<p> Ionic currents were used to probe amorphous MnO<p style="font-variant: small-caps">2</p>, which is a battery cathode material in lithium ion batteries, that was template electrodeposited in polycarbonate cylindrical nanopores. The porous MnO<p style="font-variant: small-caps"> 2</p> occupies the volume extending approximately 1 &mu;m into the pore from one end and nanovoid channels, in the MnO<p style="font-variant: small-caps">2</p>, allow for electrolyte solution to pass through from one end to the other. </p><p> Presented in this thesis are the results of ionic current studies used to probe ion transport through amorphous MnO<p style="font-variant: small-caps">2</p>, in different oxidation states, with 100 mM LiClO₄ electrolyte in propylene carbonate (PC) solvent. Current-voltage curves, from ionic current-measurements, were unable to resolve excess surface charge in the electrodeposited MnO<p style="font-variant: small-caps"> 2</p>. A comparison of current-voltage curves from when the MnO<p style="font-variant: small-caps"> 2</p> was cycled between lithium inserted and deinserted oxidation states showed a trend of increasing resistance over a series of three lithium insertion and deinsertion cycles.</p>

<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>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> Silicon tracking detectors are frequently used in particle collider experiments, as they can provide excellent spatial precision with little material in order to cause minimal track disruption. Due to a progressive increase in collider luminosities, a common trend in these experiments is the need for higher levels of radiation damage resistance. One proposed class of designs for pixel trackers in high luminosity colliders is the Silicon 3D trench detector. The same design can be scaled up for photon science applications. </p><p> The work discussed in this dissertation was performed as part of a collaboration between BNL, NYU, CNM and SUNY Stony Brook. The central aim of the work presented here was to evaluate the manufactured 3D trench detector prototypes and study their behavior in detail by performing a series of experimental measurements and TCAD simulations. </p><p> An experiment to measure the detector response to an Americium radioactive source was designed and used to study the noise level and charge collection efficiency of detector prototypes. An experimental system which measured the detector response to an infrared laser with computer controlled precision positioning was developed. This system was used to obtain laser pulse response maps of detectors, which in turn were utilized to investigate the dependence of charge collection efficiency of detectors on position, collection time and bias voltage. The same mapping technique was also used to study the change in irradiated detector response. </p><p> Detector response was simulated using the Silvaco TCAD Suite. These simulations were used to study depletion in large photon detectors and charge collection in response to laser hits. Approximate simulations of radiation damage were also performed to investigate the behavior of irradiated detectors. Leakage current and capacitance simulations before and after irradiation were also performed and compared to the experimental measurements. While significant variations in detector response between different prototypes were observed during the experiments, simulation results are still capable of explaining the general properties of the detectors. The combination of the simulation and the experimental results provides an understanding of the signal generation process in these detectors. </p><p> One observed problem is the large bias currents due to manufacturing surface defects. A double-sided version of the trench detector is proposed to mitigate this problem. Electric fields, depletion region shape and formation, bias voltage and transient current response of these detectors are simulated and compared with those of the standard trench detectors. Computer simulations show that the double-sided detectors also have some performance advantages over the original designs including larger more uniform spatial charge collection efficiency and higher radiation damage resistance. These simulation results and the general insensitivity of the proposed detectors to surface defects make the double-sided detectors worthy of further study.</p><p>

<p> Neutrino oscillation is a phenomenon in which neutrinos produced from charged current weak interactions can change flavor as they propagate. The mixing between the three flavor eigenstates and mass eigenstates can be measured through neutrino oscillations as the oscillation probabilities depend on the mixing angles and neutrino mass squared differences. </p><p> T2K is a long baseline neutrino experiment, in which a nearly pure muon neutrino or muon antineutrino beam is produced at J-PARC on the east coast of Japan and travels 295 km through the Earth&rsquo;s crust towards the far detector, Super-Kamiokande (Super-K), a 50 kiloton water Cherenkov detector, in the west of Japan. The neutrino fluxes in the absence of oscillation are measured by the near detectors 280 meters away from the target, and again with oscillation effects at Super-K. Aside from the beam neutrino from J-PARC, Super-K also measures neutrino oscillations independently through the neutrinos produced in the Earth's atmosphere. </p><p> This thesis presents the first analysis in which both the T2K beam neutrino data and the sub-GeV atmospheric neutrino data at Super-K are used in a unified framework to measure neutrino oscillation parameters. The beam neutrino samples are selected for optimal sensitivity to sin²&thetas;₂₃ and &delta;_CP. A Bayesian analysis using a Markov Chain Monte Carlo method is performed. Using T2K Runs 1&ndash;8 data which amounts to 14.7 &times; 10₂₀ protons on target (POT) in neutrino-mode and 7.6 &times; 10₂₀ POT in antineutrino-mode, and 2520 days of Super-K data, the oscillation parameters are measured to be sin²&thetas;₂₃ = 0.528^+0.032_&ndash;0.028, |&Delta;<i> m</i>²₃₂| = 2.46^+0.084_&ndash;0.060(10^&ndash;3eV²), sin²&thetas;₁₃ = 0.0270^+0.0065_{&ndash;0.0047}; and the 90% credible interval of &delta;_CP is [&ndash;&pi;, &ndash;0.18]&amp;[2.33, &pi;]. When the data is also combined with the constraint on sin² 2&thetas;₁₃ = 0.0857 &plusmn; 0.046 from reactor neutrino experiments, the oscillation parameters are measured to be sin²&thetas;₂₃ = 0.543^+0.026_&ndash;0.023, |&Delta;<i>m</i>² 32| = 2.49^+0.042_&ndash;0.090(10^&ndash;3eV²), sin²&thetas;₁₃ = 0.0223^+0.0012_{&ndash;0.0013}; the 90% credible interval of &delta;_CP is [&ndash;&pi;, &ndash;0.628], and the CP-conserving value &delta;_CP = 0 is excluded at 2&sigma;.</p><p>

