Study Of The Higgs Boson Pair Production With Run 2 Atlas Data Using Cut Based And Machine Learning Approaches
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Study Of The Higgs Boson Pair Production With Run 2 Atlas Data Using Cut Based And Machine Learning Approaches
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Author : Jia-Yu Yan
language : en
Publisher:
Release Date : 2024
Study Of The Higgs Boson Pair Production With Run 2 Atlas Data Using Cut Based And Machine Learning Approaches written by Jia-Yu Yan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2024 with categories.
After the groundbreaking discovery of the Higgs boson, associated with the Higgs field responsible for imparting mass to other particles, by the CMS and ATLAS experiments at CERN, a promising opportunity has emerged to delve into its properties and explore new physics beyond the standard model (SM). A crucial property to be measured is the Higgs self-coupling, which directly probes the test of the Higgs potential and electroweak symmetry breaking. Higgs pair (HH) production at the Large Hadron Collider (LHC) provides a direct probe for measuring the Higgs self-coupling parameter. In this analysis, we focus on HH production through Vector Boson Fusion (VBF), which is the second-leading HH production channel. We consider the decay channel HH->bbtautau, where one tau decays leptonically and the other tau decays hadronically. The analysis uses the dataset with an integrated luminosity of 140 fb^{-1} collected by the ATLAS detector at \sqrt{s} = 13 TeV. We introduce two methods to perform the optimization, which are cut-based studies and machine learning studies, specifically using Boosted Decision Trees (BDTs), by comparing the significance and upper limits set on the cross-section. The expected upper limits by BDTs (cut-based studies), considering only statistical uncertainties, are set at the 95% confidence level on the SM HH production cross section, which is 77.7 (212.0) times the SM prediction.
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.
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.
Pair Production Of Higgs Bosons In The Final State With Bottom Quarks And Leptons In The Atlas Experiment
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Author : Petar Bokan
language : en
Publisher:
Release Date : 2020
Pair Production Of Higgs Bosons In The Final State With Bottom Quarks And Leptons In The Atlas Experiment written by Petar Bokan and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
After the discovery of the Higgs boson, the ultimate test of the electroweak symmetry breaking and the Standard Model (SM) of particle physics is to establish evidence of Higgs boson self-coupling, which can be achieved by searching for pair production of Higgs bosons. In addition, many theories beyond the SM predict heavy resonances that could decay into pairs of Higgs bosons. A search for non-resonant and resonant pair production of Higgs bosons in the final state with two bottom quarks and two $ tau$ leptons ($b bar{b} tau^+ tau^-$) is presented for 36.1 fb$^{-1}$ of proton-proton collis...
Search For The Higgs Boson In The Tt H H Bb Channel In The Atlas Experiment At The Lhc Using Machine Learning Methods And Synchronization Of The Itk Geometry Description For Simulation And Radiation Studies For The Hl Lhc Atlas Upgrade
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Author : Ziyu Guo
language : en
Publisher:
Release Date : 2019
Search For The Higgs Boson In The Tt H H Bb Channel In The Atlas Experiment At The Lhc Using Machine Learning Methods And Synchronization Of The Itk Geometry Description For Simulation And Radiation Studies For The Hl Lhc Atlas Upgrade written by Ziyu Guo and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.
The Higgs-top coupling (top Yukawa coupling) measurement can further test the standardmodel, being much stronger than the ones for the other quarks. The associated production of aHiggs boson with a top quark pair (ttH) allows to do a direct measurement. With the ATLASdetector at the LHC, this thesis presents a search for ttH in the H->bb decay mode, rarelyproduced compared with the tt backgrounds. Both processes have final states with multiple jetsand b-jets making the analysis heavily relying on advanced techniques. The large tt modelinguncertainties are a driving factor of the sensitivity.This thesis searches to increase the ttH (H->bb) sensitivity by exploring machine learningmethods. Using early Run 2 data, boosted decision trees are exploited to firstly solve the jet-parton assignment in the reconstruction of the ttH signal, and in a second step classify ttH andtt. The observed significance under the background only hypothesis is 1.4 standard deviations.Targeting a contribution to the analysis round using full Run 2 data, deep learningtechniques are explored: recurrent neural networks as binary classifier solving reconstructionand classification in one step, physics-expertise-aware deep neural networks exploiting rawfeatures, RNN-based multi-classifier for event categorization, and adversarial neural networkaimed to decrease the tt modeling uncertainty.Coping with the new LHC phase starting in mid-2020's, ATLAS will be upgradedto have a new inner tracker. The author contributes to synchronize its geometry descriptionsindependently implemented and used by simulation and radiation studies, which is importantto validate a radiation estimation.
