<p> This dissertation shows the first evidence of the process <i>e</i>⁺<i>e</i>^&minus; &rarr; &gamma;&eta;<i>_c</i>(1<i>S</i>) using data collected by the BESIII experiment operating at BEPCII. This process can be used as a probe to study the nature of recently discovered charmonium-like Y states between 4.0 and 4.6 GeV, including the <i>Y</i>(4260) and <i>Y</i>(4360). Data collected at six center-of-mass energies are analyzed, namely: 4.01, 4.23, 4.26, 4.36, 4.42, and 4.60 GeV, corresponding to a total integrated luminosity of 4.6 fb^&minus;1. We measure the Born cross section, &sigma;<i>_E</i>(<i>e</i>⁺<i>e</i>^&minus; &rarr; &gamma;&eta;<i>_c</i>(1<i> S</i>)), at each energy using a combination of twelve &eta;<i>_c</i>(1<i>S</i>) decay channels. Because the significance of the signal is marginal at each energy (&le; 3.0&sigma;), we also combine all six energies under various assumptions for the energy-dependence of the cross section. If a <i>Y</i>(4260) is assumed, we measure &sigma;4_.26(<i>e</i>⁺<i>e</i>^&minus; &rarr; &gamma;&eta;<i>_c</i>(1<i>S</i>)) = 2.11 &plusmn; 0.49 (stat.) &plusmn; 0.33 (syst.) pb with a significance of 4.2&sigma;. With our current statistics we are unable to distinguish the <i> Y</i>(4260) process from others.</p>

<p> T2K is a long baseline neutrino oscillation experiment located in Japan. It was built mainly to detect muon neutrino to electron neutrino oscillation and to measure the mixing angle &thetas;₁₃ of the PMNS matrix, along with the precision measurement of &thetas;₂₃ and mass differences. A &nu;_&mu; beam is produced at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai and travels to the far detector in Kamioka, Japan. There is an ensemble of detectors at 280 m downstream of the target that form the near detector. Super-Kamiokande, a water Cherenkov detector, located 295 km away from the target serves as the far detector. </p><p> The two main backgrounds for electron neutrino appearance at the Super-Kamiokande are the inherent electron neutrino component of the beam and the \pizero{} particle produced via neutral current channel (NC1&pi;⁰) that mimics the electron neutrino interaction signature. To effectively constrain the NC1&pi;⁰ interaction rate on water, the Pi0 Detector (P0D) was built as one of the near detectors. This detector can be filled and drained with water periodically to enable extraction of neutrino interactions on water. </p><p> This analysis measures the NC1&pi;⁰ interaction rate on water in the P0D. It uses neutrino beam data of 3.53 &times; 10²⁰ protons-on-target (POT) for the water-in configuration of the P0D and 6.70 &times; 10²⁰ POT for the water-out configuration. A set of selections are implemented to obtain a sample enriched in signal events. </p><p> The &pi;⁰ invariant mass distribution is compared between data and Monte Carlo. Parameter estimation using Markov Chain Monte Carlo sampling method is performed to measure the signal events in data. </p><p> The data fit results in 130 &plusmn; 20 events on water including both statistical and systematic uncertainties for an expected value of 167 events predicted by the NEUT Monte Carlo. The ratio between nominal Monte Carlo and the best fit value is 0.78 &plusmn; 0.12.</p><p>

<p> The search for phenomena Beyond the Standard Model (BSM) is the primary motivation for the experiments at the Large Hadron Collider (LHC). This dissertation assesses the experimental status of supersymmetric theories based on analyses of data collected by the ATLAS experiment during the first and second run of the LHC. Both R-parity preserving theories defined within the framework of the Minimally Supersymmetric Standard Model (MSSM) as well as R-parity violating models are studied. Further, a framework for systematic reinterpretation, RECAST, is presented which enables a streamlined, community-wide, approach to the search for BSM physics through the preservation of data analyses as parametrized computational workflows. A language and execution engine for such workflows of heterogeneous workloads on distributed computing systems is presented. Additionally, a new implementation of the HistFactory class of binned likelihoods based on auto-differentiable computational graphs is developed for accelerated and distributed inference computation. Finally, to enable efficient reinterpretation, a method of estimating excursion sets of one or more resource-intensive, multivariate, black-box functions, such as p-value functions, through an information-based Bayesian Optimization procedure is introduced.</p><p>

