 58 Ni(0 + ) β transition (81.2±0.5 %), which serves as a calibration in deducing the Gamow-Teller strength distribution from high-resolution 58 Ni( 3 He,t) 58 Cu data [2], and (iii) an attempt to reach a precision of 4 parts in 10 4 for the half-life of the superallowed 0 + →0 + βdecay of 62 Ga by accumulating about 2×10 6 positron events. Finally, an outlook will be given, including in particular the novel technique of extracting short-lived tin isotopes as singly charged sulfide molecules from the ion source, which opens exciting perspectives for future β-decay experiments on 102 Sn and 100 Sn. [1] A. Jokinen et al., submitted to Eur. Phys. J. A. [2] Z. Janas et al., Eur. Phys. J. A 12, 143 (2001). Group Report HK 3.3 Mon 17:15 B Investigation of the level scheme of 144 Gd and lifetimes of the triaxial quadrupole band — •R.M. Lieder 1 , W. Gast 1 , H.M. Jäger 1 , L. Mihailescu 1 , A.A. Pasternak 2 , E.O. Podsvirova 2 , D. Bazzacco 3 , R. Menegazzo 3 , S. Lunardi 3 , C. Rossi Alvarez 3 , G. de Angelis 4 , E. Farnea 4 , A. Gadea 4 , D.R. Napoli 4 , T. Rza¸ca- Urban 5 , W. Urban 5 ,andA. Dewald 6 — 1 IKP, FZ Jülich, D-52425 Jülich — 2 A.F. Joffe PTI, RU-194021 St. Petersburg — 3 INFN, Sezione di Padova, I-35131 Padova — 4 INFN, LNL, I-35020 Legnaro — 5 IEP, Univ. Warsaw, PL-00-681 Warsaw — 6 IKP, Univ. Köln, D-50937 Köln High-spin states in 144 Gd have been excited in the 100 Mo( 48 Ti,4n) reaction at 215 MeV and studied with EUROBALL at the LNL, Italy. Several dipole and stretched E2 cascades have been observed. The study of lifetimes of the E2 cascades is of importance for the understanding of the transition from highly to superdeformed states between the A ≈ 130 and A ≈ 150 regions. This transition is expected to occur via triaxial shapes. The strongest E2 cascade in 144 Gd is considered to have a configuration involving rotation aligned h11/2 protons as well as rotation aligned h11/2 neutron holes and h9/2 neutrons resulting in a well deformed triaxial nuclear shape. More information on the configuration of this band was obtained in a DSA study with GASP at the LNL, Italy using the 114 Cd( 36 S,6n) reaction at E = 182 MeV. The target consisted of a 1.2 mg/cm 2 114 Cd foil backed by a 1.2 mg/cm 2 Ta and a 55 mg/cm 2 Bi layer. Because most of the γ-lines of interest are contaminated by background lines special techniques have been developed for the analysis. The results of the lifetime analysis support the proposed interpretation. HK 3.4 Mon 17:45 B New methods for measuring nuclear skins — •A. Krasznahorkay 1,2 , H. Akimune 3 , A.M. van den Berg 2 , N. Blasi 4 , S. Brandenburg 2 , M. Csatlós 1 , H. Fujimura 3 , M. Fujiwara 3,5 , J. Gulyás 1 , M. Hagemann 6 , K. Hara 3 , M. N. Harakeh 2 , M. Hunyadi 2 , M. de Huu 2 , F. Ihara 3 , T. Ishikawa 7 , Z. Máté 1 , D. Sohler 1 , S.Y. van der Werf 2 ,andL. Zolnai 1 — 1 ATOMKI, Debrecen, Hungary — 2 KVI, Groningen, The Netherlands — 3 RCNP, Osaka, Japan — 4 INFN, Milano, Italy — 5 JAERI, Tokai, Japan — 6 Univ. Gent, Belgium — 7 Univ. Kyoto, Japan The neutron-skin thickness of 208 Pb and 114,124 Sn has been investigated in order to constrain the symmetry energy term of the nuclear energy functional. The precise knowledge of the symmetry energy is essential not only for describing the structure of neutron-rich nuclei, but also for describing the properties of the neutron-rich matter in nuclear astrophysics. We have used inelastic alpha scattering to excite the giant dipole resonance (GDR). The cross section of this process depends strongly on ∆Rnp/R, the radial difference of the neutron and proton densities [1]. We have also used the excitation of the spin-dipole resonance (SDR) to measure the neutron-skin thickness since the total L=1 strength of the SDR is sensitive to it [2]. Recently new experiments were carried out at the KVI using 196 MeV α and 177 MeV 3 He beams from the AGOR superconducting cyclotron. A critical test of both the GDR and SDR methods will be discussed. [1] A. Krasznahorkay et al., Phys. Rev. Lett. 66, 1287 (1991) [2] A. Krasznahorkay et al., Phys. Rev. Lett. 82, 3216 (1999). HK 3.5 Mon 18:00 B Nuclear matter distribution of light neutron rich He nuclei from elastic proton scattering at large momentum transfer — •Oleg Kisselev for the S174 collaboration — Gesellschaft für Schwerionenforschung