Search for excited muons in the process pp \rightarrow \mu\mu* \rightarrow \mu\muZ \rightarrow 4\mu with CMS data

Some theories concerning new physics predict the existence of a substructure of leptons and quarks. Such a substructure could answer some of the open questions addressed to the Standard Model of Particle Physics. Therefore, many searches for excited fermions are performed at particle colliders, also at the LHC experiments CMS and ATLAS. This thesis presents a search for excited muons in the channel µµ∗ → µµZ → 4µ where the µ∗ is produced together with a Standard Model muon via contact interaction. The analysis is based on the complete 2012 dataset of proton-proton collisions recorded by the CMS experiment and corresponds to an integrated luminosity of 19.7 fb−1 at a center-of-mass energy of √s = 8 TeV. For this purpose, several selection criteria have been implemented to distinguish between signal and background, also taking into account influences of a Z-boson decay to nearby muons. Since there is no deviation from the Standard Model expectation, an exclusion limit has been set as a function of the compositeness scale Λ for the coupling parameters f = f′ = 1 and f = −f′ = −1. The existence of excited muons can be excluded up to Mµ∗ = 1.64 TeV for f = f′ = 1 and Mµ∗ = 1.85 TeV for f = −f′ = −1 (95 % C.L.) assuming a compositeness scale of Λ = Mµ∗. In addition, a combination with the channel µµ∗ → µµZ → 2µ2e has been performed, yielding a limit of Mµ∗ > 1.75 for f = f′ = 1 and Λ = Mµ∗.