Samuel Nathan Webb

The Phase-I upgrade of the ATLAS Trigger and Data Acquisition (TDAQ) system is to allow the ATLAS experiment to efficiently trigger and record data at instantaneous luminosities that are up to three times that of the original LHC design while maintaining trigger thresholds close to those used in the initial run of the LHC.

The aim of this study was to investigate the effect of pre-induced inspiratory muscle fatigue (IMF) on race-paced swimming and acid-base status. Twenty-one collegiate swimmers performed two discontinuous 400-m race-paced swims on separate days, with (IMF trial) and without (control trial) pre-induced IMF. Swimming characteristics, inspiratory and expiratory mouth pressures, and blood parameters were recorded. IMF and expiratory muscle fatigue (P < 0.05) were evident after both trials and swimming time was slower (P < 0.05) from 150-m following IMF inducement. Pre-induced IMF increased pH before the swim (P < 0.01) and reduced bicarbonate (P < 0.05) and the pressure of carbon dioxide (PCO2) (P < 0.05). pH (P < 0.05), bicarbonate (P < 0.01) and PCO2 (P < 0.05) were lower during swimming in the IMF trial. Blood lactate was similar before both trials (P > 0.05) but was higher (P < 0.01) in the IMF trial after swimming. Pre-induced IMF induced respiratory alkalosis, reduced bicarbonate buffering capacity and slowed swimming speed. Pre-induced and propulsion-induced IMF reflected metabolic acidosis arising from dual role breathing and propulsion muscle fatigue.

This document collects the proceedings of the PHOTON 2017 conference ("International Conference on the Structure and the Interactions of the Photon", including the 22th "International Workshop on Photon-Photon Collisions", and the "International Workshop on High Energy Photon Colliders") held at CERN (Geneva) in May 2017. The latest experimental and theoretical developments on the topics of the PHOTON conference series are covered: (i) $γ\,γ$ processes in e$^+$e$^-$, proton-proton (pp) and nucleus-nucleus (AA) collisions at current and future colliders, (ii) $γ$-hadron interactions in e$^\pm$p, pp, and AA collisions, (iii) final-state photon production (including Standard Model studies and searches beyond it) in pp and AA collisions, and (iv) high-energy $γ$-ray astrophysics. These proceedings are dedicated to the memory of Maria Krawczyk.

Sulfur (S) isotope compositions of pyrites in the sedimentary record have played an important part in our understanding of biogeochemical cycling in the geologic record. However, the kinetics of pyritization are complex and depend strongly on the reactivity and mineralogy of available iron. As a second major sink for sulfide in anoxic sediments, organic matter (OM) provides essential context for reconstructing the distribution and isotopic composition of environmental sulfide. To first order, roughly parallel pyrite and OM δ34S profiles reflect changes in sulfide, while independent patterns require alternative explanations, including changes in iron availability or OM characteristics. We apply this framework to Ocean Anoxic Event 2 (OAE-2, 94 Mya), a period of enhanced reduced C and S burial (in OM and pyrite) that was associated with expanded marine anoxia. We present paired S-isotope records for pyrite and OM along with profiles of OM S:C ratio and S redox speciation from four well-characterized lithologic sections (Pont d’Issole, Cismon, Tarfaya Basin, and Demerara Rise) to reconstruct both local redox structure and global mechanisms impacting the C, S and Fe cycles around OAE-2. OM sulfurization appears to be a major control on OM preservation at all four sites. Similar to modern anoxic environments, there is a positive correlation between OM S:C ratios and OM concentrations for sites with more reducing conditions, implying a link between OM sulfurization and burial. At consistently anoxic sites like Tarfaya Basin and Demerara Rise, strongly sulfurized OM with a consistent S redox speciation and S-isotope composition most likely formed rapidly in sinking particles before, during, and after OAE-2. Particle-hosted OM sulfurization may therefore have been a central mechanism facilitating the massive burial of OM in anoxic environments during this and other periods of enhanced global carbon burial. At the same time, a nearly 25‰ negative shift in the δ34S values of pyrite – but not OM – occurs at multiple, globally distributed sites near the onset of OAE-2, indicating slower pyritization reactions that likely reflect changes in iron delivery due to expanding regional or global anoxia. The combination of pyrite and organic S isotopes thus provides novel constraints on the interwoven cycles of carbon, iron, and sulfur across a major carbon cycle perturbation.

Two analyses of data recorded in proton-proton collisions at the ATLAS detector in 2012 are presented in this thesis. The first pertains to the beam separation (van der Meer) scans required to calibrate the absolute luminosity. An estimate is made for the size of the correction needed to the standard van der Meer calibration method, which assumes that the proton bunch density profiles are factorisable. This is done by observing and modelling the evolution of various beam spot phenomena during the separation scans.The second analysis described is a series of measurements of the Z/gamma cross-section, differential in the phi star observable, for different ranges of the boson invariant mass and absolute rapidity. In particular the events in which the boson decays to electron-positron pairs are considered. The phi star observable is defined in terms of the well-measured lepton directions and enables a probe of initial state gluon radiation in the non-perturbative regime of QCD.

This paper describes the concept, technical realisation and validation of a largely data-driven method to model events with Z→ττ decays. In Z→μμ events selected from proton-proton collision data recorded at √s=8 TeV with the ATLAS experiment at the LHC in 2012, the Z decay muons are replaced by τ leptons from simulated Zarrowττ decays at the level of reconstructed tracks and calorimeter cells. The τ lepton kinematics are derived from the kinematics of the original muons. Thus, only the well-understood decays of the Z boson and τ leptons as well as the detector response to the τ decay products are obtained from simulation. All other aspects of the event, such as the Z boson and jet kinematics as well as effects from multiple interactions, are given by the actual data. This so-called τ-embedding method is particularly relevant for Higgs boson searches and analyses in ττ final states, where Zarrowττ decays constitute a large irreducible background that cannot be obtained directly from data control samples. In this paper, the relevant concepts are discussed based on the implementation used in the ATLAS Standard Model H→ττ analysis of the full datataset recorded during 2011 and 2012.

The measurement of the transverse momentum of W bosons in hadron collisions provides not only an important test of QCD calculations, but also is an important input for the precision measurement of the W boson mass. While the measurement of the Z boson transverse momentum is experimentally well under control, the available unfolding techniques for the W boson final states lead generically to relatively large uncertainties. In this paper, we present a new methodology to estimate the W boson transverse momentum spectrum, significantly improving the systematic uncertainties of current approaches.

Two analyses involving photon interactions in ultra-peripheral lead-lead collisions in the ATLAS detector at the LHC are described, namely the study of dijet production in photo-nuclear ultra-peripheral collisions and a measurement of light-by-light scattering. The first, is an important way to probe and constrain nuclear parton distribution functions, which are known to exhibit suppression at low Bjorken-x with respect to proton PDFs, as well as enhancement at higher Bjorken-x. Light-by-light scattering is forbidden in classical electrodynamics as it violates the super-position principle and is a fundamental prediction of quantum mechanics. The first direct evidence for this interaction with two quasi-real initial state photons is presented.