mbH, Planckstrasse 1, D-64291 Darmstadt Elastic proton scattering from the 6 He and 8 He halo nuclei was investigated in inverse kinematics at energies around 700 MeV/u at GSI Darmstadt. The experimental setup consisted of a liquid hydrogen target, a forward spectrometer for tracking and identifying the projectile nuclei, and a tracking system for the detection of the recoil protons. This setup allowed for a high precision and low background measurement. The aim of the experiment was to deduce the differential p 6 He and p 8 He cross sections for the region of high momentum transfer close to the expected first diffraction minimum. This new information together with the data obtained at small momentum transfer provides additional knowledge about the structure of the alpha-like core in 6 He and 8 He. The present status of the data analysis and first results will be presented. HK 3.6 Mon 18:15 B Alpha decay of 114 Ba — •C. Mazzocchi for the GSI-ISOL collaboration — GSI, Darmstadt, Germany Alpha decay is a rich source of nuclear-structure information, offering insight into properties such as ground-state binding energies and spectroscopic factors for α-particle emission, in particular for neutron-deficient isotopes beyond the doubly-magic nucleus 100 Sn. Based on this motiva- tion we searched for the α decay of 114 Ba (T1/2 = 430 +300 −150 ms [1]). The 114 Ba nuclei were produced through the 58 Ni( 58 Ni,2n) reaction, separated from other reaction products as a mass-separated and chemically clean beam of 114 Ba 19 F + ions by means of the ISOL facility of GSI Darmstadt, implanted into a stopper foil, and studied by using silicon-detector telescopes for decay spectroscopy. We measured for the first time the α-particle energy (3410±40 keV) of 114 Ba, the half-life (160 +290 −60 ms) of its daughter nucleus 110 Xe, and the α-branching ratios and widths for these two isotopes and for the granddaughter nucleus 106 Te [2]. The increase of the α-particle energies along the α-decay chain from 114 Ba to 102 Sn is a clear signature of the double shell-closure occurring at 100 Sn. The experimental values obtained for the α-decay Q values of these three isotopes as well as for the Q value for 12 C emission from 114 Ba (19000±40 keV) will be dicussed in comparison with theoretical predictions. In view of the large uncertainties of the reduced α-widths, no firm conclusions can be drawn concerning the occurrence of superallowed α decay. [1] Z. Janas et al., Nucl. Phys. A 627, 119 (1997). [2] C. Mazzocchi et al., submitted to Phys. Lett. B. HK 3.7 Mon 18:30 B Simple Parametrization of neutron separation energies in terms of the neutron to proton ratio N/Z ∗ — •K. Vogt, T. Hartmann, and A. Zilges — Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany It is shown that single- and two-nucleon separation energies can be parametrized in a new way using the neutron to proton ratio N/Z and the mass number A. Very simple empirical formulas have been achieved using a least squares fit to all available experimental data [1]. It is demonstrated that the observed N/Z dependence can be derived from the Fermi Gas model. For an estimate of the usefulness of these formulas, the resulting neutron separation energies are compared to results from several mass formulas currently in use [2,3]. As an outlook, possible practical applications are discussed. ∗ supported by the DFG (contract Zi 510/2-1 and FOR 272/2-1). [1]K.Vogt,T.Hartmann,A.Zilges,Phys.Lett.B517 (2001) [2] P. Möller, J. R. Nix, W. D. Myers, and W. J. Swiatecki, At. Data Nucl. Data Tables, 59, 185 (1995) [3] F.Tondeur,S.Goriely,J.M.Pearson,andM.Onsi,Phys. Rev. C 62, 024308 (2000) HK 3.8 Mon 18:45 B Calculated groundstate properties of Er-isotopes in comparison with messured 2 + -states — •Thomas Cornelius 1 , M. Bender 2 , T. Bürvenich 1 , A. Sulaksono 1 , P. Fleischer 3 , S . S chramm 4 , J. A. Maruhn 1 , P.–G. Reinhard 3 , J. H. Hamilton 5 , and W. Greiner 1 — 1 Institut für Theoretische Physik, Universität Frankfurt am Main — 2 Service de Physique Nucléaire Théorique, Université Librede Bruxelles — 3 Institut für Theoretische Physik II, Universität Erlangen- Nürnberg — 4 Nuclear Theory Group, Argonne National Laboratory — 5 Department of Physics, Vanderbilt University, Nashville Self-consistent mean-field models are nowadays well developed and provide a pertinent picture of nuclear properties throughout the whole mass table. We consider two different models, the Skyrme-Hartree-Fock approach (SHF) and the relativistic mean-field model (RMF). In our former investigations deformed calculations appear to be important for some observables like the 2-proton-shell-gap [1]. In our talk we want to show a possible correlation of the lowest, exper-
