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 center-of-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.
Highlights
Background samplesIn addition, we use simulated samples of W+jets, Z+jets, γ+jets, tt, and QCD multijet events for auxiliary studies
The ST value is preserved by the final-state radiation, which is the dominant source of extra jets beyond leading order (LO) 2 → 2 QCD processes, as long as the additional jets are above the pT threshold used in the definition of ST
Since there is a pT threshold on the objects whose transverse energies count toward the ST value, the minimum possible ST value depends on the number of objects in the final state, and the shape invariance for an ST spectrum with N ≥ N min is only observed above a certain ST threshold, which increases with N min
Summary
Gravity is the weakest of all known forces. the Newton constant, ∼10−38 GeV−2, which governs the strength of gravity, is much smaller than the Fermi constant, ∼10−4 GeV−2, which characterizes the strength of EW interactions. We look for the manifestation of the ADD model that postulates the existence of nED ≥ 2 “large” (compared to the inverse of the EW energy scale) extra spatial dimensions, compactified on a sphere or a torus, in which only gravity can propagate This framework allows one to elude the hierarchy problem by explaining the apparent weakness of gravity in the three-dimensional space via the suppression of the fundamentally strong gravitational interaction by the large volume of the extra space. Quantum BHs [28,29,30] are expected to decay before they thermalize, resulting in low-multiplicity final states Another model of semiclassical BH precursors is the SB model [31], which predicts the formation of a long, jagged string excitation, folded into a “ball”. The analogous limits on the minimum SB mass depend on the choice of the string scale and coupling and are in the 6.6−9 TeV range for the parameter choices considered in refs. [34, 36]
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