Monday, March 11, 2002 - DPG-Tagungen

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Nuclear Physics Monday will be presented for the data of 2001 in combination with the 98/99 measurements. Work sponsored by BMBF: FKZ 06Mz866I/5. HK 4.7 Mon 18:30 C Superfluidity in Nuclear Matter — •Jan Kuckei and Herbert Müther — Institut f¨r Theoretische Physik, Universität Tübingen Superfluidity plays an important role in the physics of nuclear matter. It is paramount for several properties of neutron stars, such as their cooling mechanism and certain dynamical features. We present calculations of the superfluid pairing gap for isospin T=0 and isospin T=1 pairing. The sensitivity of the pairing correlations on the nucleon-nucleon interaction as well as the determination of the singleparticle spectra are discussed in detail. For asymmetric nuclear matter HK5 Electromagnetic and Hadronic Probes I we observe proton and neutron pariring with a total momentum different from zero. HK 4.8 Mon 18:45 C COBRA - Search for Double Beta Decays using CdTe Detectors — •Henning Kiel 1 , Kai Zuber 1 , Yorck Ramachers 2 ,andDaniel Muenstermann 1 — 1 Lehrstuhl fuer Experimentelle Physik IV, Universitaet Dortmund — 2 Nuclear and Particle Physics Laboratory, University of Oxford The physics potential of CdTe semiconductor detectors for double beta and rare decay searches is explored. The principle layout of the planned COBRA experiment is presented. Finally first results of measurements done with the current test setup and the feasibility of the experiment are shown. Time: Monday 16:15–19:00 Room: D Group Report HK 5.1 Mon 16:15 D Study of the meson production in the 1 GeV/c 2 mass range — •Pawe̷l Moskal for the COSY-11 collaboration — Institut für Kernphysik, Forschungszentrum Jülich, Germany — Nuclear Physics Institute, Jagellonian University, Cracow, Poland A study of the 1 GeV/c 2 mass range is motivated by the continuing discussion on the nature of the scalar resonances f0(980) and a0(980), which have been interpreted as exotic four quark objects[1], conventional qq states[2] or molecular like KK bound state[3]. Utilizing the missing mass technique we investigated the pp → ppX and pp → ppK + X − reactions by scanning beam energies in the range permitting to create a mass close to that of the f0 and a0 resonances. Experiments have been carried out at the COSY–11 facility[4] installed at the cooler synchrotron COSY[5]. In the presentation the notion of the close to threshold total cross section for broad resonances will be introduced, and a trial of its estimation in case of f0(980) and a0(980) mesons excitations will be presented and critically discussed. [1] R. Jaffe, Phys. Rev. D15(1997) 267. [2] D. Morgan, M. R. Pennington, Phys. Rev. D48(1993) 1185. [3]J.Weinstein,N.Isgur,Phys.Rev.D41(1990) 2236. [4] S. Brauksiepe et al., Nucl. Instr. & Meth. A 376 (1996) 397. [5] D. Prasuhn et al., Nucl. Instr. & Meth. A 441 (2000) 167. Group Report HK 5.2 Mon 16:45 D Recent results from the EDDA experiment at COSY — •Oleg Eyser for the EDDA collaboration — Institut für Experimentalphysik, Universität Hamburg The EDDA experiment ist dedicated to the measurement of excitation functions for various observables in elastic proton proton scattering. The detector consists of two concentric double layers of scintillators that cover over 80% of the solid angle for momenta ranging from 0.8 to 3.3 GeV/c. EDDA, an internal experiment at COSY, makes use of a hydrogen atomic beam target and the recirculating COSY proton beam. While the polarization in COSY is limited to the y-direction normal to the accelerator plane, the polarization of the target protons can be aligned arbitralily in space, namely along the x, y, and z axis. A cyclic combination of different polarizations makes three spin correlation coefficients accessible: ASS, ANN,andASL. After completion of the excitation functions