Cross-section measurements of top-quark pair production in association with a hard photon at 13 TeV with the ATLAS detector

25 years after the top quark's discovery, the Large Hadron Collider at CERN produces proton-proton collision data on unprecedented scales at unprecedented energies - and has heralded an era of top-quark precision measurements. The production of a top-quark pair in association with a photon ($t\bar{t}\gamma$) gives access to the electromagnetic top-photon coupling, one of the fundamental properties of the top quark. Various extensions of the Standard Model predict modifications of the coupling strength or structure, and deviations from the Standard Model prediction of the $t\bar{t}\gamma$ production cross-section would indicate new physics. With enough statistics available from the Large Hadron Collider, the electron-muon channel has gained particular interest due to its high signal purity and precise available theory predictions. This thesis presents results with the full Run 2 dataset collected with the ATLAS detector in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at 13 TeV centre-of-mass energy, corresponding to an integrated luminosity of 139 fb$^{-1}$. In order to compare the results to fixed-order calculations that include non-doubly-resonant diagrams, a combined measurement of $t\bar{t}\gamma + tW\gamma$ is performed. The focus is placed on a measurement of the fiducial inclusive cross-section in the electron-muon channel. Furthermore, the ATLAS data is unfolded to parton level and measurements of differential cross-sections as functions of several observables are presented. Both fiducial inclusive and differential results are compared to state-of-the-art fixed-order calculations at next-to-leading order in QCD. An additional focus of the thesis is placed on studies to use machine-learning techniques, in particular deep neural networks, for the identification of prompt photons.Comment: PhD dissertation (Univ. of G\"ottingen), 173 pages, 75 figures, 25 tables. Available on CERN CDS at https://cds.cern.ch/record/2725289

Neuronal underpinnings of stuttering

Fluent speech production depends on robust connections between brain regions that are crucial for auditory processing, motor planning and execution. The ability of the speech apparatus to produce effortless, continuous and uninterrupted flow of speech is compromised in people who stutter (PWS). Stuttering is a multifactorial speech fluency disorder that results in unintended occurrences of sound syllable repetitions, prolongations, and blocks, particularly on the initial part of words and sentences. Decades of research on the topic have produced an extensive amount of data but the mechanism behind the symptoms associated with stuttering is not clear. The aim of the present study was to investigate the neuronal basis of stuttering by looking at the brains neurochemistry utilizing the proton magnetic resonance spectroscopy (1H - MRS) technique. In particular, we looked at the neurotransmitters N-acetyl Aspartate (NAA), an aggregate of Glutamate and Glutamine (Glx) and myo-inositol (mI) as potential candidates for understanding the biochemical manifestations of stuttering. We have also collected behavioral data from the PWS group and correlated it with their spectroscopy results. Finally, we combined the measurements of neuronal activity behind speech production, probed with functional magnetic resonance imaging (fMRI), with 1H-MRS measurements in order to achieve information on the interaction between neuronal activation and underlying neurochemical function. The inferior frontal gyrus (IFG) was chosen as a target region for this investigation, given its' involvement in speech motor control. Neurotransmitter mI showed the main group effect. The cerebral metabolite pattern of PWS is characterized by the pronounced reduction in myo-inositol level in the IFG. Myo- inositol is considered a glial marker and its concentration may reflect the condition of myelin in the brain. The myelination process is referred to as the maturation process of the fibers that facilitates rapid neural innervation of speech muscles underlying speech fluency. Hence, given the existing literature on the topic and our main findings we suggested that delayed or impaired myelination of the speech-related neuronal network in the postnatal period might be responsible for the later development of stuttering.Flytende tale er avhengig av solide forbindelser mellom hjerneområder involvert i auditorisk prosessering, motorisk planlegging og utførelse. Taleapparatets evne til uanstrengt å produsere flytende uforstyrret tale er forstyrret hos personer som stammer (PWS). Stamming er en sammensatt forstyrrelse av taleflyt som resulterer i ufrivillige gjentagelser av stavelser, utvidelser, og blokkeringer, spesielt i begynnelsen av ord og setninger. Gitt tiår med forskning på området er det ennå ikke klart hvilke mekanismer som ligger til grunn for stammingen. Hensikten med dette studiet har vært å utforske det nevrale grunnlaget til stamming ved å se på hjernens nevrokjemi ved å ta i bruk proton-magnetisk resonsansspektroskopi (1H-MRS) teknikk. Vi har sett på om nevrotransmitterene: N-acetyl Asparatate (NAA); glutamat og glutamin (Glx) og myo-inositol kan bidra til forståelsen av de biokjemiske manifestasjonene av stamming. Vi har også samlet inn atferdsdata fra PWS-gruppen og korrelert dette med spektroskopi-dataen. Til slutt kombinerte vi målingene av den nevral aktiviteten av taleproduksjon med 1H-MRS målingene for å se på interaksjon mellom nevral aktivering og underliggende nevrokjemisk funksjon. Inferior frontal gyrus (IFG) var målområdet for undersøkelsen, siden området er viktig for motorisk kontroll av tale. Nevrotransmitteren myo-inositol viste en hovedgruppeeffekt. Metabolittene i hjernen til personer som stammer var karakterisert av en tydelig reduksjon i nivå av myo-inositol i IFG. Myo-inositol er ansett som en glial markør, og dets konsentrasjon kan muligens fortelle om myelinets tilstand i hjernen. Myelineringsprosessen av nerveceller er en modningsprosess som fasiliterer rask signaloverføring fra hjernen til muskelfibrene involvert i tale. Vi foreslår derfor på bakgrunn av foreliggende litteratur på området og våre resultater at forsinket eller hemmet myelinering av tale-relaterte nevrale nettverk i spedbarnsperioden kan føre til senere utvikling av stamming.LOGO345MAPS-LOG0

Numerical modeling study of a neutron depth profiling (NDP) system for the Missouri S&T reactor

”For decades, Neutron Depth Profiling has been used for the non-destructive analysis and quantification of boron in electronic materials and lithium in lithium ion batteries. NDP is one of the few non-destructive analytical techniques capable of measuring the depth profiles of light elements to depths of several microns with nanometer spatial resolution. The technique, however, is applicable only to a handful of light elements with large neutron absorption cross sections. This work discusses the possibility of coupling Particle Induced X-ray Emission spectroscopy with Neutron Depth Profiling to yield additional information about the depth profiles of other elements within a material. The technical feasibility of developing such a system at the Missouri University of Science and Technology Reactor (MSTR) beam port is discussed. This work uses a combination of experimental neutron flux measurements with Monte Carlo radiation transport calculations to simulate a proposed NDP-PIXE apparatus at MSTR. In addition, the possibility of implementing an Artificial Neural Network to perform automated data analysis of NDP is presented. It was found that the performance of the Artificial Neural Network is at least as accurate as traditional processing approaches using stopping tables but with the added advantage that the Artificial Neural Network method requires fewer geometric approximations and accounts for all charged particle transport physics implicitly”--Abstract, page iii