Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Wednesday
of so-called eta-mesic nuclei into account. These quasi bound states of η
and nucleus might be responsible for the near threshold behaviour of the
cross section.
In another experiment, the meson photoproduction off carbon was
studied. This experiment offers the possibility to investigate in-medium
modifications of the ω meson. On the proton, the ω (mω=782 MeV) is
out of reach of the MAMI energy regime. But, assuming a modification
of the omega mass and width in the carbon nucleus, the cross section
for incident photon energies up to 882 MeV becomes measurable. First
results are shown and compared to theoretical calculations [2].
[1] N. V. Shevchenko et.al., nucl-th/0108031
[2] W. Cassing, private communications
HK 32.2 Wed 14:30 D
Static Magnetic Moment of the ∆ + (1232) — •Martin Kotulla
for the TAPS/A2 collaboration — II. Physikalisches Institut, Heinrich-
Buff-Ring 16, 35392 Giessen
Static magnetic moments of baryons are important properties which
provide a crucial test for hadron structure calculations. SU(3) e.g., predicts
µ∆ = Q(∆)µp for the ∆ isobars. Information on µ ∆ + can be obtained
from the observation of a γ transition within the ∆ resonance.
Therefore, the reaction γ p → π ◦ γ ′ p wasmeasuredwiththeBaF2
calorimeter TAPSat the Mainz Microtron accelerator facility. The extraction
of µ ∆ +, however, requires the application of a reaction model.
The experimental results will be presented and the feasibility to extract
µ ∆ + based on theoretical models [1],[2] will be discussed.
[1] D. Drechsel, M. Vanderhaeghen, Phys.Rev.C64:065202,2001
[2] A.I. Machavariani, A. Faessler, to be submitted
HK 32.3 Wed 14:45 D
Photoproduction of pion pairs from nuclei — •Silke Janssen for
the TAPS- und A2 collaboration — II. Physikalisches Institut, Heinrich-
Buff-Ring 16, 35392 Giessen
The photoproduction of pion pairs from nuclei has been studied in the
range of incident photon energies from 400-460 MeV. The experiments
were performed with the tagged photon beam at the MAMI electron accelerator
facility using the photon spectrometer TAPSfor the detection
of neutral and charged pion pairs. The invariant mass distribution of the
two pions shows a different behaviour as a function of the target mass
HK33 Heavy Ions IV
depending on the isospin of the pion pair. For the π 0 π 0 (I=0) channel a
shift in the invariant mass distribution towards the 2π - threshold is observed
for increasing nuclear mass number while no change in the shape
of the invariant mass distribution is found for the π 0 π ± (I=1) channel.
This observation can not be explained by final state interaction but is
consistent with theoretical predictions for a partial restoration of chiral
symmetry at normal nuclear matter density.
[1] R.Rapp et al., Phys.Rev.C 59(99)1237
[2] M.Lutz et al., NPA 542(92)521
[3] T.Hatsuda et al., Phys.Rev.Lett. 82(99)2840
HK 32.4 Wed 15:00 D
Investigation of the 3He(e, e ′ pn)p reaction at MAMI — •P.J.
Barneo — NIKHEF, Amsterdam, in collaboration with the Universities
of Mainz, Tübingen and Glasgow.
The 3He(e, e ′ pn)p reaction has been studied in the spectrometer-hall of
the A1-collaboration at MAMI (Mainz). Data were taken at an energy
transfer of 220 MeV and three-momentum transfer of 375 MeV/c.
The reaction cross section is sensitive to nucleon-nucleon correlations
in the three-nucleon system and the contributions of two-body mechanisms,
i.e. intermediate ∆-excitation and meson-exchange currents.
The data analysis will be discussed and preliminary experimental results
will be compared to existing data for the complementary reaction
3 ′ He(e, e pp)n, measured at AmPS(Amsterdam), and to continuum Faddeev
calculations of the Bochum group, performed with realistic NN interactions.
