Jet Substructure Without Trees

We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods.Comment: 22 pages, 16 figures, version accepted by JHE

Jet Dipolarity: Top Tagging with Color Flow

A new jet observable, dipolarity, is introduced that can distinguish whether a pair of subjets arises from a color singlet source. This observable is incorporated into the HEPTopTagger and is shown to improve discrimination between top jets and QCD jets for moderate to high pT.Comment: 8 pages, 6 figures (updated to JHEP version

New methods for testing phylogenetic niche conservatism with an application to the Squamates of Madagascar

Phylogenetic niche conservatism (PNC), whereby closely-related species share similar ecological preferences, is often assumed to play a role in speciation processes. However, this trend is challenged by cases of phylogenetic niche divergence (PND), whereby closely-related species diverge in their ecological preferences. I examine the incidence of PNC and PND in the endemic scaled reptiles (Order, Squamata) of Madagascar. Firstly, I develop new tools to test for PNC and PND for a pair of species or populations. I introduce a novel measure of niche overlap and a null biogeographic test. I begin by comparing their performance with existing methods and case studies and I find the outputs from this new methodology to be consistent with evolutionary theory. I then conduct an assessment on the sensitivity of these tools to common sources of uncertainty identified in other niche-based methodologies. The methodology shows sensitivity to environmental spatial autocorrelation but not size of background region or sampling bias. I then applied these tools to sister taxa of squamates in Madagascar. I find cases of both PNC and PND and a tendency for niche conservatism in regions of high topographic complexity. In order to have an understanding of factors driving species divergence at a local scale, I also test for character displacement. I find character displacement to also be positively associated with topographic complexity. These findings suggest potential shifts in local scale niche traits and conservatism of broad scale niche traits. Overall in this thesis, I describe novel approaches to the study of PNC and PND. I also propose topographic complexity as an important factor in speciation processes in Madagascar. These findings provide hypotheses on the ecological processes involved in speciation on topographic complex regions while the tools presented in this thesis can be applied to many study systems

Measuring the Polarization of Boosted Hadronic Tops

We propose a new technique for measuring the polarization of hadronically decaying boosted top quarks. In particular, we apply a subjet-based technique to events where the decay products of the top are clustered within a single jet. The technique requires neither b-tagging nor W-reconstruction, and does not rely on assumptions about either the top production mechanism or the sources of missing energy in the event. We include results for various new physics scenarios made with different Monte Carlo generators to demonstrate the robustness of the technique.Comment: v2: version accepted for publication in JHE

Diboson-Jets and the Search for Resonant Zh Production

New particles at the TeV-scale may have sizeable decay rates into boosted Higgs bosons or other heavy scalars. Here, we investigate the possibility of identifying such processes when the Higgs/scalar subsequently decays into a pair of W bosons, constituting a highly distinctive "diboson-jet." These can appear as a simple dilepton (plus MET) configuration, as a two-prong jet with an embedded lepton, or as a four-prong jet. We study jet substructure methods to discriminate these objects from their dominant backgrounds. We then demonstrate the use of these techniques in the search for a heavy spin-one Z' boson, such as may arise from strong dynamics or an extended gauge sector, utilizing the decay chain Z' -> Zh -> Z(WW^(*)). We find that modes with multiple boosted hadronic Zs and Ws tend to offer the best prospects for the highest accessible masses. For 100/fb luminosity at the 14 TeV LHC, Z' decays into a standard 125 GeV Higgs can be observed with 5-sigma significance for masses of 1.5-2.5 TeV for a range of models. For a 200 GeV Higgs (requiring nonstandard couplings, such as fermiophobic), the reach may improve to up to 2.5-3.0 TeV.Comment: 23 pages plus appendices, 9 figure

Identifying Boosted Objects with N-subjettiness

We introduce a new jet shape -- N-subjettiness -- designed to identify boosted hadronically-decaying objects like electroweak bosons and top quarks. Combined with a jet invariant mass cut, N-subjettiness is an effective discriminating variable for tagging boosted objects and rejecting the background of QCD jets with large invariant mass. In efficiency studies of boosted W bosons and top quarks, we find tagging efficiencies of 30% are achievable with fake rates of 1%. We also consider the discovery potential for new heavy resonances that decay to pairs of boosted objects, and find significant improvements are possible using N-subjettiness. In this way, N-subjettiness combines the advantages of jet shapes with the discriminating power seen in previous jet substructure algorithms.Comment: 26 pages, 26 figures, 2 tables; v2: references added; v3: discussion of results extende

