1,427 research outputs found
Magnetic interaction induced by the anomaly in kaon-photoproductions
We study the role of magnetic interaction in the photoproduction of the kaon
and hyperon. We find that the inclusion of a higher order diagram induced by
the Wess-Zumio-Witten term has a significant contribution to the magnetic
amplitude, which is compatible to the observed photon asymmetry in the forward
angle region. This enables us to use the K^* coupling constants which have been
determined in a microscopic way rather than the phenomenological ones which
differ largely from the microscopic ones.Comment: 8 pages, 3 figure
The effect of age and font size on reading text on handheld computers
Though there have been many studies of computer based text reading, only a few have considered the small screens of handheld computers. This paper presents an investigation into the effect of varying font size between 2 and 16 point on reading text on a handheld computer. By using both older and younger participants the possible effects of age were examined. Reading speed and accuracy were measured and subjective views of participants recorded. Objective results showed that there was little difference in reading performance above 6 point, but subjective comments from participants showed a preference for sizes in the middle range. We therefore suggest, for reading tasks, that designers of interfaces for mobile computers provide fonts in the range of 8-12 point to maximize readability for the widest range of users
The ABCD of usability testing
We introduce a methodology for tracking and auditing feedback, errors and suggestions for software packages. This short paper describes how we innovate on the evaluation mechanism, introducing an (Antecedent, Barrier, Consequence and Development) ABCD form, embedded within an eParticipation platform to enable end users to easily report on any usability issues. This methodology will be utilised to improve the STEP cloud eParticipation platform (part of the current STEP Horizon2020 project http://step4youth.eu. The platform is currently being piloted in real life contexts, with the participation of public authorities that are integrating the eParticipation platform into their regular decision-making practices. The project is involving young people, through engagement and motivation strategies and giving them a voice in Environmental decision making at the local level. The pilot evaluation aims to demonstrate how open engagement needs to be embedded within public sector processes and the usability methodology reported here will help to identify the key barriers for wide scale deployment of the platform
KKbar photoproduction from protons
We study the contribution of the Drell mechanism driven by K^+ and K^-
exchange to the reaction gamma N -> KKbar N. Our calculation implements the
full KN and KbarN reaction amplitudes in the form of partial wave amplitudes
taken from a meson-exchange model (KN) and a partial wave analysis (KbarN),
respectively. Comparing our results to data of the LAMP2 collaboration we
observe that the Drell mechanism alone cannot describe the large Lambda(1520)
photoproduction rate observed experimentally. We argue that the discrepancy
could be due to significant contributions from K*-meson exchange with
subsequent excitation of the Lambda(1520) resonance. After adding such
contributions to our model a good agreement of the LAMP2 experiment is
achieved. When applying the same model to the recent SAPHIR data we find an
excellent description of the K^+p spectrum and can determine the parameters of
the Lambda(1600) P01 resonance, M_R = 1617 +/- 2 MeV and Gamma_R = 117 +/- 4
MeV, from the K^-p mass distribution.Comment: updated version, analysis of new CLAS data included, 11 pages, 11
figure
Photoproduction of mesons in nuclei at GeV energies
In a transport model that combines initial state interactions of the photon
with final state interactions of the produced particles we present a
calculation of inclusive photoproduction of mesons in nuclei in the energy
range from 1 to 7 GeV. We give predictions for the photoproduction cross
sections of pions, etas, kaons, antikaons, and invariant mass
spectra in ^{12}C and ^{208}Pb. The effects of nuclear shadowing and final
state interaction of the produced particles are discussed in detail.Comment: Text added in summary in general reliability of the method,
references updated. Phys. Rev. C (2000) in pres
An attempt to understand exclusive pi+ electroproduction
Hard exclusive pi+ electroproduction is investigated within the handbag
approach. The prominent role of the pion-pole contribution is demonstrated. It
is also shown that the experimental data require a twist-3 effect which ensues
from the helicity-flip generalized parton distribution H_T and the twist-3 pion
wave function. The results calculated from this handbag approach are compared
in detail with the experimental data on cross sections and spin asymmetries
measured with a polarized target. It is also commented on consequences of this
approach for exclusive \pi^0 and vector-meson electroproduction.Comment: 35 pages, 12 figures, using Latex, a number of additional comments
have been included in the text, e.g. in paragraph above (3) or at end of
sect.
