Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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This report summarises the physics opportunities in the search and study of physics beyond the Standard Model at a 100 TeV pp collider.

Abstract:We consider interpretations of the recent ∼ 3σ reports by the CMS and ATLAS collaborations of a possible X(∼ 750 GeV) state decaying into γγ final states. We focus on the possibilities that this is a scalar or pseudoscalar electroweak isoscalar state produced by gluon-gluon fusion mediated by loops of heavy fermions. We consider several models for these fermions, including a single vector-like charge 2/3 T quark, a doublet of vector-like quarks (T, B), and a vector-like generation of quarks, with or without leptons that also contribute to the X → γγ decay amplitude. We also consider the possibility that X(750) is a dark matter mediator, with a neutral vector-like dark matter particle. These scenarios are compatible with the present and prospective direct limits on vector-like fermions from LHC Runs 1 and 2, as well as indirect constraints from electroweak precision measurements, and we show that the required Yukawa-like couplings between the X particle and the heavy vector-like fermions are small enough to be perturbative so long as the X particle has dominant decay modes into gg and γγ. The decays X → ZZ, Zγ and W + W − are interesting prospective signatures that may help distinguish between different vector-like fermion scenarios.