Search For The Production Of A Higgs Boson Decaying Into A Pair Of Bottom Quarks In Association With A Pair Of Top Quarks At 13 Tev With The Atlas Detector
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Search For The Higgs Boson Produced In Association With Top Quarks With The Cms Detector At The Lhc
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Author : Cristina Martin Perez
language : en
Publisher: Springer Nature
Release Date : 2022-02-09
Search For The Higgs Boson Produced In Association With Top Quarks With The Cms Detector At The Lhc written by Cristina Martin Perez and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2022-02-09 with Science categories.
In this work, the interaction between the Higgs boson and the top quark is studied with the proton-proton collisions at 13 TeV provided by the LHC at the CMS detector at CERN (Geneva). At the LHC, these particles are produced simultaneously via the associate production of the Higgs boson with one top quark (tH process) or two top quarks (ttH process). Compared to many other possible outcomes of the proton-proton interactions, these processes are very rare, as the top quark and the Higgs boson are the heaviest elementary particles known. Hence, identifying them constitutes a significant experimental challenge. A high particle selection efficiency in the CMS detector is therefore crucial. At the core of this selection stands the Level-1 (L1) trigger system, a system that filters collision events to retain only those with potential interest for physics analysis. The selection of hadronically decaying τ leptons, expected from the Higgs boson decays, is especially demanding due to the large background arising from the QCD interactions. The first part of this thesis presents the optimization of the L1 τ algorithm in Run 2 (2016-2018) and Run 3 (2022-2024) of the LHC. It includes the development of a novel trigger concept for the High-Luminosity LHC, foreseen to start in 2027 and to deliver 5 times the current instantaneous luminosity. To this end, sophisticated algorithms based on machine learning approaches are used, facilitated by the increasingly modern technology and powerful computation of the trigger system. The second part of the work presents the search of the tH and ttH processes with the subsequent decays of the Higgs boson to pairs of τ lepton, W bosons or Z bosons, making use of the data recorded during Run 2. The presence of multiple particles in the final state, along with the low cross section of the processes, makes the search an ideal use case for multivariant discriminants that enhance the selectivity of the signals and reject the overwhelming background contributions. The discriminants presented are built using state-of-the-art machine learning techniques, able to capture the correlations amongst the processes involved, as well as the so-called Matrix Element Method (MEM), which combines the theoretical description of the processes with the detector resolution effects. The level of sophistication of the methods used, along with the unprecedented amount of collision data analyzed, result in the most stringent measurements of the tH and ttH cross sections up to date.
Higgs Boson Decays Into A Pair Of Bottom Quarks
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Author : Cecilia Tosciri
language : en
Publisher: Springer Nature
Release Date : 2021-10-22
Higgs Boson Decays Into A Pair Of Bottom Quarks written by Cecilia Tosciri and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-10-22 with Science categories.
The discovery in 2012 of the Higgs boson at the Large Hadron Collider (LHC) represents a milestone for the Standard Model (SM) of particle physics. Most of the SM Higgs production and decay rates have been measured at the LHC with increased precision. However, despite its experimental success, the SM is known to be only an effective manifestation of a more fundamental description of nature. The scientific research at the LHC is strongly focused on extending the SM by searching, directly or indirectly, for indications of New Physics. The extensive physics program requires increasingly advanced computational and algorithmic techniques. In the last decades, Machine Learning (ML) methods have made a prominent appearance in the field of particle physics, and promise to address many challenges faced by the LHC. This thesis presents the analysis that led to the observation of the SM Higgs boson decay into pairs of bottom quarks. The analysis exploits the production of a Higgs boson associated with a vector boson whose signatures enable efficient triggering and powerful background reduction. The main strategy to maximise the signal sensitivity is based on a multivariate approach. The analysis is performed on a dataset corresponding to a luminosity of 79.8/fb collected by the ATLAS experiment during Run-2 at a centre-of-mass energy of 13 TeV. An excess of events over the expected background is found with an observed (expected) significance of 4.9 (4.3) standard deviation. A combination with results from other \Hbb searches provides an observed (expected) significance of 5.4 (5.5). The corresponding ratio between the signal yield and the SM expectation is 1.01 +- 0.12 (stat.)+ 0.16-0.15(syst.). The 'observation' analysis was further extended to provide a finer interpretation of the V H(H → bb) signal measurement. The cross sections for the VH production times the H → bb branching ratio have been measured in exclusive regions of phase space. These measurements are used to search for possible deviations from the SM with an effective field theory approach, based on anomalous couplings of the Higgs boson. The results of the cross-section measurements, as well as the constraining of the operators that affect the couplings of the Higgs boson to the vector boson and the bottom quarks, have been documented and discussed in this thesis. This thesis also describes a novel technique for the fast simulation of the forward calorimeter response, based on similarity search methods. Such techniques constitute a branch of ML and include clustering and indexing methods that enable quick and efficient searches for vectors similar to each other. The new simulation approach provides optimal results in terms of detector resolution response and reduces the computational requirements of a standard particles simulation.
