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A Search for Muon Neutrino to Electron Neutrino Oscillations in the MINOS Experiment (Springer Theses)
by Juan Pedro Ochoa-RicouxThe centerpiece of the thesis is the search for muon neutrino to electron neutrino oscillations which would indicate a non-zero mixing angle between the first and third neutrino generations (θ13), currently the "holy grail" of neutrino physics. The optimal extraction of the electron neutrino oscillation signal is based on the novel "library event matching" (LEM) method which Ochoa developed and implemented together with colleagues at Caltech and at Cambridge, which improves MINOS' (Main Injector Neutrino Oscillator Search) reach for establishing an oscillation signal over any other method. LEM will now be the basis for MINOS' final results, and will likely keep MINOS at the forefront of this field until it completes its data taking in 2011. Ochoa and his colleagues also developed the successful plan to run MINOS with a beam tuned for antineutrinos, to make a sensitive test of CPT symmetry by comparing the inter-generational mass splitting for neutrinos and antineutrinos. Ochoa's in-depth, creative approach to the solution of a variety of complex experimental problems is an outstanding example for graduate students and longtime practitioners of experimental physics alike. Some of the most exciting results in this field to emerge in the near future may find their foundations in this thesis.
Search for New Phenomena in Dijet Angular Distributions at √s = 8 and 13 TeV (Springer Theses)
by Lene Kristian BryngemarkThis thesis describes the use of the angular distributions of the most energetic dijets in data recorded by the ATLAS experiment, at CERN's Large Hadron Collider (LHC), the goal of which is to search for phenomena beyond what the current theory of Particle Physics (the Standard Model) can describe. It also describes the deployment of the method used in ATLAS to correct for the distortions in jet energy measurements caused by additional proton-proton interactions. The thesis provides a detailed introduction to understanding jets and dijet searches at the LHC. The experiments were carried out at two record collider centre-of-mass energies (8 and 13 TeV), probing smaller distances than ever before. Across a broad momentum transfer range, the proton constituents (quarks and gluons) display the same kinematical behaviour, and thus still appear to be point-like. Data are compared to predictions corrected for next-to-leading order quantum chromodynamics (NLO QCD) as well as electroweak effects, demonstrating excellent agreement. The results are subsequently used to set limits on parameters of suggested theoretical extensions to the Standard Model (SM), including the effective coupling and mass of a Dark Matter mediator.
Search for New Phenomena in Top-Antitop Quarks Final States with Additional Heavy-Flavour Jets with the ATLAS Detector (Springer Theses)
by Daiki YamaguchiThis book reports on the search for a new heavy particle, the Vector-Like Top quark (VLT), in the Large Hadron Collider (LHC) at CERN. The signal process is the pair production of VLT decaying into a Higgs boson and top quark (TT→Ht+X, X=Ht, Wb, Zt). The signal events result in top–antitop quarks final states with additional heavy flavour jets. The book summarises the analysis of the data collected with the ATLAS detector in 2015 and 2016. In order to better differentiate between signals and backgrounds, exclusive taggers of top quark and Higgs boson were developed and optimised for VLT signals. These efforts improved the sensitivity by roughly 30%, compared to the previous analysis. The analysis outcomes yield the strongest constraints on parameter space in various BSM theoretical models. In addition, the book addresses detector operation and the evaluation of tracking performance. These efforts are essential to properly collecting dense events and improving the accuracy of the reconstructed objects that are used for particle identification. As such, they represent a valuable contribution to data analysis in extremely dense environments.
Search for New Physics in Mono-jet Final States in pp Collisions
by Giuliano GustavinoThis thesis provides a detailed and comprehensive description of the search for New Physics at the Large Hadron Collider (LHC) in the mono-jet final state, using the first 3. 2 fb$^{{-1}}$ of data collected at the centre of mass energy of colliding protons of 13 TeV recorded in the ATLAS experiment at LHC. The results are interpreted as limits in different theoretical contexts such as compressed supersymmetric models, theories that foresee extra-spatial dimensions and in the dark matter scenario. In the latter the limits are then compared with those obtained by other ATLAS analyses and by experiments based on completely different experimental techniques, highlighting the role of the mono-jet results in the context of dark matter searches. Lastly, a set of possible analysis improvements are proposed to reduce the main uncertainties that affect the signal region and to increase the discovery potential by further exploiting the information on the final state.
