Search for narrow resonances in dilepton mass spectra in proton–proton collisions at √s=13TeVand combination with 8TeV data

A search for narrow resonances in dielectron and dimuon invariant mass spectra has been performed using data obtained from proton–proton collisions at √s=13TeVcollected with the CMS detector. The integrated luminosity for the dielectron sample is 2.7fb−1and for the dimuon sample 2.9fb−1. The sensitivity of the search is increased by combining these data with a previously analyzedset of data obtained at √s=8TeVand corresponding to a luminosity of 20fb−1. No evidence for non-standard-model physics is found, either in the 13TeV data set alone, or in the combined data set. Upper limits on the product of production cross section and branching fraction have also been calculated in a model-independent manner to enable interpretation in models predicting a narrow dielectron or dimuon resonance structure. Limits are set on the masses of hypothetical particles that could appear in new-physics scenarios. For the Z_SSM particle, which arises in the sequential standard model, and for the superstring inspired Z_ψ particle, 95% confidence level lower mass limits for the combined data sets and combined channels are found to be 3.37 and 2.82TeV, respectively. The corresponding limits for the lightest Kaluza–Klein graviton arising in the Randall–Sundrum model of extra dimensions with coupling parameters 0.01 and 0.10 are 1.46 and 3.11TeV, respectively. These results significantly exceed the limits based on the 8TeV LHC data.