A search for microscopic black holes, string balls, and sphalerons in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for microscopic black holes, string balls, and sphalerons in proton-proton collisions at 13 TeV, setting new limits on their production and excluding certain mass ranges.

Contribution

It introduces new model-dependent methods for identifying collider events with distinct kinematic features and extends the exclusion limits for black holes and sphalerons.

Findings

Excluded semiclassical black holes below 8.4-11.4 TeV.

Excluded string balls below 9.0-10.7 TeV.

Set an upper limit of 0.0034 on sphaleron transition fraction.

Abstract

A search for microscopic black holes, string balls, and electroweak sphalerons using proton-proton collisions at $\sqrt{s}$ = 13 TeV recorded with the CMS detector at the CERN LHC during the 2016$-$2018 data taking, and corresponding to an integrated luminosity of 138 fb$^{-1}$, is presented. Two search strategies based on control samples in data are used. Model-independent limits on the cross section of physics phenomena with multiple energetic jets, leptons, and photons are set using a method that relies on the shape invariance of the scalar sum of the transverse momenta of all objects in the event. Model-dependent limits on black hole and sphaleron production are set using a newly introduced method that has been developed for the identification of collider events with distinct kinematic features by separating them into classes based on phase space proximity. In the context of models with large extra dimensions, semiclassical black holes and string balls with masses below 8.4$-$11.4 TeV and 9.0$-$10.7 TeV, respectively, are excluded at 95% confidence level, significantly extending the reach beyond previous searches. Results of a dedicated search for electroweak sphalerons are used to derive an upper limit of 0.0034 at 95% confidence level on the fraction of quark-quark interactions above the nominal sphaleron transition energy threshold of 9 TeV.