Sessions - DPG-Tagungen

Nuclear Physics Tuesday
HK 14 Poster Session: Heavy Ions
Time: Tuesday 13:30–15:30 Room: Foyer
HK 14.1 Tue 13:30 Foyer
Isospin dependence in the production of heavy-element
nucleifrom complete-fusion neutron-evaporation reactions —
•Alexander Yakushev 1 , Willy Bruechle 2 , Egon Jaeger 2 ,
Matthias Schaedel 2 , Erwin Schimpf 2 , Andreas Tuerler 1 , and
Birgit Wierzinski 1 — 1 Institut fuer Radiochemie TU Muenchen —
2 Gesellschaft fuer Schwerionenforschung mbH
This work is aimed at investigations on the projectile isospin dependence
of heavy element fusion-evaporation residue cross sections at
Coulomb barrier energies. For this, it is planned to exploit the potential
of radioactive ion-beam facilities like SPIRAL which shall provide n-rich
radioactive ion beams. The system Ar on Sm is a well studied heavy-ion
reaction. The wide span of Sm nuclides ranging from 144-Sm to 154-Sm
provided the basis to study different projectile-target-Z combinations.
The goal of this work is to extend these studies to probe the neutron
excess in radioactive Ar projectiles - up to 44-Ar - on the evaporation
residue cross section at near barrier energies. Hg as the complete-fusion
n-evaporation product is chemically well studied, mainly as the lighter
homologue of element 112. Highly efficient separation and detection techniques
are at hand to identify individual nuclei. This provides us with
an important advantage over other techniques; e.g. those which do not
measure evaporation residue cross section but indirectly infer fusion cross
sections from fission measurements. A first experiment with 36-Ar beam
was performed at GSI. The cross sections for 2n-, 3n-, 4n- and 5n-neutron
evaporation channels were measured for the complete fusion reaction 36-
Ar + 148-Sm.
HK 14.2 Tue 13:30 Foyer
Baryon Nuggets in Heavy Ion Collisions — •Kerstin Paech
and Adrian Dumitru — Institut fuer Theoretische Physik Universität
Frankfurt
We introduce a model for the real-time evolution of a relativistic fluid
of quarks coupled to non-equilibrium dynamics of the long wavelength
(classical) modes of the chiral condensate. We solve the equations of
motion numerically in 3+1 space-time dimensions.
Starting the evolution at high temperature in the symmetric phase,
we study dynamical trajectories that either cross the line of first-order
phase transitions or evolve through its critical endpoint.
For those cases, we study the formation of baryon density fluctuations
in dependence on different initial conditions.
HK 14.3 Tue 13:30 Foyer
Why a long-lives source can be compatible with HBT measurements
— •Thorsten Renk — Technische Universität München
The common interpretation of HBT data measured at top SPS energies
leads to apparent source lifetimes of 6–8 fm/c and emission duration of
approximately 2–3 fm/c. We investigate a scenario with continuous pion
emission from a long-lived (∼ 17 fm/c) thermalized source in order to
show that it is not excluded by the data. Starting from a description of
the source’s spacetime expansion based on gross thermodynamical properties
which is well tested for several observables, we introduce the pion
emission function with a contribution from continuous emission during
the source’s lifetime and another contribution from final breakup and
proceed by calculating the HBT parameters Rout and Rside. The results
are compared with experimental data measured at SPS for 158 AGeV
central Pb-Pb collisions. We achieve good agreement with the data, provided
that some minor modifications of the fireball evolution scenario are
made. We find that the parameter Rout is not sensitive to the fireball
lifetime, but only to the duration of the final breakup, in spite of the fact
that emission takes place throughout the whole lifetime.
Work supported in part by BMBF and GSI.
HK 14.4 Tue 13:30 Foyer
Light clusters in nuclear matter of finite temperature — •M.