<p> X-ray absorption spectroscopy (XAS) is a powerful technique to determine the structure and function of molecules. It provides element-specific information on geometry, chemical bonding, oxidation state, and spin state, and its applications range from biology to material science. For dilute samples, XAS is measured by partial fluorescence yield (PFY), where the intensity of a weak fluorescence line is recorded as a measure of absorption as the energy of the incident x-ray beam is scanned across an absorption edge of the element of interest. PFY increases the sensitivity for XAS if an x-ray detector is used that can efficiently separate the small fluorescence signal of interest from the x-ray background due to other elements in the sample. </p><p> This dissertation describes the development of a high-resolution x-ray detector based on arrays of superconducting tunnel junctions (STJs). It is cooled to its operating temperature below 0.3 K with a liquid-cryogen-free adiabatic demagnetization refrigerator cryostat, and offers more than an order of magnitude improvement in energy resolution over conventional Ge- or Si-based solid state detectors. For operation in XAS experiments at a synchrotron, the STJ detector array is held at the end of a cold finger that can be inserted into an ultra-high vacuum endstation. This dissertation describes the design and performance of the STJ x-ray spectrometer, and demonstrates its use in PFY-XAS experiments in metallo-organic compounds at the Advanced Light Source synchrotron.</p>

<p>Many Beyond-the-Standard-Model theories predict the existence of one or more additional neutral gauge bosons, or <i>Z'</i> bosons, with masses at the TeV scale or higher. A search for resonances of <i>Z'</i> bosons decaying to &tau;⁺ &tau;^- pairs in [special characters omitted]<i>s</i> = 8 TeV <i>pp</i> collisions from the LHC is presented. The data was collected by the ATLAS detector and corresponds to an integrated luminosity of 19.5-20.3 fb^-1. The search is performed in ditau decay channels in which at least one tau decays hadronically. In each channel, the numbers of ditau events in high-mass regions of data are counted and compared to the expected numbers from Standard Model backgrounds and <i>Z'</i> signals. No statistically significant excess above the Standard Model expectation is observed in any channel. Bayesian 95% credibility upper limits are placed on the <i>Z'</i> production cross section times <i>Z'</i> &rarr; &tau;&tau; branching ratio as functions of the <i>Z'</i> resonance mass for each channel and for a combination of the channels. Sequential Standard Model <i>Z'</i> bosons with masses below 2.02 TeV are excluded at 95% credibility. The impacts on the cross section limits from varying the <i>Z_ssM</i> decay width and couplings to fermions are evaluated. Limits are also placed on the cross section times branching ratio of Non-Universal <i>G</i>(221) <i> Z'</i> bosons with enhanced couplings to third-generation fermions. These are evaluated as functions of the <i>Z'_NU</i> mass and another free parameter. <i>Z'_Nu</i> bosons with masses below 1.3-2.1 TeV are excluded at 95% credibility.</p>

<p> The DarkSide-50 experiment seeks to directly detect dark matter in a liquid argon time projection chamber. In this dissertation, I present an algorithm of my design that determines the position of particle interactions with the liquid argon. This position reconstruction algorithm will be used by DarkSide-50 to reject backgrounds, particularly backgrounds from radioactive elements on the detector surface.</p><p> The position reconstruction algorithm functions by constructing light response functions (LRFs) that map locations in the detector to the expected distribution of signal in DarkSide-50's 38 photomultiplier tubes. Accurate LRFs cannot be produced by simulations of DarkSide-50's optics because such simulations are known to be flawed. Instead, this algorithm constructs LRFs using an iterative process driven by data. Initial, flawed LRFs are produced using simulated events but then used to produce new LRFs from data events. Multiple generations of LRFs are created from data with each generation driven to better satisfy a known feature of the detector: the dominant argon-39 background is uniformly distributed.</p><p> I also discuss a method of discriminating against surface background as an alternative to the common approach of fiducialization. This method considers the difference in goodness-of-fit between the best-fit reconstructed position and the best-fit position at the detector's surface.</p><p> I conclude by presenting results on the performance and validity of this algorithm, including some discussion of reconstruction errors. </p>

