Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Tuesday
momentum reconstruction of elastically scattered protons using a set of
two drift chambers and a scintillation wall. Additionally, a granulated
silicon pad detector enables to detect the corresponding deuterons in
coincidence.
The experimental method will be discussed and recent results will be
presented.
[1] H.-H. Adam, diploma thesis, Universität Münster, Germany (2000).
[2] I. Geck, Staatsexamensarbeit, Universität Münster, Germany (2001).
HK 12.22 Tue 10:30 Foyer Chemie
Luminosity determination in pp experiments at ANKE — •P.
Fedorets 1 , M. Büscher 2 , V. Chernyshov 1 , S.Dymov 3 , V. Komarov
3 , and Yu. Uzikov 3 for the ANKE collaboration — 1 ITEP,
Moscow — 2 Forschungszentrum Jülich — 3 JINR, Dubna
In Jan./Feb. 2001 a first beam time on the a + 0 production in the
reaction pp → da + 0 was performed using the cluster jet target at the
magnetic spectrometer ANKE at COSY Jülich. One way to determine
the average luminosity during this beam time is to use the elastic
proton-proton scattering where the differential cross section is well
known. With ANKE one of the elastically scattered proton is detected
in the forward detection system. The value obtained by this method
yields L =(2.70 ± 0.55) × 10 31 s −1 cm −2 .
HK 12.23 Tue 10:30 Foyer Chemie
Investigation of the reaction pp → nK + Σ + — •Peter Schönmeier
for the COSY-TOF collaboration — Institut für Kern- u. Teilchenphysik,
Technische Universität Dresden *
Reactions of the type pp → NKY are presently studied at COSY in
very detail, in particular the channels Y = (Λ, Σ 0 ). Data on Σ + , Σ − are
not known close to threshold. The COSY-TOF spectrometer complemented
by the neutron detector COSYnus provides access to the nK + Σ +
channel. Its identification is rendered possible by the detection of a neutron,
kaon, and Σ + → nπ + ,pπ 0 decay which results, in general, in an
angle between the tracks of the charged primary and secondary particle.
However, one neutral particle remains undetected. Hence, control of the
large background due to pp → npπ + reactions is of utmost importance
in order to obtain a clear nK + Σ + -signal. We present first results from a
measurement performed at a beam momentum of 2.85 GeV/c.
∗ supported by BMBF and FZJ
HK 12.24 Tue 10:30 Foyer Chemie
Hyperon Production in the channel pp → K + Λp at COSY-TOF ∗
— •W. Schroeder, W. Eyrich, M. Fritsch, F. Stinzing, M.
Wagner,andS.Wirthfor the COSY-TOF collaboration — Physikalisches
Institut, Universität Erlangen-Nürnberg
The exclusive measurement of hyperon production reactions in proton
proton collisions near threshold is one of the main topics at the timeof-flight
spectrometer COSY-TOF. For the hyperon program a complex
start detector system is used in combination with a segmented stop detector.
The setup covers the full phase space and allows the extraction and
reconstruction of the reaction pp → K + Λp almost without background.
The extension of the stop detector by a ring and a barrel-hodoscope to
a 3 m version increases the detector efficiency and improves the angular
and time-of-flight resolution.
Using this upgraded detector version in a measurement in January 2000
Λ-samples with large statistics were recorded at the two beam momenta
of 2.95 and 3.20 GeV/c.
After a short introduction to the analysis methods the preliminary results
of these data will be discussed and compared to Λ-data of previous
measurements at COSY.
∗ supported by BMBF and FZ Jülich
HK 12.25 Tue 10:30 Foyer Chemie
The Reaction pd → 3 Heη at COSY-11 — •H.-H. Adam for the
COSY-11 collaboration — Institut für Kernphysik, Universität Münster,
Germany
The production of mesons in proton-deuteron interactions provides the
possibility to study reaction processes with more than only one involved
target nucleon, i.e. two-step processes [1,2]. Such data might also be of
importance in the context of meson production in heavy ion collisions.
Of considerable interest is the production of η mesons in the
pd → 3 He η reaction channel, which exposes remarkable features [3,4].
The unexpected large threshold amplitude decreases by a factor of three
from threshold up to an excess energy of Q ∼ 7 MeV. This strong
decrease in the near threshold region is commonly attributed to a
strong η 3 He final state interaction and is therefore of special interest
in view of the existence of η-mesic nuclei. Although being topic of
several theoretical investigations, the possibility for the formation of
quasi-bound 3 He − η states is still an open question. Therefore, the
COSY-11 physics program has been extended to near-threshold meson
production experiments in the proton-deuteron interaction. Recent
results on the pd → 3 Heη reaction, studied at excess energies ranging
from Q = 5 MeV to Q = 40 MeV will be presented.
