Frankfurt (Main), Univ., Diss., 1993

Universiẗat, Diss., 1993--Frankfurt (Main).

We report investigations of physical possibilities beyond the Standard Model, performed in the years between Runs I and II of the Large Hadron Collider (LHC). First, we explore the feasibility of using a hadron collider to unmask hidden sectors by means of a novel signal, the ``monocline". Dilepton production provides the cleanest channel to anticipate a monocline. A compelling sector to seek is dark matter with scalar messengers coupling it to standard fermions. We present current bounds from dilepton spectrum measurements at the LHC and make predictions for sensitivities at Run II of the LHC as well as at a future 100 TeV collider. Second, we corner the space of parameters of supersymmetric frameworks with an appreciable Yukawa coupling between the Higgs fields and a gauge singlet, the so-called Fat Higgs and $\lambda$-SUSY models, in the context of the discovery of the 125 GeV Higgs particle. These models are motivated by their alleviation of the electroweak fine-tuning that supersymmetry breaking entails, via raising the tree-level quartic coupling Higgs boson. Heavy Higgs scalars that couple strongly to the standard Higgs boson induce large radiative corrections to the Higgs quartic coupling, which is crucial to phenomenology; in particular, a very large ratio of the Higgs VEVs ($\tan \beta$), that was previously presumed unfavorable in these models, becomes viable and can be probed by future experiments. In such regions, the most stringent limits come from dark matter constraints on the lightest neutralino. Finally, we place limits on colored scalar production at the LHC in supersymmetric models where gauginos acquire both Dirac and Majorana masses, that we call ``mixed gauginos". While it was known that purely Dirac gluinos were less constrained by LHC searches than their purely Majorana counterparts, we find that the constraints further weaken or strengthen depending on which of the ``mixed" colored fermions acquires a Majorana mass. Also explored are the effects on squark production of turning on Majorana masses for electroweak gauginos. This dissertation consists of previously published and unpublished co-authored material.

No description available.

Geology and tunnelling was given by the U.S. Department of Energy (DOE) as the most important criteria in siting the SSC. The impact of ground water on construction and vice-versa is an important part of a sites geologic and tunnelling attributes, and its potential environmental impacts. Because of the site's undeveloped nature, only limited reconnaissance-type investigations of the regions hydrogeology had occurred prior to the siting of the SSC. To overcome this ignorance geological, geotechnical, and geophysical characteristics of the site were used to describe the hydrogeology. A hydrologically ideal site would lie above any aquifers, have little or no surface water interaction, and yet, have an adequate and reliable supply of good quality water nearby. The Maricopa site possesses all of these characteristics while apparently being absent of subsidence due to ground-water withdrawal.

The Sierrita Mountains were investigated as a site for the proposed Superconducting Supercollider, which was to be housed in a ring-shaped tunnel more than 80 km (50 miles) in circumference. Geostatistical techniques including kriging were used to interpolate the potentiometric surface of the ground water and quantify its uncertainty along the proposed ring alignment to assess potential dewatering problems, based on the sparse water-level information available. Potential water supplies for the Superconducting Supercollider complex include local and imported good-quality ground water, poorer quality but abundant Central Arizona Project water, and Tucson or Green Valley municipal water. Ground water has the most suitable quality, but its development within the Tucson Active Management Area is restricted by state law.

This thesis presents work towards the first measurement of the mass of the W boson (m_W) at ATLAS at the Large Hadron Collider using √s = 7 TeV collision data taken in 2011. The electron energy calibration is presented, including a detailed study of the linearity of the ATLAS electromagnetic calorimeter. Separately, the measurement of the W boson recoil is calibrated using Z boson events. Recoil corrections for the underlying event, pileup, recoil magnitude resolution, recoil angular resolution and recoil response mismodelling are determined, with statistical uncertainties on these corrections corresponding to an estimated uncertainty on m_W of 3.9 MeV. The corrections for calorimeter non-linearity and recoil modelling improve the description of the data, though systematic biases remain. To achieve a precision commensurate with the statistics of the data, these biases will need to be understood.

The two-particle correlation function is measured for neutral current DIS events with 5 < Q2 < 100 GeV2 with data taken by the H1 detector at HERA with -vFs = 300 GeV during the 1994 run period corresponding to an integrated luminosity of 1.3 pb-1. The diffractive and non-diffractive selections of the data are analysed separately, and both exhibit an enhanced correlation for small 4-momentum difference for like-sign pairs as expected from Bose-Einstein interference in the production amplitudes for identical boson pairs. Fits using a Gaussian parametrisation of the enhancement yield no statistically significant difference between the diffractive and non-diffractive samples. The non-diffractive data sample is further separately analysed in three bins of each of the kinematic variables x, Q2, and W as well as mean particle density, (dn/dry*), in the hadronic centre of mass frame. Of these a strong evolution of the Gaussian fit parameters is observed with increasing particle density only. The non-diffractive data are also compared to three fit parameterisations: Gaussian, exponential, and power-law. The most favourable X2 is obtained for the exponential fit, though the power-law attains a similarly successful description of the data in the region of low 4-momentum difference.

This thesis presents the measurement and results of the Z/γ* → μ⁺μ⁻ Drell-Yan triple-differential cross-section, using 20.24 fb⁻¹ of ATLAS data recorded in 2012 at a centre-of-mass energy of √s = 8TeV. The triple-differential cross-section is measured as a function of dimuon invariant mass, m_μμ, dimuon rapidity, γ_μμ , and lepton decay angle in the Collins-Soper frame, cosθ*. These dimensions provide sensitivity to the parton composition of the proton through the parton density functions, PDFs, and the weak effective mixing angle, sin²θeff./W, via the forward-backward asymmetry, A_FB. The measurement is performed on and around the Z-boson's invariant mass peak, 46 < m_μμ < 200 GeV, in a kinematic ducial volume of muon transverse momentum, pT > 20 GeV, and muon pseudo-rapidity |η|≤2.4. The results are unfolded from the detector level to the Born, bare and dressed levels, where a precision of < 0:6% is reported in the central bins. The data is combined with an electron channel measurement resulting in a combined result with reduced total uncertainty. The combined result is shown to constrain PDF uncertainties and achieve the most constrained sin²θeff./W uncertainty yet reported at the LHC.

This thesis presents the results for two searches for new physics performed with the ATLAS experiment. The first, a search for the rare B-meson decay Bs → μμ and measurement of its branching ratio, uses 25 fb⁻¹ of √s = 7 and 8 TeV data recorded during 2011 and 2012. After observing a small number of these decays, a branching ratio of B(Bs → μμ) = (0.9⁺¹·¹₋₀.₈) x 10⁻⁹ is measured, assuming non-negative event yields. This is compatible with the Standard Model at the 2σ level. The second, a search for direct pair production of the supersymmetric top quark partner, is performed using 36.07 fb⁻¹ of √s = 13 TeV data recorded during 2015 and 2016. Final states with a high jet multiplicity, no leptons and large missing transverse momentum are selected to target these decays, with several signal regions designed to cover a wide range of particle masses. No excess is observed, with all signal regions being compatible with the Standard Model within 2σ. Limits are set on the stop mass, excluding up to mt̃1 = 940 GeV for values of mx̃⁰₁ below 160 GeV, assuming a 100% branching fraction to t̃1 → tX̃⁰₁ decays. In addition two reinterpretations of this data are presented, for a gluino-mediated stop production scenario and a direct dark matter production scenario. No excess is observed for either model, and limits are set on the mass of the relevant particles. Finally a viability study into using machine learning techniques to improve on existing SUSY search methods has been performed, with the initial results proving promising.