Sessions - DPG-Tagungen

Nuclear Physics Monday
HK 3.5 Mon 17:30 B
Electrodisintegration of the deuteron in the ∆-region —
•Michael Schwamb and Hartmuth Arenhövel — Institut für
Kernphysik, Johannes Gutenberg-Universität, D-55099 Mainz, Germany
A recently developed model for photodisintegration of the deuteron[1]
has been extended to electrodisintegration. Our approach is based on a
nonrelativistic coupled-channel approach with nucleonic, mesonic and ∆degrees
of freedom and contains for the first time full retardation in the
potential and in the pionic meson-exchange currents. Moreover, hadronic
as well as electromagnetic offshell contributions are considered. Our results
show that retardation effects are significant above pion threshold,
in particular in the ∆-region.
[1] M. Schwamb and H. Arenhövel, Nucl. Phys. A 690, 647 (2001), Nucl.
Phys. A 690 682 (2001), Nucl. Phys. A 696 556 (2001)
HK 3.6 Mon 17:45 B
The NN-final-state interaction in two-nucleon knockout
reactions — •Michael Schwamb 1 , Sigfrido Boffi 2 , Carlotta
Giusti 2 , and Franco Davide Pacati 2 — 1 Institut für Kernphysik,
Johannes Gutenberg-Universität, D-55099 Mainz, Germany —
2 Dipartimento di Fisica Nucleare e Teorica dell’Università degli Studi di
Pavia, and INFN, Sezione di Pavia, I-27100 Pavia, Italy
The influence of the mutual interaction between the two outgoing nucleons
(NN-FSI) in electro- and photoinduced two-nucleon knockout from
16 O has been investigated perturbatively[1]. It turns out that the effect
of NN-FSI depends on the kinematics and on the type of reaction considered.
In superparallel kinematics NN-FSI leads in the (e, e ′ pp) channel
to a strong increase of the cross section, that is mainly due to a strong
enhancement of the ∆-current contribution. In pn-emission, however,
this effect is partially cancelled by a destructive interference with the
seagull current. For photoreactions NN-FSI is considerably reduced in
superparallel kinematics.
[1] M. Schwamb, S. Boffi, C. Giusti and F. D. Pacati, nucl-th/0307003
HK 3.7 Mon 18:00 B
High Resolution (γ,NN)-Experiments on 16 O — P. Grabmayr,
T. Hehl, J. Heim, •I. Martin, and F. Moschini for the A2 collaboration
— Physikalisches Institut der Universität Tübingen, Auf der
Morgenstelle 14, D-72076 Tübingen
Photoinduced two-nucleon knockout experiments are a promising tool
for the investigation of correlated nucleon pairs in nuclei. The present
experiments focus on the improvement of energy resolution for the final
states in order to increase the sensitivity when comparing with model
calculations. Due to the large level spacing of the residual A=14 nuclei
and the availability of complementary (e,e ′ NN) data, 16 O is a preferred
target. Thus, the reactions 16 O(γ,np) 14 N and 16 O(γ,pp) 14 C were investigated
at the tagged photon facility of the electron accelerator MAMI,
Mainz. In these measurements, the new HPGe array Ge6 from Edinburgh
was used in coincidence with the Tübingen time-of-flight neutron
spectrometer TOF for the first time. To improve the energy resolution of
the tagged photon beam, a microscope in the focal plane of the Glasgow
tagger was employed. A report on the experiment and the ongoing data
analysis is given, and first missing-energy spectra are presented.
This work is supported by the DFG (GRK 683 Basel-Tübingen and SPP 1034).
HK 4 Instrumentation and Applications I
HK 3.8 Mon 18:15 B
Single-Particle Structure of 7 He from the 7 Li(d, 2 He) Reaction*
— •N. Ryezayeva 1 , C. Bäumer 2 , A. van den Berg 3 , D. Frekers
2 , D. De Frenne 4 , P. Haefner 2 , E. Jacobs 4 , H. Johanson 5 ,
B. Jonson 6 , Y. Kalmykov 1 , A. Negret 4 , P. von Neumann-
Cosel 1 , L. Popescu 4 , S. Rakers 2 , A. Richter 1 , G. Schrieder 1 ,
A. Shevchenko 1 , H. Simon 5 , and H.J. Wörtche 3 for the EURO-
SUPERNOVA collaboration — 1 Institut für Kernphysik, Techische Universität
Darmstadt, Germany — 2 Institut für Kernphysik, Universität
Münster, Germany — 3 KVI Groningen, Netherlands — 4 Vakgroup Subatomaire
en Strahlingsfysica, Universiteit Gent, Belgium — 5 GSI Darmstadt,
Germany — 6 Chalmers University of Technology, Göteberg, Sweden
The spin-orbit interaction in neutron-rich nuclei is of much current interest
because of the disappearance of the usual magic numbers in such
nuclei. A recent GSI experiment [1] claims the observation of a low-lying
state at Ex ≈ 0.7 MeV assumed to be the p1/2 spin-orbit partner of the
7 He ground state. A study of the 7 Li(d, 2 He) 7 He reaction has been performed
at KVI searching for the allowed GT transition populating the
p3/2−p1/2 doublet. The unbound 2 He system was identified by measuring
coincidences between two protons with small relative energy. The setup
at KVI offers a resolution ∆E/E ≈100 keV, better than the line width
of the ground state of 7 He. Data were obtained at Ed = 171 MeV and
Θ2 He = 0 ◦ − 8 ◦ . First results will be presented.
