3,437 research outputs found
Jet Vetoes Interfering with H->WW
Far off-shell Higgs production in , is a particularly
powerful probe of Higgs properties, allowing one to disentangle Higgs width and
coupling information unavailable in on-shell rate measurements. These
measurements require an understanding of the cross section in the far off-shell
region in the presence of realistic experimental cuts. We analytically study
the effect of a jet veto on far off-shell cross sections, including
signal-background interference, by utilizing hard functions in the soft
collinear effective theory that are differential in the decay products of the
. Summing large logarithms of , we find that the
jet veto induces a strong dependence on the partonic centre of mass energy,
, and modifies distributions in or . The
example of is used to demonstrate these
effects at next to leading log order. We also discuss the importance of jet
vetoes and jet binning for the recent program to extract Higgs couplings and
widths from far off-shell cross sections.Comment: 31 pages, 8 figures. v2: Journal Versio
Event generation with SHERPA 1.1
In this paper the current release of the Monte Carlo event generator Sherpa,
version 1.1, is presented. Sherpa is a general-purpose tool for the simulation
of particle collisions at high-energy colliders. It contains a very flexible
tree-level matrix-element generator for the calculation of hard scattering
processes within the Standard Model and various new physics models. The
emission of additional QCD partons off the initial and final states is
described through a parton-shower model. To consistently combine multi-parton
matrix elements with the QCD parton cascades the approach of Catani, Krauss,
Kuhn and Webber is employed. A simple model of multiple interactions is used to
account for underlying events in hadron--hadron collisions. The fragmentation
of partons into primary hadrons is described using a phenomenological
cluster-hadronisation model. A comprehensive library for simulating tau-lepton
and hadron decays is provided. Where available form-factor models and matrix
elements are used, allowing for the inclusion of spin correlations; effects of
virtual and real QED corrections are included using the approach of Yennie,
Frautschi and Suura.Comment: 47 pages, 21 figure
Quantitation in MRI : application to ageing and epilepsy
Multi-atlas propagation and label fusion techniques have recently been developed for segmenting
the human brain into multiple anatomical regions. In this thesis, I investigate
possible adaptations of these current state-of-the-art methods. The aim is to study ageing
on the one hand, and on the other hand temporal lobe epilepsy as an example for a
neurological disease.
Overall effects are a confounding factor in such anatomical analyses. Intracranial volume
(ICV) is often preferred to normalize for global effects as it allows to normalize for estimated
maximum brain size and is hence independent of global brain volume loss, as seen
in ageing and disease. I describe systematic differences in ICV measures obtained at 1.5T
versus 3T, and present an automated method of measuring intracranial volume, Reverse
MNI Brain Masking (RBM), based on tissue probability maps in MNI standard space. I
show that this is comparable to manual measurements and robust against field strength
differences.
Correct and robust segmentation of target brains which show gross abnormalities, such as
ventriculomegaly, is important for the study of ageing and disease. We achieved this with
incorporating tissue classification information into the image registration process. The
best results in elderly subjects, patients with TLE and healthy controls were achieved using
a new approach using multi-atlas propagation with enhanced registration (MAPER).
I then applied MAPER to the problem of automatically distinguishing patients with TLE
with (TLE-HA) and without (TLE-N) hippocampal atrophy on MRI from controls, and
determine the side of seizure onset. MAPER-derived structural volumes were used for
a classification step consisting of selecting a set of discriminatory structures and applying
support vector machine on the structural volumes as well as morphological similarity
information such as volume difference obtained with spectral analysis. Acccuracies were
91-100 %, indicating that the method might be clinically useful.
Finally, I used the methods developed in the previous chapters to investigate brain regional
volume changes across the human lifespan in over 500 healthy subjects between 20
to 90 years of age, using data from three different scanners (2x 1.5T, 1x 3T), using the IXI
database. We were able to confirm several known changes, indicating the veracity of the
method. In addition, we describe the first multi-region, whole-brain database of normal
ageing
Higher-Order Corrections to Timelike Jets
We present a simple formalism for the evolution of timelike jets in which
tree-level matrix element corrections can be systematically incorporated, up to
arbitrary parton multiplicities and over all of phase space, in a way that
exponentiates the matching corrections. The scheme is cast as a shower Markov
chain which generates one single unweighted event sample, that can be passed to
standard hadronization models. Remaining perturbative uncertainties are
estimated by providing several alternative weight sets for the same events, at
a relatively modest additional overhead. As an explicit example, we consider Z
-> q qbar evolution with unpolarized, massless quarks and include several
formally subleading improvements as well as matching to tree-level matrix
elements through alpha_s^4. The resulting algorithm is implemented in the
publicly available VINCIA plugin to the PYTHIA 8 event generator.Comment: 72 pages, 78 figure
tWH associated production at the LHC
We study Higgs boson production in association with a top quark and a
boson at the LHC. At NLO in QCD, interferes with and a
procedure to meaningfully separate the two processes needs to be employed. In
order to define production for both total rates and differential
distributions, we consider the diagram removal and diagram subtraction
techniques that have been previously proposed for treating intermediate
resonances at NLO, in particular in the context of production. These
techniques feature approximations that need to be carefully taken into account
when theoretical predictions are compared to experimental measurements. To this
aim, we first critically revisit the process, for which an extensive
literature exists and where an analogous interference with
production takes place. We then provide robust results for total and
differential cross sections for and at 13 TeV, also matching
short-distance events to a parton shower. We formulate a reliable prescription
to estimate the theoretical uncertainties, including those associated to the
very definition of the process at NLO. Finally, we study the sensitivity to a
non-Standard-Model relative phase between the Higgs couplings to the top quark
and to the boson in production.Comment: v3: expanded some discussions in the text, improved some plots
(results unchanged
The geography of taste: analyzing cell-phone mobility and social events
This paper deals with the analysis of crowd mobility during special events. We analyze nearly 1 million cell-phone traces and associate their destinations with social events. We show that the origins of people attending an event are strongly correlated to the type of event, with implications in city management, since the knowledge of additive flows can be a critical information on which to take decisions about events management and congestion mitigation
A Comprehensive Survey on Particle Swarm Optimization Algorithm and Its Applications
Particle swarm optimization (PSO) is a heuristic global optimization method, proposed originally by Kennedy and Eberhart in 1995. It is now one of the most commonly used optimization techniques. This survey presented a comprehensive investigation of PSO. On one hand, we provided advances with PSO, including its modifications (including quantum-behaved PSO, bare-bones PSO, chaotic PSO, and fuzzy PSO), population topology (as fully connected, von Neumann, ring, star, random, etc.), hybridization (with genetic algorithm, simulated annealing, Tabu search, artificial immune system, ant colony algorithm, artificial bee colony, differential evolution, harmonic search, and biogeography-based optimization), extensions (to multiobjective, constrained, discrete, and binary optimization), theoretical analysis (parameter selection and tuning, and convergence analysis), and parallel implementation (in multicore, multiprocessor, GPU, and cloud computing forms). On the other hand, we offered a survey on applications of PSO to the following eight fields: electrical and electronic engineering, automation control systems, communication theory, operations research, mechanical engineering, fuel and energy, medicine, chemistry, and biology. It is hoped that this survey would be beneficial for the researchers studying PSO algorithms
Cluster analysis based on density estimates and its application to LANDSAT imagery
Includes bibliographical footnotes.This study was funded partly by the Federation of Rocky Mountain States, the U.S. Army Corps of Engineers, St. Paul District, Contract no. DAC 37-77-C-0133 and the Colorado State University Experiment Station 107
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