Abstract
Event isotropy \( {\mathcal{I}}^{\mathrm{sph}} \), 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 λmax, 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 λmax) and in \( {\mathcal{I}}^{\mathrm{sph}} \) separately often have much narrower distributions, and are more easily distinguished, in the (\( {\mathcal{I}}^{\mathrm{sph}} \), λmax) plane. An intuitive, semi-analytic estimation technique clarifies why this is the case and assists with the interpretation of the distributions.
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ArXiv ePrint: 2011.06599
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Cesarotti, C., Reece, M. & Strassler, M.J. The efficacy of event isotropy as an event shape observable. J. High Energ. Phys. 2021, 215 (2021). https://doi.org/10.1007/JHEP07(2021)215
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DOI: https://doi.org/10.1007/JHEP07(2021)215