<p> Recent advances in the development of intense short pulse lasers are significant. It is available now to access laser with intensity 10²¹ W/cm² by focusing a petawatt class laser, at which intensity hot dense plasmas with relativistic electrons, energy greater than 100 MeV, are produced. High energy x-rays, so called &gamma;-rays, are emitted strongly from such plasmas via Bremsstrahlung. </p><p> In a few years the laser intensity is expected to exceed 10²² W/cm². In such extreme intense laser-matter interaction, the radiative damping is significant, namely, electrons accelerated by the laser fields lose their energies and emit &gamma;-rays. So that we will see intense &gamma;-ray flash from the laser produced plasmas via two competing processes, Bremsstrahlung and radiative damping. However It is not clearly understood which process is dominant at what laser or what target conditions. My research is focus on making the radiation models to understand the &gamma;-ray emissions and studying the extremely intense laser-matter interaction to optimize the &gamma;-ray emissions under the given laser and target conditions. </p><p> Since these relativistic plasmas are non-thermal and non-equilibriated, it is necessary to develop a kinetic plasma code with the radiation physics. We had developed a collisional particle-in-cell code, PICLS, coupled to a radiation transport module to consider the &gamma;-ray emissions. The emissivities of &gamma;-rays had been derived for the relativistic Bremsstrahlung and the radiative damping. In the radiative damping, especially, not only the first order damping term, but up to 4-th order damping terms had been derived from the Lorentz-Dirac equation for the first time. Especially, the 2nd term is found to be important since it is a damping term of the Lorentz force, indicating the particle acceleration including ions would be much less efficient than that what we expected when the laser intensity become greater than 10²³ W/cm². </p><p> The laser energy dependence of the &gamma;-ray energy and the intensity dependence of the angular distribution of &gamma;-rays are studied. By solving the emission and transport of &gamma;-ray it was found that the radiative damping is not significant until the laser intensity exceeds 10²³ W/cm². While the Bremsstrahlung is dominant &gamma;-rays emission process, which can also boost by changing the target with higher Z material or increasing the mass (volume) of the target. As an application of &gamma;-ray production, the pair creation, forming a pair plasma, is attractive. The number of positrons via pair creation from the Bethe-Heitler process is also computed in the code. The optimal parameters of laser and target to increase &gamma;-ray yields as well as positrons yields are identified.</p>

The thesis can be divided roughly into two parts. The first part deals with the design, construction and operation of the accelerator, whilst the second is devoted mainly to a theoretical study of the process of betatron injection. The section on design is concerned with problems associated with synchrotron magnets and a critical survey of the important design criteria and techniques is presented. The 30 MeV. magnet is given as a particular example and some original work on the application of relaxation methods is described. The ways in which power can be supplied to the magnet are considered and also some experiments on the use of an on-load tap changer. Experimental results of magnet excitation characteristics are compared with calculated values and a detailed account is given of magnetic field measurements involving the use of new techniques. In the operation of the machine, original experiments are described and discussed on the effect of varying a number of operating parameters. An attempt is made to determine the relative importance of these and compare the working efficiency of American betatrons with the 30 MeV synchrotron. The theoretical study of the injection process can again be sub-divided into two main parts. The first is an original investigation of the Influence of charge and current images on the maximum theoretical circulating current. In the second part an attempt is made to develop a quantitative expression for Kerst Self-contraction and to compare theoretical calculations with experimental results. Whilst the comparison is favourable and, for the first time, a number of observed phenomena can be explained by the use of the theory, the validity of Kerst Self-contraction is questioned.

A wide gap streamer chamber has been designed and constructed. Its performance in various modes has been investigated. It is shown that an angular accuracy of 1.5 m rad can be achieved for a 20 centimetre track. The chamber has been applied to the study of multiple scattering of 100 Mev muons in one inch of lead. A large departure from theory has been observed, and the analysis has indicated a second narrow component of the distribution of the particles plotted against the projected angles of scattering. The chamber has been modified to study low energy particles.

A new model for two-body high energy scattering is presented as part of an investigation into the phenomenological consequences of the non-planar structure of Reggeon-particle scattering. The model is a modification of the weak cut reggeized Absorption model for Pion-Nucleon scattering and is developed in form of a correlation modified quasi eikonal where the Reggeon and an arbitrary number of Pomerons are allowed to change the projection of the nucleon spin. A correlation parameter - the "Gribov c" - which has its origin in Gribov's theory, provides an indication about the failure of the traditional weak cut reggeized absorption model and restores its most profound shortcoming - the prediction of an incorrect phase behaviour of the helicity isovector nonflip amplitude in the reaction while retaining the model's attractive simplicity. The vertices of the Reggeon-calculus depend in general on the angle between the momenta of the exchanged reggepoles. By parameterizing this dependence we take into account the effective contribution of inelastic intermediate states in the unitarity expansion of the Regge-particle scattering amplitude. We obtain a reasonable phase energy description of the isovector amplitude. We demonstrate in detail the mechanism by which the correct phase behaviour is restored. The spin-structure of the amplitudes is investigat ed and observables of N scattering between 6 and 200 GeV/c within a range of momentum transfer of are being produced.