for the analyzing power AN ([1]), several energies have been scanned with high accuracy. Recent results for the three spin correlation coefficients will be presented in this talk and will be compared to existing und accordingly updated phase shift anlyses. This work is supported by the BMBF and the FZ Jülich. [1] M. Altmeier et al., Phys. Rev. Lett. 85, 1819 (2000) HK 5.3 Mon 17:15 D LIFETIME OF THE Λ–HYPERON BOUND IN HEAVY HY- PERNUCLEI — SUMMARY OF THE COSY–13 RESULTS — •Pawel Kulessa for the COSY–13 collaboration — Institut für Kernphysik, Forschungszentrum Jülich, Germany — H. Niewodniczański Institute of Nuclear Physics, Poland The nonmesonic decay of Λ–hyperons has been investigated by the observation of delayed fission of heavy hypernuclei produced in proton – Au, Bi and U collisions at COSY-Jülich. The lifetime of heavy hypernuclei obtained by the COSY–13 collaboration τΛ = (138 ± 6(stat.) ± 17(syst.)) ps for p+U, (161±7(stat.)±14(syst.)) ps for p+Bi and (130±13(stat.)±15(syst.)) ps for p+Au are the most accurate result for proton and antiproton induced collisions on these targets so far. This result together gives an average value for the lifetime of heavy hypernuclei with masses A>180: τΛ = (145 ± 11)ps. By comparing the lifetimes of light and heavy hypernuclei we found – on the confidence level of 0.98 – a violation of the phenomenological ∆I=1/2 rule known from the the weak mesonic decays of strange particles. HK 5.4 Mon 17:30 D First results of π 0 − η mixing angle measurement — P. Hawranek 1 , H. Machner 2 , •P. Hawranek 1 , and H. Machner 2 for the GEM collaboration and the GEM collaboration — 1 Jagellonian University, Cracow, Poland — 2 Institut für Kernphysik, Forschungszentrum Jülich, Jülich, Germany Isospin symmetry may be broken - except for trivia reasons like Coulomb effects - via π 0 − η mixing. The mixing angle is related to the difference of the squared up and down quark masses. In order to measure this mixing angle we have studied the ratio of the two isospin related reactions pd → 3 Heπ 0 and pd → 3 Hπ + close to the η-threshold. A simple model Ref. 1 predicts the effect to be largest at large momentum transfer. The reactions have been measured at five different momenta in the vicinity of the η-threshold. Both recoils were measured simultaneously with an unusual magnetic spectrograph having two focal planes. The experiment will be presented as well as first data. [1] A. Magiera and H. Machner, Nucl. Phys. A674 (2000) 515 HK 5.5 Mon 17:45 D Energy dependence of the Λ/Σ0 cross section ratio — •Piotr Kowina for the COSY–11 collaboration — Research Centre Jülich, Germany — University of Silesia, Katowice, Poland Measurements of the near threshold Λ and Σ0 production via the pp → pK + Λ/Σ0 reaction at COSY–11 [1] showed a strong discrepancy compared to high energy data [2]. Close to threshold at excess energies ɛ ≤ 13 MeV the Λ/Σ0 cross section ratio has been determined to be 28 +6 −9 which exceeds the value at high excess energies (ɛ ≥ 150 MeV) of about 2.5 by an order of magnitude. In order to get a further understanding additional data have been taken between 13 MeV and 150 MeV excess energy. The final analysis will be presented and will be discussed in view of different interpretations. Calculations within a meson exchange model [3] taking into account pion and kaon exchange reproduce the measured ratio by a destructive interference of π and K exchange amplitudes. Within a factor of two also other models [4,5] describe the data by including heavier exchange mesons and/or nucleon resonances. [1] S. Sewerin, G. Schepers et al., Phys. Rev. Lett. 83(1999) 682. [2] V. Flaminio et al., Compilation of Cross sections, CERN HERA 84 01 (1984). [3] A. Gasparian et al., Phys. Lett.B 480 (2000) 273. [4] A. Sibirtsev et al., e-Print Archive nucl-th/0004022 (2000). [5] R. Shyam, G. Penner, U. Mosel, Phys.Rev.C 63 (2001) 022202.
