Es werden Messungen der totalen Wirkungsquerschnitte der Prozesse pp → W/Z → ll′ in Endzuständen mit Elektronen und Myonen präsentiert. Für diese Analyse werden Daten, die im Jahr 2013 mit dem ATLAS-Detekor am LHC bei einer Schwerpunktsenergie von √s= 2.76 TeV aufgezeichnet wurden und einer integrierten Luminosität von pb−1 entsprechen, verwendet. In dieser Analyse werden mehrere Quellen systematischer Unsicherheiten berücksichtigt. Die Untergründe werden sowohl mittels Simulationen (für elektroschwache und tt ̄ Un- tergründe) als auch mithilfe datengetriebener Methoden (für den Multi-Jet Untergrund) abgeschätzt. Die Resultate der Elektron- und Myon-Kanäle werden kombiniert und ergeben die folgenden Wirkungsquerschnitte: sigma_fid(W → lν) = 2206.3±20.2(stat.)±10.6(sys.)±68.4(lumi.)[pb], sigma_fid(Z → ll) = 200.4±6.1(stat.)±0.3(sys.)±6.2(lumi.)[pb]. Die kombinierten Wirkungsquerschnitte werden zur Berechnung der Wirkungsquerschnitts- Verhältnisse W/Z und W+/W− benutzt. Die Ergebnisse werden mit QCD-Berechnungen unterschiedlicher Ordnungen verglichen. Der Einfluss dieser Messung auf Partonverteilungsfunktionen (parton distribution func- tions, PDFs) wird abgeschätzt. Die gesamte Unsicherheit dieser Messungen ist vergleich- bar mit den Unsicherheiten aktueller PDFs, weshalb diese Analyse zur Einbeziehung in zukünftige PDF-Bestimmungen geeignet ist. Außerdem wurden Studien zur Frozen Showers Methode zur schnelleren Simulation von Ereignissen im ATLAS-Detektor durchgeführt. Es wurde eine neue Methode zur Gener- ierung einer Frozen Showers Bibliothek entwickelt, die eine Reduzierung der für diesen Abschnitt benötigten Zeit erlaubt. / Measurements of the total pp → W/Z → ll′ cross sections in the electron and muon s = 2.76 TeV with the ATLAS detector at the LHC (in 2013), corresponding to a total integrated luminosity of 4 channels are presented. Data collected at a center-of-mass energy pb−1, are used for this analysis. In this measurement, several sources of systematic uncertainties are estimated. The back- ground contribution is estimated using simulation (for electroweak and tt ̄ backgrounds) as well as data-driven methods (for the multijet background). The combined results for electron and muon channels provide the following cross sections: sigma_fid(W → lν) = 2206.3±20.2(stat.)±10.6(sys.)±68.4(lumi.)[pb], sigma_fid(Z → ll) = 200.4±6.1(stat.)±0.3(sys.)±6.2(lumi.)[pb]. The combined cross sections are used for the calculation of the W/Z and W+/W− cross section ratios. These results are compared with different orders of QCD calculations. The effect of the addition of the measured cross sections to the parton density functions (PDF) is estimated. The total uncertainty of the measurements is comparable to the current global PDF uncer- tainties, which makes them applicable for future PDF determination. Additionally, studies of the Frozen Showers method for fast simulation have been per- formed. A new method of Frozen Showers library generation, allowing to reduce time spend on this stage, is developed.