Search for New Physics in tt Final States with Additional Heavy-Flavor Jets with the ATLAS Detector
by Javier Montejo BerlingenThis doctoral thesis focuses on the search for new phenomena in top-antitop quark (tt) final states with additional b-quark jets at the LHC. It uses the full Run 1 dataset collected by the ATLAS experiment in proton-proton collisions at √s=8 TeV. The final state of interest consists of an isolated lepton, a neutrino and at least six jets with at least four b-tagged jets, a challenging experimental signature owing to the large background from tt+heavy-flavor production. This final state is characteristic of ttH production, with the Higgs boson decaying into bb, a process that allows direct probing of the top-Higgs Yukawa coupling. This signature is also present in many extensions of the Standard Model that have been proposed as solutions to the hierarchy problem, such as supersymmetry or composite Higgs models, which predict the pair production of bosonic or fermionic top quark partners, or the anomalous production of four-top-quark events. All these physics processes have been searched for using an ambitious search strategy that has been developed on the basis of a combination of state-of-art theoretical predictions and a sophisticated statistical analysis to constrain in-situ the large background uncertainties. As a result, the most restrictive bounds to date on the above physics processes have been obtained.
Search for Scalar Top Quarks and Higgsino-Like Neutralinos
by Takuya NobeThis book reports a search for theoretically natural supersymmetry (SUSY) at the Large Hadron Collider (LHC). The data collected with the ATLAS detector in 2012 corresponding to 20 /fb of an integrated luminosity have been analyzed for stop pair production in proton-proton collisions at a center-of-mass energy of 8 TeV at the Large Hadron Collider (LHC) in the scenario of the higgsino-like neutralino. The author focuses on stop decaying into a bottom quark and chargino. In the scenario of the higgsino-like neutralino, the mass difference between charginos and neutralinos (Δm) is expected to be small, and observable final-state particles are likely to have low-momentum (soft). The author develops a dedicated analysis with a soft lepton as a probe of particles from chargino decay, which suppresses the large amount of backgrounds. As a result of the analysis, no significant SUSY signal is observed. The 95% confidence-level exclusion limits are set to masses of stop and neutralino assuming Δm = 20 GeV. The region with ΔM (the mass difference between stop and neutralino) 120 GeV up to 600 GeV of stop mass with neutralino mass of less than 280 GeV. The author clearly shows very few remaining parameter spaces for light stop (e. g. , topology of stop decay is extremely similar to the SM top quark) by combining his results and previous ATLAS analyses. His results provide a strong constraint to searches for new physics in the future.
The Search for Superstrings, Symmetry, and the Theory of Everything
by John GribbinNo one is more successful than this author when it comes to making the cutting edge of physics more accessible to a broad lay audience. In Schrodinger's Kittens, he took readers to the eerie world of subatomic particles & waves. Now, he explores the most exciting area of research in physics today: string theory. Following a series of major breakthroughs in the 1990s, physicists are putting together a clearer picture of how subatomic particles work. By hypothesizing particles as a single loop of vibrating "string," they are on the brink of discovering a way to explain all of nature's forces in a single theory. Grandly named "superstrings,"& incorporating the ideas of "supersymmetry," these models are the prime candidate for the long sought-for "Theory of Everything." Written in clear & accessible language. The Search for Superstrings, Symmetry, & the Theory of Everything brings to life the remarkable scientific research that is on the cusp of radically altering our conception of the universe.