A Beauty Ful Boson
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Author : Giulia Di Gregorio
language : en
Publisher: Springer Nature
Release Date : 2023-01-01
A Beauty Ful Boson written by Giulia Di Gregorio and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023-01-01 with Science categories.
The analysis described in this thesis is the search for the Higgs boson, decaying into bb pair, in the associated production with a vector boson, in the extreme Higgs boson transverse momentum region where the Higgs boson is reconstructed using the large-R jet technique. The use of the large-R jets allows to add a part of the phase space unexplored so far, which is particularly sensitive to possible new physics. The analysed data have been collected at LHC by the ATLAS detector between 2015 and 2018 at a centre-of-mass energy of √s = 13 TeV. The same dataset has been used to perform the differential pp → ZH and pp → WH cross-section measurements used to extract the information on the Higgs couplings and to put limits on Beyond the Standard Model effects. Furthermore the analysis has been re-used to perform a cross-section measurement of the diboson ZZ and WZ processes because the diboson and the Higgs processes have a similar topology. For the first time the ZZ(bb) and WZ(bb) cross-sections are measured at √s = 13 TeV and the observed cross-section measurements are consistent with the Standard Model predictions.
Higgs From Top To Bottom
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Author : Tim Michael Heinz Wolf
language : en
Publisher:
Release Date : 2018
Higgs From Top To Bottom written by Tim Michael Heinz Wolf and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018 with categories.
In the Standard Model (SM) of particle physics, it is expected that the Higgs boson as a scalar spin-0 particle gives mass to all other elementary particles. In addition, the coupling to the top quark, as the heaviest elementary particle, is expected to be of order unity. Proton--proton collision data at a center of mass energy of 13 TeV collected by the ATLAS experiment during Run 2 of the Large Hadron Collider is used to study the interaction between the Higgs boson and the top quark. Data of up to 79.8 fb−1 in various Higgs boson decay modes is analyzed to study Higgs boson production in association with a pair of top quarks (ttH) and probe the SM expectation. This thesis focuses on Higgs decays to bottom quarks and faces the challenges inherent to this decay mode such as limited amount of Monte Carlo statistics and limited understanding of the background modeling. In this thesis, the collected data is used to establish the Higgs boson-top quark coupling by combining analyses targeting different Higgs boson decay modes, employing cutting edge statistical methods. The extracted cross-section ratio with respect to the SM prediction of the ttH process is measured to be 1.32 (+0.28 -0.26) in agreement with the SM expectation. This constitutes a discovery with a significance of 5.8 standard deviations and establishes the coupling between the Higgs boson and the top quark.
Using Atlas To Investigate The Associated Production Of A Higgs Boson With A Pair Of Top Quarks
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Author : L. Asquith
language : en
Publisher:
Release Date : 2010
Using Atlas To Investigate The Associated Production Of A Higgs Boson With A Pair Of Top Quarks written by L. Asquith and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
This thesis describes the study of the channel t \overline{t} H {0}(H {0}\rightarrowb\overline{b} with the ATLAS detector with 30fb -1 of data and a center of mass energy of 10 TeV. Chapter 1 provides a description of the ATLAS detector, followed by a theoretical background in Chapter 2 and a discussion of phenomenology and event generation in Chapter 3. Issues associated with leptons and missing energy are presented in Chapter 4, with focus on optimising the preselection cuts to reduce the rate of background processes, including those previously unconsidered for this channel but found to be important as a consequence of this study. In addition, the reconstruction of the leptonically decaying W Boson from lepton and missing energy is described. The treatment of jets is introduced in Chapter 5, with the focus being again on the optimisation of preselection cuts. Studies presented here are on corrections for energy lost via both muons and neutrinos in semi-leptonic bdecays and preselection cuts based on the transverse momenta and b-weights of individual jets. The issues associated with combinatorial background and the use of jet charge to reduce it is also introduced here. The choice of jet algorithm is considered of great importance for this channel, thus is presented in detail in Chapter 6. Chapter 7 explores the reconstruction of the Higgs Boson from jet pairs, focusing on the segregation of jets by b-weight. The reconstruction of the t \overline{t} H {0} system is studied with various techniques; an investigation of the use of jet charge to discriminate between b and \overline{b} jets is presented as a novel likelihood variable. Chapter 8 summarises the results obtained using the optimised preselection, jet algorithm and jet charge method. Systematic uncertainties are discussed throughout the thesis where relevant and also summarised.
