8,680 research outputs found
Phi meson production in near threshold proton-nucleus collisions
The cross section for production of Phi mesons in proton-nucleus reactions is
calculated as a function of the target mass. The decay width of the Phi meson
is affected by the change of the masses of the Phi, K+ and K- mesons in the
medium. A strong attractive K- potential leads to a measurable change of the
behavior of the cross section as a function of of the target mass. Comparison
between the kaon and electron decay modes are made.Comment: 4 pages, 1figure, new figure, new reference
Dispersion analysis of the nucleon form factors including meson continua
Dispersion relations provide a powerful tool to analyse the electromagnetic
form factors of the nucleon for all momentum transfers. Constraints from
meson-nucleon scattering data, unitarity, and perturbative QCD can be included
in a straightforward way. In particular, we include the 2pi, rho-pi, and KKbar
continua as independent input in our analysis and provide an error band for our
results. Moreover, we discuss two different methods to include the asymptotic
constraints from perturbative QCD. We simultaneously analyze the world data for
all four form factors in both the space-like and time-like regions and
generally find good agreement with the data. We also extract the nucleon radii
and the omega-NN coupling constants. For the radii, we generally find good
agreement with other determinations with the exception of the electric charge
radius of the proton which comes out smaller. The omega-NN vector coupling
constant is determined relatively well by the fits, but for the tensor coupling
constant even the sign can not be determined.Comment: 24 pages, 9 figure
The role of the N*(1535) resonance and the pi^- p --> KY amplitudes in the OZI forbidden pi N --> phi N reaction
We study the pi N --> phi N reaction close to the phi N threshold within the
chiral unitary approach, by combining the pi^- p --> K^+ Sigma^-, pi^- p -->
K^0 Sigma^0 and pi^- p --> K^0 Lambda amplitudes with the coupling of the phi
to the K components of the final states of these reactions via quantum loops.
We obtain a good agreement with experiment when the dominant pi^- p --> K^0
Lambda amplitude is constrained with its experimental cross section. We also
evaluate the coupling of the N*(1535) to phi N and find a moderate coupling as
a consequence of partial cancellation of the large KY components of the
N*(1535). We also show that the N*(1535) pole approximation is too small to
reproduce the measured cross section for the pi N --> phi N reaction.Comment: 10 pages, 6 figure
Contribution of the nucleon-hyperon reaction channels to K production in proton-nucleus collisions
The cross sections for producing K mesons in nucleon-hyperon elementary
processes are estimated assuming one-pion exchange and using the experimentally
known pion-hyperon cross sections. The results are implemented in a transport
model which is applied to calculation of proton-nucleus collisions. In
significant difference to earlier estimates for heavy-ion collisions the
inclusion of the nucleon-hyperon cross section roughly doubles the K
production in near-threshold proton-nucleus collisions
Silicon Photo-Multiplier radiation hardness tests with a beam controlled neutron source
We report radiation hardness tests performed at the Frascati Neutron
Generator on silicon Photo-Multipliers, semiconductor photon detectors built
from a square matrix of avalanche photo-diodes on a silicon substrate. Several
samples from different manufacturers have been irradiated integrating up to
7x10^10 1-MeV-equivalent neutrons per cm^2. Detector performances have been
recorded during the neutron irradiation and a gradual deterioration of their
properties was found to happen already after an integrated fluence of the order
of 10^8 1-MeV-equivalent neutrons per cm^2.Comment: 7 pages, 6 figures, Submitted to Nucl. Inst. Meth.
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