Global ETD Search

1	Determining backgrounds with misidentified leptons in the ATLAS Higgs boson analysis / Bestämning av bakgrunder med misrekonstruerade leptoner i Higgsbosonanalysen i ATLAS Hu, Leo Qiyuan January 2023 (has links) This thesis presents an analysis of misidentified leptons in the Higgs boson decaychannel H → W W ∗ → lνlν. Misidentified leptons, resulting from jets misidentifiedas leptons, mimic the signal of a Higgs boson decay, resulting in a backgroundcontribution to the signal. The analysis is performed on proton-proton collisions ata center-of-mass energy of 13.6 TeV recorded by the ATLAS experiment at CERN’sLarge Hadron Collider. The estimation of misidentified leptons is done using theso-called Fake Factor method, which is used to assess the contributed backgroundwith misidentified leptons in the signal region. The Fake Factor values increasewith increasing momenta for misidentified electrons while it remains constant formisidentified muons. An analysis of the impact parameters d0 and z0 show thatthe accuracy of the Monte Carlo simulation to correctly predict the contribution ofmisidentified leptons from heavy quarks is high. / Denna avhandling presenterar en analys av felaktigt identifierade leptoner i Higgsbosonens sönderfallskanal H → W W ∗ → lνlν. Felaktigt identifierade leptoner frånhadroner imiterar signalen av ett sönderfall från en Higgs boson, vilket resulterar ibakgrund till signalen. Analysen utförs på proton-proton kollisioner med energier på13.6 TeV som samlats in av ATLAS-experimentet vid CERNs Large Hadron Collider.Denna avhandling fokuserar främst på uppskattningen av felaktigt identifieradeleptoner genom användningen av Fake Factor-metoden, vilket används för att bedömaden bidragande bakgrunden med felidentifierade leptoner i signalregionen. Värdenaför Fake Factors ökar med ökande rörelsemängd för felidentifierade elektroner medanför det förblir konstant för felidentifierade muoner. En analys av ”impact parameters”d0 och z0 visar att Monte Carlo-simuleringens noggrannhet att uppskatta antaletfelidentifierade leptoner från tunga kvarkar är hög. Particle Physics ATLAS detector Fake Factor method Higgs boson lepton misreconstruction misidentified events Partikelfysik ATLAS detektorn Fake Factor-metoden Higgs boson lepton felrekonstruktion felidentifierade händelser Physical Sciences Fysik
2	Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at the LHC Chiu, Justin 22 December 2020 (has links) This thesis presents the search for the dark sector process h -> Zd Zd -> 4l in events collected by the ATLAS detector at the Large Hadron Collider in 2015--2018. In this theorized process, the Standard Model Higgs boson (h) decays to four leptons via two intermediate Beyond-the-Standard-Model particles each called Zd. This process arises from interactions of the Standard Model with a dark sector. A dark sector consists of one or more new particles that have limited or zero interaction with the Standard Model, such as the new vector boson Zd (dark photon). It could have a rich and interesting phenomenology like the visible sector (the Standard Model) and could naturally address many outstanding problems in particle physics. For example, it could contain a particle candidate for dark matter. In particular, Higgs decays to Beyond-the-Standard-Model particles are well-motivated theoretically and are not tightly constrained; current measurements of Standard Model Higgs properties permit the fraction of such decays to be as high as approximately 30%. The results of this search do not show evidence for the existence of the h -> Zd Zd -> 4l process and are therefore interpreted in terms of upper limits on the branching ratio B(h -> Zd Zd) and the effective Higgs mixing parameter kappa^prime. / Graduate dark sector dark photon ATLAS LHC Higgs boson Higgs BSM SM Standard Model beyond the Standard Model search Zd Zdark Large Hadron Collider electrons muons Higgs decays hidden sector kinetic mixing Higgs mixing U(1) hypercharge Higgs portal dark matter symmetry breaking data-driven fake background Z_d detector particle physics hep hep-ex high energy physics CERN run-2 fake factor

Search results

Determining backgrounds with misidentified leptons in the ATLAS Higgs boson analysis / Bestämning av bakgrunder med misrekonstruerade leptoner i Higgsbosonanalysen i ATLAS

Search for Higgs boson decays to beyond-the-Standard-Model light bosons in four-lepton events with the ATLAS detector at the LHC