2,137 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
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
Phylogeography of Japanese encephalitis virus:genotype is associated with climate
The circulation of vector-borne zoonotic viruses is largely determined by the overlap in the geographical distributions of virus-competent vectors and reservoir hosts. What is less clear are the factors influencing the distribution of virus-specific lineages. Japanese encephalitis virus (JEV) is the most important etiologic agent of epidemic encephalitis worldwide, and is primarily maintained between vertebrate reservoir hosts (avian and swine) and culicine mosquitoes. There are five genotypes of JEV: GI-V. In recent years, GI has displaced GIII as the dominant JEV genotype and GV has re-emerged after almost 60 years of undetected virus circulation. JEV is found throughout most of Asia, extending from maritime Siberia in the north to Australia in the south, and as far as Pakistan to the west and Saipan to the east. Transmission of JEV in temperate zones is epidemic with the majority of cases occurring in summer months, while transmission in tropical zones is endemic and occurs year-round at lower rates. To test the hypothesis that viruses circulating in these two geographical zones are genetically distinct, we applied Bayesian phylogeographic, categorical data analysis and phylogeny-trait association test techniques to the largest JEV dataset compiled to date, representing the envelope (E) gene of 487 isolates collected from 12 countries over 75 years. We demonstrated that GIII and the recently emerged GI-b are temperate genotypes likely maintained year-round in northern latitudes, while GI-a and GII are tropical genotypes likely maintained primarily through mosquito-avian and mosquito-swine transmission cycles. This study represents a new paradigm directly linking viral molecular evolution and climate
Proposed Search for Mixing in Polarization Phenomena
The and meson mass difference induces the mixing of the
and resonances, the amplitude of which, between the
and thresholds, is large in magnitude, of the order of , and possesses the
phase sharply varying by about 90. We suggest performing the polarized
target experiments on the reaction at high energy in
which the fact of the existence of mixing can be
unambiguously and very easily established through the presence of a strong jump
in the azimuthal asymmetry of the wave production cross section
near the thresholds. The presented estimates of the polarization
effect to be expected in experiment are to a great extent model independent.Comment: RevTeX, 9 pages, 1 figure. A number of typographical and grammatical
errors correcte
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
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