Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Tuesday
The results of this analysis are reported together with measurements of
B → charmonium branching fractions.
HK 19.3 Tue 17:45 D
Hard exclusive electroproduction of real photons and π + on the
proton at HERMES — •Björn Seitz for the HERMEScollaboration
— II. Physikalisches Insitut, Justus–Liebig Universität Giessen,
Heinrich–Buff Ring 16, 35392 Giessen, F.R.G.
The production of mesons (or photons) in deep–inelastic lepton scattering
gives access to information on the structure of hadrons that is
otherwise hard to obtain. When the production process involves at least
on hard scale and is exclusive, the data can be interpreted in terms of
the recently introduced generalized parton distributions (GPDs). These
GPDs provide a unified description of hadronic structure, which can be
applied to many different reactions.
Single Spin Asymmetries in the hard, exclusive electroproduction of
real photons (DVCS) and π + on the proton have been measured for the
first time by HERMES. Sizeable asymmetries for DVCS using a polarized
beam and unpolarized target have been observed. A large asymmetry
using an unpolarized beam and a longitudinal polarized target has been
observed in the exclusive electroproduction of π + . These data provide a
first testing ground for the GPD formalism.
HK 19.4 Tue 18:00 D
Azimuthal asymmetries in pion and kaon production in SIDIS
off longitudinally polarized proton and deuterium targets at
HERMES — •Peter Schweitzer 1 , Klaus Goeke 2 ,andAnatoli
Efremov 3 — 1 Dipartimento di Fisica Nucleare e Teorica, Universitá
degli Studi di Pavia, Pavia, Italy — 2 Institut für Theoretische Physik
II, Ruhr-Universität Bochum, Germany — 3 Joint Institute for Nuclear
Research, Dubna, 141980 Russia
Recently azimuthal asymmetries in pion production from SIDIS off
a polarized proton target have been measured by HERMESand SMC.
New HERMESdata from a longitudinally polarized deuetrium target
will be released soon (possibly in February). The asymmetries can be
explained by the Collins effect and contain information on the transversity
distribution function and the T-odd Collins’ fragmentation function.
Recently a very successful approach has been developed which is based
on 2 ingredients and explains well existing data and allows unambigous
predictions for new experiments with no free parameters. Ingredient (1)
HK20 Heavy Ions II
is experimental information on the Collins fragmentation function from
DELPHI. Ingredient (2) are results from non-perturbative calculations
of the transversity distribution function in the chiral quark soliton model
and in the instanton model of the QCD-vacuum.
HK 19.5 Tue 18:15 D
Extraction of polarized quark distributions of the nucleon at
HERMES — •Brecht Hommez — University of Gent, Proeftuinstraat
86, B 9000 Gent, Belgium
New results from the HERMESexperiment on polarized quark distributions
for the valence and the sea quarks in the nucleon will be presented.
The HERMESexperiment has measured double spin asymmetries in
the cross section for deep-inelastic scattering of longitudinal polarised
positrons off longitudinal polarised hydrogen and deuterium targets.
From these asymmetries, based on inclusive and semi-inclusive measurements,
polarised quark distributions were extracted as a function of x.
Since 1998, a dual-radiator Ring Imaging Cherenkov detector has been
installed in HERMES, which allows the identification of kaons, pions and
protons over almost the entire kinematic range of the experiment. Semiinclusive
kaon asymmetries will provide an enhanced sensitivity on the
polarisation of the strange sea quarks in the sea.
HK 19.6 Tue 18:30 D
η photo- and electroproduction on nucleons — •Eugenio
Marco, Bugra Borasoy, and Stefan Wetzel — Physik-
Department, Technische Universität München
The Swave contribution to photo- and electroproduction of the η ′ meson
on both the proton and neutron is investigated within a relativistic
chiral unitary approach based on coupled channels. We work with an
effective chiral Lagrangian which includes the η ′ as an explicit degree
of freedom and incorporates important features of the underlying QCD
Lagrangian such as the axial U(1) anomaly. Unitarity constraints are imposed
in performing the resummation of the amplitudes obtained from
chiral perturbation theory and cross sections of η ′ photo- and electroproduction
from nucleons are obtained. The investigation of the η ′ -nucleon
system may offer new insights into the role of gluons in chiral dynamics.
Work supported in part by the DFG and the Alexander von Humboldt
Foundation.
Time: Tuesday 16:45–18:45 Room: E
Group Report HK 20.1 Tue 16:45 E
The Compressed Baryonic Matter experiment at the future
facility at GSI — •Volker Friese 1 , Anton Andronic 1 , Peter
Braun-Munzinger 1 , Christian Finck 1 , Bengt Friman 1 , Norbert
Herrmann 2 , Romain Holzmann 1 , Wolfgang Koenig 1 ,
Matthias Lutz 1 , Peter Senger 1 , Yanghwan Shin 1 , Reinhard
Simon 1 , Herbert Ströbele 3 , and Joachim Stroth 1,3 — 1 GSI
Darmstadt — 2 Univ. Heidelberg — 3 Univ. Frankfurt
A major field of research at the proposed accelerator facility at GSI will
be the production and investigation of super-dense strongly-interacting
matter. The exploration of the QCD phase diagram in the region of high
baryon densities is complementary to the studies of matter at high temperatures
performed at the CERN-SPS, RHIC and the future LHC. The
planned experimental program will focus on diagnostic probes which have
not been measured before in the beam energy range between 2 and 40
AGeV: light vector mesons decaying into electron-positron pairs, hidden
and open charm and multi-strange hyperons. In addition, hadronic observables
such as protons, pions and kaons will be detected with large acceptance.
The experimental challenge is the efficient identification of rare
probes (both hadrons and electrons) embedded in events with charged
particle multiplicities of up to 1000 at reaction rates of up to 10 MHz.
The proposed layout of the detector system and performance simulations
will be presented.
Group Report HK 20.2 Tue 17:15 E
Kaon and Antikaon Production in Nucleus-Nucleus Collisions
at SIS Energies — •Florian Uhlig for the KaoScollaboration —
TU Darmstadt
The study of the
properties of hadrons in dense matter and the nuclear equation-of-state
at high baryon densities represents a major goal of today’s
heavy-ion collision experiments.
The production of strange particles
serves as a sensitive tool for probing both issues [1][2].
Systematic measurements of kaons and antikaons emitted in C+C,
Ni+Ni
and Au+Au collisions were performed with the Kaon Spectrometer
KaoSat
SIS/GSI. The particle yields were determined as function of momentum,
collision centrality and emission angle. Of particular interest with
respect to in-medium effects is the azimuthal emission pattern of
kaons and antikaons. Recent results will be presented.
[ ∗ ] supported by BMBF and GSI
[1] F. Laue, C. Sturm et al., Phys. Rev. Lett. 82 (1999) 1640
[2] C.Sturm et al., Phys. Rev. Lett. 86 (2001) 39
HK 20.3 Tue 17:45 E
Measurement of long-lived strange resonances in FOPI ∗ —
•Markus Merschmeyer for the FOPI collaboration — Physikalisches
Institut der Universität Heidelberg
K 0 and Λ have been measured in the reactions Ni+Ni at 1.93 AGeV
and Ru+Ru at 1.69 AGeV. Spectra and rapidity distributions are discussed
and point, as is the case for charged kaons, in the theoretical
description to the necessity for introducing in-medium potentials. Further
information on this topic can be gained from the investigation of
subthreshold production of double strange baryons at SIS energies. The