Search for resonant and nonresonant new phenomena in high-mass dilepton final states at $\sqrt{s} = $ 13 TeV

A search for physics beyond the standard model (SM) is presented using electron or muon pairs with high invariant mass. A data set of proton-proton collisions collected by the CMS experiment at the LHC at $\sqrt{s}=13$ TeV recorded in years 2016 to 2018 and corresponding to a total integrated luminosity of up to 140 $\mathrm{fb}^{-1}$ is analyzed. No significant deviation is observed with respect to the expectation from the SM backgrounds. Upper limits are set on the ratio of the product of production cross section and branching fraction in a dilepton channel of a new narrow resonance to that of the Z boson and converted into lower limits on the masses of various hypothetical particles. A spin-1 $\mathrm{Z}^{\prime}_{\mathrm{SSM}}$ ($\mathrm{Z}^{\prime}_{\psi}$) particle, arising in the sequential SM (superstring-inspired model) is excluded below a mass of 5.15 (4.56) TeV at 95% confidence level. Lower limits of 2.47--4.78 TeV on the mass of spin-2 gravitons in the Randall-Sundrum are set for values of the dimensionless coupling parameter $k/\overline{M}_{\mathrm{Pl}}$ between 0.01 and 0.1. Limits on the mass of a spin-1 mediator between the SM and dark matter particles ranging from 1.04 to 4.64 TeV are set in multiple signal models. In case of a four-fermion contact interaction, lower limits on the ultraviolet cutoff parameter $\Lambda$ ranging from 23.6 to 36.6,\TeV are set. In the Arkani-Hamed, Dimopoulos, and Dvali model with large extra dimensions, lower limits on $\Lambda$ ranging from 6.0 to 8.9 TeV are set, depending on the parameter convention. For the first time in the same-flavor final state, lepton flavor universality is tested at high mass comparing the dimuon and dielectron mass spectra, corrected for detector effects. No significant deviation from the SM expectation of unity is observed.