Search for Supersymmetry in Hadronic Final States
by Hannsjörg Artur WeberThe project reported here was a search for new super symmetric particles in proton-proton collisions at the LHC. It has produced some of the world's best exclusion limits on such new particles. Furthermore, dedicated simulation studies and data analyses have also yielded essential input to the upgrade activities of the CMS collaboration, both for the Phase-1 pixel detector upgrade and for the R&D studies in pursuit of a Phase-2 end cap calorimeter upgrade.
The Search for Supersymmetry in Hadronic Final States Using Boosted Object Reconstruction (Springer Theses)
by Giordon StarkThis thesis represents one of the most comprehensive and in-depth studies of the use of Lorentz-boosted hadronic final state systems in the search for signals of Supersymmetry conducted to date at the Large Hadron Collider. A thorough assessment is performed of the observables that provide enhanced sensitivity to new physics signals otherwise hidden under an enormous background of top quark pairs produced by Standard Model processes. This is complemented by an ingenious analysis optimization procedure that allowed for extending the reach of this analysis by hundreds of GeV in mass of these hypothetical new particles. Lastly, the combination of both deep, thoughtful physics analysis with the development of high-speed electronics for identifying and selecting these same objects is not only unique, but also revolutionary. The Global Feature Extraction system that the author played a critical role in bringing to fruition represents the first dedicated hardware device for selecting these Lorentz-boosted hadronic systems in real-time using state-of-the-art processing chips and embedded systems.
Search for Supersymmetry in pp Collisions at √s = 8 TeV with a Photon, Lepton, and Missing Transverse Energy
by Yutaro IiyamaThis Ph. D. thesis is a search for physics beyond the standard model (SM) of particle physics, which successfully describes the interactions and properties of all known elementary particles. However, no particle exists in the SM that can account for the dark matter, which makes up about one quarter of the energy-mass content of the universe. Understanding the nature of dark matter is one goal of the CERN Large Hadron Collider (LHC). The extension of the SM with supersymmetry (SUSY) is considered a promising possibilities to explain dark matter. The nominated thesis describes a search for SUSY using data collected by the CMS experiment at the LHC. It utilizes a final state consisting of a photon, a lepton, and a large momentum imbalance probing a class of SUSY models that has not yet been studied extensively. The thesis stands out not only due to its content that is explained with clarity but also because the author performed more or less all aspects of the thesis analysis by himself, from data skimming to limit calculations, which is extremely rare, especially nowadays in the large LHC collaborations.
Search for the Decay K_L → π^0\nu\bar{\nu} at the J-PARC KOTO Experiment (Springer Theses)
by Kota NakagiriThis book reports on a new result from the KL→π0νν search at the J-PARC KOTO experiment, which sets an upper limit of 3×10-9 for the branching fraction of the decay at the 90% confidence level, improving the previous best limit by an order of magnitude. To explain the matter–antimatter asymmetry in the universe, still unknown new physics beyond the standard model (SM) that breaks CP symmetry is necessary. The rare decay of a long-lived neutral K meson, KL→π0νν, is a CP-violating decay. It is an excellent probe to search for new physics because new physics can contribute to the decay and change its branching fraction, while the SM is as small as 3×10-11. However, it is extremely difficult to search for because all of the decay products are neutral and two neutrinos are undetectable. The KL→π0νν signal is identified by measuring two photons from a π0 with a calorimeter and confirming the absence of any other detectable particles with hermetic veto counters. The book contributes to the analysis of neutron-induced backgrounds which were the dominant background sources in the search. For the background caused by two consecutive hadronic showers in the calorimeter due to a neutron, the author evaluated the background yield using a data-driven approach. For another background caused by an η meson production—η decays two photons—by a neutron that hits a veto counter near the calorimeter, the author developed an original analysis technique to reduce it. The book also contributes to the analysis of the normalization modes (KL→3π0, KL→2π0, KL→2γ) to measure KL yield, the estimation of the signal acceptance based on a simulation, and the evaluation of the trigger efficiency. As a result, significant improvements in the measurement were achieved, and this is an important step in the continuing higher sensitivity search, which can reach new physics with the energy scales up to O(100-1000 TeV).
