Abstract
A search for narrow resonances in dielectron and dimuon invariant mass spectra has been performed using data obtained from proton–proton collisions at s=13 TeV collected with the CMS detector. The integrated luminosity for the dielectron sample is 2.7 fb−1 and for the dimuon sample 2.9 fb−1. The sensitivity of the search is increased by combining these data with a previously analyzed set of data obtained at s=8 TeV and corresponding to a luminosity of 20 fb−1. No evidence for non-standard-model physics is found, either in the 13 TeV 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 ZSSM′ particle, which arises in the sequential standard model, and for the superstring inspired Zψ′ particle, 95% confidence level lower mass limits for the combined data sets and combined channels are found to be 3.37 and 2.82 TeV, 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 3.11 TeV, respectively. These results significantly exceed the limits based on the 8 TeV LHC data.
Highlights
The observation of a new narrow resonance in the invariant mass spectrum of lepton pairs would provide compelling evidence for physics beyond the standard model (SM)
The energy deposited in the hadron calorimeter (HCAL) in a cone of radius R = 0.14 around the direction of the electron candidate must be less than 5% of the energy of the electron measured in the electromagnetic calorimeter (ECAL)
As the limits in this Letter are obtained on the on-shell cross section and the pythia event generator includes off-shell e√ffects, the cross section is calculated in a mass window of ±5% s centered on the resonance mass, following the advice of Ref. [35]
Summary
The observation of a new narrow resonance in the invariant mass spectrum of lepton pairs would provide compelling evidence for physics beyond the standard model (SM). This Letter describes a search for such narrow resonances in dielectron and dimuon mass√spectra based on proton–proton (pp) collision data collected at s = 13 TeV in 2015 by the CMS experiment at the CERN LHC. The primary results of the analysis are expressed in terms of the ratio of the product of production cross section and branching fraction for a possible new resonance to that for the Z boson. We present lower limits on the masses of hypothetical particles that are derived from cross sections calculated in the context of certain specific models
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