Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Thursday
interaction between the outgoing pions is generated using the Jülich meson
exchange model with dispersion theoratical form factors for t-channel
exchanges.
HK44 Theory VIII
[1] J.Gunter et al., Phys.Rev.D 64,072003(2001)
[2] V.V.Anisovich et al., Phys.Lett.B 355,363 (1995)
Time: Thursday 16:00–18:00 Room: C
Group Report HK 44.1 Thu 16:00 C
Self-consistent many-body approach and properties of neutron
star matter — •Tobias Frick, Khalaf Gad, Jan Kuckei, Fernando
Montani, andHerbert Müther — Institut für theoretische
Physik der Universität Tübingen
Within a Green’s functions approach, the neutron and the proton properties
are studied in asymmetric nuclear matter, starting from realistic
NN potentials. Going beyond a quasi-particle approximation, we account
for the depletion of the hole states in the many-body system by
introducing multiple poles in the two-particle propagator that appears in
the ladder-equation for the effective interaction, each of them carrying a
strength that is deduced from the nuclear single-particle spectral functions.
The nuclear self-energies are calculated within different approximations,
treating the backward-propagation of intermediate two-holeone-particle
configurations perturbatively, but also in a non-perturbative
Galitsii-Feynman approach. Due to a non-vanishing spectral distribution
of the single-particle strength for momenta very close to the Fermi
surface, a gap is introduced in the single-particle spectrum. In a natural
way, this leads to a supression of the well-known pairing instability. The
results of this Green’s function approach for the equation of state are
compared to corresponding predicitions of the conventional Brueckner-
Hartree-Fock approach. Furthermore we present the predicitions for the
spectral function and momentum distribution. The sensitivity of theses
on the NN interaction is discussed.
Group Report HK 44.2 Thu 16:30 C
Energy dependence of QCD cross sections: Saturation effects
from HERA to RHIC and LHC — •Heribert Weigert 1 ,
Kari Rummukainen 2 , Andreas Schäfer 1 ,andRainer Fries 1 —
1 Universität Regensburg — 2 Nordita, Kopenhagen
Gluon evolution enhances the importance of multiple interaction effects
in eA and AA collisions at high energies. These mimic properties
such as screening and saturation in ways otherwise only known from
dense media. They are responsible for the unitarization of cross sections,
the infrared safety of properly resummed perturbation theory and allow
us to calculate the energy dependence of various cross sections semiperturbatively.
I will try to highlight the key ingredients to the underlying
physical picture and the ensuing technology (a renormalization group
w.r.t. xBj) and its conceptual relevance to HERA, eRHIC, RHIC and
LHC experiments.
HK 44.3 Thu 17:00 C
Energy loss of high pt hadrons by final hadronic state in ultrarelativistic
heavy ion collisions — •Kai Gallmeister, Carsten
Greiner, Gunnar Martens, andZhe Xu — Institut für Theoretische
Physik, Universität Gießen, Germany
When discussing the parton jet quenching phenomena in ultrarelativistic
heavy ion collisions typically hadronization is assumed to take place
in vacuum outside the reaction zone. On the other hand simple quantum
mechanical estimates give a hadronization time τh ≈ E/GeV ∗ fm.For
pt ≤ 10 GeV hadronization thus might well take place inside the fireball.
Typical (in-)elastic collisions of these high pt particles with the dominant
low momentum hadrons of the fireball have √ s ≤ 4 GeV and are
thus soft and nonperturbative. The mean free path in the late hadronic
stage is estimated to be λ ≈ 1 − 5 fm, resulting in in a few collisions
L/λ =0, 1, 2,.... An analysis within this opacity expansion by means
of the FRITIOF collisions scheme for various hadrons will be presented
and it shows that these collisions can account for the modification of the
pt-spectrum observed for central collisions at RHIC.
Work supproted by BMBF.
HK 44.4 Thu 17:15 C
Dispersion Effects in Nucleon Polarisabilities — •Robert Hildebrandt,
Harald Griesshammer, andThomas Hemmert —Institute
for Theoretical Physics (T39), TU Muenchen, Germany
The dynamical nucleon polarisabilities can be defined via a multipole
expansion of the structure amplitudes in nucleon Compton scattering [1].
In contradistinction to the static polarisabilities, dynamical polarisabilities
gauge the response of the internal degrees of freedom of a nucleon
to an external, real photon field of arbitrary energy but definite multipolarity.
Being energy dependent, they therefore contain additional information
about dispersive effects induced by internal relaxation, baryon
resonances or meson production thresholds of the nucleon.
We present the different diagrams contributing in leading order ChPT —
i. e. on the one pion loop level — in theories with and without explicit
∆(1232) degrees of freedom [2]. We further compare our results with
a dispersion relation analysis. Once two counter terms are fixed at the
static values, we obtain excellent predictions even well above the pion
mass.
Work supported in part by DFG and BMBF.
1) H. Grießhammer, T. Hemmert: nucl-th/0110006
2) T. R. Hemmert, H. W. Griesshammer, R. P. Hildebrandt: in preparation
HK 44.5 Thu 17:30 C
Hadron formation in high energy photonuclear reactions —
•Thomas Falter and Ulrich Mosel — Institut für Theoretische
Physik, Universität Gießen, Germany
Photo- and electroproduction on nuclei offer a great opportunity to investigate
the physics of hadron formation. The results are usually interpreted
using simple Glauber theory to describe the final state interactions
(FSI) of the produced particles. We show that this purely absorptive
treatment of the FSI might lead to wrong estimates of formation time
and color transparency effects. We use a semi-classical transport model
based on the BUU equation which allows for a realistic coupled channel
description of the FSI that goes far beyond simple Glauber theory. The
model has already been successfully used to describe heavy ion collisions,
pion and proton induced reactions as well as photon and electron induced
reactions in the resonance region. We present a possibility to account for
coherence length effects within this model, which makes it possible to
describe photo- and electroproduction at higher energies. As an example
we will discuss inclusive and exclusive meson photoproduction in the
energy range from 1 to 7 GeV.
Work supported by DFG.
HK 44.6 Thu 17:45 C
PP bremsstrahlung and low energy NN interaction — •Mircea
Dan Cozma 1 , Olaf Scholten 1 , John Tjon 1,2 ,andRob Timmermans
1 — 1 KVI, Zernikelaan 27, 9747 AA Groningen, The Netherlands
— 2 ITP, Utrecht, The Netherlands
For the study of bremsstrahlung several microscopic models have been
developed. Despite of the richness of included physics, these models are
posed with problems; predictions differ substantially from experiment
in some kinematical regions. It appears that this is mainly due to the
high sensitivity of the bremsstrahlung process with respect to the NN
interaction at low energies.
The high accuracy KVI bremsstrahlung experiments showed that microscopical
bremsstrahlung models using np potentials were observed to
fail describing the data in the above mentioned way. We will consider
a field theoretical model of the NN interaction in the 1 S0 channel which
also takes into account the Coulomb interaction. This model is then incorporated
in a field theoretical toy model for bremsstrahlung. Phase
shifts of the NN toy model are in good agreement with the experimental
pp phase shift in the low energy region.
We end by presenting a fit of the NN potential of Fleischer and Tjon
to the experimental pp phase shifts. Bremsstrahlung is then computed
within the microscopic model of Martinus et al.. Although they are reduced,
the discrepancies are still present.