Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Tuesday
bution describes the probability to find a transversely polarized quark
in a transversely polarized nucleon. The unpolarized quark density q(x),
the longitudinally polarized quark density ∆q(x) and the transversity
distribution δq(x) together provide a complete description of the quark
and spin density distributions in leading order (twist-2).
For semi-inclusively produced π + and π 0 on a hydrogen target a significant
moment of sin φ is observed in the azimuthal distribution. For π −
the sin φ moment is found to be small. Since 1998 HERMES is taking
data with a polarized deuteron target.
An investigation of the flavour dependence of the transversity distribution
δq(x) will be possible with the measurement of single-spin asymmetries
for different hadrons (π + , π 0 , π − and K + ) and different target
nucleons.
This project is supported by the German BMBF.
HK 12.14 Tue 10:30 Foyer Chemie
Measurement of inclusive K-meson production in B-meson decays
using the BABAR detector — •Stefan Christ for the
BABAR collaboration — AG Elementarteilchenphysik, Universitätsplatz
3, 18051 Rostock
A method to measure the K-meson spectrum from B 0 , ¯ B 0 , B + and
B − decays at the BABAR detector is presented. The BABAR detector is
operated at the PEP-II asymmetric B-meson factory at SLAC. B-mesons
are produced in pairs from Υ(4S) decays with opposite b-quark flavour.
Fully reconstructing one B-meson that decayed into a flavour tagging
channel provides information about the b-quark flavour of this second
B-meson. All particles not used for the reconstruction have to originate
from the second B-meson. By identifying these particles the K-meson
spectrum can be measured for each flavour individually. The analysis
method is presented. The performance of the particle identification is
determined without Monte Carlo simulation.
HK 12.15 Tue 10:30 Foyer Chemie
Measurement of Inclusive η Production in e + e − -Annihilation
Reactions with the BABAR Experiment — •Denis Altenburg
for the BABAR collaboration — TU Dresden, Institut fuer Kern- und
Teilchenphysik, 01062 Dresden
The η momentum spectra and multiplicities in multihadronic events
from e + e − -annihilation reactions are measured using 14.3 fb −1 on the
Υ(4S) resonance ( √ s ≈ 10.58 GeV) and 2.6 fb −1 off resonance data
( √ s ≈ 10.54 GeV) collected with the BABAR detector. The η mesons
are reconstructed using the decay mode η → γγ. The inclusive branching
ratio of B mesons to η mesons B(B →ηX ) has been determined and has
been found to be in reasonable agreement to the corresponding CLEO
result.
HK 12.16 Tue 10:30 Foyer Chemie
Search for the Decay D ∗ s → Dsπ 0 and Measurement of the Partial
Widths Ratio Γ(D ∗ s → Dsπ 0 )/Γ(D ∗ s → Dsγ) with BABAR —
•Martin Dickopp for the BABAR collaboration — Inst. f. Kern- und
Teilchenphysik, TU Dresden, 01062 Dresden
The search for the isospin violating decay D ∗ s → Dsπ 0 in data accumulated
with the BABAR detector located at the asymmetric e + e −
storage facility PEP-II at SLAC is presented. Furthermore, the partial
widths ratio Γ(D ∗ s → Dsπ 0 )/Γ(D ∗ s → Dsγ) has been measured. The
result improves the precision of a measurement by CLEO in 1995.
HK 12.17 Tue 10:30 Foyer Chemie
Search for Eta-nucleus bound state at COSY, Juelich — B. Roy,
H. Machner, •B. Roy, andH. Machner for the GEM collaboration
and the GEM collaboration — Institut für Kernphysik, Forschungszentrum
Jülich, Jülich, Germany
In contrast to the π -nucleon interaction, the η-nucleon interaction
is strong and attractive at low energies ( S-wave ). This provides an
interesting possibility of the existence of the eta-nucleus bound states,
and their production in near threshold η production in proton nucleus
collisions. We plan to produce these η-nuclei in p+ A ZX → 3 He+ A−2
Z−1Yη
or p+ A Z
X → d+A−1
Z Xη reactions by choosing the “magic momentum”of
the proton-beam and the detection angle of 3 He/d such that the η is
produced with very small momentum. In order to detect the η -mesic
nucleus events in the presence of large background, it would be necessary
to demand a triple coincidence of 3 He and the η -mesic nucleus decay
particles, namely, protons and pions. In order to tag the η -mesic nucleus
through its decay products, a large acceptance plastic scintillator
detector “ENSTAR” is being built in Mumbai, India. The detector fab-
rication is at an advanced stage at BARC, Mumbai and will be shipped
to Jülich immediately after the completion of the construction work.
