Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Wednesday
HK 34.4 Wed 15:15 F
GRID Computing ∗ — •Rüdiger Berlich — Lehrstuhl für Experimentalphysik
1, Ruhr-Universität Bochum, 44780 Bochum
The availability of high-performance network connections and the need
to process and store huge amounts of data has led to a natural progression
in the way the existing computer infrastructure is perceived and used.
The requirements of the LHC experiments have led to a new paradigm
in distributed computing, called ”the GRID”. The huge amounts of
data produced by the upcoming LHC experiments cannot be processed
entirely at CERN anymore. Instead, processing and storage capacities
from participating institutions around the world are seemlessly bundled
HK35 Plenary Session
together, effectively creating a ”virtual supercomputer”. Today, GRID
computing is an important research topic beyond the boundaries of particle
physics. Within Germany, GRID research is funded by the BMBF,
European-wide projects like the European Data Grid are realised with
the help of the European Union. The talk highlights the current developments
in parallel and distributed computation with special emphasis
on GRID computing. It gives examples from particle physics (BaBar)
and explains the mission of the newly founded competence centre for
GRID computing at the Forschungszentrum Karlsruhe, which will play
an important role in the BaBar computing model.
∗ supported by the BMB+F
Time: Thursday 08:30–10:30 Room: Plenarsaal
Plenary Talk HK 35.1 Thu 08:30 Plenarsaal
The Muon Magnetic Moment — •Klaus Jungmann 1 and on behalf
of the muon g-2 collaboration 2 — 1 Kernfysisch Versneller
Instituut, Zernikelaan 25, NL 9747 AA Groningen — 2 Brookhaven National
Laboratory, Upton, New York, USA
The anomaly of the muon magnetic moment describes the deviation
of the particles magnetic g-factor from the value 2 predicted in the Dirac
theory for spin 1/2 particles. The quantity can be calculated to very
high precision using standard theory. The by far largest contribution
arises from Quantum Electrodynamical effects, i.e. photon and lepton
fields. There are contributions of some 60 ppm due to hadronic vacuum
polarization and some 1.3 ppm from weak interaction. Compared to the
electron magnetic anomaly, the muon is more sensitive to the heavier
particles by the square of the mass ratio. Therefore, precision calculations
and accurate measurements together offer a possibility to search
for physics beyond the standard theory. Either hints to yet unknown
forces in nature may be gained (in case of disagreement) or parameters
in existing speculative models can be significantly bounded (in case of
agreement). At the Brookhaven National Laboratory, USA, a magnetic
storage ring experiment reached a first result which at the time of publication
disagreed with the most recent and most accurate calculations.
Careful reevaluations of the theoretical situation were started and are
being continued. Of special interset are the hadronic contributions in
particular hadronic light by light scattering. The experiment has in the
mean time taken more data which is being analyzed. Work in progressing.
Plenary Talk HK 35.2 Thu 09:00 Plenarsaal
High-temperature QCD and relativistic heavy ion collisions —
•Dietrich Bödeker —Fakutät für Physik, Universität Bielefeld, D-
33516 Bielefeld
Relativistic collisions of large nuclei create strongly interacting matter
at high energy densities. If there are sufficiently many interactions
such a system will thermalize which would allow for a study of Quantum
Chromodynamics at finite temperature. I discuss recent theoretical developments
in this field and their confrontation with experimental data.
Plenary Talk HK 35.3 Thu 09:30 Plenarsaal
Experimental verification of the GDH sum rule at ELSA and
MAMI — •Klaus Helbing for the GDH-Collaboration collaboration
— Erlangen: Universität Erlangen-Nürnberg, Physikalisches Institut,
Abteilung IV, Erwin-Rommel-Str. 1, D-91058 Erlangen
The Gerasimov-Drell-Hearn (GDH) sum rule connects static properties
of the nucleon like the anomalous magnetic moment κ and the nucleon
mass m, with the helicity dependent photoabsorption cross sections σ3/2
and σ1/2, which are observables of the dynamics of the excitation spec-
trum.
�∞
HK36 Plenary Session
0
dν
ν
�
σ3/2(ν) − σ1/2(ν) �
= 2π2 α
m 2 · κ 2
For the first time this fundamental sum rule is verified experimentally
with circularly polarized real photons and longitudinally polarized nucleons.
First results of our measurements on the proton in the photon
energy range 200-800 MeV at the Mainz electron accelerator MAMI have
been published. The measurements of the GDH-Collaboration have been
continued at the accelerator ELSA in Bonn where a tagged photon facility
allows to study photon energies from 680 MeV up to 3 GeV. Our new
data provide up to now unaccessible information about the spin structure
of the proton from the resonance region up to the onset of the Regge
regime.
Plenary Talk HK 35.4 Thu 10:00 Plenarsaal
Compton Scattering off the Nucleon at MAMI Energies —
•Stefan Scherer — Institut für Kernphysik, Johannes Gutenberg-
Universität, 55099 Mainz
In recent years, real and virtual Compton scattering off the nucleon
have attracted considerable interest from both the experimental and theoretical
side. Real Compton scattering gives access to the so-called electromagnetic
polarizabilities containing the structure information beyond
the global properties of the nucleon such as its charge, mass, and magnetic
moment. These polarizabilities have an intuitive interpretation in
terms of induced dipole moments and thus characterize the response of
the constituents of the nucleon to a soft external stimulus. The use
of virtual photons considerably increases the possibilities to investigate
structure and dynamics of the target. The virtual Compton scattering
reaction e − p → e − pγ allows one to map out the local response to external
fields and can be described in terms of generalized electromagnetic polarizabilities.
We will discuss experimental results for the polarizabilities of
the proton which have been obtained at the Mainz Microtron (MAMI)
and compare them with theoretical predictions. A simple classical interpretation
in terms of the induced electric and magnetic polarization
densities is proposed.
Time: Thursday 11:00–12:45 Room: Plenarsaal
Plenary Talk HK 36.1 Thu 11:00 Plenarsaal
Chiral Symmetry and the Medium Modifiaction of Hadrons —
•Jochen Wambach —IKPTU-Darmstadt
A fundamental question in strong interaction physics is how mass is
generated in the sector of light quarks. The answer lies in the nonperturbative
structure of the QCD vacuum itself in which quarks and
gluons condense. This is in marked contrast to the heavy-quark sector
where the masses of the hadrons are determined by the quark masses
themselves. When nuclear matter is subjected to extreme conditions in
density and temperature such as in the interior of neutron stars or in
central relativistic heavy-ion collisions, the QCD vacuum will be altered,
eventually leading to the liberation of the elementary constituents in a
new state of matter. Such a restructuring of the vacuum must be accompanied
by significant changes in the spectral properties of hadrons. In
the framework of effective field theory this relationship and observable
consequences for the meson spectrum will be addressed.