Searches For Pair Production Of Higgs Bosons In The Bbbb Final State Using The Atlas Detector Or
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Author : Sean Gasiorowski
language : en
Publisher:
Release Date : 2021
Searches For Pair Production Of Higgs Bosons In The Bbbb Final State Using The Atlas Detector Or written by Sean Gasiorowski and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021 with categories.
This thesis discusses searches for pair production of Higgs bosons in the bbbb final state using data recorded by the ATLAS detector from $\sqrt{s} = 13$ TeV proton-proton ($pp$) collisions during the full period of LHC Run 2. It develops two separate analysis strategies: one targeting resonant pair production of Higgs bosons, in which Beyond the Standard Model resonances are produced which subsequently decay to two Higgs bosons, and one targeting non-resonant pair production of Higgs bosons, which is sensitive to Standard Model $HH$ production as well as to variations of the Higgs trilinear self-coupling. In the resonant searches, no significant excesses are seen, and upper limits on cross section are set on both spin-0 and spin-2 resonant hypotheses. Such limits are competitive with other leading ATLAS full Run 2 searches, and represent a significantly stronger statement than previous, beating the early Run 2 combined ATLAS results above 350 GeV and leading the ATLAS full Run 2 sensitivity above 700 GeV. In the non-resonant, no evidence of Standard Model $HH$ production is seen, but upper limits on cross section of $pp\rightarrow HH$ via gluon-gluon fusion are set to be 4.4 (5.9) observed (expected) times the value predicted by the Standard Model. Such limits represent a significant improvement in sensitivity over the early Run 2 bbbbresults, achieving a 30 (40)~\% additional gain in sensitivity beyond that predicted from a pure increase in dataset size. These limits are competitive with other leading ATLAS full Run 2 searches. Cross section limits are additionally set for a range of values of the Higgs self coupling, parametrized via its ratio to the value predicted by the Standard Model, $\kappa_{\lambda} = \lambda_{HHH}/\lambda_{HHH}^{SM}$. This is restricted to have values $-4.9 \leq \kappa_{\lambda} \leq 14.4$ observed ($-3.9 \leq \kappa_{\lambda} \leq 10.9$ expected). An excess of data over background is seen for values of $\kappa_{\lambda} \geq 5$, with maximum local significance of $3.8\sigma$ at $\kappa_{\lambda} = 6$. Such an excess is demonstrated to be due to low mass, where the bbbb channel has limited sensitivity, and is not seen in more sensitive channels in this region. Results on the development of two methods for the improvement of hadronic shower modeling in ATLAS fast calorimeter simulation are also presented.
The Beauty And The Boost A Higgs Boson Tale
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Author : Brian Moser
language : en
Publisher: Springer Nature
Release Date : 2023-09-19
The Beauty And The Boost A Higgs Boson Tale written by Brian Moser and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2023-09-19 with Science categories.
Precision measurements of the Higgs boson’s properties are a powerful tool to look for deviations from the predictions of the Standard Model (SM) of particle physics. The 139/fb of proton-proton collision data which have been collected by the ATLAS experiment during Run 2 of the LHC, offer an opportunity to investigate rare Higgs-boson topologies, which are particularly sensitive to new physics scenarios but experimentally difficult to access. Several such measurements, which target Higgs-boson decays to heavy-flavour quarks, as well as their combinations are presented in this thesis. A novel analysis that measures Higgs-boson production in association with a heavy vector boson V (VH, with V=W,Z) at high energies is presented. Dedicated Higgs-boson reconstruction techniques are applied to reconstruct the highly Lorentz-boosted Higgs-boson decays into pairs of bottom quarks. The measurement is subsequently combined with a VH cross-section measurement at low and intermediate pT(V) to provide a differential cross-section measurement in kinematic fiducial volumes over the largest possible pT(V) range. All cross-section measurements agree with the SM predictions within relative uncertainties that range from 30% to 300%. The results are furthermore interpreted as limits on the parameters of a SM effective field theory. Finally, a combination of measurements of Higgs decays to heavy-flavour quarks is used to experimentally determine that the Higgs-boson coupling to charm quarks is weaker than to bottom quarks, as predicted by the SM. The target audience for the thesis are physicists and physics students, in particular those with a background in high energy physics.