HK 12.18 Tue 10:30 Foyer Chemie
Search for a quasi-bound 3 Heη state at the COSY-TOF spectrometer
— •A. Gillitzer for the COSY-TOF collaboration — IKP,
Forschungszentrum Jülich
The peculiar behavior of the pd → 3 Heη cross section close to threshold
has been interpreted as being the result of a quasi-bound state of the
3 Heη system just below the threshold. We will study this longstanding
question in a formation experiment at the COSY-TOF spectrometer, by
measuring the excitation function of the reaction pd → pppπ − in the
bound region of the 3 Heη system. This is a sensitive observable because
the decay of a quasi-bound 3 Heη state is expected to be dominated by
the ηN → πN channel with two spectator nucleons, a final state having
a characteristic kinematical topology. The COSY-TOF spectrometer including
the forward calorimeter is particularly well-suited for the study
the of the pppπ − final state, i.e. the absorption of the η mesononthe
neutron in 3 He, since the TOF spectrometer has both large acceptance
for the pπ − pair and good particle identification for the pp spectator pair.
The outline of the experiment will be presented, including a discussion
of expected background reactions.
HK 12.19 Tue 10:30 Foyer Chemie
Study of η production on light nuclei — M. Ulicny 1 , H. Machner
2 , •M. Ulicny 1 ,andH. Machner 2 for the GEM collaboration and
the GEM collaboration — 1 University of P. J. ˇ Safárik, Koˇsice, Slovakia
— 2 Institut für Kernphysik, Forschungszentrum Jülich, Jülich, Germany
The production of η-mesons on light nuclei in proton induced reactions
is of interest, because of the high momenta transferred in the reaction,
considerably larger than in pion production. Such high momenta can not
be transferred in a NN-interaction This makes the p + 6 Li → 7 Be + η
reaction especially interesting. We have started to study this reaction
near the kinematical threshold. A proton beam of 1297 MeV/c from the
Cosy accelerator has been used to test the experimental setup. For the
detection of the recoiling nuclei, the magnetic spectrograph BIG KARL
operates as a full solid angle detector. A new introduced detection system
in the focal plane area being completely in vacuum ensures high
kinematical resolution of the heavy recoil. Results of the test run as well
as further detector improvements are discussed.
HK 12.20 Tue 10:30 Foyer Chemie
Deeply bound pionic states in Sn isotopes — •A. Gillitzer 1 , M.
Fujita 2 , H. Geissel 3 , H. Gilg 4 , R.S. Hayano 5 , S. Hirenzaki 2 , K.
Itahashi 6 , M. Iwasaki 6 , P. Kienle 4 , L. Maier 4 , M. Matos 3 , G.
Münzenberg 3 , T. Ohtsubo 7 , M. Sato 6 , M. Shindo 5 , K. Suzuki 5 ,
T. Suzuki 5 , H. Weick 3 , M. Winkler 3 , T. Yamazaki 8 , and T.
Yoneyama 6 — 1 IKP, Forschungszentrum Jülich — 2 Nara Women’s
University — 3 GSI Darmstadt — 4 Technische Universität München —
5 University of Tokyo — 6 Tokyo Institute of Technology — 7 Niigata University
— 8 RI Beam Science Lab., RIKEN
The comparative measurement of binding energy and width of deeply
bound pionic states in nuclei with different N/Z ratio allows to separately
determine the isoscalar and the isovector part of the pion-nucleus potential.
For this purpose the population of deeply bound pionic states in Sn
isotopes was studied in a recent experiment at the GSI Fragmentseparator
(FRS), using the (d, 3 He) reaction from 112,116,120,124 Sn targets. The
incident d beam kinetic energy was chosen to be 500 MeV in order to allow
the formation of substitutional pionic 1s states coupled to 3s1/2 neutron
hole states in recoilfree kinematics. Prominent peaks in the excitation
energy spectrum corresponding to the pionic 1s state were observed in
the irradiation of 116,120,124 Sn. First results of the data analysis will be
presented.
HK 12.21 Tue 10:30 Foyer Chemie
Luminosity determination at COSY-11 using the pd elastic scattering
— •S .Steltenkampfor the COSY-11 collaboration — Institut
für Kernphysik, Universität Münster, Germany
Measurements on the near-threshold η and η ′ meson production in
the reaction channel pd → 3 HeX have been performed at the internal
beam experiment COSY-11 [1,2]. To extract total and differential cross
sections, the proton-deuteron elastic scattering has been measured simultaneously
as reference reaction for normalization purposes. Close to
the η and η ′ meson production thresholds (pthr.,η = 1.570 GeV/c, pthr.,η ′
= 2.434 GeV/c) the COSY-11 facility allows for an identification and