Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Tuesday
tigated for several reaction systems studied at beam energies between 40
and 150 AMeV during the INDRA@GSI campaign. The observed dependence
of the source size on the impact parameter and on the collision
partners agree well with the expectations for the reaction geometry.
HK 13.4 Tue 10:30 Foyer Chemie
Pions in Spectator Fragmentation Induced by Relativistic 12 C
Projectiles — •Ketel Turzó for the ALADIN-INDRA collaboration
— GSI Darmstadt, Planckstr. 1, D-64291 Darmstadt
As part of the INDRA@GSI campaign in 1998/1999, fragmentation
in asymmetric systems like 12 C+ 197 Au and 12 C+ 112,124 Sn was studied
at bombarding energies ranging from 95 to 1800 AMeV. At angles
θlab ≥ 45 ◦ , particle detection and identification with high resolution was
achieved with the Si-Si-CsI(Tl) calibration telescopes of the INDRA multidetector
system, including the identification of charged pions.
Delta and pion production and absorption represent an efficient heating
mechanism in collisions at relativistic energies. The present data permit
the study of correlations between pion and fragment emissions, i.e. between
emissions reflecting properties of the primary heating phase of the
collision and of the subsequent decay of a highly equilibrated spectator
system. First results, indicating an anticorrelation between the multiplicities
of pions and intermediate-mass fragments for lower spectator
excitations, will be presented.
HK 13.5 Tue 10:30 Foyer Chemie
Particle Intensities at the GSI Secondary Beam Facility —
•M. Ardid 1 , J. Diaz 1 , A. Andronic 2 , A. Banu 2 , O. Busch 2 , M.
Gersabeck 2 ,andR.S. Simon 2 — 1 Institut de Física Corpuscular, Universitat
de València and Centro Superior de Investigaciones Científicas,
E-46071 València, Spain — 2 Gesellschaft für Schwerionenforschung, D-
64291 Darmstadt, Germany
Using protons and 12 Cand 14 N ions from the 18 Tm heavy–ion synchrotron
SIS, secondary beams of electrons and pions are produced and
delivered to the experimental areas in the SIS target hall. We discuss
the production mechanism in the pencil–like thick target rods and address
the transport performance of the beam lines as well as the impact
of diagnostic detectors for monitoring and precise momentum definition.
Mixed π − /e − beams with momenta between 0.5 and 2.0 GeV/c have been
extensively used for prototype tests of the ALICE Transition Radiation
Detector, while π + beams around 1 GeV/c with maximum intensity and
optimal π + /p ratio are required for physics runs at the HADESand Kaon
Spectrometer.
HK 13.6 Tue 10:30 Foyer Chemie
Λ - Production in C+C Reactions at 158 AGeV* — •I. Kraus 1 ,
L. Betev 2 , A. Billmeier 1 , C. Blume 1 , R. Bramm 2 , P. Buncic 2 , P.
Dinkelaker 2 , M. Ga´zdzicki 2 , T. Kollegger 2 , C. Markert 3 , R.
Renfordt 2 , A. Sandoval 1 , R. Stock 2 , H. Ströbele 2 , D. Vranić 1 ,
A. Wetzler 2 ,andJ. Zaranek 2 for the NA49 collaboration — 1 GSI,
Darmstadt — 2 Institut für Kernphysik, Frankfurt — 3 Yale, New Haven,
USA
The number of hyperons (Λ) per participating nucleon is higher in
A+A than in p+p collisions [1]. It is interesting to measure the detailed
behavior of hyperon production as a function of the system size in order
to determine the onset of this type of strangeness enhancement.
NA49 has taken data not only on Pb+Pb but also C+C collisions.
The results from the light C+C system are compared to earlier measurements
of Λ hyperons in central S+S (NA35), central Pb+Pb and p+p
interactions.
[1] A.Mischke et al. (NA49 Collab.), Proceedings of the 6th International
Conference on Strangeness in Quark Matter 2001
* Supported by GSI and BMBF
HK 13.7 Tue 10:30 Foyer Chemie
Production of φ → e + e − in central Pb+Pb collisions at
158AGeV ∗ — •Peter Dinkelaker 1 , L. Betev 1 , C. Blume 2 , R.
