Estimation of the Irreducible Z → νν Background for Searches with Jets and Missing Transverse Momentum at CMS

Simon Kurz
Nov 2014

Thesis Type:

Supersymmetry (SUSY) is one of the most promising extensions of the Standard Model of particle physics (SM), since it provides solutions of various shortcomings of the Standard Model. In many SUSY models final states with jets, no light leptons (electrons or muons) and large amounts of missing transverse energy are expected. One of the irreducible SM backgrounds for a search in this final state are events in which a Z boson is produced in association with jets, with the Z decaying to two neutrinos.
An estimation of this background can be done by exploiting the similar kinematic behavior between Z+jets events and γ+jets events at high transverse momenta of the boson. Unfortunately, the theoretical uncertainty of this method is large, in particular for high jet multiplicities. This thesis focuses on an alternative approach for which events with the Z decaying into a pair of light leptons are used.
The missing transverse momentum signature is faked by removing the leptons from the event. The main challenge of this method is the large statistical uncertainty especially for search regions with hard cuts on the missing transverse energy and the associated hadronic activity. Thus dedicated extrapolation methods are developed in this thesis.

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