Hafnium based Heavy Metal Fluoride glasses have been produced and evaluated in a search for new dense scintillating materials. The principal motivation was the electromagnetic calorimeter of the Compact Muon Solenoid (CMS), a proposed detector for the Large Hadron Collider (LHC) at CERN, Geneva. Incorporating CeF 3 in these transparent glasses results in scintillators with fast time constants that are typical of crystalline CeF 3. Typical decay components of 9 ns (30 %) and 25 ns (70 %) have been measured. To record the time distribution of scintillation light, an extension to the single-photon method, has been developed, it is optimised for materials with low light output. An alternative acquisition system which used a Multi-Channel Scaler has been critically evaluated for this application. A low dose rate (1.2 rads- I) 60CO irradiation has been used to determine the radiation tolerance of the glasses. Radiation induced optical absorbance was predominantly located in the UV with tails extending into the visible region. These glasses show partial recovery of optical absorbance at room temperature. Compositional optimisation has shown that Indium and Cerium enhance radiation tolerance.

A study is presented of general features of the reaction e⁺e^-→ hadrons. The data are interpreted in terms of current models of the underlying QCD and hadronisation processes. These models are outlined in detail and their predictions are compared with most of the available experimental data collected between 12.0 and 46.8 GeV mean centre of mass energies. The model arbitrary parameters were optimised to give a generally good description of the global properties of the large hadronic event sample accumulated by the TASSO detector at 35 GeV: The Lund O(α²_s) model describes properties in the event plane very well, but is deficient in the properties transverse to this plane. The Webber LLA model gives a good description of the transverse observables, but overestimates those quantities in the plane. The Lund LLA + O(α²_s) model provides a good representation of the transverse properties but underestimates some quantities in the plane, though the discrepancy is much smaller than for the LLA model. The evolution of the observables as a function of c.m. energy between 12.0 and 41.5 GeV is generally well described, the Lund LLA + O(α²_s) model representing the data best. It is concluded that this model is successful in reproducing accurately most features of the data because it includes QCD calculations of both hard and multiple soft gluon emission processes. The model predictions are extended up to W = 200 GeV, where the two parton cascade models give similar predictions of the event properties which differ significantly from those of the 0(α²_s) model. Top quark production is simulated at W = 200 GeV for a top mass of 60 GeV/c² and the distributions of thrust, aplanarity, PT_in,PT_out and rapidity are found to be most sensitive to its presence. The data at 35 GeV are also analysed in terms of explicit multijet final states and compared with the QCD model calculations. The 0(&alpha;²_s ) model is unable to account for the observed rates of 4- and 5- jets per event, though it reproduces the 2- and 3- jet rates reasonably well. The LLA model gives a better description of the rates of ≥ 4-jets but gives too few 3-, and too many 2-jet events. The LLA + O(α²_s) model is able to reproduce all jet rates well. All the models describe the trend of the evolution of the jet rates between <√s> = 14 and 43.8 GeV. It is shown that the rate of 3-jet events seen in the data decreases as s increases in a manner consistent with the Q² dependence of α_s as predicted by QCD.

We formulate and apply a three-body Glauber model and an adiabatic theory, as alternative approaches to the DWBA method, to study breakup and charge exchange reactions of loosely bound nuclei. The theories derive full finite-range transition amplitudes, which incorporate three-body effects. The formulated Glauber three-body breakup transition amplitude is applied to the (d, pn) deuteron breakup reaction. Three-body s-wave breakup calculations are performed to analyse 260 MeV 63Cu(d, pn) and 270 MeV 12C(d, pn) reaction differential cross-section data. The calculations describe the data fairly well, for low p-n relative energies. The adiabatic theory, in a special limit, is applied to enable computational checks of the Glauber three-body breakup calculations, and for estimation of non-s-wave breakup contributions to the (d, pn) reaction. An adiabatic theory of Coulomb breakup is presented which derives a closed-form adiabatic transition amplitude for Coulomb breakup. Calculations describe deuteron breakup at forward angles at 56, 140 and 270 MeV reasonably well. Previous DWBA analyses are also discussed, and assumptions made in those DWBA calculations are discussed critically. The three-body Glauber model is extended to study the (d, pp) charge-exchange reaction. Three-body effects in the 12C(d, pp)12B reaction are investigated by comparing Glauber calculations with their DWBA limits. The results indicate that these three-body effects are significant and might be responsible for ad hoc modifications needed in DWBA analyses of the same reaction.