Search for the Higgs Boson in the Vector Boson Fusion Channel at the ATLAS Detector
by Eric OuelletteThis Thesis describes the first measurement of, and constraints on, Higgs boson production in the vector boson fusion mode, where the Higgs decays to b quarks (the most common decay channel), at the LHC. The vector boson fusion mode, in which the Higgs is produced simultaneously with a pair of quark jets, provides an unparalleled opportunity to study the detailed properties of the Higgs, including the possibility of parity and CP violation, as well as its couplings and mass. It thus opens up this new field of study for precision investigation as the LHC increases in energy and intensity, leading the way to this new and exciting arena of precision Higgs research.
Search for the Pentaquark Θ+ via the π--p K--X Reaction at J-PARC
by Manabu MoritsuThistheses reports on an experimental search for an exotic hadron, &ThΗ+(1540)pentaquark, which is a genuine exotic hadron with a five-quark system of uuddsbar. Theresults of this book support that the existence of &ThΗ+ wasstrongly constrained. The &ThΗ+ pentaquark was searched for via the Π- p ⇒ K- Xreaction using a beam momentum of 2. 01 GeV/c at the J-PARC hadron experimentalfacility, taking advantage of high-statistics and high-resolution compared withprevious experiments, some of which claimed the evidence of &ThΗ+. Inorder to realize a good missing-mass resolution of 2 MeV, the beam spectrometerand superconducting kaon spectrometer were constructed. No clear peak was observed in the missing mass spectrum of the Π- p ⇒ K- Xreaction, and the upper limit of the production cross section was found to beless than 0. 28 Μb/sr at the 90% confidence level in a mass region of1500-1560 MeV/c2. This upper limit is an order of magnitude smallerthan that of the previous KEK experiment. Compared with a theoreticalcalculation using the effective Lagrangian approach, the decay width of &ThΗ+ wasevaluated. The upper limits on the decay width were estimated to be 0. 36 and1. 9 MeV for the &ThΗ+ spin-parity of 1/2+ and 1/2-,respectively. These are quite small for a width of ordinary hadron resonances,and the existence of &ThΗ+ was strongly constrained and isdoubtful.
Search for the Standard Model Higgs Boson in the H → ZZ → l + l - qq Decay Channel at CMS
by Francesco PandolfiThe theoretical foundations of the Standard Model of elementary particles relies on the existence of the Higgs boson, a particle which has been revealed for the first time by the experiments run at the Large Hadron Collider (LHC) in 2012. As the Higgs boson is an unstable particle, its search strategies were based on its decay products. In this thesis, Francesco Pandolfi conducted a search for the Higgs boson in the H ZZ l + l - qq Decay Channel with 4.6 fb -1 of 7 TeV proton-proton collision data collected by the Compact Muon Solenoid (CMS) experiment. The presence of jets in the final state poses a series of challenges to the experimenter: both from a technical point of view, as jets are complex objects and necessitate of ad-hoc reconstruction techniques, and from an analytical one, as backgrounds with jets are copious at hadron colliders, therefore analyses must obtain high degrees of background rejection in order to achieve competitive sensitivity. This is accomplished by following two directives: the use of an angular likelihood discriminant, capable of discriminating events likely to originate from the decay of a scalar boson from non-resonant backgrounds, and by using jet parton flavor tagging, selecting jets compatible with quark hadronization and discarding jets more likely to be initiated by gluons. The events passing the selection requirements in 4.6 fb -1 of datacollected by the CMS detector are examined, in the search of a possible signal compatible with the decay of a heavy Higgs boson. The thesis describes the statistical tools and the results of this analysis. This work is a paradigm for studies of the Higgs boson with final states with jets. The non-expert physicists will enjoy a complete and eminently readable description of a proton-proton collider analysis. At the same time, the expert reader will learn the details of the searches done with jets at CMS.