The Higgs Boson Produced With Top Quarks In Fully Hadronic Signatures
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Author : Daniel Salerno
language : en
Publisher: Springer Nature
Release Date : 2019-10-25
The Higgs Boson Produced With Top Quarks In Fully Hadronic Signatures written by Daniel Salerno and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-10-25 with Science categories.
The work presented in this PhD dissertation is the first search at CMS for Higgs bosons produced in association with top quarks (ttH) in a final state consisting of only jets. The results presented in this book uncover a new class of ttH events that will help us elucidate our understanding of the Yukawa sector interactions between the Higgs boson and the top quark. Despite this being the most common decay signature for ttH, a large contamination of SM backgrounds makes it the most challenging for extracting a signal from data. The PhD thesis presents many sophisticated tools and techniques that were developed in order to overcome these challenges. These tools pave the way for future analyses to investigate other standard model and beyond-standard model physics.
Search For Higgs Boson Decays To Charm Quarks With The Atlas Experiment And Development Of Novel Silicon Pixel Detectors
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Author : Maria Mironova
language : en
Publisher: Springer Nature
Release Date : 2023-07-20
Search For Higgs Boson Decays To Charm Quarks With The Atlas Experiment And Development Of Novel Silicon Pixel Detectors written by Maria Mironova and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023-07-20 with Science categories.
This book explores the Higgs boson and its interactions with fermions, as well as the detector technologies used to measure it. The Standard Model of Particle Physics has been a groundbreaking theory in our understanding of the fundamental properties of the universe, but it is incomplete, and there are significant hints which require new physics. The discovery of the Higgs boson in 2012 was a substantial confirmation of the Standard Model, but many of its decay modes remain elusive. This book presents the latest search for Higgs boson decays into c-quarks using a proton-proton collision dataset collected by the ATLAS experiment at the Large Hadron Collider (LHC). This decay mode has yet to be observed and requires advanced machine learning algorithms to identify c-quarks in the experiment. The results provide an upper limit on the rate of Higgs boson decays to c-quarks and a direct measurement of the Higgs boson coupling strength to c-quarks. The book also discusses the future of particle physics and the need for significant improvements to the detector to cope with increased radiation damage and higher data rates at the High-Luminosity LHC. It presents the characterization of the ATLAS pixel detector readout chip for the inner detector upgrade (ITk). The chip was subjected to irradiations using X-rays and protons to simulate the radiation environment at the HL-LHC. The tests showed that all readout chip components, including the digital logic and analogue front-end, are sufficiently radiation-tolerant to withstand the expected radiation dose. Finally, this book describes monolithic pixel detectors as a possible technology for future pixel detectors. This book is ideal for individuals interested in exploring particle physics, the Higgs boson, and the development of silicon pixel detectors.
Search For Higgs Boson Pair Production In The Bb Decay Channel
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Author : Luca Cadamuro
language : en
Publisher: Springer
Release Date : 2018-12-06
Search For Higgs Boson Pair Production In The Bb Decay Channel written by Luca Cadamuro and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-12-06 with Science categories.
This thesis presents innovative contributions to the CMS experiment in the new trigger system for the restart of the LHC collisions in Run II, as well as original analysis methods and important results that led to official publications of the Collaboration. The author's novel reconstruction algorithms, deployed on the Field-Programmable Gate Arrays of the new CMS trigger architecture, have brought a gain of over a factor 2 in efficiency for the identification of tau leptons, with a very significant impact on important H boson measurements, such as its decays to tau lepton pairs and the search for H boson pair production. He also describes a novel analysis of HH → bb tautau, a high priority physics topic in a difficult channel. The original strategy, optimisation of event categories, and the control of the background have made the result one of the most sensitive concerning the self-coupling of the Higgs boson among all possible channels at the LHC.
