562 research outputs found
Near-threshold production of a0(980) mesons in the reaction pp -> d K^+ \bar{K}^0
Using an effective Lagrangian approach as well as the Quark-Gluon Strings
Model we analyze near-threshold production of a0(980)-mesons in the reaction NN
-> d K \bar{K} as well as the background of non-resonant K\bar{K}-pair
production. We argue that the reaction pp -> d K^+ \bar{K}^0 at an energy
release Q<=100 MeV is dominated by the intermediate production of the
a0(980)-resonance. At larger energies the non-resonant K^+\bar{K}^0-pair
production - where the kaons are produced in a relative P-wave - becomes
important. Then effects of final-state interactions are evaluated in a
unitarized scattering-length approach and found to be in the order of a 20%
suppression close to threshold. Thus in present experiments at the Cooler
Synchrotron COSY-J\"ulich for Q<=107 MeV the a_0^+ signal can reliably be
separated from the non-resonant K^+\bar{K^0} background.Comment: 14 pages, 12 figures, submitted to EPJ
Production of -mesons in the reactions and at GeV energies
We investigate the reactions and near
threshold and at medium energies. An effective Lagragian approach and the Regge
pole model are applied to analyze different contributions to the cross section
of the reaction . These results are used to calculate the
differential and total cross sections of the reaction within
the framework of the two-step model in which two nucleons produce an
-meson via -meson exchange and fuse to a deuteron. The necessity of
new measurements on production and branching fractions (of its decay to
the and channels) is emphasized for clarifying the
structure. Detailed predictions for the reaction are presented
for the energy regime of the proton synchrotron COSY-J\"ulich.Comment: 9 pages, including 6 eps figure
Method to make a single-step etch mask for 3D monolithic nanostructures
Current nanostructure fabrication by etching is usually limited to planar
structures as they are defined by a planar mask. The realisation of
three-dimensional (3D) nanostructures by etching requires technologies beyond
planar masks. We present a method to fabricate a 3D mask that allows to etch
three-dimensional monolithic nanostructures by using only CMOS-compatible
processes. The mask is written in a hard-mask layer that is deposited on two
adjacent inclined surfaces of a Si wafer. By projecting in single step two
different 2D patterns within one 3D mask on the two inclined surfaces, the
mutual alignment between the patterns is ensured. Thereby after the mask
pattern is defined, the etching of deep pores in two oblique directions yields
a three-dimensional structure in Si. As a proof of concept we demonstrate 3D
mask fabrication for three-dimensional diamond-like photonic band gap crystals
in silicon. The fabricated crystals reveal a broad stop gap in optical
reflectivity measurements. We propose how 3D nanostructures with five different
Bravais lattices can be realised, namely cubic, tetragonal, orthorhombic,
monoclinic, and hexagonal, and demonstrate a mask for a 3D hexagonal crystal.
We also demonstrate the mask for a diamond-structure crystal with a 3D array of
cavities. In general, the 2D patterns for the different surfaces can be
completely independent and still be in perfect mutual alignment. Indeed, we
observe an alignment accuracy of better than 3.0 nm between the 2D mask
patterns on the inclined surfaces, which permits one to etch well-defined
monolithic 3D nanostructures.Comment: 18 pages, 10 figure
a0(980)-f0(980) mixing and isospin violation in the reactions pN -> d a0, pd -> 3He/3H a0 and dd -> 4He a0
It is demonstrated that f_0-a_0 mixing can lead to a comparatively large
isospin violation in the reactions pN -> da_0, pd -> ^3He/^3H a_0 and dd ->
^4He a_0 close to the corresponding production thresholds. The observation of
such mixing effects is possible, e.g., by measuring the forward-backward
asymmetry in the reaction pn -> d a_0^0 -> d eta pi^0.Comment: 14 pages, 5 figure
Polarization observables in high-energy deuteron photodisintegration within the Quark-Gluon Strings Model
Deuteron two-body photodisintegration is analysed within the framework of the
Quark-Gluon Strings Model. The model describes fairly well the recent
experimental data from TJNAF in the few GeV region. Angular distributions at
different -energies are presented and the effect of a forward-backward
asymmetry is discussed. New results from the QGSM for polarization observables
from 1.5 -- 6 GeV are presented and compared with the available data.Comment: 3 pages, LaTeX, 4 postscript figures; contribution to QNP2002,
Juelich, June 10-14, 200
Deuteron photodisintegration within the Quark-Gluon Strings Model and QCD motivated nonlinear Regge trajectories
We investigate deuteron two-body photodisintegration within the framework of
the Quark-Gluon Strings Model with nonlinear baryon Regge trajectories. Special
attention is paid to the use of QCD motivated Regge trajectories of the
logarithmic and square-root form which have been suggested recently by
Brisudov\'{a}, Burakovsky and Goldman. We find that the recent experimental
data from TJNAF in the few GeV region can reasonably be described by the model.
Angular distributions at different -energies are presented and the
effect of a forward-backward asymmetry is discussed. Predictions for the energy
dependence of at higher energies and different are
presented, too.Comment: 21 pages, LaTeX, including 6 postscript figures; submitted to Phys.
Rev.
K^- ^3He and K^+K^- interactions in the pd -> ^3He K^+K^- reaction
We investigate the K^- ^3He and K^+ K^- interactions in the reaction pd ->
^3He K^+ K^- near threshold and compare our model calculations with data from
the MOMO experiment at COSY-Juelich. A large attractive effective K^- p
amplitude would give a significant K^- ^3He final-state interaction effect
which is not supported by the experimental data. We also estimate upper limits
for the a_0(980) and f_0(980) contributions to the produced K^+ K^- pairs.Comment: 5 pages, 2 figures, accepted for publication in PR
Omega- and phi-meson production in p n -> d M reactions near threshold and OZI-rule violation
We investigate the reactions p n -> d omega and p n -> d phi close to the
corresponding thresholds. The S-wave amplitudes are calculated within the
framework of the two-step model which is described by a triangle graph with pi,
rho and omega mesons in the intermediate state. The cross sections of the
reactions p n -> d omega and p n -> d phi are predicted to be significantly
larger than the cross sections of the corresponding reactions p p -> p p omega
and p p -> p p phi at the same values of the c.m. excess energy Q. The ratio of
the yields of phi to omega is found to be (30 +/- 7) x 10^-3
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