The efficacy of event isotropy as an event shape observable

Abstract

Abstract Event isotropy I sph $$ {\mathcal{I}}^{\mathrm{sph}} $$ , an event shape observable that measures the distance of a final state from a spherically symmetric state, is designed for new physics signals that are far from QCD-like. Using a new technique [1] for producing a wide variety of signals that can range from near-spherical to jetty, we compare event isotropy to other observables. We show that thrust T and the C parameter (and λ max, the largest eigenvalue of the sphericity matrix) are strongly correlated and thus redundant, to a good approximation. By contrast, event isotropy adds considerable information, often serving to break degeneracies between signals that would have almost identical T and C distributions. Signals with broad distributions in T (or λ max) and in I sph $$ {\mathcal{I}}^{\mathrm{sph}} $$ separately often have much narrower distributions, and are more easily distinguished, in the ( I sph $$ {\mathcal{I}}^{\mathrm{sph}} $$ , λ max) plane. An intuitive, semi-analytic estimation technique clarifies why this is the case and assists with the interpretation of the distributions.

Keywords

• Phenomenological Models
• Phenomenology of Field Theories in Higher Dimensions