<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 goal of this thesis is to determine power counting rules at next-to-leading order (NLO) in the hard thermal loop (HTL) resummation. The original paper by Braaten and Pisarski discusses NLO HTL resummation and argues that there are potentially three types of contributions. We start by studying these terms in the specific case of the boson and fermion self energies in QED and QCD, as these quantities have been calculated in previous literature. For the real and imaginary parts of the fermion and gluon self energies, one needs to calculate only one type of term, as the other two are found to be subleading. However, for the real and imaginary parts of the photon self energy, all types of terms need to be calculated.

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.

The photoproduction of the p and the w was studied using data taken by the NA1 experiment at the CERN SPS. The beam was that of a tagged photon with energy between 70-225 GeV incident on an active target, which consisted of a monolithic germanium block and strips of silicon detector. The decay products were detected by the forward FRAMM spectrometer. The p and the w events were identified by their decays into and channels respectively. Using clean samples of events and taking into account their respective branching ratios and simulated geometrical acceptances the ratio was measured to be 9.64 +/- 0.54. The interaction-point distribution of a trimmed sample of p events resulted in the ratio of the interaction rates in the germanium and the silicon parts of the target, leading to the value of a, which describes the A-dependence of the nuclear cross-section by [equation] where A is the nuclear mass number. The measured [alpha] values for the overall and the coherent event samples, respectively, are [alpha] = 1.45 +- 00.5 and [alpha]Coh = 1.44+-0.06.

A preliminary measurement is presented of the lifetime of the ground state neutral charm meson, the D0. This study utilised data taken by the NA1 experiment running on the CERN SPS accelerator. A tagged photon beam was used with energies between 70 and 175Gev and the FRAMM spectrometer provided final state particle identification. The D meson production and decay points were measured with an electronically read out monolithic germanium target followed by silicon strip detectors. Charm events were identified by the reconstruction of D0 meson invariant masses where the D0 originated from a D* decay and decayed to final states containing charged kaons. A sample of 90 D0/D0 decay events was found.

An analysis of data collected In the NA1 high energy photoproduction experiment at the CERN SPS is presented. The theoretical status of charmed particle decay is reviewed. The NA1 experimental apparatus is discussed. Experiment NA1 used an active semiconductor target exposed to a 70-225 GeV tagged photon beam and the forward spectrometer FRAMM to collect data on the decay of particles carrying the charm quantum number. FRAMM was equipped with three lever arms for charged particle momentum analysis, electromagnetic calorimeters for neutral particle reconstruction and Cerenkov detectors for charged particle identification. The active target measured the charged particle multiplicity development along the beam axis to determine the decay length of particles. The proper time resolution of the target was -0.2x10^-13s. A sample of sixty-three Ac charmed baryons are isolated in the decay channel via an inclusive analysis. Twenty-four of these Acs havedecay lengths resolved in the NA1 active target which can be matched to the information in the forward spectrometer FRAMM. A study of the sixty-three reconstructed in FRAMM indicates that a large proportion decayed via the channel, a decay which is believed to proceed exclusively through W exchange.

<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>