Innovative development of the inspired sinewave device to measure lung functions and inhomogeneity for diagnosis and evaluations of early lung diseases

Surprisingly, lung disease is still one of the leading causes of deaths in the developed countries, including UK. According to the UK National Health Service (NHS), Chronic Obstructive Pulmonary Disease (COPD) is the fifth biggest killer disease in the UK, killing approximately 25,000 people a year. This prob-lem is even worse in developing countries such as Vietnam, India and China, where air pollution is a big problem and the disease awareness is under-recognised. The NHS has set out one of its challenges is to identify people with lung disease earlier in the disease’s development pathway, in order to pro-vide more effective and timely intervention and treatment. This paper presents a novel Inspired Sinewave Device (ISD) to measure lung function and inhomogeneity. Both set of infor-mation are important for diagnosis and detection of early lung diseases. ISD has the potential to replace or supplement the traditional spirometry in the routine lung function testing. The paper describes both the principle of ISD and a set of experi-mental results demonstrating the capability of ISD to asymp-totically detect asthmatic symptoms. Finally the paper discuss-es the future plan, including the testing of 300+ COPD patients at the Oxford Respiratory Trials Unit in UK, and the potential collaborations among research institutions in Vietnam and UK about cost-effective and innovative developments of smart devices, biosensors, lab-on-chips and telehealth solutions for the routine lung function testing, diagnosis and evaluations of early lung diseases

The mass area of jets

We introduce a new characteristic of jets called mass area. It is defined so as to measure the susceptibility of the jet's mass to contamination from soft background. The mass area is a close relative of the recently introduced catchment area of jets. We define it also in two variants: passive and active. As a preparatory step, we generalise the results for passive and active areas of two-particle jets to the case where the two constituent particles have arbitrary transverse momenta. As a main part of our study, we use the mass area to analyse a range of modern jet algorithms acting on simple one and two-particle systems. We find a whole variety of behaviours of passive and active mass areas depending on the algorithm, relative hardness of particles or their separation. We also study mass areas of jets from Monte Carlo simulations as well as give an example of how the concept of mass area can be used to correct jets for contamination from pileup. Our results show that the information provided by the mass area can be very useful in a range of jet-based analyses.Comment: 36 pages, 12 figures; v2: improved quality of two plots, added entry in acknowledgments, nicer form of formulae in appendix A; v3: added section with MC study and pileup correction, version accepted by JHE

Heavy Squarks at the LHC

The LHC, with its seven-fold increase in energy over the Tevatron, is capable of probing regions of SUSY parameter space exhibiting qualitatively new collider phenomenology. Here we investigate one such region in which first generation squarks are very heavy compared to the other superpartners. We find that the production of these squarks, which is dominantly associative, only becomes rate-limited at mSquark > 4(5) TeV for L~10(100) fb-1. However, discovery of this scenario is complicated because heavy squarks decay primarily into a jet and boosted gluino, yielding a dijet-like topology with missing energy (MET) pointing along the direction of the second hardest jet. The result is that many signal events are removed by standard jet/MET anti-alignment cuts designed to guard against jet mismeasurement errors. We suggest replacing these anti-alignment cuts with a measurement of jet substructure that can significantly extend the reach of this channel while still removing much of the background. We study a selection of benchmark points in detail, demonstrating that mSquark= 4(5) TeV first generation squarks can be discovered at the LHC with L~10(100)fb-1

Non-global logarithms and jet algorithms in high-pT jet shapes

We consider jet-shape observables of the type proposed recently, where the shapes of one or more high-pT jets, produced in a multi-jet event with definite jet multiplicity, may be measured leaving other jets in the event unmeasured. We point out the structure of the full next-to-leading logarithmic resummation specifically including resummation of non-global logarithms in the leading-Nc limit and emphasising their properties. We also point out differences between jet algorithms in the context of soft gluon resummation for such observables.Comment: 22 pages, 4 figures. Title and a few words changed. Several typos corrected. Version accepted by JHE