1,410 research outputs found
Searches for new physics through single top
Nowadays particle physics research involves building the largest machines ever built. Detectors the size of a palace buried deep underground, aligned to tiny fractions of a millimeter, observe billions of collisions a second. Large collaborations of thousands of people analyze the unfathomably large amounts of data the detectors produce. A million computers sort through the data running software that is so complex that no-one can even come close to understanding every detail. These experiments search for deviations from the Standard Model that may point to so-called new physics. The new physics may lead to answers to some of the big open questions of science, such as: Why does our universe contain primarily matter, and hardly any anti-matter? This question of baryogenesis is the main motivation for the analyses described in this thesis. Chapter 1 gives a short theoretical introduction to single top processes, and describes the theory behind the analyses. Experiment follows the theory, with a description of the ATLAS experiment and the LHC in chapter 2. Once your appetite has been whetted, chapter 3 will provide you with many details on the performance of the detector, the reconstruction of physics objects in the detector and the simulation of collisions and detector response. Now comes the analysis: a search for excited b quarks in the single top Wt-channel is described in chapter 4. Then we switch channels: an analysis in single top t-channel is spread over two chapters: chapter 5 describes a cut and count measurement of the t-channel cross section and finally chapter 6 describes a search for CP-violation in the t-channel
Detecting multivariate interactions in spatial point patterns with Gibbs models and variable selection
We propose a method for detecting significant interactions in very large
multivariate spatial point patterns. This methodology develops high dimensional
data understanding in the point process setting. The method is based on
modelling the patterns using a flexible Gibbs point process model to directly
characterise point-to-point interactions at different spatial scales. By using
the Gibbs framework significant interactions can also be captured at small
scales. Subsequently, the Gibbs point process is fitted using a
pseudo-likelihood approximation, and we select significant interactions
automatically using the group lasso penalty with this likelihood approximation.
Thus we estimate the multivariate interactions stably even in this setting. We
demonstrate the feasibility of the method with a simulation study and show its
power by applying it to a large and complex rainforest plant population data
set of 83 species
In Memoriam Bas Edixhoven (1962–2022): genereus, optimistisch en betrokken
Op 16 januari 2022 overleed Bas Edixhoven, hoogleraar meetkunde aan de Universiteit Leiden. Naast zijn onderzoek en onderwijs was Bas betrokken bij vele internationale en nationale wiskunde-organisaties. In Nederland onder andere bij de commissie Onderzoek en de commissie Onderwijs van Platform Wiskunde Nederland, Mastermath, Wisk4all, DIAMANT, Vierkant voor Wiskunde, Compositio Mathematica, Indagationes Mathematicae, en de Bèta-lerarenkamer. Tevens was hij lid van de Koninklijke Nederlandse Akademie van Wetenschappen. Zijn nabije collega’s Robin de Jong, Jaap Top, Gerard van der Geer en René Schoof herdenken hem.Number theory, Algebra and Geometr
The class of the locus of intermediate Jacobians of cubic threefolds
We study the locus of intermediate Jacobians of cubic threefolds within the
moduli space of complex principally polarized abelian fivefolds, and its
generalization to arbitrary genus - the locus of abelian varieties with a
singular odd two-torsion point on the theta divisor. Assuming that this locus
has expected codimension (which we show to be true for genus up to 5), we
compute the class of this locus, and of is closure in the perfect cone toroidal
compactification, in the Chow, homology, and the tautological ring.
