523 research outputs found
Extraction of the D13(1520) photon-decay couplings from pion- and eta-photoproduction data
We compare results for the D13(1520) photon-decay amplitudes determined in
analyses of eta- and pion-photoproduction data. The ratio of helicity
amplitudes (A_3/2 / A_1/2), determined from eta-photoproduction data, is quite
different from that determined in previous analyses of pion-photoproduction
data. We consider how strongly the existing pion-photoproduction data constrain
both this ratio and the individual photon-decay amplitudes.Comment: 7 pages, 2 figure
J/Psi Suppression in Heavy Ion Collisions at the CERN SPS
We reexamine the production of J/Psi and other charmonium states for a
variety of target-projectile choices at the SPS. For this study we use a newly
constructed cascade code LUCIFER II, which yields acceptable descriptions of
both hard and soft processes, specifically Drell-Yan and hidden charm
production, and soft energy loss and meson production, at the SPS. Glauber
calculations of other authors are redone, and compared directly to the cascade
results. The modeling of the charmonium states differs from that of earlier
workers in its unified treatment of the hidden charm meson spectrum, which is
introduced from the outset as a set of coupled states. The result is a
description of the NA38 and NA50 data in terms of a conventional hadronic
picture. The apparently anomalous suppression found in the most massive Pb+Pb
system arises from three sources: destruction in the initial nucleon-nucleon
cascade, use of coupled channels to exploit the larger breakup in the less
bound Chi and Psi' states, and comover interaction in the final low energy
phase.Comment: 36 pages (15 figures
A Review of Recent Developments in Atomic Processes for Divertors and Edge Plasmas
The most promising concepts for power and particle control in tokamaks and
other fusion experiments rely upon atomic processes to transfer the power and
momentum from the edge plasma to the plasma chamber walls. This places a new
emphasis on processes at low temperatures (1-200 eV) and high densities
(10^20-10^22 m^-3). The most important atomic processes are impurity and
hydrogen radiation, ionization, excitation, recombination, charge exchange,
radiation transport, molecular collisions, and elastic scattering of atoms,
molecules and ions. Important new developments have occurred in each of these
areas. The best available data for these processes and an assessment of their
role in plasma wall interactions are summarized, and the major areas where
improved data are needed are reviewed.Comment: Preprint for the 11th PSI meeting, postscript with 22 figures, 40
page
The research-teaching nexus: A case study of students' awareness, experiences and perceptions of research
This paper presents a case study of students' awareness, experiences and perceptions of research in a 'new' university in the UK. The findings are based on a questionnaire of almost 200 students and five small group interviews. Many of the students participating in this research perceived clear benefits to their learning from staff research, including being taught by enthusiastic staff, enhanced staff credibility, and the reflected glory of being taught by well-known researchers. However, they also perceived disadvantages, particularly with regard to staff availability, and did not believe that staff research should take priority over their needs as learners. They recognised that their awareness of the nature of research and the development of research skills increased most when they were actively involved in undertaking research projects. Several students also perceived benefits for future employment from their participation in research activities. The questionnaire has been used by several other universities around the world to benchmark their practices. © 2010 Taylor & Francis
Ionic and electronic structure of sodium clusters up to N=59
We determined the ionic and electronic structure of sodium clusters with even
electron numbers and 2 to 59 atoms in axially averaged and three-dimensional
density functional calculations. A local, phenomenological pseudopotential that
reproduces important bulk and atomic properties and facilitates structure
calculations has been developed. Photoabsorption spectra have been calculated
for , , and to
. The consistent inclusion of ionic structure considerably
improves agreement with experiment. An icosahedral growth pattern is observed
for to . This finding is supported by
photoabsorption data.Comment: To appear in Phys. Rev. B 62. Version with figures in better quality
can be requested from the author
Higgs-boson production associated with a bottom quark at hadron colliders with SUSY-QCD corrections
The Higgs boson production p p (p\bar p) -> b h +X via b g -> b h at the LHC,
which may be an important channel for testing the bottom quark Yukawa coupling,
is subject to large supersymmetric quantum corrections. In this work the
one-loop SUSY-QCD corrections to this process are evaluated and are found to be
quite sizable in some parameter space. We also study the behavior of the
corrections in the limit of heavy SUSY masses and find the remnant effects of
SUSY-QCD. These remnant effects, which are left over in the Higgs sector by the
heavy sparticles, are found to be so sizable (for a light CP-odd Higgs and
large \tan\beta) that they might be observable in the future LHC experiment.
The exploration of such remnant effects is important for probing SUSY,
especially in case that the sparticles are too heavy (above TeV) to be directly
discovered at the LHC.Comment: Results for the Tevatron adde
The Stern-Gerlach Experiment Revisited
The Stern-Gerlach-Experiment (SGE) of 1922 is a seminal benchmark experiment
of quantum physics providing evidence for several fundamental properties of
quantum systems. Based on today's knowledge we illustrate the different
benchmark results of the SGE for the development of modern quantum physics and
chemistry.
The SGE provided the first direct experimental evidence for angular momentum
quantization in the quantum world and thus also for the existence of
directional quantization of all angular momenta in the process of measurement.
It measured for the first time a ground state property of an atom, it produced
for the first time a `spin-polarized' atomic beam, it almost revealed the
electron spin. The SGE was the first fully successful molecular beam experiment
with high momentum-resolution by beam measurements in vacuum. This technique
provided a new kinematic microscope with which inner atomic or nuclear
properties could be investigated.
The original SGE is described together with early attempts by Einstein,
Ehrenfest, Heisenberg, and others to understand directional quantization in the
SGE. Heisenberg's and Einstein's proposals of an improved multi-stage SGE are
presented. The first realization of these proposals by Stern, Phipps, Frisch
and Segr\`e is described. The set-up suggested by Einstein can be considered an
anticipation of a Rabi-apparatus. Recent theoretical work is mentioned in which
the directional quantization process and possible interference effects of the
two different spin states are investigated.
In full agreement with the results of the new quantum theory directional
quantization appears as a general and universal feature of quantum
measurements. One experimental example for such directional quantization in
scattering processes is shown. Last not least, the early history of the
`almost' discovery of the electron spin in the SGE is revisited.Comment: 50pp, 17 fig
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Standard Model backgrounds to supersymmetry searches
This work presents a review of the Standard Model sources of backgrounds to
the search of supersymmetry signals. Depending on the specific model, typical
signals may include jets, leptons, and missing transverse energy due to the
escaping lightest supersymmetric particle. We focus on the simplest case of
multijets and missing energy, since this allows us to expose most of the issues
common to other more complex cases. The review is not exhaustive, and is aimed
at collecting a series of general comments and observations, to serve as
guideline for the process that will lead to a complete experimental
determination of size and features of such SM processes.Comment: To appear in the J. Wess memorial volume, "Supersymmetry on the Eve
of the LHC", to be published in European Physical Journal
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