HK 32.5 Wed 15:15 D
Analyse der Photoproduktion der Vektormesonen ω und Φ—
•Jens Barth for the SAPHIR collaboration — Physikalisches Institut,
Nussallee 12, 53115 Bonn
Zur Analyse der Photoproduktion der Vektormesonen ω und Φ wurden
die beiden Reaktionen γp → pω → pπ + π−π 0 und γp → pΦ →
pK + K− aus den Daten des SAPHIR-Detektors am Elektronen-Stretcher-
Ring ELSA untersucht. Es sind totale und differentielle Wirkungsquerschnitte,
sowie Zerfallswinkelverteilungen im Gottfried-Jackson- und im
Helizitätssystem bei Photonenergien von der Reaktionsschwelle bis zu 2.6
GeV bestimmt worden.
Time: Wednesday 14:00–15:30 Room: E
HK 33.1 Wed 14:00 E
Strangeness production in p+p interactions and collisions of
light ions at Elab=158 AGeV/c — •Claudia Höhne, Volker
Friese, and Falk Pühlhofer for the NA49 collaboration — Fachbereich
Physik, Philipps-Universität Marburg*
New data of the CERN experiment NA49 allow a systematic study of
strangeness production varying not only the beam energy and the centrality
of the interaction but also the size of the colliding system using
protons and light ions as reaction partners. Of particular interest are
small systems in which no phase transition into the QGP is expected
and the role of multiple nucleon-nucleon collisions can be investigated.
According to UrQMD calculations rescattering of newly created particles
should play a minor role in such reactions.
The production of kaons and φ-mesons in p+p, C+C and Si+Si collisions
was measured at the CERN SPS with a beam energy of 158 AGeV.
Phase space distributions of these particles as well as for pions were extracted.
Strangeness enhancement with respect to p+p collisions is found
already in semicentral C+C interactions; it increases further in Si+Si reactions.
*supported by BMBF
HK 33.2 Wed 14:15 E
Correlation Study of Strange Baryons in Pb+Pb Reactions
at 158 AGeV ∗ — •C. Blume 1 , L. Betev 2 , A. Billmeier 2 , R.
Bramm 2 , P. Buncic 2 , P. Dinkelaker 2 , M. Ga´zdzicki 2 , T. Kollegger
2 , I. Kraus 1 , C. Markert 1 , A. Mischke 1 , R. Renfordt 2 ,
A. Sandoval 1 , R. Stock 2 , H. Ströbele 2 , D. Vranić 1 , A. Wetzler
2 ,andJ. Zaranek 2 — 1 GSI Darmstadt — 2 IKF Frankfurt
The large number of strange baryons produced in ultrarelativistic
heavy ion collisions makes the study of their correlations feasible. Of
special interest is the measurement of the correlation function of Λ pairs,
since it can shed light on the nature of their mutual interaction. Since, on
the other side, the interaction of Λs with protons is rather well known,
the pΛ correlation function can be used to extract information on the
spacial extent of the emitting source. Compared to the analysis of pp
correlations this method has the advantage of avoiding the influence of
the Coulomb interaction.
We will present preliminary results on ΛΛ and pΛ correlations in central
Pb+Pb reactions at 158 AGeV. The measurements will be compared to
theoretical caluclations and their implications will be discussed.
∗ Supported by BMBF und GSI
HK 33.3 Wed 14:30 E
Energy Dependence of Kaon and Pion Production in Central
Pb+Pb Collisions — •Roland Bramm 1 , L. Betev 2 , C. Blume 3 ,
P. Buncic 2 , P. Dinkelaker 2 , M. Gazdzicki 2 , T. Kollegger 2 , I.
Kraus 3 , A. Mischke 3 , R. Renfordt 2 , A. Sandoval 3 , R. Stock 2 ,
H. Ströbele 2 , D. Vranic 3 , A. Wetzler 2 ,andJ. Zaranek 2 for the
NA49 collaboration — 1 CERN, Genève — 2 IKF, Universität Frankfurt
— 3 GSI, Darmstadt
The experiment NA49 investigates pion and kaon production in central
Pb+Pb collisions at CERN-SPS energies (20-158 AGeV). The pion
spectra are obtained from the analysis of distributions of all negatively
charged hadrons. The kaon spectra are acquired using the particle identification
based on the analysis of the specific energy loss (dE/dx) and in
the midrapidity region via the analysis of the time of flight data (ToF).
Rapidity and transverse momentum spectra at 40, 80 and 158 AGeV
will be presented. A transition from a ”pion suppression” to a ”pion
enhancement” compared to the p+p data at a collision energy around
40 AGeV is observed. The K+ to pi+ ratio shows a non-monotonic be-