Top Partners at the LHC: Spin and Mass Measurement

Abstract

If one takes naturalness seriously and also assumes a weakly coupled extension of the Standard Model (SM) then there are predictions for phenomenology that can be inferred in a model independent framework. The first such prediction is that there must be some colored particle with mass O(TeV) that cancels the top loop contribution to the quadratic divergence of the Higgs mass. In this paper we begin a model independent analysis of the phenomenology of this “top partner,” t ′. We make one additional assumption that it is odd under a parity which is responsible for the stability of a WIMP dark matter candidate, N. We focus on three questions to be explored at the LHC: discovery opportunities, mass determination, and spin determination of this top partner. We find that within a certain region of masses for the t′ and N, t ′¯t ′ is easily discovered in the tt¯+ 2N decay with the tops decaying fully hadronically. We show that without having to rely on other channels for new physics that for a a given t ′ spin the masses of t′ and N can be measured using kinematic information (e.g. average 6ET or HT ) and total cross section. A degeneracy due to the spin remains, but with several hundred fb−1 of luminosity we demonstrate potentially useful new methods for determining the t′ spin over a wide range of masses. Our methods when could be useful for distinguishing supersymmetric and non-supersymmetric models.