Search for dark matter with the CMS detector at the Large Hadron Collider

The standard model of particle physics has booked enormous successes in the past few decades. It is able to describe experimental processes with astonishing precision and predicted the existence of several particles, such as the top quark, and the Higgs boson. Being a fundamental description of the processes of nature makes it one of most well-tested theories that ever existed. However, many observations indicate the presence of phenomena beyond the standard model. An example thereof are the many astronomical measurements indicating the presence of additional unseen sources of gravity. Movements of faraway galaxies cannot always be explained by the gravity of the observed matter in its environment, hinting the presence of dark matter. Whether it can interact with the standard model particles, besides through the gravitational force, remains an open question, although cosmological measurements indicate an additional interaction that cannot be much stronger than the scale of the weak force. Many expansions to the standard model have been proposed, attempting to provide particles fulfilling the role of dark matter. ​In this work, a generalised model is examined, specifying the mediators between the hidden particles and the observable particles. The lightest particle of the dark sector corresponds to the dark matter candidate. Other content of the hidden sector is intentionally left out of the model description to widen its relevance. To abide the cosmological observations, an additional U'(1) local gauge symmetry is introduced, yielding an extra Z'-boson. The signature feature of the model is the inclusion of a new scalar field, spontaneously breaking this U'(1) symmetry, thereby generating the mass of the particles in the hidden sector, and adding a dark Higgs boson to the model content. Predictions of the dark Higgs model decaying the dark Higgs to two W-bosons in the semi-leptonic decay channel, are held against observed data from the LHC machine, collected with the CMS detector. The data sample was gathered over the run 2 period spanning three years 2016, 2017 and 2018, with an integrated luminosity of 137/fb. In this period the LHC was operating with a centre of mass energy of 13 TeV. ​Results are combined with the full-leptonic decay channel, observing no significant excess over the standard model predictions. A large portion of the dark Higgs model phase space is excluded.

Jaar van publicatie:2022

Trefwoorden:Doctoral thesis

Toegankelijkheid:Open