Download or read book Searches for Supersymmetric Particles in Final States with Multiple Top and Bottom Quarks with the Atlas Detector written by Chiara Rizzi and published by Springer Nature. This book was released on 2020-09-01 with total page 279 pages. Available in PDF, EPUB and Kindle. Book excerpt: This 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.
Download or read book Search for Supersymmetry in Final States with Multiple Bottom Quarks with the ATLAS Detector written by Meisam Ghasemi Bostanabad and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The theoretical development of the Standard Model in the 1960s and 1970s has led to the discovery of its missing piece, the Higgs boson, at the ATLAS experiment (together with its sister experiment, CMS) at the Large Hadron Collider at CERN in 2012. In order to solve the problem of large quantum corrections to the leading expansion of the Higgs boson mass, additional symmetries need to be added to the Standard Model. A possible solution to this problem of Higgs mass quantum corrections is the theory of Supersymmetry, which includes partners to each Standard Model particle, such as gluinos, squarks, and the lightest supersymmetric particle. This dissertation describes a search for pair-produced gluinos, where each gluino decays via a top squark or a bottom squark to the lightest supersymmetric particle (a neutralino). Events which contain a large jet multiplicity in the final state (i.e. at least four jets of which at least three must be b-jets), and large amounts of missing transverse energy, are obtained for further studies. The dataset used for this search includes 139 fb^−1 of integrated luminosity recorded by the ATLAS experiment between 2015 and 2018 at a center-of-mass energy √s = 13 TeV. No significant excess is observed in data above the Standard Model backgrounds, and gluino masses up to 2.3 TeV for both the Gtt and the Gbb models are excluded at a 95% confidence level. This dissertation also contains an overview of, and the author's work on, the data quality monitoring of the ATLAS liquid argon calorimeter during 2017 data taking.
Download or read book Search for Supersymmetry Using a Higgs Boson in the Decay Cascade with the ATLAS Detector at the Large Hadron Collider written by Claire David and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Standard Model of particle physics is a successful theory, yet it is incomplete. Supersymmetry is one of the favoured extensions of the Standard Model, elegantly addressing several unresolved issues. This thesis presents a search for the pair production of supersymmetric particles chargino one and neutralino two, where the neutralino two decays to the lightest neutralino and the 125 GeV Higgs boson. The final states considered for the search have large missing transverse momentum, an isolated lepton and two jets identified as originating from bottom quarks. The analysis is based on 20.3 inverse femtobarns of 8 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. No excess over Standard Model predictions is observed. The analysis has been combined with three independent searches that probe other decay modes of the Standard Model Higgs boson. Limits are set at 95% confidence level in the context of a simplified supersymmetric model. Common masses of chargino one and neutralino two are excluded up to 250 GeV for a massless neutralino one. The analysis of this dissertation has been reinterpreted in the context of a large scan of the phenomenological Minimal Supersymmetric Standard Model, along with 22 other ATLAS Run 1 searches. The resulting summary paper represents the most comprehensive assessment of the ATLAS constraints on Supersymmetry models to date.
Download or read book Search for Supersymmetry in Final States with Two Same Sign Leptons Or Three Leptons and Jets with the ATLAS Detector at the LHC written by Othmane Rifki and published by . This book was released on 2017 with total page 528 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Search for the Supersymmetric Partner of the Top Quark with the ATLAS Detector Via tildet 1 rightarrow T widetilde chi 0 1 and tildet 1 rightarrow B widetilde chi pm 1 Decays written by Francesca Consiglia Ungaro and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Zusammenfassung: The elementary particles composing matter and their interactions are described by the Standard Model of particle physics. The Standard Model of particle physics enabled predictions that were experimentally verified and has been confirmed throughout the past decades by data. Nevertheless, there are several theoretical reasons not to consider it as the ultimate theory.The strongest motivation to expect Physics beyond the Standard Model is the hierarchy problem. The radiative corrections to the mass of the Higgs boson grow quadratically with the square of the energy scale at which the Standard Model is considered to be valid. As a result, the parameters of the Standard Model need to be fine-tuned in order for the mass of the Higgs boson to acquire the value experimentally measured, despite the possibly large corrections.Supersymmetry is a promising theory extending the Standard Model which solves many of its shortcomings, including the hierarchy problem. Supersymmetry postulates a new fermion-boson symmetry resulting in the introduction of new particles, called superpartners, with the same quantum numbers and masses as the Standard Model particles, except for the spin, differing by half a unit. This new symmetry enables a cancellation of the radiative corrections due to the Standard Model particles with the corrections due to the newly introduced superpartners, contributing with opposite sign. Since no superpartners with the same mass as the Standard Model particles have been observed, Supersymmetry must be broken to allow the superpartners to have a mass