Search for physics beyond the standard model in pp collisions at the CMS experiment with a signature of a Z boson plus missing transverse energy

Abstract

The Standard Model of elementary particles is a theory that describes the fundamental structure of matter and interactions among the elementary particles. While the gravitational evidence for the existence of Dark Matter (DM) is overwhelming, there is no good DM candidate in the Standard Model framework, and there is no evidence yet for non-gravitational interactions between DM and Standard Model particles. Therefore, the first analysis performed in this dissertation searches for evidence of particle DM production at the LHC. It uses events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 fb^-1 of proton-proton collisions at the LHC at a center-of-mass energy of 8 TeV. No excess of events is observed above the number expected from the Standard Model contributions. The results are interpreted in terms of 90% confidence level limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios. Limits are set on the effective cutoff scale, and on the annihilation rate for DM particles, assuming that their branching fraction to quarks is 100%. Additionally, the most stringent 95% confidence level limits to date on the unparticle model parameters are obtained.