Search for Unparticles in the Z + MET channel with the CMS Experiment at $\sqrt{s}$ = 8 TeV
Lars Daniel Reusch · CERN Document Server (European Organization for Nuclear Research) · 2017
In particle physics, there are many proposals how to expand the Standard Model. Most of those theories postulate new particles. Supersymmetry e.g. pairs every parti- cle with a superpartner, effectively doubling the number of particles. The unparticle theory however does not predict new particles in the traditional sense. Instead H. Georgi proposed in 2007 [1] that the interaction of a conformal field with the Standard Model field at very high energies could lead to ”unparticle stuff” at lower (experimen- tally observable) energies. Because of their continuous mass distribution unparticles are not particles in the common sense. In this thesis, a search for unparticles is conducted on the 19.7 fb−1 of data taken by the CMS experiment in 2012. The analysis is performed in the channel with a Z boson and missing transverse energy, because the signal is the associated production of an unparticle and a Z boson. The Z then decays into two leptons and the unparticle leaves the detector unseen. Therefore, evidence can only be found by considering the missing transverse energy. To better discriminate background processes with a very similar signature from the signal, certain cuts are applied. They are designed to effectively suppress the back- ground while ensuring a high signal efficiency. Furthermore, the systematic uncer- tainties on signal and background are investigated. As data and background are in good agreement, upper exclusion limits on the sig- nal cross section are calculated. Limits of comparable experiments can be slightly enhanced.