Signs of Susy

Abstract

This doctoral thesis addresses aspects of Supersymmetry (Susy) phenomenology. In addition to previously published work, it contains introductions to the following topics: from classical mechanics to quantum field theory for the more casual reader, electroweak naturalness, the Higgs as a pseudo-Nambu-Goldstone boson, the MSSM and NMSSM, simple and less simple models of gauge-mediated Susy breaking (GMSB), collider searches for Susy and other new theories, transverse mass observables with missing energy, and Brazil-band plots. The previously published work is as follows. The optimally natural Higgs-stop sector in the MSSM in light of the 2012 discovery of a Higgs boson is derived, namely that of almost maximal mixing, with the scalar top partners almost as light as can be. The discovery is also interpreted numerically in the NMSSM, with greater emphasis placed on the visibility of the Higgs boson at the observed mass, i.e. on signal strengths. I investigate the role played by the mediation scale of GMSB: this is found to be as a control of the extent to which Yukawa couplings de-tune flavour-blind relations set by gauge couplings. Finally, issues relating to the discovery or exclusion of Susy at colliders are discussed. Bounds are derived for the masses of new particles from LHC searches for excesses of jets and missing energy without leptons, and compared to constraints arising from Higgs boson searches, for models of GMSB and the Constrained Minimal Supersymmetric Standard Model. I present a novel search strategy for new physics signatures with two neutral, stable particles, when such particles are produced by boosted decays. (Susy motivations include models with light gravitinos, pseudo-goldstinos, singlinos or new photinos.) The method is shown to produce sharp mass peaks that enhance the visibility of the signal, with mass reconstruction to 5% from O(100) events.