Photons, Missing Energy and the Quest for Supersymmetry at the LHC

Author: 
Ulla Gebbert
Date: 
Mar 2012

Thesis Type:

In this thesis a search for supersymmetry in events with at least one photon, jets and missing transverse energy in an integrated luminosity of $4.32\mbox{ fb}^{-1}$ of pp collisions at sqrt(s) =7 TeV is presented. The data is recorded by the CMS detector in 2011. Final states with photons are expected in models with gauge mediated supersymmetry breaking, where the lightest supersymmetric particle is the gravitino. The gravitino leaves the detector without energy deposition and thus leads to missing transverse momentum in the event.

Missing transverse momentum is crucial to distinguish the signal from the Standard Model events and is reconstructed from all energy deposits in the detector. Due to the non-linearity of the response in the calorimeter, additional corrections are required. In this thesis, a data driven technique to determine the correction for unclustered energy deposits, using the transverse momentum balance between a Z boson and the hadronic recoil, is presented.

For the search for supersymmetry the missing transverse energy distribution measured in data is compared to the expected Standard Model distribution. For this purpose the main Standard Model background processes from QCD multi- and photon-jet or electro-weak processes are modelled using data events. No excess over the Standard Model expectation is observed. Exclusion limits at the 95 % CL are set and interpreted in the GMSB parameter space.

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