different from the mass of the corresponding Standard Model particles.In the minimal version of Supersymmetry in terms of new particles, the Minimal Supersymmetric Standard Model, the hierarchy problem can still be solved with a moderate amount of fine-tuning if the masses of at least some of the superpartners are at the TeV energy scale. The conservation of a new multiplicative quantum number, the R-parity, can be assumed to prevent phenomena in contrast with experimental evidences, as the proton decay. Superpartners have R-parity -1, and Standard Model particles R-parity +1. If the conservation of R-parity is assumed, in collider experiments supersymmetric particles can only be produced in even numbers (usually two), and the lightest supersymmetric particles (LSP, usually taken to be the neutralino), is stable.The LHC (Large Hadron Collider), is a hadron collider able to accelerate protons to unprecedented energies. Between 2010 and 2012 it operated at a centre-of-mass energy of the proton-proton collisions of 7 and 8 TeV.Its general-purpose experiments, ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Spectrometer) collected data corresponding to about 5 $fb^{-1}$ at $\sqrt{s}$ = 7 TeV and 20 $fb^{-1}$ at $\sqrt{s}$ = 8 TeV. The LHC and its experiments have been built with the main motivations of searching for the Higgs boson, discovered by the ATLAS and CMS experiments in 2012, and searching for signals of Supersymmetry.There are strong theoretical reasons to expect the supersymmetric particles to lie at the TeV energy scale, which would make them accessible at the LHC.In the Minimal Supersymmetric Standard Model, the lightest superpartner of the top quark, light stop is very likely to be lighter than the superpartners of the other quarks. This thesis focuses on the search for direct stop pair production with the data collected by the ATLAS experiment. Two analyses have been performed, addressing different final states and decay modes.The first analysis targets stop masses close to the mass of the top quark, ideal to solve the hierarchy problem.The mass spectrum assumed is such that m(stop)
Download or read book Search for Scalar Bottom Quarks in Compressed Final States with B jets and Missing Transverse Momentum with the ATLAS Detector written by Mario Spina and published by . This book was released on 2022 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Search for Supersymmetry in Charm Quark Final States with the ATLAS Detector written by Jan Schäffer and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Search for Supersymmetry with the ATLAS Detector at the Large Hadron Collider in Final States with Two Hadronically Decaying leptons written by Mario Grandi and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book A Search for Supersymmetry in Final States with Two Same flavor Opposite sign Leptons Jets and Missing Transverse Momentum with the ATLAS Detector written by Giulia Ripellino and published by . This book was released on 2017 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Search for New Phenomena with Top Quark Pairs in Final States with One Lepton Jets and Missing Transverse Momentum in Pp Collisions at square Root s written by ATLAS Collaboration CERN and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are designed to search for two-, three-, and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediators that are produced in association with a pair of top quarks and decay into a pair of dark-matter particles. The search is performed using the Large Hadron Collider proton-proton collision dataset at a centre-of-mass energy of s√ = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb−1. No significant excess above the Standard Model background is observed, and limits at 95% confidence level are set in the stop-neutralino mass plane and as a function of the mediator mass or the dark-matter particle mass. Stops are excluded up to 1200 GeV (710 GeV) in the two-body (three-body) decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop-neutralino mass difference of 60 GeV. Scalar and pseudoscalar dark-matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to Standard Model and dark-matter particles are both equal to one and when the mass of the dark-matter particle is 1 GeV
Download or read book Search for Supersymmetry Using Heavy Flavour Jets with the ATLAS Detector at the Large Hadron Collider written by Alan Tua and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Standard Model of particle physics, despite being extremely successful, is not the ultimate description of physics. The nature of dark matter is not well described, unification of the forces is not achieved and the theory is plagued by a hierarchy problem. One of the proposed solutions to these issues is supersymmetry. This thesis describes numerous searches for supersymmetry carried out using the ATLAS detector at the Large Hadron Collider. In scenarios where R-parity is conserved, supersymmetric final states contain large amounts of missing transverse energy. Furthermore, should supersymmetry correctly describe Nature, the scalar partners of the third generation quarks might be the lightest scalar quarks. The searches reported here exploit these possibilities and make use of signatures which are rich in missing transverse energy and jets coming from heavy flavour quarks. Searches are carried out for direct pair production of third generation scalar quarks as well as gluino-mediated production of these particles. A data driven technique to estimate the backgrounds coming from multijet production is described and shown to work in analyses targeting heavy flavour quarks. No significant excesses are observed in a number of analyses. In each case limits are set on the allowed masses of supersymmetric particles in a variety of phenomenological models and in specific supersymmetry breaking scenarios.
