Study of electroweak W±W±jj production with the CMS detector
8 March 2018
Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim
Organization / co-organization:
Department of Physics
Nick Van Remortel
Public defence of the PhD thesis of Mr. Jasper Lauwers - Faculty of Science - Department of Physics
The standard model of particle physics (SM) provides a theoretic framework for fundamental particles and their interactions. Despite its successes, many observations cannot be explained by the standard model in its current form. Searches for new particles to explain these phenomena, as performed at the Large Hadron Collider (LHC) at unexplored center-of-mass energies, are crucial to push the limits of our knowledge. This is complemented with precision measurements of the standard model and the Higgs boson in particular.
By studying the scattering of weak vector bosons (VBS), an important contribution is made to both fronts. The scattering of the weak vector bosons is strongly connected to electroweak symmetry breaking (EWSB) in the SM, regulated by the Higgs mechanism. It is through the EWSB that the weak vector bosons acquire mass, turning the massless Goldstone bosons in their longitudinal polarization. Measuring VBS provides information on the degrees of freedom of the Higgs field that are absorbed by the weak bosons. The VBS process also contains information on the quartic vector boson interactions, a part of the SM which has not been well tested yet and could be modified by new physics.
The vector boson scattering process can be studied at the LHC from the electroweak production of vector bosons in association with jets. It can be measured with the highest sensitivity in the case of two W bosons with the same charge decaying to leptons. The measurement of this process in data recorded with the Compact Muon Solenoid (CMS) detector during 2016 is described in this thesis, which lead to the first discovery of a process dominated by vector boson scattering. The electroweak production of two same-charge W bosons at the LHC operating at a center-of-mass energy of 13 TeV has a cross section of only 0.35 pb, which is two orders of magnitude smaller than the total production cross section of the Higgs boson discovered in 2012. The small cross section in combination with the backgrounds from strong diboson production and misreconstructions make this a challenging analysis.
To uncover the properties of VBS, the study of this process during the further operation of the LHC remains of great importance. A feasibility study for measuring VBS properties is described in the last chapter, with 3 ab−1 of data that will be collected with the CMS detector in the next decades at the upgraded High Luminosity LHC.