School of Physics - Theses

Permanent URI for this collection

http://hdl.handle.net/11343/310

Filters

2018 1
1
Reset filters

Settings
Statistics
Citations
Author: Rados, Petar × Subject: CERN ×

Search Results

Now showing 1 - 1 of 1
  • Item
    Thumbnail Image
    Search for the Higgs boson in the WH production mode with H→WW* decay using the ATLAS detector
    Rados, Petar ( 2018)
    In order for fundamental particles to attain mass, the electroweak symmetry of the Standard Model (SM) of particle physics must be broken. The simplest way of breaking this symmetry is via the SM Higgs Mechanism, and it predicts the existence of a new particle called the SM Higgs boson. This particle should be experimentally accessible at the high-energy frontier, and so its discovery is considered as one of the most important goals in modern particle physics. This goal was partially achieved in July 2012, when the ATLAS and CMS experiments at the Large Hadron Collider (LHC) announced the discovery of a Higgs-like particle with a mass of around 125 GeV. The next step for both experiments is to scrutinize the properties of this new particle in order to determine whether it is, in fact, the SM Higgs boson. One high-priority objective of the ATLAS experiment is to confirm the SM predictions for Higgs boson production at the LHC. The main result presented in this thesis contributes to this objective by searching for the WH production mode with subsequent H→WW* decay. The H→WW* decay channel provides a sensitive probe of WH production due to its large branching ratio and clean detector signature. Moreover, this signal process provides important information on the Higgs boson couplings, since it only involves couplings to W bosons at both the production and decay vertices at tree-level. The search for this signal process was conducted using LHC proton-proton collision data collected by the ATLAS detector. This data was recorded at centre-of-mass energies of 7, 8 and 13 TeV corresponding to integrated luminosities of 4.5, 20.3 and 5.8 fb−1, respectively. The analysis strategy was first developed using the 7 and 8 TeV data samples and it was used to measure the relative signal strength with respect to the SM expectation. For a Higgs boson of mass 125 GeV, the observed value of the signal strength was determined to be 0.72 +1.2−1.1 (stat.) +0.4−0.3 (sys.). The analysis method was then extended to perform the first measurement of the signal strength at 13 TeV, with this quantity measured to be 3.2 +3.7−3.2 (stat) +2.3−2.7 (sys). An overall excess was observed at 0.66σ (0.77σ) significance with respect to the background-only hypothesis in the 7+8 TeV (13 TeV) data. All measurements are in agreement with the SM expectations.