657 research outputs found

    Cross section measurement and novel deep learning approach to background modelling of the Higgs boson decays to bottom quarks at the ATLAS detector

    Get PDF
    This thesis describes an updated cross section measurement of the Higgs boson decaying into bottom quarks in the VH production channel using the Run 2 data collected by the ATLAS detector at the Large Hadron Collider. The analysis builds upon two already-published analyses and introduces improvements that lead to a more accurate, more precise and more granular measurement of the VH(bb) cross section. The cross section is measured in bins of the vector boson transverse momentum and the jet multiplicity according to the Simplified Template Cross Section (STXS) prescription. This thesis documents contributions to the analysis made by the author. In particular, a novel method of modelling systematic uncertainties based on deep neural networks is introduced. The method is shown to be superior to the previously used method, which is based on boosted decision trees. Expected results using Asimov datasets are presented. The inclusive signal strength of the VH(bb) process is expected to be measured with a precision of 14%. The signal strengths of the WH(bb) and ZH(bb) processes are expected to be measured with a precision of 18% and 21%, respectively. Both signal strength measurements are expected to achieve higher significance than any previously published VH(bb) measurement. The VH(bb) Cross Section measurement in 11 fiducial STXS bins is expected to achieve precision ranging between 33% and 166% for the individual bins. Once the analysis is unblinded, the cross section measurement will constitute another test of the Standard Model. Any discrepancy observed between the measured cross section and the cross section predicted by the Standard Model might hint new physics beyond the Standard Model

    Studies of new Higgs boson interactions through nonresonant HH production in the b¯bγγ fnal state in pp collisions at √s = 13 TeV with the ATLAS detector

    Get PDF
    A search for nonresonant Higgs boson pair production in the b ¯bγγ fnal state is performed using 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this fnal state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifer κλ but also of the quartic HHV V (V = W, Z) coupling modifer κ2V . No signifcant excess above the expected background from Standard Model processes is observed. An observed upper limit µHH < 4.0 is set at 95% confdence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confdence intervals for the coupling modifers are −1.4 < κλ < 6.9 and −0.5 < κ2V < 2.7, assuming all other Higgs boson couplings except the one under study are fxed to the Standard Model predictions. The results are interpreted in the Standard Model efective feld theory and Higgs efective feld theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions

    Search for resonant WZ production in the fully leptonic final state in proton–proton collisions at √s=13 TeV with the ATLAS detector