<p> As the LHC enters its second run at 13 TeV, new parameter space will become available that will allow for a more extensive search for supersymmetric partners. This thesis explores limits on a baryon number violating R-parity-violating (RPV) extension of the s-channel production of top squarks, examining the experimental signature for the R-parity conserving decay of the top squark into the lightest neutralino and a hadronically decaying top quark. Using Monte Carlo simulations I calculate upper bounds for the RPV coupling parameters &lambda;'' for a range of top squark and neutralino masses that would allow for its existence. </p><p>

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Hadrons containing heavy quarks, in particular b quarks, play an important role in high energy physics. Measurements of their electroweak interactions are used to test the Standard Model and search for new physics. For the comparison of experimental results with theoretical predictions, nonperturbative calculations of hadronic matrix elements within the theory of quantum chromodymanics are required. Such calculations can be performed from first principles by formulating QCD on a Euclidean spacetime grid and computing the path integral numerically. Including b quarks in lattice QCD calculations requires special techniques as the lattice spacing in present computations usually can not be chosen fine enough to resolve their Compton wavelength. In this work, improved nonrelativistic lattice actions for heavy quarks are used to perform calculations of the bottom hadron mass spectrum and of form factors for heavy-to-light decays. In heavy-to-light decays, additional complications arise at high recoil, when the momentum of the light meson reaches a magnitude comparable to the cutoff imposed by the lattice. Discretisation errors at high recoil can be reduced by working in a frame of reference where the heavy and light mesons move in opposite directions. Using a formalism referred to as moving nonrelativistic QCD (mNRQCD), the nonrelativistic expansion for the heavy quark can be performed around a state with an arbitrary velocity. This dissertation begins with a review of the fundamentals of lattice QCD. Then, the construction of effective Lagrangians for heavy quarks in the continuum and on the lattice is discussed in detail. A highly improved lattice mNRQCD action is derived and its effectiveness is demonstrated by nonperturbative tests involving both heavy-heavy and heavy-light mesons at several frame velocities. This mNRQCD action is then used in combination with a staggered action for the light quarks to calculate hadronic matrix elements relevant for rare B decays, including B --&gt; K* gamma and B --&gt; K l l. A major contribution to the uncertainty of the results also comes from statistical errors. The effectiveness of random-wall sources to reduce these errors is studied. As another application of a nonrelativistic heavy quark action, the spectrum of bottomonium is calculated and masses of several bottom baryons are predicted. In these computations, the light quarks are implemented with a domain wall action.

For several theoretically and experimentally motivated reasons, super- symmetry (SUSY) has for some time been identified as an interesting candidate for a theory of fundamental particle physics beyond the Stan- dard Model. The ATLAS collaboration, of which I am a member, possess a detector emplaced in the Large Hadron Collider experiment at CERN. If SUSY does in fact describe our universe, then it is hoped that evidence of it will be visible in data collected in the ATLAS detector. I present an analysis looking for a particular signature that could indicate the presence of SUSY; events containing two like-charge leptons (e or μ). This signature benefits from having both low Standard Model backgrounds as well as potential to observe several SUSY scenarios, par- ticularly those involving strong production processes. These include pair production of squarks and gluinos. The latter of these are particularly relevant for the analysis presented herein since gluinos are Majorana fermions; hence they can decay to produce like-charge leptons. The analysis considers several SUSY production topologies determined from a variety of simplified and phenomenological models. One of the core pieces of any ATLAS analysis is estimating the expected backgrounds in the signal regions. These backgrounds arise both from known Standard Model production processes that can produce the same final state as the SUSY models being targeted, as well as detector mismeasurement effects. One important background in the like-charge analysis is that of “fake” leptons; these are jets that have been misclassified as either electrons or muons by the reconstruction algorithms. A large portion of this thesis is dedicated to introducing novel techniques for robustly estimating these backgrounds, and evaluating their relative performance.

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