A Search for Displaced Leptons in the ATLAS Detector


Book Description

This thesis presents a search for long-lived particles decaying into displaced electrons and/or muons with large impact parameters. This signature provides unique sensitivity to the production of theoretical lepton-partners, sleptons. These particles are a feature of supersymmetric theories, which seek to address unanswered questions in nature. The signature searched for in this thesis is difficult to identify, and in fact, this is the first time it has been probed at the Large Hadron Collider (LHC). It covers a long-standing gap in coverage of possible new physics signatures. This thesis describes the special reconstruction and identification algorithms used to select leptons with large impact parameters and the details of the background estimation. The results are consistent with background, so limits on slepton masses and lifetimes in this model are calculated at 95% CL, drastically improving on the previous best limits from the Large Electron Positron Collider (LEP).




Lepton Flavor Violation from Low Scale Seesaw Neutrinos with Masses Reachable at the LHC


Book Description

Flavor physics is fundamental to test the Standard Model of particle physics and could be the key to discover new physics. This book explores lepton flavor violating implications in the low scale seesaw models, a well-motivated scenario for explaining the still open problem of neutrino mass generation. It studies the lepton flavor violating Higgs decays in depth, developing useful simple expressions for making fast estimations of this observable. It also introduces a new parametrization optimized for the study of lepton flavor violation in these models, showing that high rates could be obtained for Higgs and Z decays if these new heavy neutrinos have masses in the TeV range. Lastly, it goes on to explore the possibility of their production and decay at the Large Hadron Collider through events with two charged leptons of different flavor.




The Physics Associated with Neutrino Masses


Book Description

This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact.










Searching for New Physics in b → sl+l− Transitions at the LHCb Experiment


Book Description

This thesis presents two analyses of semileptonic b → sl+l− decays using Flavour Changing Neutral Currents (FCNCs) to test for the presence of new physics and lepton flavour universality, and the equality of couplings for different leptons, which on the basis of experimental evidence is assumed to hold in the Standard Model, free from uncertainties as a result of knowledge of the hadronic matrix elements. It also includes the angular analysis of Lambda_b->Lambda mumu decay and the RK* measurement, both of which are first measurements, not yet performed by any other experiment.




B Decays


Book Description

This 2nd edition is an extensive update of "B Decays?. The revisions are necessary because of the extensive amount of new data and new theoretical ideas. This book reviews what is known about b-quark decays and also looks at what can be learned in the future.The importance of this research area is increasing, as evidenced by the approval of the luminosity upgrade for CESR and the asymmetric B factories at SLAC and KEK, and the possibility of experiments at hadron colliders.The key experimental observations made thus far, measurement of the lifetimes of the different B species, B0-B0 mixing, the discovery of ?Penguin? mediated decays, and the extraction of the CKM matrix elements Vub and Vcb from semileptonic decays, as well as more mundane results, are described in great detail by the experimentalists who have been closely involved with making the measurements. Theoretical progress in understanding b-quark decays using HQET and lattice gauge techniques are described by theorists who have developed and used these techniques.Synthesizing the experimental and theoretical information, several articles discuss the implications for the ?Standard Model? and how further tests can be done using measurements of CP violation in the B system.




The Physics of the B Factories


Book Description

This comprehensive work thoroughly introduces and reviews the set of results from Belle and BaBar - after more than two decades of independent and complementary work - all the way from the detectors and the analysis tools used, up to the physics results, and the interpretation of these results. The world’s two giant B Factory collaborations, Belle at KEK and BaBar at SLAC, have successfully completed their main mission to discover and quantify CP violation in the decays of B mesons. CP violation is a necessary requirement to distinguish unambiguously between matter and antimatter. The shared primary objective of the two B Factory experiments was to determine the shape of the so-called unitarity triangle, an abstract triangle representing interactions of quarks, the elementary constituents of matter. The area of the triangle is a measure of the amount of CP violation associated with the weak force. Many other measurements have been performed by the B Factories and are also discussed in this work.




Search for Dark Matter with the ATLAS Detector


Book Description

This book discusses searches for Dark Matter at the CERN’s LHC, the world’s most powerful accelerator. It introduces the relevant theoretical framework and includes an in-depth discussion of the Effective Field Theory approach to Dark Matter production and its validity, as well as an overview of the formalism of Simplified Dark Matter models. Despite overwhelming astrophysical evidence for Dark Matter and numerous experimental efforts to detect it, the nature of Dark Matter still remains a mystery and has become one of the hottest research topics in fundamental physics. Two searches for Dark Matter are presented, performed on data collected with the ATLAS experiment. They analyze missing-energy final states with a jet or with top quarks. The analyses are explained in detail, and the outcomes and their interpretations are discussed, also in view of the precedent analysis of theoretical approaches. Given its depth of coverage, the book represents an excellent reference guide for all physicists interested in understanding the theoretical and experimental considerations relevant to Dark Matter searches at the LHC.




New Physics In B Decays


Book Description

The Standard Model (SM) of particle physics has withstood thus far every attempt by experimentalists to show that it does not describe data. We discuss the SM in some detail, focusing on the mechanism of fermion mixing, which represents one of its most intriguing aspects. We discuss how this mechanism can be tested in b-quark decays, and how b decays can be used to extract information on physics beyond the SM. We review experimental techniques in b physics, focusing on recent results and highlighting future prospects. Particular attention is devoted to recent results from b decays into a hadron, a lepton and an anti-lepton, that show discrepancies with the SM predictions — the so-called B-physics anomalies — whose statistical significance has been increasing steadily. We discuss these experiments in a detailed manner, and also provide theoretical interpretation of these results in terms of physics beyond the SM.