Nuclear Physics Monday HK 5.6 Mon 18:00 D Erste Messung der Analysierstärke Ay in der Reaktion �pp → ppη am Experiment COSY-11 — •Peter Winter für die COSY-11-Kollaboration — Institut für Kernphysik, Forschungszentrum Jülich, 52425 Jülich Unter Verwendung der am Detektorsystem COSY-11 gemessenen Daten in der Reaktion �pp → ppη werden erste Ergebnisse der Analysierstärke bei einem Strahlimpuls pStrahl =2.096 GeV/c – entsprechend einer Überschußenergie von Q = 40 MeV – vorgestellt [1]. Eine Selektion der ppη-Endzustände erfolgt mittels kinematisch vollständiger Rekonstruktion dieses Drei-Teilchen-Systems. Die Bestimmung der relativen Luminosität beider Spineinstellungen beruht auf der Messung der elastischen Proton-Proton-Streuung. Die zeitlich gemittelte Strahlpolarisation wird durch simultane Messung der elastischen pp-Streuung am EDDA-Experiment [2] bestimmt. Eine Extraktion einzelner Interferenzterme von Partialwellenamplituden wird durchgeführt und ermöglicht einen Vergleich mit theoretischen Vorhersagen. [1] P. Winter, Erste Messung der Analysierstärke Ay in der Reaktion �pp → ppη am Experiment COSY-11, Diplomarbeit, Rheinische Friedrich-Wilhelms-Universität Bonn, 2001. [2] M. Altmeier et al., Phys. Rev. Lett., 85 (2000) 1819 und F. Bauer, private Mitteilung. HK 5.7 Mon 18:15 D Two Kaon Production at the φ - Meson Threshold with the MOMO-Experiment at COSY — •R. Jahn 1 , F. Bellemann 1 , A. Berg 1 , J. Bisplinghoff 1 , G. Bohlscheid 1 , J. Ernst 1 , F. Hinterberger 1 , R. Ibald 1 , L. Jarczyk 2 , R. Joosten 1 , A. Kozela 3 , H. Machner 4 , A. Magiera 2 , R. Maschuw 1 , T. Mayer-Kuckuk 1 , G. Mertler 1 , J. Munkel 1 , P.v. Rossen 4 , H. Schnitker 1 , J. Smyrski 2 , A. Strzalkowski 2 ,andR. Tölle 4 for the MOMO collaboration — 1 Institut für Strahlen- und Kernphysik, Universität Bonn — 2 Institute of Physics, Jagellonian University Cracow, Poland — 3 Institute of Nuclear Physics, Cracow, Poland — 4 Institut für Kernphysik, Forschungszentrum Jülich The reaction pd → 3 HeK + K − was measured kinematically complete at the COSY synchroton at beam momenta near 2.6 GeV/c corresponding to c.m. energies above the K + K − threshold of 35 MeV, 40 MeV and 56 MeV. In total, some 6000 kaon pairs could be uniquely identified. The KK mass spectra are consistent with phase space topped by a clear signal of the φ meson, even at 35 MeV, which corresponds to just 2.8 MeV avbove the φ threshold. In contrast to the MOMO two pion production data measured with the reaction pd → 3 Heπ + π − (Phys. Rev. C60 (1999) 061002) the two kaon angular distributions indicate pure s-wave production. The obtained cross sections, ranging into the sub-nanobarn domain, will be presented and discussed. Supported by the BMBF. HK 5.8 Mon 18:30 D Hyperon Production in the Reaction Channel pp → K 0 Σ + p at COSY-TOF ∗ — •M. Wagner, W. Eyrich, M. Fritsch, F. Stinzing, W. Schroeder und S.Wirthfür die COSY-TOF-Kollaboration — Physikalisches Institut, Universität Erlangen-Nürnberg HK6 Heavy Ions I In the framework of the exclusive hyperon measurement program in proton-proton collisions at the COSY-TOF experiment the reaction channel pp → K 0 Σ + p has been measured at three beam momenta in the threshold region: 2.85 GeV/c, 2.95 GeV/c and 3.2 GeV/c. The combination of the complex start detector system, which is designed and optimized for the reconstruction of hyperon reactions, and the stop detector arrangement ensure full phase space coverage. The data of the lowest beam momentum are based on a beam time in 1998 and have been taken using a short version of the stop detector. The beam momenta of 2.95 GeV/c and 3.2 GeV/c have been measured with an extended stop detector setup including both the barrel and the ring hodoscope in the endcap especially improving the efficiency for the Σ + channel. In the first part of the talk analysis methods - in particular the background suppression - will be presented. In the second part for the first time in the threshold region differential data including Dalitz analysis are presented. ∗ supported by BMBF and FZ Jülich HK 5.9 Mon 18:45 D The Deuteron Break-up Experiment at ANKE/COSY — •S. Dymov 1,2 , R. Engels 3 , P. Jansen 4 , A. Kacharava 5 , F. Klehr 4 , H. Kleines 6 , V. Komarov 2 , V. Koptev 7 , P. Kravtsov 7 , A. Kulikov 2 , V. Kurbatov 2 , B. Lorentz 1 , G. Macharashvili 2 , M. Mikirtytchiants 1,7 , M. Nekipelov 1,7 , V. Nelyubin 7 , D. Prasuhn 1 , A. Petrus 2 , F. Rathmann 1 , J. Sarkadi 6 , H. Seyfarth 1 , H. Paetz gen. Schieck 3 , E. Steffens 5 , H. Ströher 1 , Yu. Uzikov 2 , A. Vassiliev 7 , S.Yaschenko 5 , B. Zalikhanov 2 ,andK. Zwoll 6 for the ANKE collaboration — 1 IKP, FZJ, Germany — 2 LNP, JINR Dubna, Russia — 3 IKP, Universität zu Köln, Germany — 4 ZAT, FZJ, Germany — 5 PI II, Universität Erlangen-Nürnberg, Germany — 6 ZEL, FZJ, Germany — 7 HEPD, PNPI Gatchina, Russia For nucleon-nucleon interaction studies with polarized beams and targets at COSY/Jülich our group is currently developing a polarized internal storage-cell gas target for the magnetic spectrometer ANKE. The polarized atomic beam source is already performing well. Since nuclear reactions involving polarized deuterons have not been measured sufficiently well in the COSY energy range, our group is setting up a Lamb- Shift target polarimeter. The implementation of the internal target into the ring constitutes a major technological enterprise. First tests with different apertures at the ANKE target location have been carried out. Last year a first measurement of the cross section of the deuteron breakup reaction pd → ppn in collinear kinematics with detection of a proton pair near 0 ◦ was carried out. For the first time proton pairs from the break-up reaction at relative energy Tpp < 3 MeV have been detected. Time: Monday 16:15–19:00 Room: E Group Report HK 6.1 Mon 16:15 E Exploring Nuclear Matter at Extreme Temperatures and Densities: Results from the PHENIX Experiment at RHIC — •Klaus Reygers for the PHENIX collaboration — Institut für Kernphysik, Westfälische Wilhelms-Universität, Münster, Germany The Relativistic Heavy Ion Collider (RHIC) in Brookhaven/USA became operational in the summer of 2000. This machine collides gold ions at energies of up to √ snn = 200 GeV. The primary objective of the experiments at RHIC is to study a form of nuclear matter in which quarks and gluons are no longer confined within hadrons. The PHENIX experiment consists of a multitude of specialized detector systems and is therefore capable of measuring a variety of observables. A selection of PHENIX results will be discussed in this talk. Among the presented results will be the centrality dependence of identified hadron spectra and data on the elliptic flow pattern of particle production. Furthermore hadron production at large transverse momenta will be discussed. A striking difference compared to results at lower energies is found - an observation that belongs to the most important results of the first RHIC beamtime. Group Report HK 6.2 Mon 16:45 E Excitation Function of Λ and charged KProduction at CERN-SPS Energies ∗ — •André Mischke 1,2 , L. Betev 2 , A. Billmeier 1,2 , C. Blume 1 , R. Bramm 2 , P. Buncic 2 , P. Dinkelacker 2 , M. Ga´zdzicki 2 , T. Kollegger 2 , I. Kraus 1,2 , C. Markert 1,2 , R. Renfordt 2 , A. Sandoval 1,2 , R. Stock 2 , H. Ströbele 1,2 , D. Vranic 2 , A. Wetzlar 2 , and J. Zaranek 2 — 1 GSI, Planckstrasse 1, D-64291 Darmstadt — 2 Institut f. Kernphysik, August Eulerstr.6, D-60486 Frankfurt Within the framework of the NA49 energy scan program, Λ hyperons and charged Kaons were measured in central 208 Pb+ 208 Pb collisions at 40, 80 and 158 A·GeV with a large acceptance hadron spectrometer over a large range of rapidity and transverse momentum. Neutral
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Nuclear Physics Friday HK49 Plenary
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M. Ding3 , M.O. Distler3 , P. Drago
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4 Institut for Fysik og Astronomi,
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8Gesellschaft für Schwerionenforsc
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Friese, J. . HK 14.1, HK 14.3, HK 4
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Rusev, G. ..................HK 10.1
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Monday, March 11, 2002 - DPG-Tagungen

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