Der International Linear Collider (ILC) ist ein Elektron-Positron-Beschleuniger mit einer Schwerpunktsenergie zwischen 200 und 500 GeV und einer Spitzenluminositaet von $2\cdot 10^{34}\mbox{ cm}^{-2}\mbox{s}^{-1}$. Fuer das Physikprogramm dieser Maschine ist eine exzellente paketweise Messung der Strahlenergie von grundlegender Bedeutung. Um das zu erreichen, sind am ILC verschiedene Techniken vorgesehen. Insbesondere wurden Energiespektrometer vor und nach dem $e^+/e^-$-Wechselwirkungspunkt vorgeschlagen. Die gegenwaertige Standardoption fuer das Spektrometer vor dem Wechselwirkungspunkt ist ein auf Strahllagemonitoren basierendes Magnetspektrometer. In den Jahren 2006/2007 wurde ein Prototyp eines solchen Spektrometers in der End Station A am Stanford Linear Accelerator Center (SLAC) aufgebaut, um die Leistungsfaehigkeit und Zuverlaessigkeit einer derartigen Anlage zu pruefen. Ausserdem wurde eine neue Methode zur Messung der Strahlenergie vorgeschlagen. Diese beruht auf Compton-Streuung von Laserlicht an den Strahlelektronen und erlaubt, die geforderte Energiegenauigkeit von $\Delta E_b / E_b = 10^{-4}$ zu erreichen. Erfahrungen von dem Large Electron-Positron Collider (LEP) und dem Stanford Linear Collider (SLC) zeigten, dass komplementaere Energiemessmethoden notwendig sind, um die Ergebnisse des BPM-Spektrometers zu ueberpruefen. In der vorliegenden Arbeit werden eine Uebersicht ueber das Experiment am SLAC und erste Ergebnisse praesentiert. Des Weiteren wird die neue Methode der Laser-Compton-Streuung beschrieben und wichtige Aspekte detailliert besprochen. / The International Linear Collider (ILC) is an electron-positron collider with a center-of-mass energy between 200 and 500 GeV and a peak luminosity of $2\cdot 10^{34}\mbox{cm}^{-2}\mbox{s}^{-1}$. For the physics program at this machine, an excellent bunch-by-bunch control of the beam energy is mandatory. Several techniques are foreseen to be implemented at the ILC in order to achieve this request. Energy spectrometers upstream and downstream of the electron/positron interaction point were proposed and the present default option for the upstream spectrometer is a beam position monitor based (BPM-based) spectrometer. In 2006/2007, a prototype of such a device was commissioned at the End Station A beam line at the Stanford Linear Accelerator Center (SLAC) in order to study performance and reliability. In addition, a novel method based on laser Compton backscattering has been proposed, since as proved at the Large Electron-Positron Collider (LEP) and the Stanford Linear Collider (SLC), complementary methods are necessary to cross-check the results of the BPM-based spectrometer. In this thesis, an overview of the experiment at End Station A is given, with emphasis on the performance of the magnets in the chicane and first energy resolution estimations. Also, the novel Compton backscattering method is discussed in details and found to be very promising. It has the potential to bring the beam energy resolution well below the requirement of $\Delta E_b / E_b = 10^{-4}$.

Doctor of Philosophy / Physics / Andrew G. Ivanov / In this thesis the measurement of production cross section of top-quark pairs in association with a photon in proton-proton collisions at a center of mass energy of 8 TeV is presented. The data was recorded at the CMS experiment at the LHC in 2012. This measurement aims to extend our knowledge of top quark properties and help to test consistency of the Standard Model (SM) of particle physics. Data-driven methods are used to estimate the photon identification efficiency and purity. The measured cross-section agrees with the standard model expectation.

Angular distributions of jet pairs (dijets) produced in proton-proton collisions at a centre-of- mass energy √s = 7 TeV have been studied with the ATLAS detector at the Large Hadron Collider using the full 2011 data set with an integrated luminosity of 4.8 fb−1, and reaching dijet masses up to 4.5 TeV. All angular distributions are consistent with QCD predictions. Analysis of the dijet angular distribution, using a novel technique simultaneously employing the dijet mass, is employed. This analysis is sensitive to both resonant new physics and phenomena with a slow-onset in mass. Using this technique, new exclusion limits have been set at 95% credibility level for several hypotheses of physics beyond the standard model including: quantum gravity scales, with 6 extra dimensions, below 4.11 TeV, quark contact interactions below a compositeness scale of 7.6 TeV, and excited quarks with a mass below 2.75 TeV. In a large and complex scientific experiment, such as ATLAS, the collection, management and usability of coherent data and metadata is a challenging operation. The availability of these data to physicists within the experiment is essential to all analysis efforts. A new web-based interface called “RunBrowser”, which makes ATLAS and LHC operations data available to the ATLAS Collaboration, is introduced.

With the start of the Large Hadron Collider(LHC) at CERN, we will obtain a new understanding of the physics beyond our current limits. New discoveries will be made; but we will require a deeper understanding, which the LHC machine, being a hadron collider, will not be able to elucidate. Instead, we will need an e+e- collider to make precision measurements of the newly discovered phenomena. Electroweak symmetry breaking and the origin of fermion and boson masses are fundamental issues in our understanding of particle physics. The essential piece of electroweak symmetry breaking - the Higgs boson - will probably be discovered at the LHC. If there are one, or more, Higgs boson(s) precise measurements of all properties of the Higgs will be very important. In this thesis I present two measurements of Standard Model Higgs boson properties in the context of the International Linear Collider (ILC) at √s = 500 GeV, using the proposed International Linear Detector (ILD). First a performance study of ILD to measure the branching ratios of the Higgs boson with mH = 120 GeV, where the Higgs boson is produced with a Z-boson via the Higgsstralung process, and the Z decays into e+e- or μ+μ-. It will also be essential to study the Higgs Yukawa coupling. Therefore, in the second part of this thesis, I present a study of e+e- → tt¯H with the aim of making a direct measurement of the the top-Higgs coupling, using the semi-leptonic nal state and mH of 120 GeV. I show that the top-Higgs coupling can be measured with an accuracy of better than 28%.