[1] K. Kilian, H. Nann, AIP Conf. Proc. No. 221 (1990) 185.
[2]G.Fäldt and C. Wilkin, Nucl. Phys. A 587 (1995) 769.
[3] J. Berger et al., Phys. Rev. Lett. 61 (1988) 919.
[4] B. Mayer et al., Phys. Rev. C 53 (1996) 2068.
HK 12.26 Tue 10:30 Foyer Chemie
Messung und Analyse der Reaktion γp → K0Σ+ — •Ralf Lawall
für die SAPHIR-Kollaboration — Nussallee 12, 53115 Bonn
Eine neue Messung der Reaktion γp → K0Σ + ist mit dem
SAPHIR-Detektor am Elektronen-Stretcher-Ring ELSA durchgeführt
worden. Die Daten überspannen den Photonenergiebereich von der
Schwelle bis 2.6 GeV und den vollen Produktionswinkelbereich des
2-Teilchenendzustandes. Totale und differentielle Wirkungsquerschnitte
und die Σ + -Polarisation sind bestimmt worden.
HK 12.27 Tue 10:30 Foyer Chemie
Messung der Reaktion γp → K + π + Σ− — •Inez Schulday für die
SAPHIR-Kollaboration — Nussallee 12, 53115 Bonn
Zur Analyse der Reaktion γp → K + π + Σ− sind Daten ausgewertet worden,
die mit dem 4π-SAPHIR-Detektor am Elektronen-Stretcher-Ring
ELSA aufgenommen wurden. Totale und differentielle Wirkungsquerschnitte
sind für den Energiebereich von der Schwelle bis 2.6 GeV bestimmt
worden.
HK 12.28 Tue 10:30 Foyer Chemie
Messung des Differentiellen Wirkungsquerschnitts der Reaktion
γp → pη mit η → 2γ bei Photonenenergien von 0.7 GeV bis
1.3 GeV mit dem CB-ELSA Detektor — •Imrich Fabry für die
CB-ELSA-Kollaboration — ISKP, Universität Bonn
Nach nahezu einem Jahrzehnt erfolgreicher Datennnahme am
CERN wurde der Crystal Barrel Detektor nach Bonn gebracht, wo
am Elektronen-Stretcher-Ring ELSA des Physikalischen Instituts der
Universität Bonn die erste Serie von Experimenten bei ELSA-Energien
bis zu 3.2 GeV durchgeführt worden ist.
Im Schwellenbereich wird die Reaktion dominiert durch die Produktion
der N(1535)S11 Nukleon-Resonanz. Diese Resonanz spielt
eine grosse Rolle in der Baryonenspektroskopie. Dieser Bereich
ist mit übereinstimmenden Ergebnissen durch frühere Experimente
(TAPS,GRAAL,PHOENICS) gut vermessen. Oberhalb von 1 GeV
existieren jedoch nur wenige Datenpunkte. Messungen bis 1.1 GeV
wurden von GRAAL und PHOENICSdurchgeführt, mit sich teilweise
widersprechenden Resultaten. Unsere Daten, die bis 2.8 GeV Photonenenergie
reichen, können zur Klärung der Situation beitragen. Eine
erste Analyse eines Teildatensatz bei einer Photonenenergie von bis
zu 1.4 GeV mit neuen, vorläufigen Ergebnissen zum Differentiellen
Wirkungsquerschnitt werden vorgestellt.
Gefördert durch die DFG.
HK 12.29 Tue 10:30 Foyer Chemie
η photoproduction cross section in η → 2γ and η → 3π 0 decays
with the CB-ELSA experiment at ELSA — •Michael Fuchs for
the CB-ELSA collaboration — ISKP, Universität Bonn
Data on η photoproduction off protons were taken by the CB-ELSA
experiment at the electron stretcher accelerator (ELSA) at Bonn. The
crystal barrel detector is a nearly 4π photon calorimeter and is – in
combination with an inner scintillating fibre trigger detector – an ideal
instrument to investigate multiphoton final states.
A topic of the experiment is the η and η’ photoproduction, especially
the production via baryon resonances. Differential cross sections for η
decaying into 3π 0 and into 2γ will be presented. The photon energy
range up to 2.8 GeV extends the one of previous experiments by a factor
of 2.
Supported by the DFG.