Search for the Ultimate Energy Source
by Stephen O. DeanWhy has the clean, limitless energy promised by fusion always seemed just out of reach? Search for the Ultimate Energy Source: A History of the U.S. Fusion Energy Program, explains the fundamentals and concepts behind fusion power, and traces the development of fusion historically by decade--covering its history as dictated by US government policies, its major successes, and its prognosis for the future. The reader will gain an understanding of how the development of fusion has been shaped by changing government priorities as well as other hurdles currently facing realization of fusion power. Advance Praise for Search for the Ultimate Energy Source: "Dr. Dean has been uniquely involved in world fusion research for decades and, in this book, describes the complicated realities like few others possibly could." -Robert L. Hirsch, a former director of the US fusion program, an Assistant Administrator of the US Energy Research and Development Administration (ERDA); an executive at Exxon, Arco, and the Electric Power Research Institute (EPRI); and lead author of the book The Impending World Energy Mess (Apogee Prime Books, 2009). "In this book, Dr. Dean provides the many reasons why fusion has progressed more slowly than many had hoped. Budget is usually cited as the culprit, but policy is equally to blame. Facilities have been closed down before their jobs were done--or in some cases, even started. It seems this situation has become endemic in fusion, and if one thinks about it, in other nationally important Science and Technology initiatives as well." -William R. Ellis, a former scientist at Los Alamos National Laboratory, Associate Director of Research at the US Naval Research Laboratory, a vice president at Ebasco Services and at Raytheon, and chair of the US ITER Industry Council and the US ITER Industrial Consortium.
Search for tt̄H Production in the H → bb̅ Decay Channel: Using Deep Learning Techniques with the CMS Experiment (Springer Theses)
by Marcel RiegerIn 1964, a mechanism explaining the origin of particle masses was proposed by Robert Brout, François Englert, and Peter W. Higgs. 48 years later, in 2012, the so-called Higgs boson was discovered in proton-proton collisions recorded by experiments at the LHC. Since then, its ability to interact with quarks remained experimentally unconfirmed. This book presents a search for Higgs bosons produced in association with top quarks tt̄H in data recorded with the CMS detector in 2016. It focuses on Higgs boson decays into bottom quarks H → bb̅ and top quark pair decays involving at least one lepton. In this analysis, a multiclass classification approach using deep learning techniques was applied for the first time. In light of the dominant background contribution from tt̄ production, the developed method proved to achieve superior sensitivity with respect to existing techniques. In combination with searches in different decay channels, the presented work contributed to the first observations of tt̄H production and H → bb̅ decays.
A Search for Ultra-High Energy Neutrinos and Cosmic-Rays with ANITA-2 (Springer Theses)
by Matthew Joseph MottramThe winner of UCL's annual HEP thesis prize, this work describes an analysis of the data from the second flight of the Antarctica Impulsive Transient Antenna (ANITA). ANITA is a balloon-borne experiment that searches for radio signals originating from ultra-high energy neutrinos and cosmic rays interacting with the Antarctic ice or air. The search for ultrahigh energy neutrinos of astrophysical origin is one of the outstanding experimental challenges of the 21st century. The ANITA experiment was designed to be the most sensitive instrument to ultra-high energy neutrinos that originate from the interactions of cosmic rays with the cosmic microwave background. The methodology and results of the neutrino and cosmic ray searches are presented in the thesis.
The Search for Ultralight Bosonic Dark Matter
by Derek F. Jackson Kimball Karl Van BibberA host of astrophysical measurements suggest that most of the matter in the Universe is an invisible, nonluminous substance that physicists call “dark matter.” Understanding the nature of dark matter is one of the greatest challenges of modern physics and is of paramount importance to our theories of cosmology and particle physics. This text explores one of the leading hypotheses to explain dark matter: that it consists of ultralight bosons forming an oscillating field that feebly interacts with light and matter. Many new experiments have emerged over the last decade to test this hypothesis, involving state-of-the-art microwave cavities, precision nuclear magnetic resonance (NMR) measurements, dark matter “radios,” and synchronized global networks of atomic clocks, magnetometers, and interferometers. The editors have gathered leading experts from around the world to present the theories motivating these searches, evidence about dark matter from astrophysics, and the diverse experimental techniques employed in searches for ultralight bosonic dark matter. The text provides a comprehensive and accessible introduction to this blossoming field of research for advanced undergraduates, beginning graduate students, or anyone new to the field, with tutorials and solved problems in every chapter. The multifaceted nature of the research – combining ideas and methods from atomic, molecular, and optical physics, nuclear physics, condensed matter physics, electrical engineering, particle physics, astrophysics, and cosmology – makes this introductory approach attractive for beginning researchers as well as members of the broader scientific community. This is an open access book.
