Search for dark matter and unparticles produced in association with a Z boson in pp collisions at $\sqrt{s}$ = 8 TeV at CMS

The Large Hadron Collider (LHC) is the biggest and the most powerful particle collider machine to be built and operated in the history of humankind. The operation of the LHC machine started in 2008 and to date a big dataset was recorded allowing for a great number of data analyses to be performed. Analyzing the proton-proton collisions, the scientists of the CMS and ATLAS collaborations were able to discover the long sought Higgs boson. Even though the Standard Model of particle physics has been very successful in the past 60 years, being tested with high precision, there still exist observations presenting strong evidence for phenomena the Standard Model can not explain. Therefore, the search for New Physics which is expected to supply the missing explanations will be gaining more and more attention in the next 20 years of the LHC operation. The present thesis analyzes the dataset corresponding to an integrated luminosity of 19.7 fb−1 which was recorded by the CMS detector in 2012 in terms of dark matter and unparticle signatures. Employing an effective field theory approach, one proposes the hypothesis of dark matter particles χ and χ¯ production along a Z boson during a collision at the LHC, whereby dark matter leaves CMS undetected and the Z boson subsequently decays into two charged leptons. The so called unparticles could also lead to the same final state. After the introduction of the standard model of particle physics followed by the CMS setup description in the first chapters of the present thesis, the aspects of event selection and background prediction for the final state with two leptons along missing transverse energy (ETmiss) are discussed and compared to the CMS measurement. No excess of data events is observed in the signal region and exclusion limits for the dark matter production are therefore set. For the unparticle scenario, the world’s best exclusion limits are obtained as the result of this analysis. The results of the present analysis are published in the Physics Analysis Summary CMS-EXO-12-054 and in the Physics Review D journal [1].