Spin Determination via Third Generation Cascade Decays

Abstract

Once new particles are discovered at the LHC and their masses are measured, it will be of crucial importance to determine their spin, in order to identify the underlying new physics model. We investigate the method first suggested by Barr and later extended by others to distinguish between Supersymmetry and alternative models, e.g. Universal Extra Dimensions, in a certain cascade decay. This method uses invariant mass distributions of the outgoing Standard Model particles to measure the spin of intermediate particles, by exploiting the quark/anti-quark asymmetry of the LHC as a pp collider, which is limited for first generation quarks. In this work, we suggest instead to measure the charge of the outgoing quark, in case it is a third generation quark. The resulting asymmetry for a bottom quark is similar to the previous method, while it is independent of hadronic uncertainties. Furthermore, for a top quark, the asymmetry allows better distinction between the models, as demonstrated by a quantitative analysis of model discrimination. We also show that the top's decay products can be used instead of the top itself, when the reconstruction of the top momentum is difficult to accomplish, and still provide information about the spin.

22 pages, 17 figures. Section on model discrimination and references added, discussion in appendix C extended

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• Flavor Physics Constraints for Physics Beyond the Standard Model
• Dark Matter Particle Spectroscopy at the LHC: Generalizing MT2 to Asymmetric Event Topologies
• A Review of the Mass Measurement Techniques proposed for the Large Hadron Collider
• From the LHC to Future Colliders
• Precise reconstruction of sparticle masses without ambiguities
• The Footprint of F-theory at the LHC
• Discovery in Drell-Yan Processes at the LHC
• Distinguishing spins at the LHC using bound state signals
• Determination of the Spin of New Resonances in Electroweak Gauge Boson Pair Production at the LHC
• A New Method for the Spin Determination of Dark Matter
• Spin and Chirality Effects in Antler-Topology Processes at High Energy $e^{+}{e}^{-}$ Colliders
• Tau reconstruction methods at an electron-positron collider in the search for new physics
• Squark flavour violation and naturalness at the LHC