The quadrupole moment-polarization potential which models the interaction of a non-penetrating Rydberg electron with a non-spherical atomic core has been derived from first principles. In order to test the model, we have determined new and highly accurate term values for the 5g, 6g, 6h, 7h and 7i levels of silicon. Some of these new energy levels are based on a detailed analysis of the ATMOS infrared solar spectra, while the higher n = 7 levels have been conclusively identified by re-analyzing the solar 12 micron silicon emission lines. By fitting the model to the new energy levels, we have shown that only the extended polarization model, which includes the complete second order shift due to the model potential, is capable of reproducing the observed data to within the experimental uncertainties. The model has been implemented using a least squares fitting routine, from which we have determined accurate values for all the leading core parameters. The new Si I ionization limit of 65 747.727 $\pm$ 0.01 cm$\sp{-1}$, represents a substantial improvement over the previously accepted value. In addition, there is strong evidence that separate dipole polarizabilities should be used for each core fine structure level. Both theoretical calculations and fits to observed levels suggests that the 3/2 core polarizability is almost 1% larger than that of the 1/2 core.

The electric dipole moment of the ground state of cesium, d$\sb{\rm Cs}$, is measured. This result is related to the electric dipole moment of the electron in a straightforward way using the results of atomic theory calculations found in the literature. The resulting limit of the electric dipole moment of the electron represents a stringent test of time reversal invariance. Cesium vapor is studied at zero magnetic field in glass cells which also contain 250 torr of nitrogen. The ground state of cesium is optically pumped by a laser beam and the atomic orientation undergoes the electrical analog of Larmor precession due to an applied electric field. The precession is detected by comparing the transmission rates of left and right circularly polarized light for a second laser beam which is orthogonal to both the initial laser beam and the applied electric field. The Hamiltonians H = $\vec\mu\cdot\vec B$ and H = $\vec d\cdot\vec E$ are interchangeable allowing calibration of the apparatus using an applied magnetic field. During data acquisition all three components of the effective magnetic field are reduced below 100 nG. Comparing signals from two cells with opposite electric fields eliminates signals due to drifts in the homogeneous magnetic field. Comparing the signals from four cells, two with electric fields and two without, reduces noise due to fluctuating magnetic fields to about 150 pG in 20 seconds of integration (a single data point.) The precession frequency is determined with a statistical precision of 0.5 $\mu$Hz in a two day data collection run. A set of 13 data runs, 9 in the two cell configuration and 4 in the four cell configuration, is used to place upper limits d$\sb{\rm Cs}$ $<$ 1.1 $\times$ 10$\sp{-24}$e-cm, d$\sb{\rm e}$ $<$ 9.3 $\times$ 10$\sp{-27}$e-cm and a limit on T-violating electron-nucleon scaler interactions of C$\sb{\rm S}$ $<$ 10$\sp{-5}\rm G\sb{\rm F}$. This limit represents an order of magnitude improvement over the previously limits on d$\sb{\rm Cs}$ and constrains theories attempting to explain the violation of CP invariance which is seen in the K meson system.

Understanding the origin or Electroweak symmetry breaking within the Standard Model was a key motivation for the construction of the Large Hadron Collider (LHC) experiment at CERN. This thesis presents a search for evidence of Higgs boson production in the 4.7 fb−1 of collision data recorded at a centre-of-mass energy of 7 TeV at the ATLAS detector during 2011. This search is focused on signal events in which a Higgs boson is produced in the mass range 100 < mH < 180 GeV/c2 and subsequently decays to a pair of W bosons or a pair of tau leptons to final states with one hadronically decaying tau lepton and one light lepton. After an event selection criteria has been applied, the number of events in this data sample is consistent with the total background estimate and an upper limit is placed on the SM Higgs boson production rate at 95% confidence level. In addition, the prospects for measuring the SM Higgs coupling strength to tau leptons with the associated Higgs production channels and the full LHC dataset are also presented.

The proposed neutrino factory, a facility for precision measurements of neutrino oscillations, requires directional neutrino beams to reach the required sensitivities. Among the few sources of such beams is the decay of muons travelling at relativistic speeds, therefore an intense source of muons and subsequent rapid acceleration must be designed so they can reach the required energy before decaying. This thesis considers several stages in this process: pions are produced from a proton beam hitting a target and pion yield optima are determined as a function of target design parameters and the proton energy. Issues related to producing the original proton beam are also discussed. The pions decay to a beam of muons, confined by a channel of solenoids and other components known as the muon front end. A design for this is found that meets the requirement of 10^21 muons per operational year [1]. The computer code MARS15 [2] is used to simulate the target, with benchmarks against GEANT4 [3] and initial results from the HARP experiment [4]. The author's code Muon1 [5] is used for muon tracking, with its techniques also explained in the thesis. To find the highest-yielding arrangement of magnets and accelerating components from the target onwards, Muon1 incorporates an optimisation feature where almost all parameters of the beamline can be varied. This produces a high-dimensionality search space where the best muon yield is sought using a genetic algorithm. As each individual evaluation of a design is itself a time-consuming simulation with tens of thousands of particles, the code has been deployed as a distributed computing project that is able to perform millions of simulations per optimisation. [1] "GROUP REPORT: Physics at a Neutrino Factory", C. Albright et al. (Eds. S. Geer and H. Schellman), Report to the Fermilab Directorate, FERMILAB-FN-692, hep-ex/0008064 (2000). [2] "The MARS Code System" version 15.07, by N.V. Mokhov, available from http://www-ap.fnal.gov/MARS/ [3] "GEANT4 - a simulation toolkit", S. Agostinelli et al., Nuclear Instruments and Methods A 506, pp.250-303 (2003), available from http://geant4.web.cern.ch/geant4/ [4] "Status and prospects of the HARP experiment", M. Ellis, J. Phys. G 29, pp.1613-1620 (2003). [5] Muon1 Distributed Particle Accelerator Design project website, http://stephenbrooks.org/muon1

