Search for Black Holes and Sphalerons Using Novel MachineLearning Techniques at CMS

A comprehensive search for microscopic black holes and electroweak sphalerons is presented, using proton-proton collision data collected by the CMS detector during 2016–2018, corresponding to an inte-grated luminosity of 138 fb−1. A novel tool has been developed to identify collider events with distinctkinematic features, based on the phase space distance between events. In the context of models with largeextra dimensions, semiclassical black holes with masses below 9.0-11.4 TeV are excluded by this search,significantly extending previous sensitivity. Additionally, a dedicated search for electroweak sphalerontransitions has been performed. An upper limit of 0.0025 is set at 95% confidence level on the fraction ofquark-quark interactions with center-of-mass energy above the nominal threshold of 9 TeV that result insphaleron transitions.