79 research outputs found
Two-pion production in deuteron-deuteron collisions at low energies
The cross section for the dd -> 4He pi pi reaction is estimated near
threshold in a two-step model where a pion created in a first interaction
produces a second pion in a subsequent interaction. This approach, which
describes well the rates of 2pi and eta production in the pd -> 3He pi pi and
dd -> 4He eta reactions, leads to predictions that are much too low compared to
experiment. Alternatives to this and the double-Delta model will have to be
sought to explain these data.Comment: 5 pages with 4 postscript figure
The pd --> ^3He eta pi0 reaction at T_p = 1450 MeV
The cross section for the pd --> ^3He eta pi0 reaction has been measured at a
beam energy of 1450 MeV using the WASA detector at the CELSIUS storage ring and
detecting one ^3He and four photons from the decays of the two photons. The
data indicate that the production mechanism involves the formation of the
Delta(1232) isobar. Although the beam energy does not allow the full peak of
this resonance to be seen, the invariant masses of all three pairs of final
state particles are well reproduced by a phase space Monte Carlo simulation
weighted with the p-wave factor of the square of the pi^0 momentum in the
^3Hepi^0 system.Comment: 10 pages, 5 figure
Polarisation of the omega meson in the pd-->3He+omega reaction at 1360 and 1450 MeV
The tensor polarisation of omega mesons produced in the pd-->3He+omega
reaction has been studied at two energies near threshold. The 3He nuclei were
detected in coincidence with the pi0pi+pi- or pi0gamma decay products of the
omega. In contrast to the case of phi meson production, the omega mesons are
found to be unpolarised. This brings into question the applicability of the
Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low
energy hadronic reactions.Comment: 11 pages, 4 figure
Production of eta and 3pi mesons in the pd->3HeX reaction at 1360 and 1450 MeV
The cross sections of the pd -> 3He eta, pd -> 3He pi0 pi0 pi0 and pd -> 3He
pi+ pi- pi0 reactions have been measured at beam kinetic energies T_p= 1360 MeV
and T_p= 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the
differential cross section dsigma/dOmega of the eta meson in the pd -> 3He eta
reaction shows a strong forward-backward asymmetry in the CMS. The ratio
between the pd -> 3He pi+ pi- pi0 and the pd -> 3He pi0 pi0 pi0 cross sections
has been analysed in terms of isospin amplitudes. The reconstructed invariant
mass distributions of the pi-pi, 3He-pi and 3He-2pi systems provide hints on
the role of nucleon resonances in the 3pi production process.Comment: Shorter version accepted to EPJA 10 pages 14 figure
Tests of the fundamental symmetries in eta meson decays
Patterns of chiral symmetry violation and tests of the conservation of the
fundamental C, P and CP symmetries are key physics issues in studies of the
pi0, eta and eta' meson decays. These tests include searches for rare or
forbidden decays and searches for asymmetries among the decay products in the
not-so-rare decays. Some examples for the rare decays are eta-->2pi, eta-->4pi0
(CP tests), decays into an odd number of photons (e.g., eta-->3g) and the decay
eta-->pi0e+e- (C tests). The experimental studies of the pi0, eta and eta'
meson decays are carried out at four European accelerator research facilities:
KLOE/KLOE-2 at DAFNE (Frascati), Crystal Ball at MAMI (Mainz), WASA at COSY
(J\"ulich), Crystal Barrel at ELSA (Bonn).Comment: 9 pages, 2 figures, proceedings of Symposium on Prospects in the
Physics of Discrete Symmetries, DISCRETE 2010, 6 - 11 December, Rome; v2:
added reference
Performance of HPGe Detectors in High Magnetic Fields
A new generation of high-resolution hypernuclear gamma$-spectroscopy
experiments with high-purity germanium detectors (HPGe) are presently designed
at the FINUDA spectrometer at DAPhiNE, the Frascati phi-factory, and at PANDA,
the antiproton proton hadron spectrometer at the future FAIR facility. Both,
the FINUDA and PANDA spectrometers are built around the target region covering
a large solid angle. To maximise the detection efficiency the HPGe detectors
have to be located near the target, and therefore they have to be operated in
strong magnetic fields B ~ 1 T. The performance of HPGe detectors in such an
environment has not been well investigated so far. In the present work VEGA and
EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN
magnet at GSI. No significant degradation of the energy resolution was found,
and a change in the rise time distribution of the pulses from preamplifiers was
observed. A correlation between rise time and pulse height was observed and is
used to correct the measured energy, recovering the energy resolution almost
completely. Moreover, no problems in the electronics due to the magnetic field
were observed.Comment: submitted to Nucl. Instrum. Meth. Phys. Res. A, LaTeX, 19 pages, 9
figure
Double-Pionic Fusion of Nuclear Systems and the ABCEffect -- Aproaching a Puzzle by Exclusive and Kinematically Complete Measurements
The ABC effect - a puzzling low-mass enhancement in the invariant
mass spectrum - is well-known from inclusive measurements of two-pion
production in nuclear fusion reactions. Here we report on first exclusive and
kinematically complete measurements of the most basic double pionic fusion
reaction at 1.03 and 1.35 GeV. The measurements, which
have been carried out at CELSIUS-WASA, reveal the ABC effect to be a
channel phenomenon associated with both a resonance-like
energy dependence in the integral cross section and the formation of a
system in the intermediate state. A corresponding simple
s-channel resonance ansatz provides a surprisingly good description of the
data
Measurement of the eta->pi+pi-e+e- decay branching ratio
The reaction pd->3He eta at threshold was used to provide a clean source of
eta mesons for decay studies with the WASA detector at CELSIUS. The branching
ratio of the decay eta->pi+pi-e+e- is measured to be (4.3+/-1.3+/-0.4)x10^-4.Comment: 10 pages,6 figures revised versio
Technical Design Report for the PANDA Solenoid and Dipole Spectrometer Magnets
This document is the Technical Design Report covering the two large
spectrometer magnets of the PANDA detector set-up. It shows the conceptual
design of the magnets and their anticipated performance. It precedes the tender
and procurement of the magnets and, hence, is subject to possible modifications
arising during this process.Comment: 10 pages, 14MB, accepted by FAIR STI in May 2009, editors: Inti
Lehmann (chair), Andrea Bersani, Yuri Lobanov, Jost Luehning, Jerzy Smyrski,
Technical Coordiantor: Lars Schmitt, Bernd Lewandowski (deputy),
Spokespersons: Ulrich Wiedner, Paola Gianotti (deputy
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