Search for the production of VZγ at the CMS experiment at 13 TeV and Effective Field Theories interpretation of anomalies in triboson production processes

The discovery of the Higgs boson in 2012 is one of the most important confirmations of the Standard Model of particle physics. However, some experimental evidence and theoretical considerations suggest that the Standard Model may be valid only at low energies. In particular, the Standard Model predictions of rare processes involving triple and quartic gauge couplings require further measurements and confirmations. The Standard Model predicts many different triboson production processes to involve trilinear and quadrilinear vertices at the tree level, but at the time of writing this thesis (beginning of 2025), many of them have never been observed. This thesis focuses on the search of rare triboson Vzgamma (V=W,Z) production processes in a semi-leptonic channel from high-energy proton-proton collisions. The analysis is performed on the full dataset collected by the Compact Muon Solenoid experiment at the CERN Large Hadron Collider in proton-proton collisions at 13 TeV in the 2016 – 2018 period, corresponding to an integrated luminosity of 137/fb. The measured fiducial cross-section of pp –> VZgamma –> 2 jets + 2l + gamma is 1.79 +0.66 -0.55 fb, with an observed (expected) significance of 4.4 (1.8) standard deviations. A dedicated sensitivity study of VZgamma and other triboson production processes to any deviation from the Standard Model predictions is also discussed in this thesis. The Effective Field Theories provide a framework for interpreting this kind of anomaly. These models generalize the dimension- 4 Lagrangian of the Standard Model, including higher-dimension operators in the most general way. In particular, the analysis performed aims to interpret the kinematic effects due to the presence of dimension-6 operators in the Lagrangian.