This thesis presents the design qualification and construction of the Beam Scintillator Counter (BSC) for the CMS Collaboration at CERN in 2007 - 2008. The BSC detector is designed to aid in the commissioning of the Compact Muon Solenoid (CMS) during the first 2 years of operation and provide technical triggering for beam halo and minimum-bias events. Using plastic scintillator tiles mounted at both ends of CMS, it will detect minimum ionizing particles through the low-to-mid luminosity phases of the Large Hadron Collider (LHC) commissioning. During these early phases, the BSC will provide probably the most interesting and widely used data of any of the CMS sub-detectors and will be employed in the track based alignment procedure of the central tracker and commissioning of the Forward Hadron Calorimeter.

The Standard Model (SM) of particle physics is widely taken as an elegant effective theory of nature at the electroweak scale, with new physics expected at higher energy. Collider searches and other experimental inputs play a vital role in our hunt for the unknown physics, offering great insights along the way and eventually establishing the extension to the SM. Here we present our studies on prospects of direct and indirect searches for three types of models beyond the SM. The Inert Doublet Model (IDM) extends the SM electroweak sector by an extra Higgs doublet with a Z₂-symmetry. We first examine the IDM dilepton signal at the LHC with a center-of-mass energy of 14 TeV and find it exceeding SM backgrounds at 3σ–12σ significance level, with 100 fb⁻¹ integrated luminosity. We further show that it is possible to obtain the IDM trilepton signal at the 5σ significance level, with an integrated luminosity of 300 fb⁻¹. The Left-Right Twin Higgs (LRTH) model solves the little Hierarchy problem by taking the SM Higgs as a pseudo-Goldstone boson from the spontaneous breaking of a global symmetry. We focus on the discovery potential of the heavy top quark partner in the LRTH model at the LHC. With a luminosity of 30 fb⁻¹ at the early stage of the LHC operation, we conclude that the heavy top partner could be observed at a significance level above 5σ. Supersymmetric extensions of the SM enable cancellations among loop corrections to the Higgs mass from bosonic and fermionic degrees of freedom, leading to a solution to the well-known Hierarchy problem. However, the supersymmetry has to be broken by certain mechanism. We present an exploration of the B-physics observables and electroweak precision data in three distinct soft supersymmetry-breaking scenarios. Projection for future sensitivities of the precision data is also explored.

No description available.

Two sites around the Maricopa and Sierrita Mountains respectively were investigated to provide supporting data for the State of Arizona proposal to the Department of Energy to construct a Superconducting Super Collider (SSC) facility. The main feature of the facility is a 53 mile racetrack shaped tunnel. The proposed Maricopa SSC tunnel passes through three main types of rock--approximately 35 miles of indurated fanglomerates, 10 miles of granodiorites and 8 miles of volcanic and sedimentary rocks. The proposed Sierrita SSC tunnel also passes through three main rock types--approximately 19 miles of indurated fanglomerates, 18 miles of granodiorites and granites and 16 miles of volcanic and associated rocks. Data were obtained from three sources--existing data; field investigations including drill logs and geophysics and laboratory testing. Empirical design approaches were compared with rock classifications (RQD, RMR, Q) at the tunnel horizon. Results indicate mostly routine tunneling at both sites. Recommendations are made for: further logging and testing of existing core; further field mapping; additional boreholes in rock and alluvium; and in situ testing of alluvium.

The efficient identification of photons is a crucial aspect in the search for the Higgs boson at ATLAS. With the high luminosity and collision energies provided by the Large Hadron Collider, rejection of backgrounds to photons is of key importance. It is often not feasible to fully simulate background processes that require large numbers of events, due to processing time and disk space constraints. The standard fast simulation program, ATLFAST-I, is able to simulate events ∼1000 times faster than the full simulation program but does not always provide enough detailed information to make accurate background estimates. To bridge the gap, a set of photon reconstruction efficiency parameterisations, for converted and unconverted photons, have been derived from full simulation events and subsequently applied to ATLFAST-I photons. Photon reconstruction efficiencies for isolated photons from fully simulated and ATLFAST-I, plus parameterisations, events are seen to agree within statistical error. A study into a newly proposed Two Higgs Doublet Model channel, gg → H → hh → γγγγ, where the light Higgs (h) boson is fermiophobic, has been investigated. The channel is of particular interest as it exploits the large production cross-section of a heavy Higgs (H) boson via gluon-fusion at the LHC in conjunction with the enhanced branching ratio of a light fermiophobic Higgs (h) boson to a pair of photons. This channel is characterised by a distinct signature of four high pT photons in the final state. Samples of signal events have been generated across the (mh,mH) parameter space along with the dominant backgrounds. An event selection has been developed with the search performed at generator-level. In addition, the search was also performed with simulated ATLFAST-I events utilising the above photon reconstruction efficiency parameterisations. For both analyses, the expected upper limit on the cross-section at 95% confidence level is determined and exclusion regions of the (mh,mH) parameter space are defined for integrated luminosities of 1 f b−1 and 10 f b−1 in seven fermiophobic model benchmarks.