One of the main motivating factors for the construction of the Large Hadron Collider (LHC) was the search for the Higgs boson, postulated to explain the origin of fundamental gauge boson masses. This thesis presents the results of the first search for the Higgs boson at the LHC, using 35 pb^−1 of proton-proton collision data with a centre of mass energy of 7 TeV collected by the ATLAS experiment throughout 2010. The search is performed in the H -> WW channel, since the branching ratio for Higgs boson decays to W bosons is large for a wide range of Higgs boson masses. Two different search methods are presented: a straightforward cut-based method and a method using a matrix-element-based discriminant to provide additional separation between signal and background. The matrix element method is shown to give better expected sensitivity at all Higgs boson masses. Using these methods, a SM-like Higgs boson with a mass of 160 GeV with a production rate of 1.2 times the SM rate is excluded at 95% Confidence Level and limits are placed on the production rate of the SM Higgs boson in the range of masses from 120 < mH < 200 GeV. In addition, a measurement of the SM WW cross section is performed. It is essential to understand this channel since it is the major background to the H -> WW search. SM WW production is also sensitive to new physics processes, which would enhance its cross section. The SM WW cross section is measured to be σ(WW) = 40+20−16(stat.)±7(syst.) pb, which is consistent with the NLO SM expectation of 46 ± 3 pb.

The ATLAS experiment is used to observe the √s=7 TeV proton-proton collisions produced by the LHC at CERN. This gives an unprecedented opportunity to search for physics beyond the Standard Model at hitherto unexplored kinematic regimes. Supersymmetry (SUSY) provides interesting solutions to a variety of theoretical problems that may be encountered in the Standard Model at high energy scales, while providing signatures that may be observed at the LHC. However, in order to produce a search that is sensitive to SUSY it is vital to understand how the physics that has been discovered to date may produce signatures that mimic those expected from SUSY. Statistical models are constructed using both Monte Carlo and data-driven predictions of various background processes. The expectations are compared to the observed data for selections containing one electron or muon, each in association with jets and missing transverse momentum. Kinematic variable shapes, in the form of histograms, are used to enhance the sensitivity of the search. Squark and gluino masses in a MSUGRA SUSY model are excluded up to 1200 GeV, while gluino masses up to 900 GeV are excluded in a simplified SUSY model. Model-independent limits are also set, excluding theoretical models with efficiency times cross section above 1 fb.

Apresentamos um estudo do setor da quebra espontânea de simetria da teoria eletrofraca através do formalismo de lagrangianas quirais, analisando os operadores que geram vértices anômalos genuinamente quárticos entre os bósons de gauge, os quais podem ser sondados pela próxima geração de aceleradores: LHC e NLC. Com o objetivo de obter vínculos aos acoplamentos anômalos relativos a esses operadores, estudamos as reações e POT. +e POT. - W POT. + W POT. Z e e POT. +e POT. - ZZZ no NLC operando com energias no centro de massa de s = 0.5 TeV e 1 TeV, estendendo as nossas análises para a colisão com o feixe de elétrons polarizado. Avaliamos também o impacto desses mesmos acoplamentos ao processo pp VV + 2 jatos (V = W±, Z) no LHC. No intuito de desenvolver cálculos realísticos, todas as amplitudes de espalhamento das reações estudadas foram determinadas sem qualquer tipo de aproximação. / We present a study of electroweak symmetry breaking sector in the framework or chiral Lagrangians, analyzing the operators that lead to genuine quartic gauge boson couplings, which could be probed by the next generation accelerators; LHC and NLC. In order to get bounds on the anomalous couplings related to these operators, we studied the reactions e+e- W+W-Z and e+e- ZZZ at the NLC operating with center-or-mass energy of s = 0.5 TeV and 1 TeV, extending our analysis to polarized electron beam collisions. We also estimate the impact of these couplings to the process pp VV + 2 jets (V = W±, Z) at the LHC. In order to develop realistic calculations, all the scattering amplitudes considered have been determined without any kind of approximation.

