Any Sign of Quantum Gravity? Search for excited gravitons G* in 13 TeV proton-proton collisions with the ATLAS detector at the LHC

Abstract

The Standard Model (SM) of particle physics does not incorporate gravity. In addition, it suffers from the hierarchy problem. An approach to these two predicaments is the idea of introducing extra spatial dimensions. The Randall-Sundrum (RS) model proposes that we live in a multi-dimensional Universe consisting of two (3+1)-dimensional branes separated from each other by a five-dimensional bulk in which gravity propagates. The hypothetical massless mediators of gravity, “gravitons”, can be detected experimentally in a detector via the leptonic decay of their massive Kaluza-Klein partners. In this thesis we search for high-mass resonances of the lightest Kaluza-Klein graviton G* in the invariant mass distributions of electron and muon pairs. The exclusion limits for the G* in pp collisions recorded in the ATLAS detector at √s = 13 TeV, corresponding to an integrated luminosity of 139 fb −1 , are extracted. The data are consistent with the background consisting mainly of SM Drell-Yan, top and diboson processes. “Fake” electrons stemming from non-prompt backgrounds are also taken into account. We interpret the data in terms of a hypothetical RS graviton with coupling strengths 0.1, 0.2 and 0.3 to leptons. Both statistical and systematic uncertainties are taken into account. Masses less than 4.10 TeV, 4.01 TeV and 4.38 TeV are excluded at 95% C.L. for coupling 0.1, while masses less than 5.27 TeV, 4.98 TeV and 5.40 TeV are excluded for coupling 0.3 in the electron, muon and combined channels, respectively.