Download or read book Search for Supersymmetry in Multilepton Final States with the ATLAS Detector at the LHC written by Valentina Santina Gallo and published by . This book was released on 2012 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Search for New Physics with Top and Bottom Quarks with ATLAS written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The studies performed by the principal investigator during the period of the grant constitute the ground work for search for new physics in channels including top and bottom quarks with the ATLAS detector at the Large Hadron Collider. The PI has been involved in search for heavy charged Higgs bosons decaying into top and bottom quark pairs, and top quark rare decays involving Higgs bosons and c-quarks. Both channels have the top quark pair production as their main background, which was studied in detail. The search for heavy charged Higgs and top quark rare decays requires signi cant amount of data accumulated by the experiment. In case no signal is observed in the present data sample collected by ATLAS (5 fb−1 of integrated luminosity at proton-anti proton center-of-mass energy of 7 TeV and 20 fb−1 at 8 TeV), data from the upgraded detector running at 14 TeV needs to be analyzed. The PI has been working on physics and performance studies at upgraded detector.
Download or read book Searching for Squarks written by Samuel Jones and published by Springer. This book was released on 2020-08-28 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis focuses on searches for squarks with the ATLAS detector in "compressed" scenarios where the scalar top is very close in mass to the lightest supersymmetric particle. These models are theoretically appealing because the presence of a quasi-degenerate scalar top enhances the self-annihilation cross-section of the lightest supersymmetric particle, acting therefore as a regulator of the dark matter relic density. Two main analyses are presented: the first is a search for scalar tops decaying to charm quarks. The identification of jets originating from the charm quark is very challenging due to its short lifetime. The calibration of tools for charm-tagging has paved the way to measuring the decay of the Higgs boson to pairs of charm quarks. The second analysis presented is the development of a novel technique for reconstructing low momentum b-hadrons. This tool has enabled the ATLAS collaboration to explore topologies that were previously inaccessible.
Download or read book Search for Supersymmetry in Hadronic Final States with Missing Transverse Energy Using the Variables alpha T and B quark Multiplicity in Pp Collisions at sqrt s written by and published by . This book was released on 2013 with total page 45 pages. Available in PDF, EPUB and Kindle. Book excerpt: An inclusive search for supersymmetric processes that produce final states with jets and missing transverse energy is performed in pp collisions at a centre-of-mass energy of 8 TeV. The data sample corresponds to an integrated luminosity of 11.7 fb-1 collected by the CMS experiment at the LHC. In this search, a dimensionless kinematic variable, [alpha] T, is used to discriminate between events with genuine and misreconstructed missing transverse energy. The search is based on an examination of the number of reconstructed jets per event, the scalar sum of transverse energies of these jets, and the number of these jets identified as originating from bottom quarks. No significant excess of events over the standard model expectation is found. Exclusion limits are set in the parameter space of simplified models, with a special emphasis on both compressed-spectrum scenarios and direct or gluino-induced production of third-generation squarks. For the case of gluino-mediated squark production, gluino masses up to 950-1125 GeV are excluded depending on the assumed model. Finally, for the direct pair-production of squarks, masses up to 450 GeV are excluded for a single light first- or second-generation squark, increasing to 600 GeV for bottom squarks.
Download or read book The Search for Direct Top squark Production in Hadronic Final States with the ATLAS Detector at square Roots s written by Christian Lüdtke and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Supersymmetry poses one of the best motivated theories for particle physics beyond the Standard Model. It can provide a dark matter candidate and enable grand unification. The supersymmetric partner of the top quark, the top squark, can provide a cancellation of diverging radiative corrections to the Higgs-boson mass and thereby avoid the hierarchy problem of the Standard Model. In this thesis, a search for top squarks in final states with jets and missing transverse momentum is presented. Proton-proton collisions at a centre-of-mass energy of √s = 13 TeV, produced by the Large Hadron Collider, were recorded by the ATLAS detector. The analysed dataset corresponds to an integrated luminosity of 36.1 fb-1. No significant excess above the Standard Model background was observed. The analysis results are interpreted as exclusion limits on the top-squark mass and the neutralino mass in various scenarios that address specific aspects of the supersymmetry
Download or read book Search for Supersymmetric Partner of Bottom Quark at D0 at Tevatron Studies on Missing Transverse Energy written by and published by . This book was released on 2007 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: Supersymmetry, extension of the Standard Model of Particle Physics (SM), is searched for by trying to observe the supersymmetric partner of bottom quark ({tilde b}). This search is performed using events with a final state comprising two acoplanar b-quark jets and missing transverse energy (MET) and coming from a sample of 992 pb−1 of data collected by the D0 detector at the Tevatron, the Fermilab p{bar p} collider. The absence of an excess of events in comparison to MS expectations leads to exclude sb masses up to 201 GeV, neutralino masses up to 94 GeV. The MET has been studied under two points of view, because of its fundamental role in this search. First, at the level of the trigger system which allows the online selection candidate events, and then, within the framework of the ALPGEN generator, the simulation of the Z boson transverse momentum which appears as MET when the Z boson decays into neutrino.
