Results are presented of a search for heavy particles decaying into two photons. The analysis is based on a 19.7 fb −1 sample of proton-proton collisions at √ s = 8 TeV collected with the CMS detector at the CERN LHC. The diphoton mass spectrum from 150 to 850 GeV is used to search for an excess of events over the background. The search is extended to new resonances with natural widths of up to 10% of the mass value. No evidence for new particle production is observed and limits at 95% confidence level on the production cross section times branching fraction to diphotons are determined. These limits are interpreted in terms of two-Higgs-doublet model parameters.The discovery of a standard model-like Higgs boson at the CERN LHC [1-4] opens a new phase in the understanding of the standard model (SM) of particle physics. The search for additional Higgs-like particles and the measurement of their properties provide complementary ways to test the validity of the SM and to test for the presence of physics beyond it. This analysis describes a search for new resonances in the diphoton invariant mass spectrum, using data corresponding to an integrated luminosity of 19.7 fb −1 collected with the CMS detector at a center-of-mass energy of 8 TeV at the CERN LHC. Despite the large nonresonant background, the diphoton decay mode provides a clean final-state topology that allows the mass of the decaying object to be reconstructed with high precision, exploiting the excellent performance of the electromagnetic calorimeter of the CMS experiment. The analysis searches for local excesses that could be due to the production of particles that decay into two photons with mass in the range from 150 to 850 GeV. Both narrow and wide resonances are investigated with natural widths ranging from 100 MeV to 10% of the resonance mass. This search covers the diphoton mass range above that investigated in [2,4]. The ATLAS experiment recently published a similar search for narrow resonances in the diphoton final state in the mass range between 65 and 600 GeV at a center-of-mass energy of 8 TeV [5]. Previous searches for resonant diphoton processes have been performed at the Tevatron by D0 [6] and CDF [7] at a center-of-mass energy of 1.96 TeV and by the ATLAS [8] and CMS [9] experiments at the LHC at a center-of-mass energy of 7 TeV. Several models of physics beyond the SM, such as the two-Higgs-doublet model (2HDM) [10], motivate the search for additional high-mass resonances in the diphoton channel. Generally, these models provide an extension of the Higgs sector, where a total of five Higgs bosons are predicted by the theory. The mass spectrum of the 2HDM can be split into two regions: a light SM-like Higgs boson h with mass around 125 GeV and the remaining physical Higgs bosons, H, a scalar, A, a pseudoscalar, and H ± , clustered at an equal or higher scale with m H ∼ m A ∼ m H ± .Under the assumption that the newly observed Higgs boson is the light CP-even Higgs scalar of the 2HDM, the consistency of its couplings with those predicted by th...

A search for physics beyond the standard model in events with at least three charged leptons (electrons or muons) is presented. The data sample corresponds to an integrated luminosity of 137 fb−1 of proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, collected with the CMS detector at the LHC in 2016–2018. The two targeted signal processes are pair production of type-III seesaw heavy fermions and production of a light scalar or pseudoscalar boson in association with a pair of top quarks. The heavy fermions may be manifested as an excess of events with large values of leptonic transverse momenta or missing transverse momentum. The light scalars or pseudoscalars may create a localized excess in the dilepton mass spectra. The results exclude heavy fermions of the type-III seesaw model for masses below 880 GeV at 95% confidence level in the scenario of equal branching fractions to each lepton flavor. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) and 0.04 (0.03) are excluded at 95% confidence level for masses in the range 15–75 and 108–340 GeV, respectively. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.

A search for vectorlike leptons in multilepton final states is presented. The data sample corresponds to an integrated luminosity of 77.4 fb −1 of proton-proton collisions at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2016 and 2017. Events are categorized by the multiplicity of electrons, muons, and hadronically decaying τ leptons. The missing transverse momentum and the scalar sum of the lepton transverse momenta are used to distinguish the signal from background. The observed results are consistent with the expectations from the standard model hypothesis. The existence of a vectorlike lepton doublet, coupling to the third-generation standard model leptons in the mass range of 120-790 GeV, is excluded at 95% confidence level. These are the most stringent limits yet on the production of a vectorlike lepton doublet, coupling to the third-generation standard model leptons.

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A measurement of vector boson scattering and constraints on anomalous quartic gauge couplings from events with two Z bosons and two jets are presented. The analysis is based on a data sample of proton-proton collisions at √ s = 13 TeV collected with the CMS detector and corresponding to an integrated luminosity of 35.9 fb −1 . The search is performed in the fully leptonic final state ZZ → , where , = e or µ. The electroweak production of two Z bosons in association with two jets is measured with an observed (expected) significance of 2.7 (1.6) standard deviations. A fiducial cross section for the electroweak production is measured to be σ EW (pp → ZZjj → jj) = 0.40 +0.21 −0.16 (stat) +0.13 −0.09 (syst) fb, which is consistent with the standard model prediction. Limits on anomalous quartic gauge couplings are determined in terms of the effective field theory operators T0, T1, T2, T8, and T9. This is the first measurement of vector boson scattering in the ZZ channel at the LHC.The central feature of the CMS apparatus is a superconducting solenoid of 6 m internal diameter, providing a magnetic field of 3.8 T. Within the solenoid volume are silicon pixel and strip tracking detectors, a lead tungstate crystal electromagnetic calorimeter (ECAL), and a brass and scintillator hadron calorimeter (HCAL), each composed of a barrel and two endcap sections. Forward calorimeters extend the pseudorapidity η coverage provided by the barrel and endcap detectors up to |η| < 5. Muons are measured in gas-ionization detectors embedded in the steel flux-return yoke outside the solenoid.The silicon tracker measures charged particles within the pseudorapidity range |η| < 2.5. It consists of 1440 silicon pixel and 15 148 silicon strip detector modules. For nonisolated particles with 1 < p T < 10 GeV and |η| < 1.4, the track resolutions are typically 1.5% in p T and 25-90 (45-150) µm in the transverse (longitudinal) impact parameter [19].Electrons are measured in the pseudorapidity range |η| < 2.5 using both the tracking system and the ECAL. The momentum resolution for electrons with p T ≈ 45 GeV from Z → e + e − decays ranges from 1.7% for nonshowering electrons in the barrel region (|η| < 1.479) to 4.5% for showering electrons in the endcaps [20].