The Search for Wild Relatives of Cool Season Legumes
by Gideon Ladizinsky Shahal AbboThe study of origin and domestication of legumes described in this book emerged when it became apparent that while this kind of information is adequate for cereals, the pulses lagged behind. At the end of the 1960s the senior author initiated a study on the chickpea's wild relatives followed by similar attempts for broad bean, fenugreek, common vetch, bitter vetch, and lentil. The junior author joined the project in the late 1980s with a study of the genetics of interspecific hybrid embryo abortion in lentil and later has extensively investigated chickpea domestication and wild peas. While this book mainly describes our research findings, pertinent results obtained by others are also discussed and evaluated. Studying the wild relatives of legumes included evaluation of their taxonomic status, their morphological variation, ecological requirements, exploration of their distribution, and seed collection in their natural habitats. Seeds were examined for their protein profile as preliminary hints of their affinity to the cultigens and plants grown from these seeds were used for establishing their karyotype, producing intra- and interspecific hybrids and analyses of their chromosome pairing at meiosis and fertility. The aim of these investigations was the identification of the potential wild gene pool of the domesticated forms. Assessment of genetic variation among accessions, particularly in the genus Lens, was made by isozymes and chloroplast DNA studies. The main findings include the discovery of the chickpea wild progenit∨ studies of lentil in three crossability groups; wild peas proceeded in two lines of study; faba bean and fenugreek and their wild progenitors have not yet been identified; common vetch and its related form were treated here as an aggregate (A. sativa); we found gene flow between members of different karyotypes is possib≤ bitter vetch and its relation to the domesticated form were established by breeding experiments.
Searches for CP Violation in Charmed Meson Decays
by Hamish GordonOur current understanding of the fundamental building blocks of the Universe, summarised by the Standard Model of particle physics, is incomplete. For example, it fails to explain why we do not see equal, or almost equal, numbers of particles and their antiparticle partners. To explain this asymmetry requires, among other effects, a mechanism known as charge-parity (CP) violation that causes differences between the rates at which particles and antiparticles decay. CP violation is seen in systems containing bottom and strange quarks, but not in those with up, charm or top quarks. This thesis describes searches for particle-antiparticle asymmetries in the decay rates of charmed mesons. No evidence of CP violation is found. With current sensitivities, an asymmetry large enough to observe probably could not be explained by the Standard Model. Instead an explanation could come from new physics, for example contributions from supersymmetric or other undiscovered heavy particles. In the thesis, the development of new techniques to search for these asymmetries is described. They are applied to data from the LHCb experiment at CERN to make precise measurements of asymmetries in the D^+->K^-K^+pi^+ decay channel. This is the most promising charged D decay for CP violation searches.
Searches for Dijet Resonances: Using ?s = 13 Tev Proton- Proton Collision Data Recorded By The Atlas Detector At The Large Hadron Collider (Springer Theses)
by Lydia Audrey BeresfordThis book addresses one of the most intriguing mysteries of our universe: the nature of dark matter. The results presented here mark a significant and substantial contribution to the search for new physics, in particular for new particles that couple to dark matter. The first analysis presented is a search for heavy new particles that decay into pairs of hadronic jets (dijets). This pioneering analysis explores unprecedented dijet invariant masses, reaching nearly 7 TeV, and sets constraints on several important new physics models. The two subsequent analyses focus on the difficult low dijet mass region, down to 200 GeV, and employ a novel technique to efficiently gather low-mass dijet events. The results of these analyses transcend the long-standing constraints on dark matter mediator particles set by several existing experiments.
