Mass Determination of New Particle States

Abstract

We study theoretical and experimental facets of mass determination of new particle states. Assuming supersymmetry, we update the quark and lepton mass matrices at the grand unification scale accounting for threshold corrections enhanced by large tan beta. From the hypothesis that quark and lepton masses satisfy a classic set of relationships suggested in some Grand Unified Theories (GUTs), we predict tan beta needs to be large, and the gluino's soft mass needs to have the opposite sign to the wino's soft mass. Existing tools to measure the phase of the gluino's mass at upcoming hadron colliders require model-independent, kinematic techniques to determine the masses of the new supersymmetric particle states. We discuss the current techniques to determine the mass of invisible particles. We review the transverse mass kinematic variable M_{T2} and the use of invariant-mass edges to find relationships between masses. Next, we introduce a new technique to add additional constraints between the masses of new particle states using M_{T2} at different stages in a symmetric decay chain. These new relationships further constrain the mass differences between new particle states, but still leave the absolute mass weakly determined. Next, we introduce the constrained mass variables M_{2C,LB}, M_{2C,UB}, M_{3C,LB}, M_{3C,UB} to provide event-by-event lower-bounds and upper-bounds to the mass scale given mass differences. We demonstrate mass scale determination in realistic case studies of supersymmetry models by fitting ideal distributions to simulated data. We conclude that the techniques introduced in this thesis have precision and accuracy that rival or exceed the best known techniques for invisible-particle mass-determination at hadron colliders.

Oxford D.Phil Thesis. Defended Sept 2008. Awarded March 2009. 150 pg

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