Search for black holes and sphalerons in high-multiplicity final states in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV

Abstract

A search in energetic, high-multiplicity final states for evidence of physics beyond the standard model, such as black holes, string balls, and electroweak sphalerons, is presented. The data sample corresponds to an integrated luminosity of 35.9 fb −1 collected with the CMS experiment at the LHC in proton-proton collisions at a centerof-mass energy of 13 TeV in 2016. Standard model backgrounds, dominated by multijet production, are determined from control regions in data without any reliance on simulation. No evidence for excesses above the predicted background is observed. Model-independent 95% confidence level upper limits on the cross section of beyond the standard model signals in these final states are set and further interpreted in terms of limits on semiclassical black hole, string ball, and sphaleron production. In the context of models with large extra dimensions, semiclassical black holes with minimum masses as high as 10.1 TeV and string balls with masses as high as 9.5 TeV are excluded by this search. Results of the first dedicated search for electroweak sphalerons are presented. An upper limit of 0.021 is set at 95% confidence level on the fraction of all quark-quark interactions above the nominal threshold energy of 9 TeV resulting in the sphaleron transition.

On the phenomenology of sphaleron-induced processes at the LHC and beyond

“…This is in contrast to the previous phenomenological studies, e.g. [16,17,22,44], where only an equation of the form of Eq. (2.5) was used on its own to describe the partonic cross section.…”

“…Our analysis is inspired by the CMS analysis of Ref. [44], on searches for sphaleron and mini black hole production in 13 TeV data with L = 36 fb −1 . Following this analysis, we apply cuts on two variables; N (p T > 100) and S 100 T .…”

On the modelling of energetic multi-jet QCD events

“…Other methods currently used in multijet analyses estimate a 1 -130% [9] or 40 -110% [10] uncertainty using a fit extrapolation technique or a 25% uncertainty using a jet mass template technique [11]. Thus the magnitude of the systematic uncertainties of the THm are comparable to those of conventional methods but since the sources of the uncertainties are very different the procedures compliment one another.…”

“…The accuracy of these calculations is limited as some unavoidable approximations must be imposed. Significant effort has been invested in the study of energetic multi-jet events at the LHC with the ATLAS and CMS collaborations [9][10][11]. These studies cope with a major difficulty, namely, with the need to estimate the kinematics of multi-jet events without the usage of simulation.…”

MUSiC: a model-unspecific search for new physics in proton–proton collisions at $$\sqrt{s} = 13\,\text {TeV} $$

“…It plays an important role in the EW baryogenesis theory [63], which can explain the matter-antimatter asymmetry of the universe. The CMS experiment has published the results of a search for sphalerons in inclusive final states that are dominated by jets associated with the QCD multijet process [64]. No analysis targeting leptonic final states has been performed to date.…”