Beyer 1 , S. Strauss 1 , P. Schuck 2 , and S.A. Sofianos 3 — 1 FB
Physik, U Rostock, Germany — 2 IPN Orsay, France — 3 UNISA, Pretoria,
South Africa
We investigate properties and the distribution of light nuclei (A < 4)
in symmetric nuclear matter of finite temperature within a microscopic
framework. For this purpose we have solved few-body Alt-Grassberger-
Sandhas type equations for quasi-nucleons that include self-energy cor-
rections and Pauli blocking in a systematic way. In a statistical model
we find a significant influence in the composition of nuclear matter if
medium effects are included in the microscopic calculation of nuclei. If
multiplicities are frozen out at a certain time (or volume), we expect significant
consequences for the formation of light fragments in a heavy ion
collision. Indeed the systematic inclusion of medium effects leads to an
ordering of multiplicities opposite to the law of mass action of ideal components.
This is necessary to explain the large abundance of α-particles
in a heavy ion collision that are otherwise largely suppressed in an ideal
equilibrium scenario.
Work supported by Deutsche Forschungsgemeinschaft.
HK 14.5 Tue 13:30 Foyer
Dilepton Analysis in the HADES Spectrometer for C+C at 2
AGeV Data — •J. Otwinowski for the HADES collaboration — II.
Physikalisches Institut, Universität Gießen
The light meson dilepton analysis in the HADES detection system is
based on an invariant mass reconstruction of their decay into e + e − . Methods
of the dilepton signal reconstr uction in the HADES spectrometer will
be presented. Particulary important is the reduction of a huge combinat
orial background coming out from wrong combinations of positrons and
electrons. A purity of the signal recons truction is determind by using
the GEANT simulation with a realistic HADES geometry and detector
response.
HK 14.6 Tue 13:30 Foyer
Statistical description for hadron production by means of
anisotropic momentum distributions — •Bjoern Schenke
and Carsten Greiner — Institut für Theoretische Physik, Johann
Wolfgang Goethe Universität Frankfurt, Robert-Mayer-Str. 8-10, 60054
Frankfurt
The various experimental data at AGS, SPS and RHIC energies on
hadron particle yields are investigated by employing a generalized statistical
operator, which allows for a well-defined anisotropic momentum
distribution of each particle species, specified by a common streaming velocity.
It is found that the individual particle ratios are rather insensitive
on this new intensive parameter. This leads to the important conclusion
that, when applying a statistical treatment to descibe the various experimentally
measured hadronic particle ratios, a succesful reproduction of
those does not imply the common conclusion, that one has a state of
almost complete thermal equilibrium at hadrochemical freeze-out.
HK 14.7 Tue 13:30 Foyer
Study of Open Charm production at SPS — •Wilrid Ludolphs
for the CERES collaboration — Physikalisches Institut der Universität
Heidelberg
Heavy ion collisions at ultra-relativistic energies offer the possibility to
study the behaviour of nuclear matter at high density and temperature
where one expects the existence of the quark gluon plasma. The J/Ψ
suppression has been studied as a possible signature, but it is only meaningful
if the overall charm production rate is known.
The production of charm quarks in nuclear collisions is a hard process
and should be describable in perturbative QCD. However, no measurement
of open charm hadrons in nuclear collisions has been performed yet
while there are indirect indications for a substantial enhancement.
The CERES collaboration therefore attempts a study of D meson production
focussing on the 2-body (D 0 → Kπ, 3.8%, cτ = 123.4µm) and
3-body (D → Kππ, 9.1%, cτ = 315µm) decay mode. The analysis is
based on the reconstruction of secondary vertices using the silicon drift
chambers located approximately 10 cm behind the target. An investigation
will be presented on the effectiveness of various cut strategies to
reduce the combinatorial background and on the resulting signal/noise
ratios for D meson detection.
HK 14.8 Tue 13:30 Foyer
New results from the CERES Electron Pair Spectrometer in
Pb-Au collisions at 158 GeV/c per nucleon. — •Sergey Yurevich
for the CERES collaboration — Physikalisches Institut der Universität
Heidelberg
In 2000 the CERES/NA45 experiment at the CERN SPS measured
e + e − pair production in Pb-Au collisions at 158 GeV/c per nucleon. The