We work out the cases of genus up to 5 in detail, obtaining explicit
expressions for the classes of the closures of the locus of products of an
elliptic curve and a hyperelliptic genus 3 curve, in moduli of principally
polarized abelian fourfolds, and of the locus of intermediate Jacobians in
genus 5. In the course of our computation we also deal with various
intersections of boundary divisors of a level toroidal compactification, which
is of independent interest in understanding the cohomology and Chow rings of
the moduli spaces.Comment: v2: new section 9 on the geometry of the boundary of the locus of
intermediate Jacobians of cubic threefolds. Final version to appear in
Invent. Mat
Design considerations for table-top, laser-based VUV and X-ray free electron lasers
A recent breakthrough in laser-plasma accelerators, based upon ultrashort
high-intensity lasers, demonstrated the generation of quasi-monoenergetic
GeV-electrons. With future Petawatt lasers ultra-high beam currents of ~100 kA
in ~10 fs can be expected, allowing for drastic reduction in the undulator
length of free-electron-lasers (FELs). We present a discussion of the key
aspects of a table-top FEL design, including energy loss and chirps induced by
space-charge and wakefields. These effects become important for an optimized
table-top FEL operation. A first proof-of-principle VUV case is considered as
well as a table-top X-ray-FEL which may open a brilliant light source also for
new ways in clinical diagnostics.Comment: 6 pages, 4 figures; accepted for publication in Appl. Phys.
New Simulations for Ion-Production and Back-Bombardment in GaAs Photo-guns
GaAs-based DC high voltage photo-guns used at accelerators with extensive user programs must exhibit long photocathode operating lifetime. Achieving this goal represents a significant challenge for proposed high average current facilities that must operate at tens of milliamperes or more. Specifically, the operating lifetime is dominated by ion back-bombardment of the photocathode from ionized residual gas. While numerous experiments have been performed to characterize the operating lifetime under various conditions, detailed simulations of the ion back-bombardment mechanism that explains these experiments are lacking. Recently, a new user routine was implemented using the code General Particle Tracer (GPT) to simulate electron impact ionization of residual beam line gas and simultaneously track the incident electron, the ejected electron, and the newly formed ion. This new routine was benchmarked against analytical calculations and then applied to experiments performed at the CEBAF injector at the Thomas Jefferson National Accelerator Facility to study the effectiveness of limiting ions from entering the cathode-anode gap using a positively biased anode. These simulations were performed using detailed 3D field maps produced with CST Microwave Studio describing the photo-gun electrostatics. Discussion of the experiment and the application of this new GPT routine to model the experiments will be presented at the workshop
Financial incentives for healthy living for patients with cardiac disease from the perspective of health care professionals: interview study
Health and self-regulatio
An ultrashort pulse ultra-violet radiation undulator source driven by a laser plasma wakefield accelerator
Narrow band undulator radiation tuneable over the wavelength range of 150–260 nm has been produced by short electron bunches from a 2 mm long laser plasma wakefield accelerator based on a 20 TW femtosecond laser system. The number of photons measured is up to 9 × 106 per shot for a 100 period undulator, with a mean peak brilliance of 1 × 1018 photons/s/mrad2/mm2/0.1% bandwidth. Simulations estimate that the driving electron bunch r.m.s. duration is as short as 3 fs when the electron beam has energy of 120–130 MeV with the radiation pulse duration in the range of 50–100 fs
Equidistribution Rates, Closed String Amplitudes, and the Riemann Hypothesis
We study asymptotic relations connecting unipotent averages of
automorphic forms to their integrals over the moduli space
of principally polarized abelian varieties. We obtain reformulations of the
Riemann hypothesis as a class of problems concerning the computation of the
equidistribution convergence rate in those asymptotic relations. We discuss
applications of our results to closed string amplitudes. Remarkably, the
Riemann hypothesis can be rephrased in terms of ultraviolet relations occurring
in perturbative closed string theory.Comment: 15 page
Dwarf deer of Crete.
26 pages : illustrations (some color), map ; 26 cm.Age-graded fossils of Pleistocene endemic Cretan deer (Candiacervus spp.) reveal unexpectedly high juvenile mortality similar to that reported for extant mainland ruminants, despite the fact that these deer lived in a predator-free environment and became extinct before any plausible date for human arrival. Age profiles show that deer surviving past the fawn stage were relatively long-lived for ruminants, indicating that high juvenile mortality was not an expression of their living a "fast" life. Although the effects on survivorship of such variables as fatal accidents, starvation, and disease are difficult to gauge in extinct taxa, the presence of extreme morphological variability within nominal species/ecomorphs of Candiacervus is consistent with the view that high juvenile mortality can function as a key innovation permitting rapid adaptation in insular contexts
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