Search For Tt H Production In The H Bb Decay Channel
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Author : Marcel Rieger
language : en
Publisher: Springer Nature
Release Date : 2021-02-25
Search For Tt H Production In The H Bb Decay Channel written by Marcel Rieger and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-02-25 with Science categories.
In 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.
Charming Decays Of The Higgs Z And W Bosons
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Author : Spandan Mondal
language : en
Publisher: Springer Nature
Release Date : 2025-06-13
Charming Decays Of The Higgs Z And W Bosons written by Spandan Mondal and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2025-06-13 with Science categories.
This book presents searches for the Higgs boson, Z boson, and W boson decaying into charm quark(s) performed with proton-proton collision data at √s = 13TeV collected by the CMS experiment at the LHC, CERN, corresponding to an integrated luminosity of 138 fb−1 and recorded between 2016 and 2018. The searches are carried out using events in which the Higgs/Z/W boson is produced in association with a leptonically-decaying Z or W boson. This thesis also discusses a novel calibration algorithm for charm jet identification that enables maximal use of the available information related to charm jets. The new method is used to correct the entire distribution expected as output when jet flavour identification algorithms are applied to jets of different flavours. The calibrated results improve over traditional efficiency measurements and help enhance the sensitivities of the Higgs, Z, and W searches. This book primarily reports on the so-called resolved-jet topology of the Higgs/Z/W boson searches, where the boson candidates are reconstructed using two separate small-radius (AK4) jets. Upon statistically combining the results of the resolved-jet search with a complementary merged-jet approach, the observed (expected) upper limit on the Higgs decay to charm quarks corresponds to 14 (7.6) times the Standard Model expectation at the 95% CL which is the most stringent direct limit to date. A significance of 5.7σ (5.9σ) over the background-only prediction is observed (expected) in case of the search for charmed Z boson decays. Only the resolved-jet topology is used in the search for charmed W decays and the observed (expected) significance is 5.6σ (5.7σ) over the background-only prediction. These mark the first observations of charmed decays of the Z and W bosons at a hadron collider experiment.
Atlas Measurements Of The Higgs Boson Coupling To The Top Quark In The Higgs To Diphoton Decay Channel
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Author : Jennet Elizabeth Dickinson
language : en
Publisher: Springer Nature
Release Date : 2021-11-16
Atlas Measurements Of The Higgs Boson Coupling To The Top Quark In The Higgs To Diphoton Decay Channel written by Jennet Elizabeth Dickinson and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-11-16 with Science categories.
During Run 2 of the Large Hadron Collider, the ATLAS experiment recorded proton-proton collision events at 13 TeV, the highest energy ever achieved in a collider. Analysis of this dataset has provided new opportunities for precision measurements of the Higgs boson, including its interaction with the top quark. The Higgs-top coupling can be directly probed through the production of a Higgs boson in association with a top-antitop quark pair (ttH). The Higgs to diphoton decay channel is among the most sensitive for ttH measurements due to the excellent diphoton mass resolution of the ATLAS detector and the clean signature of this decay. Event selection criteria were developed using novel Machine Learning techniques to target ttH events, yielding a precise measurement of the ttH cross section in the diphoton channel and a 6.3 $\sigma$ observation of the ttH process in combination with other decay channels, as well as stringent limits on CP violation in the Higgs-top coupling.
Search For New Physics In Tt Final States With Additional Heavy Flavor Jets With The Atlas Detector
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Author : Javier Montejo Berlingen
language : en
Publisher: Springer
Release Date : 2016-07-20
Search For New Physics In Tt Final States With Additional Heavy Flavor Jets With The Atlas Detector written by Javier Montejo Berlingen and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-07-20 with Science categories.
This 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.
Lepton Photon Interactions At High Energies Lepton Photon 2017 Proceedings Of The 28th International Symposium
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Author : Wei Wang
language : en
Publisher: World Scientific
Release Date : 2020-02-27
Lepton Photon Interactions At High Energies Lepton Photon 2017 Proceedings Of The 28th International Symposium written by Wei Wang and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020-02-27 with Science categories.
The latest of the 'Lepton Photon' symposium, one of the well-established series of meetings in the high-energy physics community, was successfully organized at the South Campus of Sun Yat-sen University, Guangzhou, China, from August 7-12, 2017, where physicists around the world gathered to discuss the latest advancements in the research field.This proceedings volume of the Lepton Photon 2017 collects contributions by the plenary session speakers and the posters' presenters, which cover the latest results in particle physics, nuclear physics, astrophysics, cosmology, and plans for future facilities.