Search for new non-resonant phenomena in high-mass dilepton final states with the ATLAS detector

TL;DR

This paper reports a search for non-resonant new physics phenomena in high-mass dilepton final states using ATLAS data, setting stringent limits on contact interaction energy scales without observing significant deviations from the Standard Model background.

Contribution

First search at the LHC for non-resonant dilepton signals using data-driven background estimation, establishing new limits on contact interaction energy scales.

Findings

No significant excess observed in data.

Lower limits on contact interaction scale reach 35.8 TeV.

Background modeled with data-driven functional fit.

Abstract

A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV is presented. This is the first search for non-resonant signals in dilepton final states at the LHC to use a background estimate from the data. The data, corresponding to an integrated luminosity of 139 fb$^{-1}$, were recorded by the ATLAS experiment in proton-proton collisions at a center-of-mass energy of $\sqrt{s} = 13$ TeV during Run 2 of the Large Hadron Collider. The benchmark signal signature is a two-quark and two-lepton contact interaction, which would enhance the dilepton event rate at the TeV mass scale. To model the contribution from background processes a functional form is fit to the dilepton invariant-mass spectra in data in a mass region below the region of interest. It is then extrapolated to a high-mass signal region to obtain the expected background there. No significant deviation from the expected background is observed in the data. Upper limits at 95 % CL on the number of events and the visible cross-section times branching fraction for processes involving new physics are provided. Observed (expected) 95 % CL lower limits on the contact interaction energy scale reach 35.8 (37.6) TeV.