A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a center-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of 18.5 fb −1 . No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, H, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral X particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For X with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically 0.5-200 fb. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of 2-40 cm, the upper limits on the cross section are typically 0.5-3 fb. The above limits are the most stringent on these channels to date.

The standard model (SM) production of four top quarks (tt tt) in proton-proton collisions is studied by the CMS Collaboration. The data sample, collected during the 2016-2018 data taking of the LHC, corresponds to an integrated luminosity of 137 fb −1 at a center-of-mass energy of 13 TeV. The events are required to contain two same-sign charged leptons (electrons or muons) or at least three leptons, and jets. The observed and expected significances for the tt tt signal are respectively 2.6 and 2.7 standard deviations, and the tt tt cross section is measured to be 12.6 +5.8 −5.2 fb. The results are used to constrain the Yukawa coupling of the top quark to the Higgs boson, y t , yielding a limit of |y t /y SM t | < 1.7 at 95% confidence level, where y SM t is the SM value of y t. They are also used to constrain the oblique parameter of the Higgs boson in an effective field theory framework,Ĥ < 0.12. Limits are set on the production of a heavy scalar or pseudoscalar boson in Type-II two-Higgs-doublet and simplified dark matter models, with exclusion limits reaching 350-470 GeV and 350-550 GeV for scalar and pseudoscalar bosons, respectively. Upper bounds are also set on couplings of the top quark to new light particles.

A search for pair production of second-generation leptoquarks is performed using proton-proton collision data collected at √ s = 13 TeV in 2016 with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 35.9 fb −1 . Final states with two muons and two jets, or with one muon, two jets, and missing transverse momentum are considered. Second-generation scalar leptoquarks with masses less than 1530 (1285) GeV are excluded for β = 1.0 (0.5), where β is the branching fraction for the decay of a leptoquark to a charged lepton and a quark. The results of the search are also interpreted as limits on the pair production of long-lived top squarks in an R-parity violating supersymmetry model that has a final state with two muons and two jets. These limits represent the most stringent limits to date on these models.

Constraints on the lifetime and width of the Higgs boson are obtained from H → ZZ → 4l events using data recorded by the CMS experiment during the LHC run 1 with an integrated luminosity of 5.1 and 19.7 fb −1 at a center-of-mass energy of 7 and 8 TeV, respectively. The measurement of the Higgs boson lifetime is derived from its flight distance in the CMS detector with an upper bound of τ H < 1.9 × 10 −13 s at the 95% confidence level (C.L.), corresponding to a lower bound on the width of Γ H > 3.5 × 10 −9 MeV. The measurement of the width is obtained from an off-shell production technique, generalized to include anomalous couplings of the Higgs boson to two electroweak bosons. From this measurement, a joint constraint is set on the Higgs boson width and a parameter f ΛQ that expresses an anomalous coupling contribution as an on-shell cross-section fraction. The limit on the Higgs boson width is Γ H < 46 MeV with f ΛQ unconstrained and Γ H < 26 MeV for f ΛQ ¼ 0 at the 95% C.L. The constraint f ΛQ < 3.8 × 10 −3 at the 95% C.L. is obtained for the expected standard model Higgs boson width.

A search for standard model production of four top quarks ( ) is reported using events containing at least three leptons ( ) or a same-sign lepton pair. The events are produced in proton–proton collisions at a center-of-mass energy of 13 at the LHC, and the data sample, recorded in 2016, corresponds to an integrated luminosity of 35.9 . Jet multiplicity and flavor are used to enhance signal sensitivity, and dedicated control regions are used to constrain the dominant backgrounds. The observed and expected signal significances are, respectively, 1.6 and 1.0 standard deviations, and the cross section is measured to be , in agreement with next-to-leading-order standard model predictions. These results are also used to constrain the Yukawa coupling between the top quark and the Higgs boson to be less than 2.1 times its expected standard model value at 95% confidence level.