Download Free Search For Supersymmetry Signatures In High Energy Proton Proton Collisions With The Atlas Experiment Book in PDF and EPUB Free Download. You can read online Search For Supersymmetry Signatures In High Energy Proton Proton Collisions With The Atlas Experiment and write the review.

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.
Astrophysical 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.
After an extensive overview of the Standard Model and of the theory and phenomenology of Supersymmetry, this book describes the recent development of the ATLAS Particle Flow algorithm, a hadronic reconstruction technique aiming at enhancing the sensitivity of the experiment to new physics through the combination of the information from different ATLAS sub-detectors. The first ever ATLAS strong SUSY search exploiting this technique is also described, reporting the results and exclusion limits obtained using the complete proton-proton collision dataset recorded by the ATLAS experiment during the second Run of the Large Hadron Collider (LHC).
This 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.
The ATLAS experiment at the CERN Large Hadron Collider (LHC) has collected a substantial amount of data to understand the Standard Model of particle physics at higher than previous center of mass energy available and to explore new physics beyond the Standard Model. This dissertation describes observations of charged particle multiplicity distributions in 7 TeV and 900 GeV data as well as searches for new physics with a signature of high energy jets and missing transverse energy using the first few months of data available at the LHC. Multiplicity distributions of charged particle tracks, one of the first observables in high energy collisions were made for a center of mass energy, sqrt (s) = 900 GeV as well as 7 TeV proton-proton collision data. Such distributions help to understand multi-particle production processes. One of the predicted features of multiplicity distribution and its moments is KNO scaling which implies that the shape and moments of the scaled multiplicity distribution is independent of the center-of-mass energy. Although a clear violation of KNO scaling is not observed within the error limits, an indication of such violation is noted. Different models of hadro-production to describe multiplicity distributions are also studied. The Negative Binomial Distribution (NBD) is an often used distribution modeling multiplicity distributions. It has been observed that NBD is satisfied in different types of collisions and over wide range of energies and it was observed that not only the full-phase-space multiplicity distribution can be successfully fitted by the NBD but also the distribution within central pseudo-rapidity intervals. Based on these findings, the model of cluster (or clan) cascading type has been proposed. Although, a good NBD fit can be obtained, it is observed for hadronic interactions that the presence of two weighted NBD or Double NBD (DNBD) components, one corresponding to soft production and the other to semi-hard one (mini-jets) seems to fit the data better for broad pseudo-rapidity ranges. It was found that the soft component follows KNO scaling while the semi-hard component does not. The proton-proton collision data at LHC has been analyzed to test the NBD and DNBD parametrization and test the energy dependence of the fitted parameters. It is well understood that the Standard model of Particle physics in incomplete. Our knowledge of cosmology also leaves several crucial questions unanswered, one of them being the composition of the dark matter that has been indirectly observed through astronomical observations. The primary objectives for constructing the Large Hadron Collider has been to solve these problems through the discovery of the Higgs particle and to find new physics processes that predict the production of massive non-interacting stable particles. Searches of such new physics producing heavy stable particles in its final state has been performed. Finding such signals would provide direct observation of a dark matter candidate particle. The exclusive event topology of two high energy jets and missing transverse energy has been explored to perform the above search, using ATLAS detector data. A summary of results of these preliminary searches in comparison with theoretical predictions has been presented. In order to understand and discriminate any new physics, a clear and coherent understanding of the detector response is crucial. Moreover, a detailed knowledge of the behavior of known standard model phenomena is required. A detailed description of the ATLAS detector and several important calibration techniques is discussed and their results summarized. Estimates of Standard Model physics, contributing to irreducible backgrounds to dark matter searches is presented in detail. One such physics process constituting an irreducible background is the production of the Z boson decaying into two neutrinos ([nu]) with associated jets. The observation of these events directly from data is an impossible task due to the non-interacting nature of the neutrinos. An estimate of the production cross section of these process is estimated using observations of photon ([gamma]) plus jet events and theoretical predictions. Estimated numbers for the [gamma] plus 2,3,4 and more associated jets production with uncertainties has been summarized.
This 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.
Results are reported from a search for physics beyond the standard model in proton-proton collisions at a center-of-mass energy of 7 TeV, focusing on the signature with a single, isolated, high-transverse-momentum lepton (electron or muon), energetic jets, and large missing transverse momentum. The data sample comprises an integrated luminosity of 36 inverse picobarns, recorded by the CMS experiment at the LHC. The search is motivated by models of new physics, including supersymmetry. The observed event yields are consistent with standard model backgrounds predicted using control samples obtained from the data. The characteristics of the event sample are consistent with those expected for the production of t t-bar and W +jets events. The results are interpreted in terms of limits on the parameter space for the constrained minimal supersymmetric extension of the standard model.
The Large Hadron Collider (LHC) and its experiments were built to explore fundamental questions of particle physics via proton-proton collisions at unprecedented center-of-mass energies, thus providing a unique environment for testing the Standard Model (SM) at the electroweak scale and searching for signs of new physics beyond the SM (BSM). The discovery of a SM-like 125 GeV Higgs boson by ATLAS and CMS hints of new physics at the electroweak scale-possibly within reach of the LHC-in order to mitigate divergent radiative corrections to the Higgs squared mass. This can systematically be accomplished by the introduction of supersymmetry (SUSY). For the experimentalist, SUSY provides a set of simplified benchmark models, with explicit and testable predictions, which are useful when searching for BSM physics. A large number of BSM searches has been carried out at the LHC. However, no evidence for SUSY has been found. It is therefore important to expand the scope. This thesis presents two ATLAS analyses for SUSY, both utilizing fully hadronic final states. The first analysis searches for the pair production of top squarks (stops), each with R-parity-violating decays into a b- and an s-quark. This analysis was performed using proton-proton collision data with an integrated luminosity of 17.4 fb-1 at a center-of-mass energy of 8 TeV. The second analysis searches for electroweak production of a chargino-neutralino pair, decaying into SM-quarks via a W boson and a SM-like 125 GeV Higgs boson, performed using an integrated luminosity of 36.1 fb-1 at a center-of-mass energy of 13 TeV. No evidence of an excess beyond the SM background prediction is observed in either search, thus exclusion limits are set at 95% CL. Stops decaying directly to hadronic final states are excluded for masses in the range 100 to 315 GeV. Charginos and neutralinos decaying via Wh to hadronic final states are excluded up to 680 GeV, by far the strongest limits on electroweak SUSY with Wh decays to date. The tools and strategies developed in the searches for SUSY with hadronic final states in this thesis should prove useful in future searches for BSM physics at the LHC.