<p>The Standard Model of particle physics has been very successful in predicting a wide range of phenomena and has so far been confirmed by all existing data to a very high precision.</p><p>The work described in this thesis tests the limits of validity of the Standard Model (SM) in two areas believed to be sensitive to deviations from the theory: the observation of unpredicted particles and CP violation. The studies were performed within the framework of experiments at two hadron colliders, the future ATLAS detector scheduled for operation in 2007 at the Large Hadron Collider in Geneva and the currently running DØ experiment at the Tevatron in Chicago.</p><p>The tau lepton’s distinctive signature is a useful tool in many new physics searches where it is present in the final state. As a first study in ATLAS a Monte Carlo analysis of two-tau final states, which are sensitive to the underlying structure of supersymmetric models, was performed. </p><p>Several extensions of the SM predict the existence of a charged Higgs boson.The major part of this thesis has consisted in using tau leptons to search for the charged Higgs in the context of the Minimal Supersymmetric extension of the SM (MSSM). Results from this thesis show that searches for the <i>H</i>^± → τν_τ decay channel extend the charged Higgs discovery reach for the ATLAS experiment compared to previous studies of other channels: the charged Higgs can be observed for masses up to ~ 600 GeV for tan<i>β</i> > 10. Its mass can be determined with an uncertainty of 1 to 2%, dominated by statistical errors. The tan<i>β</i> parameter can be derived from the absolute rate of this decay to a precision around 6% for 20 < tan <i>β</i> < 50.</p><p>By measuring precisely the unitarity triangle parameter sin2<i>β</i> the SM description of CP violation can be put to a test. As a separate study a Monte Carlo analysis was performed in ATLAS, which shows that the systematic uncertainty is half the attainable statistical uncertainty. </p><p>As part of the effort to search for the charged Higgs in the DØ experiment a trigger algorithm for tau leptons was written, extensively tested and implemented in the experiment. Trigger strategies for events containing taus were designed. These trigger studies will be useful also for many other new physics searches at DØ.</p>

<p>A search for cosmic point sources of neutrinos has been performed using data taken in 1999 with the AMANDA-B10 neutrino telescope. </p><p>This work describes methods for signal and background separation and the statistical analysis of the final data sample. In particular, the multivariate method Support Vector Machines has been applied to achieve good background rejection while at the same time retaining high signal efficiency. </p><p>A grid search covering the complete northern hemisphere revealed no statistical significant excess of events over the expected background from mis-reconstructed cosmic ray induced muons and muons induced by atmospheric neutrinos. Thus, no cosmic point sources of neutrinos have been detected. Upper limits on the neutrino flux for each cell of the grid are presented.</p><p>Twenty potential sources of neutrinos chosen among three classes of astronomical objects (Blazars, Super Nova Remnants and Microquasars) have been preselected. Upper Limits on the flux of cosmic neutrinos from those are presented.</p><p>The presence of systematic uncertainties makes the calculation of confidence limits an intricate problem. A method is presented which makes it possible to include these uncertainties into the frequentist construction of confidence intervals. Statistical properties of the presented method have been studied.</p>

The Standard Model of particle physics has been very successful in predicting a wide range of phenomena and has so far been confirmed by all existing data to a very high precision. The work described in this thesis tests the limits of validity of the Standard Model (SM) in two areas believed to be sensitive to deviations from the theory: the observation of unpredicted particles and CP violation. The studies were performed within the framework of experiments at two hadron colliders, the future ATLAS detector scheduled for operation in 2007 at the Large Hadron Collider in Geneva and the currently running DØ experiment at the Tevatron in Chicago. The tau lepton’s distinctive signature is a useful tool in many new physics searches where it is present in the final state. As a first study in ATLAS a Monte Carlo analysis of two-tau final states, which are sensitive to the underlying structure of supersymmetric models, was performed. Several extensions of the SM predict the existence of a charged Higgs boson.The major part of this thesis has consisted in using tau leptons to search for the charged Higgs in the context of the Minimal Supersymmetric extension of the SM (MSSM). Results from this thesis show that searches for the H± → τντ decay channel extend the charged Higgs discovery reach for the ATLAS experiment compared to previous studies of other channels: the charged Higgs can be observed for masses up to ~ 600 GeV for tanβ &gt; 10. Its mass can be determined with an uncertainty of 1 to 2%, dominated by statistical errors. The tanβ parameter can be derived from the absolute rate of this decay to a precision around 6% for 20 &lt; tan β &lt; 50. By measuring precisely the unitarity triangle parameter sin2β the SM description of CP violation can be put to a test. As a separate study a Monte Carlo analysis was performed in ATLAS, which shows that the systematic uncertainty is half the attainable statistical uncertainty. As part of the effort to search for the charged Higgs in the DØ experiment a trigger algorithm for tau leptons was written, extensively tested and implemented in the experiment. Trigger strategies for events containing taus were designed. These trigger studies will be useful also for many other new physics searches at DØ.