Search for resonant Higgs boson pair production in the bb̄WW* decay channel in the boosted 1-lepton final state using the full Run 2 ATLAS dataset
von Kira Abeling
Datum der mündl. Prüfung:2022-04-01
Erschienen:2022-05-03
Betreuer:Prof. Dr. Stan Lai
Gutachter:Prof. Dr. Stan Lai
Gutachter:Prof. Dr. Ariane Frey
Dateien
Name:Dissertation_online.pdf
Size:23.1Mb
Format:PDF
Zusammenfassung
Englisch
Despite the great success of the Standard Model of Particle Physics in explaining physics phenomena over a wide range of energy scales, many open questions remain and it is known that this model of nature is incomplete. The Higgs boson as the most recent discovered particle has completed the Standard Model. With its coupling to mass, it is an excellent candidate to shed light on physics beyond the Standard Model. This thesis presents the search for resonant Higgs boson pair (HH) production as well as resonant production of a Higgs boson in association with another additional scalar particle (SH) in the bb̄WW* decay channel with one charged lepton in the final state using the full Run 2 dataset recorded by ATLAS. This decay channel combines the advantages of a high branching ratio with a reasonable background level due to the lepton in the final state. The mass of the scalar resonance considered ranges between mX = 800 GeV and mX = 5 TeV for HH production and between mX = 750 GeV and mX = 3 TeV for SH production. The latter introduces a second mass scale mS which covers the range between mS = 170 GeV and mS = 2.5 TeV where mS < mX − mH is required. Assuming the scalar particle has couplings similar to the Higgs boson, the decay S → WW will be dominant for the entire considered mass range. Due to the high mass of the heavy scalar resonance, the boosted topology is exploited where the decay products of the Higgs boson decaying to a bb̄-pair as well as the decay products of the hadronically decaying W boson cannot be resolved. They are therefore reconstructed as single hadronic objects called large-R jets. Furthermore, one of the large-R jets is expected to overlap with the charged lepton making this topology not only unique but challenging to reconstruct. This dense environment requires the use of new approaches such as track assisted reclustered jets which profit from the excellent spatial resolution of tracks to describe the large-R jets. Moreover, only muons will be considered as charged leptons in the final state of this search since they are less sensitive to hadronic energy deposits close by. Since no significant excess of data over the expected backgrounds is expected in the ATLAS Run 2 dataset, expected 95% CLs upper limits are evaluated on the respective cross sections. The limits become more stringent for higher values of m X due to the reduced amount of background in this phase space, and smaller m S due to the more boosted topology. Therefore, the best expected limits without considering systematic uncertainties are σ(pp → X → HH) = 2.8 fb at mX = 5 TeV and σ(pp → X → SH) × BR(SH → bb̄W W ) = 0.87 fb at mX = 3 TeV and mS = 240 GeV.
Keywords: Higgs boson; Higgs boson pairs; ATLAS; Beyond Standard Model Physics