Abstract
A search is conducted for new physics in final states containing a photon and missing transverse momentum in proton-proton collisions at sqrt{s}=13 TeV, using the data collected in 2016 by the CMS experiment at the LHC, corresponding to an integrated luminosity of 35.9 fb−1. No deviations from the predictions of the standard model are observed. The results are interpreted in the context of dark matter production and models containing extra spatial dimensions, and limits on new physics parameters are calculated at 95% confidence level. For the two simplified dark matter production models considered, the observed (expected) lower limits on the mediator masses are both 950 (1150) GeV for 1 GeV dark matter mass. For an effective electroweak-dark matter contact interaction, the observed (expected) lower limit on the suppression parameter Λ is 850 (950) GeV. Values of the effective Planck scale up to 2.85–2.90 TeV are excluded for between 3 and 6 extra spatial dimensions.
Highlights
Background estimation5.1 Z(→ νν)+γ and W(→ ν)+γ backgroundThe most significant SM background processes in this search are the associated production of a high-energy γ with either a Z boson that subsequently decays to a pair of neutrinos, or a W boson that decays to a charged lepton and a neutrino
The physics objects are the jets, clustered using the jet finding algorithm [17, 18] with the tracks assigned to the vertex as inputs, and the associated missing transverse momentum, taken as the negative vector sum of the pT of those jets
The distribution of the cluster seed timing provides a cross-check on the beam halo background estimate and an independent means to estimate the electromagnetic calorimeter (ECAL) spikes contribution [10]
Summary
The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Global event reconstruction follows the particle-flow (PF) algorithm [15], which aims to reconstruct and identify each individual particle in an event with an optimized combination of all subdetector information In this process, the identification of the particle type (photon, electron, muon, charged hadron, neutral hadron) plays an important role in the determination of the particle direction and energy. The physics objects are the jets, clustered using the jet finding algorithm [17, 18] with the tracks assigned to the vertex as inputs, and the associated missing transverse momentum, taken as the negative vector sum of the pT of those jets. The energy of electrons is determined from a combination of the electron momentum at the primary interaction vertex as determined by the tracker, the energy of the corresponding ECAL cluster, and the energy sum of all bremsstrahlung photons spatially compatible with originating from the electron track. The energy of a photon is determined only from its corresponding ECAL cluster
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