[1] M. Meister et al., Phys. Rev. Lett. 88, 102501 (2002).
*Supported by the DFG under contract SFB 634.
HK 3.9 Mon 18:30 B
Isovector Spin-Flip Resonances in Medium-Mass and Heavy
Nuclei ⋆ — •Y. Kalmykov 1 , T. Adachi 2 , G.P.A. Berg 3 , H. Fujita
3 , Y. Fujita 2 , F. Hofmann 1 , P. von Neumann-Cosel 1 , V.Yu.
Ponomarev 1 , B. Reitz 1 , A. Richter 1 , A. Shevchenko 1 , Y. Shimbara
2 , and J. Wambach 1 for the EUROSUPERNOVA collaboration —
1 Institut für Kernphysik, Technische Universität Darmstadt, Germany —
2 Department of Physics, Osaka University, Japan — 3 Research Center
for Nuclear Physics, Osaka University, Japan
Recent progress in the understanding of isovector spin-flip resonances
is discussed. The reaction 90 Zr( 3 He,t) 90 Nb was studied at 0 ◦ with a 3 He
beam of energy E0 = 140 MeV/u. Highest energy resolution allows for
the first time to unravel the fine structure of GTR in a heavy nucleus. Recently
developed wavelet analysis techniques determine its characteristic
energy scales which provide unique insight into the damping of resonances
through internal mixing. The data also allow extraction of spin- and
parity-separated level densities by means of a fluctuation analysis. The
reaction 58 Ni(�p, �p ′ ) was investigated at incident energy of 172 MeV up
to 23 MeV and forward angles favoring the excitation of the spin-dipole
mode in the continuum. The results are compared to state-of-the-art
microscopic reaction calculations. The nuclear structure input, which
takes the coupling to complex configurations into account, allows for the
first time a satisfactory description of the spin-flip probabilities and cross
sections over a wide excitation energy and angle range.
⋆ Supported by the DFG under SFB 634 and 446 JAP 113/267/0-1.
Time: Monday 15:45–18:45 Room: C
Group Report HK 4.1 Mon 15:45 C
Calorimeter Telescope for identification of relativistic HI reaction
channels — •R. Lozeva 1,2 , S. Mandal 1 , and M. Gorska 1 for
the RISING collaboration — 1 GSI, Darmstadt, Germany — 2 Faculty of
Physics, University of Sofia ”St. Kl. Ohridski”, Sofia, Bulgaria
During a recent RISING [1] campaign at GSI, stable and radioactive
heavy-ion beams at relativistic energies between 100 MeV/u and 200
MeV/u have been used to perform fragmentation and Coulomb excitation
reactions on a secondary target. To distinguish the reaction channels, to
obtain information about the impact parameter and to identify the outgoing
projectiles, a newly developed CAlorimeter TElescope (CATE) [2]
system has been employed. CATE consists of a position sensitive Si
detector array with 9 elements for Z-identification and a corresponding
CsI(Tl) detector array for A-identification. The detectors cover a large
opening angle between 0 ◦ and 3 ◦ .
The CATE system has been used for the detection of heavy ions from
55 Ni up to 132 Xe, with instantaneous rates of up to ∼5x10 4 particles/s
and ion energies in the range 90 MeV/u and 150 MeV/u. Under
these conditions the detector system revealed an excellent Z resolution
∆Z∼1, a good position resolution (∆x,∆y)∼(5x5)mm and a mass resolution
after several corrections corresponding to Eresidual∼1% (FWHM).
[1] http://www-aix.gsi.de/ ∼ wolle/EB at GSI/rising.html
[2] http://www-linux.gsi.de/ ∼ lozeva/cate/cateweb.htm