2,037 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
Low-energy Compton scattering on the nucleon and sum rules
The Gerasimov-Drell-Hearn and Baldin-Lapidus sum rules are evaluated in the
dressed K-matrix model for photon-induced reactions on the nucleon. For the
first time the sum of the electric and magnetic polarisabilities
and the forward spin polarisability are explicitly calculated in two
alternative ways -- from the sum rules and from the low-energy expansion of the
real Compton scattering amplitude -- within the {\em same} framework. The two
methods yield compatible values for but differ somewhat for
. Consistency between the two ways of determining the
polarisabilities is a measure of the extent to which basic symmetries of the
model are obeyed.Comment: 9 pages, 4 figures, using REVTeX. More concise version, results
unchanged. To appear in 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
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
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
Density resummation of perturbation series in a pion gas to leading order in chiral perturbation theory
The mean field (MF) approximation for the pion matter, being equivalent to
the leading ChPT order, involves no dynamical loops and, if self-consistent,
produces finite renormalizations only. The weight factor of the Haar measure of
the pion fields, entering the path integral, generates an effective Lagrangian
which is generally singular in the continuum limit.
There exists one parameterization of the pion fields only, for which the weight
factor is equal to unity and , respectively. This
unique parameterization ensures selfconsistency of the MF approximation. We use
it to calculate thermal Green functions of the pion gas in the MF approximation
as a power series over the temperature. The Borel transforms of thermal
averages of a function of the pion
fields with respect to the scalar pion density are found to be
. The perturbation series over the scalar
pion density for basic characteristics of the pion matter such as the pion
propagator, the pion optical potential, the scalar quark condensate
, the in-medium pion decay constant , and the
equation of state of pion matter appear to be asymptotic ones. These series are
summed up using the contour-improved Borel resummation method. The quark scalar
condensate decreases smoothly until MeV. The temperature
is the maximum temperature admissible for thermalized non-linear
sigma model at zero pion chemical potentials. The estimate of is
above the chemical freeze-out temperature MeV at RHIC and above
the phase transition to two-flavor quark matter MeV,
predicted by lattice gauge theories.Comment: Replaced with revised and extended version. Results are compared to
lattice gauge theories. 16 pages REVTeX, 13 eps figure
New data on lichenicolous fungi of the Teteriv River Basin (Ukraine)
The data on 31 species of lichenicolous fungi (Abrothallus caerulescens, Arthonia phaeophysciae, Athelia arachnoidea, Cercidospora macrospora, Clypeococcum hypocenomycis, Cornutispora lichenicola, Erythricium aurantiacum, Heterocephalacria physciacearum, Intralichen christiansenii, Lichenochora obscuroides, Lichenoconium erodens, L. lecanorae, L. usneae, Lichenodiplis lecanorae, Lichenostigma cosmopolites, Lichenothelia convexa, L. scopularia, Marchandiomyces corallinus, Monodictys epilepraria, Muellerella pygmaea, M. erratica, Pronectria leptaleae, Pyrenochaeta xanthoriae, Sclerococcum sphaerale, Sphaerellothecium propinquellum, Stigmidium fuscatae, S. squamariae, S. xanthoparmeliarum, Taeniolella phaeophysciae, T. punctata, Xanthoriicola physciae) new to the Teteriv River Basin are provided. Further five species (Cercidospora crozalsiana, Lichenostigma epipolina, Lichenothelia tenuissima, Polysporina subfuscescens and Taeniolella beschiana) are new to Ukraine. Additional localities for all newly reported species are listed
Dynamics of diproton formation in the and reactions in the GeV region
Mechanisms for the production of diproton pairs, , in the
reaction are studied at proton beam energies 0.5 -- 2 GeV in
kinematics similar to those of backward elastic scattering. This reaction
provides valuable information on the short-range and interactions
that is complementary to that investigated in the well known and
processes. The reaction is related to the
subprocesses and using two different
one--pion--exchange (OPE) diagrams. Within both these models a reasonable
agreement could be obtained with the data below 1GeV. The similar energy
dependence of the and cross sections and the small
ratio of about 1.5% in the production of to deuteron final states
follow naturally within the OPE models.Comment: 10 pages, 7 figures, Late
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.
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