Search for Stable Stau Production at the LHC

Kolja Kaschube
Sep 2011

Thesis Type:

In this thesis, a search for heavy stable charged particle production, in particular a quasistable supersymmetric tau lepton ("stau") arising in gauge-mediated supersymmetry breaking (GMSB) models, is presented. This stable stau would cross detectors without decaying, resembling a muon, and produce signatures of high momentum or high ionization energy loss. The energy loss measurement represents a direct handle on the particle mass via the Bethe-Bloch formula. Proton-proton collisions at 7 TeV center-of-mass energy produced by the Large Hadron Collider and recorded by the CMS detector are investigated. Low-momentum collision data tracks are used to predict the background of highly ionizing tracks at high momenta. A high signal-to-background ratio is achieved by separating the search into channels with differing muon or stau multiplicities and by using the transverse momentum and energy loss measurement as the discriminating variables. Using $35.8\mbox{ pb}^{-1}$ of data recorded in the 2010 LHC run, no excess is observed with respect to the expected Standard Model background. As a result, upper limits on the mass of stable staus are derived within the context of the investigated GMSB models.

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