Searches for Supersymmetric Particles in Final States with Multiple Top and Bottom Quarks with the Atlas Detector (Springer Theses)
by Chiara RizziThis PhD thesis documents two of the highest-profile searches for supersymmetry performed at the ATLAS experiment using up to 80/fb of proton-proton collision data at a center-of-mass energy of 13 TeV delivered by the Large Hadron Collider (LHC) during its Run 2 (2015-2018). The signals of interest feature a high multiplicity of jets originating from the hadronisation of b-quarks and large missing transverse momentum, which constitutes one of the most promising final state signatures for discovery of new phenomena at the LHC. The first search is focused on the strong production of a pair of gluinos, with each gluino decaying into a neutralino and a top-antitop-quark pair or a bottom-antibottom-quark pair. The second search targets the pair production of higgsinos, with each higgsino decaying into a gravitino and a Higgs boson, which in turn is required to decay into a bottom-antibottom-quark pair. Both searches employ state-of-the-art experimental techniques and analysis strategies at the LHC, resulting in some of the most restrictive bounds available to date on the masses of the gluino,neutralino, and higgsino in the context of the models explored.
Searches for the Supersymmetric Partner of the Top Quark, Dark Matter and Dark Energy at the ATLAS Experiment (Springer Theses)
by Nicolas Maximilian KöhlerAstrophysical observations implying the existence of Dark Matter and Dark Energy, which are not described by the Standard Model (SM) of particle physics, have led to extensions of the SM predicting new particles that could be directly produced at the Large Hadron Collider (LHC) at CERN. Based on 2015 and 2016 ATLAS proton-proton collision data, this thesis presents searches for the supersymmetric partner of the top quark, for Dark Matter, and for DarkEnergy, in signatures with jets and missing transverse energy.Muon detection is key to some of the most important LHC physics results, including the discovery of the Higgs boson and the measurement of its properties. The efficiency with which muons can be detected with the ATLAS detector is measured using Z boson decays. The performance of high-precision Monitored Drift Tube muon chambers under background rates similar to the ones expected for the High Luminosity-LHC is studied.
Searching for 2D Superconductivity in La2−xSrxCuO4 Single Crystals (Springer Theses)
by Itzik KaponA new experimental method – the "Stiffnessometer", is developed to measure elementary properties of a superconductor, including the superconducting stiffness and the critical current. This technique has many advantages over existing methods, such as: the ability to measure these properties while minimally disturbing the system; the ability to measure large penetration depths (comparable to sample size), as necessary when approaching the critical temperature; and the ability to measure critical currents without attaching contacts and heating the sample. The power of this method is demonstrated in a study of the penetration depth of LSCO, where striking evidence is found for two separate critical temperatures for the in-plane and out-of-plane directions. The results in the thesis are novel, important and currently have no theoretical explanation. The stiffnessometer in a tool with great potential to explore new grounds in condensed matter physics.
Searching for Dark Matter with the ATLAS Detector
by Steven SchrammThis thesis describes the search for Dark Matter at the LHC in the mono-jet plus missing transverse momentum final state, using the full dataset recorded in 2012 by the ATLAS Experiment. It is the first time that the number of jets is not explicitly restricted to one or two, thus increasing the sensitivity to new signals. Instead, a balance between the most energetic jet and the missing transverse momentum is required, thus selecting mono-jet-like final states. Collider searches for Dark Matter have typically used signal models employing effective field theories (EFTs), even when comparing to results from direct and indirect detection experiments, where the difference in energy scale renders many such comparisons invalid. The thesis features the first robust and comprehensive treatment of the validity of EFTs in collider searches, and provides a means by which the different classifications of Dark Matter experiments can be compared on a sound and fair basis.