Precise testing of the Standard Model and search for new physics beyond the Standard Model through same-sign WW scattering and Wγ production

The Large Hadron Collider LHC at CERN is at the high energy frontier of particle physics. The multiboson process is an important tool to precisely test the electroweak symmetry spontaneous breaking mechanism, to explore the Higgs mechanism and to search for new physics beyond the Standard Model. Jie Xiao's PhD dissertation, using data collected by the CMS experiment on the LHC in 2016-2018, is focused on multiboson physics, and the choice of topic is of great physical importance. The paper utilizes data collected by CMS for proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of ~137 /fb to carry out several works as follows: 1) For the first time, the cross section of the double boson W+ photon process has been accurately measured at 13 TeV, and the dimension-six operator parameters of the effective field theory have been measured, of which the world's tightest limit is given to the Cwww parameter. 2) The first measurement of the polarized same-sign WW scattering processes gives the upper limit of the longitudinal polarization component production cross section and the significance of the single longitudinal W boson scattering component, which is of pioneering significance for the study of the electroweak symmetry spontaneous breaking mechanism and the exploration of the Higgs mechanism. 3) For the first time, we have searched for heavy Majorana neutrinos through the WW boson scattering process with the same sign of charges, and given the upper limit of the equivalent mass of Majorana neutrinos, which is the best result in the world. The doctoral dissertation is well-written, with a clear structure, rigorous research and analysis process, and accurate textual expression. The author has a solid grasp of the basic theoretical knowledge of particle physics and experimental analysis techniques and has the ability to conduct scientific research independently.