Determination of Supersymmetric Particle Masses at the LHC using Kinematic Fits

Benedikt Mura
Sep 2011

Thesis Type:

Supersymmetry is a theoretically well-motivated extension of the currently established model of particle physics. It introduces a new symmetry between bosonic and fermionic fields and predicts a large number of new particles. If supersymmetry is discovered at the LHC, a measurement of the new particle masses will be an important contribution to the determination of the fundamental model parameters.

In this thesis a novel method for mass determination is presented, which is based on the assumption of R-parity conserving supersymmetry and makes use of events with identical decay topologies. Combining a mass scan with an event-by-event kinematic fit a complete event reconstruction is possible despite two undetected lightest supersymmetric particles, and a likelihood map for the mass space is obtained.

The method is demonstrated for the mSUGRA benchmark point SPS1a and is shown to work in principle. A weakness concerning the measurement of the undetected particle at the end of the decay chain is observed, which is related to the measurement resolution of particles in the detector. Additional information from the measurement of a kinematic endpoint is applied to improve the determination of the lightest particle mass. If backgrounds are small a precise mass measurement is feasible with this method. A large amount of LHC data is required to isolate sufficient events with a suitable topology.

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