1,876 research outputs found
The Near-Threshold Production of Phi Mesons in pp Collisions
The pp->pp phi reaction has been studied at the Cooler Synchrotron
COSY-Juelich, using the internal beam and ANKE facility. Total cross sections
have been determined at three excess energies epsilon near the production
threshold. The differential cross section closest to threshold at epsilon=18.5
MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the
proton-proton final state interaction. Taken together with data for pp
omega-production, a significant enhancement of the phi/omega ratio of a factor
8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.Comment: 4 Pages, 3 Figures, 1 Table, submitted to Phys. Rev. Let
Contribution of the t-channel exchange for the reaction
Since the resonance was found to have large coupling to the
strangeness due to its possible large component, we investigate the
possible contribution of the t-channel exchange for the reaction. Our calculation indicates that the new mechanism gives
very significant contribution for the energies above 2.25 GeV and may be an
important source for evading the Okubo-Zweig-Iizuka rule in the
production from annihilation.Comment: 6 pages, 3 figure
Observation of narrow baryon resonance decaying into in pA-interactions at with SVD-2 setup
SVD-2 experiment data have been analyzed to search for an exotic baryon
state, the -baryon, in a decay mode at on IHEP
accelerator. The reaction with a limited multiplicity was
used in the analysis. The invariant mass spectrum shows a resonant
structure with and . The statistical significance of this peak was estimated to be of . The mass and width of the resonance is compatible with the recently
reported - baryon with positive strangeness which was predicted as an
exotic pentaquark () baryon state. The total cross section for
production in pN-interactions for was estimated to be
and no essential deviation from A-dependence for inelastic
events was found.Comment: 8 pages, 7 figures, To be submitted to Yadernaya Fizika. v3-v5 - Some
references added, minor typos correcte
Okubo-Zweig-Iizuka-rule violation and B\to \eta^{(\prime)}K branching ratios
We show that few-percent Okubo-Zweig-Iizuka-rule violating effects in the
quark-flavor basis for the - mixing can enhance the chiral scale
associated with the meson few times. This enhancement is sufficient
for accommodating the dramatically different data of the
and branching ratios. We comment on other proposals for resolving
this problem, including flavor-singlet contributions, axial U(1) anomaly, and
nonperturbative charming penguins. Discrimination of the above proposals by
means of the and
data is suggested.Comment: 7 pages, 2 figures, discussion on B\to\eta^{(\prime)}K* added, more
references adde
Measurements of the reaction of antiproton annihilation at rest at three hydrogen target densities
The proton-antiproton annihilation at rest into the final state
was measured for three different target densities: liquid hydrogen, gaseous
hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in
the liquid hydrogen target is smaller than in the low-pressure gas target. The
branching ratios of the channel were calculated on the basis of
simultaneous analysis of the three data samples. The branching ratio for
annihilation into from the protonium state turns out to be
about ten times smaller as compared to the one from the state.Comment: 10 pages, 3 Postscript figures. Accepted by Physics Letters
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Systematics of Inclusive Photon Production in 158 AGeV Pb Induced Reactions on Ni, Nb, and Pb Targets
The multiplicity of inclusive photons has been measured on an event-by-event
basis for 158 AGeV Pb induced reactions on Ni, Nb, and Pb targets. The
systematics of the pseudorapidity densities at midrapidity (rho_max) and the
width of the pseudorapidity distributions have been studied for varying
centralities for these collisions. A power law fit to the photon yield as a
function of the number of participating nucleons gives a value of 1.13+-0.03
for the exponent. The mean transverse momentum, , of photons determined
from the ratio of the measured electromagnetic transverse energy and photon
multiplicity, remains almost constant with increasing rho_max. Results are
compared with model predictions.Comment: 16 pages including 4 figure
Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via pi-/pi+ and K-/K+ Ratios
The effect of the final state Coulomb interaction on particles produced in
Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment
through the study of the pi-/pi+ and K-/K+ ratios measured as a function of
transverse mass. While the ratio for kaons shows no significant transverse mass
dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with
an enhancement that increases with centrality. A silicon pad detector located
near the target is used to estimate the contribution of hyperon decays to the
pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in
which the Coulomb interaction has been incorporated allows to place constraints
on the time of the pion freeze-out.Comment: 9 pages, 12 figure
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