<p> A search for Higgs boson pair production in the four b-jet final state is carried out with up to 36.1/fb of LHC proton--proton collision data collected at &radic;<i>s</i> = 13 TeV with the ATLAS detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. This thesis presents a search in events with four individually resolved b-tagged jets. Higgs bosons produced with large momenta are reconstructed as single large radius jets with substructure. The analysis of this topology is presented in CERN-THESIS-2018-118. The two analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to four b-quarks are set in each model. The combined result searches for resonance masses in the range 260&ndash;3000 GeV. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.</p><p>

<p> In this thesis, we develop manifestly covariant methods for 4 dimensional, <i> N</i> = 1 superconformal field theories. First, we generalize the embedding formalism in conformal field theories (CFTs) to <i>N</i> = 1 superconformal field theories (SCFTs). As applications we construct manifestly superconformally covariant expressions for land 3-point correlation functions involving the supercurrent multiplet or the global symmetry current superfield. Next, we combine this superembedding formalism with the shadow formalism in CFTs into a new method for computing superconformal blocks appearing in 4-point functions of SCFTs. This new method, called the supershadow formalism, expresses a superconformal block as manifestly covariant integrations over a product of 3-point functions. The supershadow formalism is much more efficient computationally than the brute force methods used previously in the literature. We obtain the superconformal blocks appearing in the 4-point functions of general scalar operator and then specialize to the 4-point functions involving chiral and global symmetry current multiplets. The results in the chiral case can be further generalized to <i> N</i> = 2 SCFTs. Finally, we present a systematic algorithm to extract the correlation functions of conformal primary component operators from the superfield correlation functions. We implemented this algorithm in <i> Mathematica</i> and applied it to the superfield 2-point function between general operators, from which we obtain all the component 2-point functions and all possible shortening conditions for a <i>N</i> = 1 superconformal multiplet. We also discuss a few potential directions for future researches. </p>

<p> A search for vector-like quarks (VLQs) decaying to a Z boson using multi-stage machine learning was compared to a search using a standard square cuts search strategy. VLQs are predicted by several new theories beyond the Standard Model. The searches used 20.3 inverse femtobarns of proton-proton collisions at a center-of-mass energy of 8 TeV collected with the ATLAS detector in 2012 at the CERN Large Hadron Collider. CLs upper limits on production cross sections of vector-like top and bottom quarks were computed for VLQs produced singly or in pairs, <i>T_single, B_single, T_pair, </i> and <i>B_pair.</i> The two stage machine learning classification search strategy did not provide any improvement over the standard square cuts strategy, but for <i>T_pair, B_pair,</i> and <i>T_single,</i> a third stage of machine learning regression was able to lower the upper limits of high signal masses by as much as 50%. Additionally, new test statistics were developed for use in the Neyman construction of confidence regions in order to address deficiencies in current frequentist methods, such as the generation of empty set confidence intervals. A new method for treating nuisance parameters was also developed that may provide better coverage properties than current methods used in particle searches. Finally, significance ratio functions were derived that allow a more nuanced interpretation of the evidence provided by measurements than is given by confidence intervals alone.</p>

<p> In this work, we consider two different models of dark matter and set limits on results of experiments. One is a dynamic dark matter scenario where we put limits on parameters observable by experiments DAMA and XMASS through nuclear recoil of detector atoms (direct detection). The second is a case of dark matter annihilation into positrons and electrons and the signal this would produce on measured values of positron flux and ratio of electron to positron (indirect detection). The values of these quantities as measured by FERMI and PAMELA experiments are observed and an explanation using a dark matter annihilation is presented vs astrophysical sources of particles. </p><p> We explore a dynamic dark matter scenario with an ensemble of dark matter particles that starts at <i>m</i>₀ and spans a comb of particles separated by <i>j</i>^&delta;&Delta;<i> m</i>. We verify the model by using &Delta;<i>m</i> = &infin; and comparing the predictions to a non dynamic model for the same mass <i> m</i>0. We then observe the wider set of possibilities available with the dynamic dark matter model compared with the single mass case vis a vis constraints set by <i>NaI</i> and <i>Xe</i> detectors published by the DAMA and XMASS collaborations and check for validity of model against these measurements. </p><p> The Fermi experiment has measured the cosmic ray electron+positron spectrum and positron fraction [&fcy;e+/(&fcy;e⁺+e^&minus;)], and PAMELA has measured the positron fraction with better precision. While the majority of cosmic ray electrons and positrons are of astrophysical origin, there may also be a contribution from dark matter annihilation in the galactic halo. The upcoming results of the AMS experiment will show measurements of these quantities with far greater precision. One dark matter annihilation scenario is where two dark matter particles annihilate directly to e⁺ and e^&minus; final states. In this article, we calculate the signature &ldquo;bumps&rdquo; in these measurements assuming a given density profile (NFW profile). If the dark matter annihilates to electrons and positrons with a cross section <i>&sigma;v</i> &sim; 10^&minus;26 cm³/s or greater, this feature may be discernible by AMS. However, we demonstrate that such a prominent spectral feature is already ruled out by the relative smoothness of the positron + electron cosmic ray spectrum as measured by Fermi. Hence we conclude that such a feature is undetectable unless the mass is less than &sim;40 GeV.</p><p>