Search for the Standard Model Higgs boson produced via vector boson fusion and decaying to bottom quarks with the CMS detector at the Large Hadron Collider

Date: 10 March 2016

Venue: UAntwerp, Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen

Time: 4:00 PM

PhD candidate: Sara Alderweireldt

Principal investigator: Nick Van Remortel

Short description: PhD defence Sara Alderweireldt, Department of Physics - Faculty of Science, Department of Physics


Our current best understanding of the particles and interactions observed in nature is encapsulated in the Standard Model of particle physics. The SM includes fermions, which constitute all matter, and gauge bosons, which mediate the interactions. It unifies three of the four known forces: electromagnetism, the weak interaction and the strong interaction. As a gauge theory, the SM reflects the symmetries observed in nature in its formulation.

A consequence thereof is that in its barest form, the SM requires all particles to be massless. To explain the existence of massive particles, it incorporates the Brout-Englert-Higgs (BEH) mechanism. This mechanism was proposed independently by several theoretical physicists in 1964, and describes how particles, seemingly required to be massless, can become massive. It postulates a scalar field – the BEH field – and an associated scalar boson – the Higgs boson. The field induces spontaneous symmetry breaking, and the coupling of particles to the field allows them to acquire mass. The Higgs boson mass itself however, is an important parameter in the SM, and cannot be predicted by theory. Instead it has to be determined experimentally.

For decades scientists have actively searched for the Higgs boson. Searches were conducted most recently at the Large Hadron Collider (LHC) at CERN, the current largest and most-powerful particle accelerator, designed to collide protons at a centre-of-mass energy of 14 TeV. Since 2009, the LHC has been recording data at centre-of-mass energies of 7, 8 and 13 TeV. On the 4th of July 2012, the ATLAS and CMS collaborations announced the discovery of a new particle, with properties matching those of the SM Higgs boson. Experiments have since continued to verify the properties of the discovered particle, which so far remains fully compatible with the SM expectation.

Higgs bosons can be produced and observed at collider experiments in a variety of ways. In this thesis, a search for the SM Higgs boson is presented, studying its production via vector boson fusion and subsequent decay to bottom quarks. The data used for this search was recorded with the CMS detector at the LHC, in 2012.