271 research outputs found
Measurement of the isospin-filtering dd -> 4He K+ K- reaction at Q=39 MeV
The total cross section for the dd -> 4He K+ K- reaction has been measured at
a beam momentum of 3.7 GeV/c, corresponding to an excess energy of 39 MeV,
which is the maximum possible at the Cooler Synchrotron COSY-J\"{u}lich. A
deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed
inside the storage ring, have been employed in this investigation. We find a
total cross section of sigma(tot) < 14 pb, which brings into question the
viability of investigating the dd -> 4He a0(980) reaction as a means of
studying isospin violation.Comment: Five pages with three eps figure
The Straw Tube Trackers of the PANDA Experiment
The PANDA experiment will be built at the FAIR facility at Darmstadt
(Germany) to perform accurate tests of the strong interaction through bar pp
and bar pA annihilation's studies. To track charged particles, two systems
consisting of a set of planar, closed-packed, self-supporting straw tube layers
are under construction. The PANDA straw tubes will have also unique
characteristics in term of material budget and performance. They consist of
very thin mylar-aluminized cathodes which are made self-supporting by means of
the operation gas-mixture over-pressure. This solution allows to reduce at
maximum the weight of the mechanical support frame and hence the detector
material budget. The PANDA straw tube central tracker will not only reconstruct
charged particle trajectories, but also will help in low momentum (< 1 GeV)
particle identification via dE/dx measurements. This is a quite new approach
that PANDA tracking group has first tested with detailed Monte Carlo
simulations, and then with experimental tests of detector prototypes. This
paper addresses the design issues of the PANDA straw tube trackers and the
performance obtained in prototype tests.Comment: 7 pages,16 figure
Comparison of nonequilibrium processes in p+Ni and p+Au collisions at GeV energies
The energy and angular dependence of double differential cross sections
d2sigma/dOmega dE were measured for p, d, t, 3,4,6He, 6,7,8Li, 7,9,10Be,
10,11B, and C produced in collisions of 1.2, 1.9, and 2.5 GeV protons with a Ni
target. The shape of the spectra and angular distributions does almost not
change whereas the absolute value of the cross sections increases by a factor
about 1.7 for all ejectiles in this beam energy range. It was found that energy
and angular dependencies of the cross sections cannot be reproduced by the
microscopic model of intranuclear cascade with coalescence of nucleons and the
statistical model for evaporation of particles from excited, equilibrated
residual nuclei. The inclusion of nonequilibrium processes, described by a
phenomenological model of the emission from fast and hot moving sources,
resulting from break-up of the target nucleus by impinging proton, leads to
very good reproduction of data. Cross sections of these processes are quite
large, exhausting approximately half of the total production cross sections.
Due to good reproduction of energy and angular dependencies of d2sigma/dOmega
dE by model calculation it was possible to determine total production cross
sections for all studied ejectiles. Results obtained in this work point to the
analogous reaction mechanism for proton induced reactions on Ni target as that
observed previously for Au target in the same beam energy range.Comment: 11 pages, 10 figures
Dispersion management in nonlinear photonic crystal fibres with nanostructured core
The subwavelength structure of the core of a photonic crystal fibre can modify its dispersion characteristic and significantly shift the zero dispersion wavelength. The dispersion properties of photonic crystal fibres with core structures made of a 2D lattice of subwavelength air holes and various glass inclusions are studied. We show that a modification of the core structure can give flat dispersion over a range of over 300 nm and can shift the zero dispersion wavelength over 700 nm while the core diameter and photonic cladding remain unchanged. The developed photonic crystal fibre with nanorod core has successfully demonstrated supercontinuum generation in NIR
Variation of nonequilibrium processes in p+Ni system with beam energy
The energy and angular dependence of double differential cross sections
dsigma/dOmega dE were measured for p, d, t, 3,4He, 6,7Li, 7,9Be, and 10,11B
produced in collisions of 0.175 GeV protons with Ni target. The analysis of
measured dfferential cross sections allowed to extract total production cross
sections for ejectiles listed above. The shape of the spectra and angular
distributions indicate the presence of other nonequilibrium processes besides
the emission of nucleons from the intranuclear cascade, and besides the
evaporation of various particles from remnants of intranuclear cascade. These
nonequilibrium processes consist of coalescence of nucleons into light charged
particles during the intranuclear cascade, of the fireball emission which
contributes to the cross sections of protons and deuterons, and of the break-up
of the target nucleus which leads to the emission of intermediate mass
fragments. All such processes were found earlier at beam energies 1.2, 1.9, and
2.5 GeV for Ni as well as for Au targets, however, significant differences in
properties of these processes at high and low beam energy are observed in the
present study.Comment: 10 pages, 9 figure
Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility
The search for 4He-eta bound states was performed with the WASA-at-COSY
facility via the measurement of the excitation function for the dd->3He n pi0
and dd->3He p pi- processes. The beam momentum was varied continuously between
2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He
eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined
based on the dd->3He n reaction and quasi-free proton-proton scattering via
dd->pp n_spectator n_spectator reactions. The excitation functions determined
independently for the measured reactions do not reveal a structure which could
be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the
total cross sections for the bound state production and decay in
dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes
were determined taking into account the isospin relation between both the
channels considered. The results of the analysis depend on the assumptions of
the N* momentum distribution in the anticipated mesic-4He. Assuming as in the
previous works, that this is identical with the distribution of nucleons bound
with 20 MeV in 4He, we determined that (for the mesic bound state width in the
range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about
3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on
the recent theoretical findings of the N*(1535) momentum distribution in the
N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector
acceptance decreases and hence the corresponding upper limits are 5 nb and 10
nb for npi0 and ppi- channels respectively.Comment: This article will be submitted to JHE
Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY
Charge symmetry breaking (CSB) observables are a suitable experimental tool
to examine effects induced by quark masses on the nuclear level. Previous high
precision data from TRIUMF and IUCF are currently used to develop a consistent
description of CSB within the framework of chiral perturbation theory. In this
work the experimental studies on the reaction dd->4He{\pi}0 have been extended
towards higher excess energies in order to provide information on the
contribution of p-waves in the final state. For this, an exclusive measurement
has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY
facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +-
13(sys) +- 8(ext)) pb and first data on the differential cross section are
consistent with s-wave pion production.Comment: 14 pages, 5 figure
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