Nuclear Physics Monday imental measured 2 + -state for Er-isotopes and their calculated deformed groundstate properties. The investigation in this region is of special interest since the measured data do not show the results that are naivly expected. HK4 Nuclear and Particle Astrophysics I Supported by the BMBF, GSI, DFG. [1] M. Bender, T. Cornelius, G. A. Lalazissis, J. A. Maruhn, W. Nazarewicz und P.–G. Reinhard , nucl-th/0110057 (2001), accepted for publication in Eur. Phys. J. A Time: Monday 16:15–19:00 Room: C Group Report HK 4.1 Mon 16:15 C The Physics of the Knee in the Cosmic-Ray Spectrum – Recent Results from KASCADE – — •Karl-Heinz Kampert for the KASCADE collaboration — Institut für Experimentelle Kernphysik, University of Karlsruhe and Forschungzzentrum Karlsruhe An update on measurements of cosmic rays in the energy range around 10 15 eV is presented. Emphasis is placed on recent KASCADE data and on progress in air shower simulations using the CORSIKA package. High energy hadrons observed in the KASCADE calorimeter exhibit a distinct sensitivity to details in the modelling of high-energy hadronic interactions, particularly to the inelastic p-Air cross section and to diffractive dissociation. Thus, the experimental data can be used to constrain models employed in EASsimulations. Electron and muon shower sizes, on the other hand, are well suited to extract the energy and mass of the primary particles. Applying unfolding methods to their size spectra and adopting a model of high energy hadronic interactions, energy distributions of 4 mass groups are reconstructed in the energy range between 10 15 and 10 17 eV. The preliminary energy spectra show a knee-like structure in each of these distributions. Their position suggests a scaling according to the rigidity of the primary particle. Astrophysical implications of this important finding will be discussed. Group Report HK 4.2 Mon 16:45 C KATRIN a next generation neutrino mass experiment — •Jochen Bonn for the KATRIN collaboration — B: Institut für Physik Universität Mainz Neutrino masses are of crucial importance for nuclear and particle physics as well as for cosmology. Our present knowledge is based on neutrino oscillation experiments and on the investigation of weak decays. The convincing evidence for neutrino oscillations found in the detection of solar and atmospheric neutrinos are a clear indication for differences in the squares of the neutrino masses but they do not allow to determine the masses themselves. To set the mass scale, direct mass measurements like e.g. the investigation of tritium β-decay are needed. The sensitivity limit of the presently running experiments in Mainz and Troitsk of about 2 eV/c 2 are not sufficient to distinguish between alternative theoretical models asking for very light neutrinos or degenerated neutrinos with cosmologically relevant masses up to about 1 eV/c 2 . The new KArlsruhe TRItium Neutrino mass experiment, KATRIN is presently designed and experiments in preparation of KATRIN are carried out. The sensitivity limit of KATRIN shall be in the sub eV range. The results of the present neutrino mass experiments will be briefly reported and the status of KATRIN will be discussed. Experiments in preparation of KATRIN are sponsored by BMBF under contract Nr. 05CK1UM1/5 and 05CK1VK1/7. Group Report HK 4.3 Mon 17:15 C A new precision measurement of the electric dipole moment of the neutron — •Reinhold Henneck for the SUNS colaboration collaboration — Paul-Scherrer-Institut, CH-5232 Villigen, Schweiz At PSI we are presently setting up a new source for ultracold neutrons (UCN) which will deliver UCN densities in excess of 1000 UCN/cm 3 .This improvement of about 2 orders of magnitude over existing facilities will open new prospects for studies of fundamental properties of the neutron and its decay. As a first experiment we intend to improve