Abstract
Dimuon and dielectron mass spectra, obtained from data resulting from proton-proton collisions at 8 TeV and recorded by the CMS experiment, are used to search for both narrow resonances and broad deviations from standard model predictions. The data correspond to an integrated luminosity of 20.6 (19.7) inverse femtobarns for the dimuon (dielectron) channel. No evidence for non-standard-model physics is observed and 95% confidence level limits are set on parameters from a number of new physics models. The narrow resonance analyses exclude a Sequential Standard Model Z'[SSM] resonance lighter than 2.90 TeV, a superstring-inspired Z'[psi] lighter than 2.57 TeV, and Randall-Sundrum Kaluza-Klein gravitons with masses below 2.73, 2.35, and 1.27 TeV for couplings of 0.10, 0.05, and 0.01, respectively. A notable feature is that the limits have been calculated in a model-independent way to enable straightforward reinterpretation in any model predicting a resonance structure. The observed events are also interpreted within the framework of two non-resonant analyses: one based on a large extra dimensions model and one based on a quark and lepton compositeness model with a left-left isoscalar contact interaction. Lower limits are established on M[S], the scale characterizing the onset of quantum gravity, which range from 4.9 to 3.3 TeV, where the number of additional spatial dimensions varies from 3 to 7. Similarly, lower limits on Lambda, the energy scale parameter for the contact interaction, are found to be 12.0 (15.2) TeV for destructive (constructive) interference in the dimuon channel and 13.5 (18.3) TeV in the dielectron channel.
Highlights
Background sourcesThe principal standard model process that contributes to the dimuon and dielectron invariant mass spectra, either directly or via τ τ, is Drell-Yan production (Z/γ∗)
Results of searches for narrow Z → + − ( = μ, e) resonances in pp collision data have previously been reported by the ATLAS and CMS Collaborations [16, 17]
D0 Collaborations have published results based on a pp collision sample at s = 1.96 TeV and ≈5 fb−1 of integrated luminosity [18,19,20,21,22,23]
Summary
The central feature of the CMS detector is a superconducting solenoid providing an axial magnetic field of 3.8 T and enclosing the all-silicon inner tracker, the crystal electromagnetic calorimeter (ECAL), and the brass and scintillator hadron calorimeter (HCAL). The level-1 (L1) trigger [30], composed of custom hardware processors, selects events of interest using information from the calorimeters and muon detectors and reduces the readout rate from the 20 MHz bunchcrossing frequency to a maximum of 100 kHz. The high level trigger (HLT) [31] uses software algorithms accessing the full event information, including that from the inner tracker, to reduce further the event rate to the 400 Hz that is recorded
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