Simple deterministic dynamical systems with fractal diffusion coefficients
We analyze a simple model of deterministic diffusion. The model consists of a
one-dimensional periodic array of scatterers in which point particles move from
cell to cell as defined by a piecewise linear map. The microscopic chaotic
scattering process of the map can be changed by a control parameter. This
induces a parameter dependence for the macroscopic diffusion coefficient. We
calculate the diffusion coefficent and the largest eigenmodes of the system by
using Markov partitions and by solving the eigenvalue problems of respective
topological transition matrices. For different boundary conditions we find that
the largest eigenmodes of the map match to the ones of the simple
phenomenological diffusion equation. Our main result is that the difffusion
coefficient exhibits a fractal structure by varying the system parameter. To
understand the origin of this fractal structure, we give qualitative and
quantitative arguments. These arguments relate the sequence of oscillations in
the strength of the parameter-dependent diffusion coefficient to the
microscopic coupling of the single scatterers which changes by varying the
control parameter.Comment: 28 pages (revtex), 12 figures (postscript), submitted to Phys. Rev.
A Study of Time-Dependent CP-Violating Asymmetries and Flavor Oscillations in Neutral B Decays at the Upsilon(4S)
We present a measurement of time-dependent CP-violating asymmetries in
neutral B meson decays collected with the BABAR detector at the PEP-II
asymmetric-energy B Factory at the Stanford Linear Accelerator Center. The data
sample consists of 29.7 recorded at the
resonance and 3.9 off-resonance. One of the neutral B mesons,
which are produced in pairs at the , is fully reconstructed in
the CP decay modes , , , () and , or in flavor-eigenstate
modes involving and (). The flavor of the other neutral B meson is tagged at the time of
its decay, mainly with the charge of identified leptons and kaons. The proper
time elapsed between the decays is determined by measuring the distance between
the decay vertices. A maximum-likelihood fit to this flavor eigenstate sample
finds . The value of the asymmetry amplitude is determined from
a simultaneous maximum-likelihood fit to the time-difference distribution of
the flavor-eigenstate sample and about 642 tagged decays in the
CP-eigenstate modes. We find , demonstrating that CP violation exists in the neutral B meson
system. (abridged)Comment: 58 pages, 35 figures, submitted to Physical Review
Lambda(1520,3/2^-) photoproduction reaction via gamma N -> K Lambda(1520)
We investigate Lambda(1520,3/2^-,D_03) photoproduction via the gamma N -> K
Lambda^* reaction process. Using effective Lagrangians, we compute the total
and differential cross sections as well as the dependence on the momentum
transfer for the photoproduction at the tree-level. We employ two different
form factors: The four-dimensional gauge-invariant type and the three
dimensional one depending on the external momenta. We find that the total cross
sections for the proton target are well reproduced as compared with the
experimental data. It turns out that the total cross sections for the neutron
target are significantly smaller than those for the proton target. We also
compare the present results with the gamma N -> bar{K} Theta^+ reaction in
order to extract information of Theta^+. Finally the role of K^*--exchange in
the production reaction is discussed.Comment: 16 pages, 31 figure
Measurement of the Branching Fraction for B- --> D0 K*-
We present a measurement of the branching fraction for the decay B- --> D0
K*- using a sample of approximately 86 million BBbar pairs collected by the
BaBar detector from e+e- collisions near the Y(4S) resonance. The D0 is
detected through its decays to K- pi+, K- pi+ pi0 and K- pi+ pi- pi+, and the
K*- through its decay to K0S pi-. We measure the branching fraction to be
B.F.(B- --> D0 K*-)= (6.3 +/- 0.7(stat.) +/- 0.5(syst.)) x 10^{-4}.Comment: 7 pages, 1 postscript figure, submitted to Phys. Rev. D (Rapid
Communications
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