the sensitivity in the measurement of the neutron electric dipole moment (EDM) to about 5 · 10 −28 e·cm. At this level Supersymmetry models predict a finite EDM value. The EDM spectrometer employs the conventional Ramsey method, but makes use of a system of 8 HV chambers and 5 chambers without HV, which will reduce the influence of systematic effects due to magnetic problems and leakage currents considerably.We shall discuss the principle of the experiment, the expected statistical uncertainty, systematic effects as well as details of the most important parts. In particular we shall focus on the problems which are connected with the magnetic field and which are being investigated in a separate Magnetic Test Experiment now. HK 4.4 Mon 17:45 C Final results of the KARMEN experiment on the search for ¯νµ → ¯νe oscillations — •Markus Steidl for the KARMEN collaboration — Forschungszentrum Karlsruhe, Institut für Kernphysik The final results from the KARMEN2 experiment in its search for ¯νµ → ¯νe oscillation are presented. The KARMEN2 experiment has been performed from 1997 until 2001 at the spallation neutron source ISIS of the Rutherford Laboratorium (UK). Beamstop Neutrinos νe,νµ und ¯νµ with energies up to 52 MeV from the π + –µ + decay chain are used for the search of neutrino oscillations. The very low ISIS beam contamination with ¯νe leads to a high sensitivity in the appearance channel ¯νµ → ¯νe . Events induced by ¯νe are detected in the 56 t liquid scintillator KAR- MEN detector via the p (¯νe ,e + ) n reaction. As the KARMEN2 search yields clearly no hints for the presence of an oscillation signal, stringent limits on the oscillation parameters sin2 (2θ)and∆m2are set. These final KARMEN2 results are then combined with the final results of the LSND experiment, which claims observed evidence in this oscillation channel. The combined analysis allows the investigation of the statistical compatibility of the two experiments and the construction of a combined confidence interval on the allowed oscillation parameters sin2 (2θ) and ∆m2 . HK 4.5 Mon 18:00 C Neutrino-nucleon scattering rate in the relativistic random phase approximation — •Lysiane Mornas1 and Armando Pérez2 — 1Departamento de Física, Universidad de Oviedo, E-33007 Oviedo (Asturias), Spain — 2Departamento de Física Teórica, Universidad de Valencia, E-46100 Burjassot (Valencia), Spain We present a calculation of the neutrino-nucleon scattering cross section which takes into account the nuclear correlations in the relativistic random phase approximation. Our approach is based on a quantum hadrodynamics model with exchange of σ, ω, π, ρ and δ mesons. In view of applications to neutrino transport in the final stages of supernova explosion and protoneutron star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-neutron asymmetry and temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor channel, coupling to the delta meson and meson mixing. In contrast with the results of other authors [1,2], it is found that RPA corrections with respect to the mean field approximation amount to only 10% to 15% at high density [3]. [1]S.Reddy,M.Prakash,J.M.LattimerandJ.Pons,Phys. Rev. C59 (1999) 2888. [2]S.YamadaandH.Toki,Phys.Rev.C61 (2000) 015803. [3] L. Mornas and A. Pérez, nucl-th/0106058 subm. to Eur. Phys. J. A HK 4.6 Mon 18:15 C Results of the 2001 measurements of the Mainz neutrino mass experiment — •Christine Kraus, Jochen Bonn, Beate Bornschein, Lutz Bornschein, Fernando Conda, Björn Flatt, Beatrix Müller, Ernst Wilhelm Otten, Jean-Pierre Schall, Thomas Thümmler, and Christian Weinheimer — Institut für Physik, Johannes Gutenberg Universität Mainz, 55099 Mainz The Mainz neutrino mass experiment investigates the endpoint region of the tritium β decay spectrum to determine the mass of the electron antineutrino. The principle of the Mainz spectrometer, Magnetic Adiabatic Collimation followed by a retarding Electrostatic Filter (MAC-E-Filter), combines both a high resolution and a large acceptance. After an optimal preparation of the apparatus, ≈ 2 month of data were taken. The data fit good together with the results of 98/99. The results of the analysis
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Rusev, G. ..................HK 10.1
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