Bramm 1 , P. Buncic 1 , M. Ga´zdzicki 1 , T. Kollegger 1 , I. Kraus 2 ,
A. Mischke 2 , R. Renfordt 1 , A. Sandoval 2 , R. Stock 1 , H.
Ströebele 1 , D. Vranic 1 , A. Wetzler 1 ,andJ. Zaranek 1 for the
NA49 collaboration — 1 Institut für Kernphysik, Universität Frankfurt
— 2 Gesellschaft für Schwerionenforschung, Darmstadt
The first results on φ → e + e − production in central Pb+Pb collisions
at 158 AGeV are presented. They are based on the NA49 data (3 million
events) taken in the dedicated run in 2000. The obtained upper limit
estimate for the φ yield is compared with the results for the hadronic decay
channel φ → K + K − measured in NA49 and for the leptonic decay
channel φ → µ + µ − measured in NA50. A review of models concerning
φ production and possible differences between results obtained from
leptonic and hadronic decay channels is given.
∗ supported by BMBF and GSI
HK 13.8 Tue 10:30 Foyer Chemie
Calibration and charged particle distributions of the Forward-
TPCs in the STAR Experiment — •Jörn Putschke, Volker
Eckardt, Andreas Gärtner, Gaspare Lo Curto, Markus
Oldenburg, Patrizia Krok, Maria Mora, Andreas Schüttauf,
Norbert Schmitz, Janet Seyboth, Peter Seyboth, Frank
Simon, and Michael Vidal — Max-Planck-Institut für Physik,
Föhringer Ring 6, 80805 München
The two Forward-TPCs, designed and constructed at the Max-Planck-
Institut für Physik in Munich, expand the overall acceptance of the STAR
detector at the Relativistic Heavy Ion Collider (RHIC) to the pseudorapidity
region 2.5 < |η| < 4. Due to the high multiplicity of approximatly
500 charged particle in each Forward-TPC in a central Au+Au collisions
at √ sNN = 200 GeV, a radial drift configuration perpendicular to the
magnetic field was choosen to improve the two-track separation.
To calibrate the drift velocity and the � E × � B corrections in the nonuniform
radial drift field a laser calibration system was used. In contrast
to a standard configuration TPC a good measurement of the drift velocity
is essential to accurately determine the spatial positions of the hit
clusters and to precisely determine the momenta of the charged particles.
Preliminary results will be discussed on the charged particle distributions
and the baryon number flow as difference in the distributions of
positively and negatively charged particle as a function of η.
HK 13.9 Tue 10:30 Foyer Chemie
The role of three-body collisions in φ mesonproduction processes
near threshold in heavy-ion reactions — •H.W. Barz 1 ,
B. Kämpfer 1 , M. Zetenyi 2 ,andGy. Wolf 2 — 1 FZ Rossendorf,
D-01314 Dresden — 2 KFKI Budapest, H-1525 Budapest
The amplitude of subthreshold φ meson production is calculated using
dominant tree-level diagrams for three-body collision. It is shown that
the production can overwhelmingly be described by two consecutive twostep
processes, i.e. the cross section factorises in two sub-cross-sections
with an intermediate on-shell particle. As a consequence to desribe the
production of heavy mesons within transport models all intermediate
particles have to be included in the calculations. The effect is demonstrated
in calculating φ production in heavy-ion collisions at bombarding
energies around 2 GeV per nucleon as recently measured by the FOPI
collaboration. Including elementary ρ − N, ρ − ∆andπ − ρ collisions the
calculated production rates increase by about a factor of three compared
to earlier calculations which do not include these channels. Momentum
spectra of φ mesons and dilepton spectra which are accessible in future
HADESand FOPI experiments are given.
HK14 Poster Session: Instrumentation and Applications
Time: Tuesday 10:30–12:45 Room: Foyer Chemie
HK 14.1 Tue 10:30 Foyer Chemie
Quantitative analysis of lepton induced Cherenkov rings in
a CsI based RICH — •L. Fabbietti, T. Eberl, J. Friese, R.
Gernhäuser, J. Homolka, H.-J. Körner, M. Münch, B. Sailer,
and S. Winkler for the HADEScollaboration — Technische Universität
München, James-Franck-Strasse 1,D-85748 Garching
A Monte-Carlo based understanding of the lepton induced Cherenkov
ring recognition in the RICH detector is crucial for the whole lepton
identification in the HADESspectrometer.
A dedicated measurement was performed which allows to study the
response of the RICH detector to the photon signal. The results of these
studies were used to optimize the digitasation procedure for the RICH detector,
in order to achieve a good agreement between real and simulated
data for the heavy ion reaction environment.