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.

Two related searches for phenomena beyond the standard model (BSM) are performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2016-2018 and corresponding to an integrated luminosity of 137 fb −1. The first search is inclusive, based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of jets identified as originating from bottom quarks, and the value of the kinematic variable M T2 for events with at least two jets. For events with exactly one jet, the transverse momentum of the jet is used instead. The second search looks in addition for disappearing tracks produced by BSM longlived charged particles that decay within the volume of the tracking detector. No excess event yield is observed above the predicted standard model background. This is used to constrain a range of BSM models that predict the following: the pair production of gluinos and squarks in the context of supersymmetry models conserving R-parity, with or without intermediate long-lived charginos produced in the decay chain; the resonant production of a colored scalar state decaying to a massive Dirac fermion and a quark; or the pair production of scalar and vector leptoquarks each decaying to a neutrino and a top, bottom, or light-flavor quark. In most of the cases, the results obtained are the most stringent constraints to date.

A data sample of events from proton-proton collisions with two isolated same-sign leptons, missing transverse momentum, and jets is studied in a search for signatures of new physics phenomena by the CMS Collaboration at the LHC. The data correspond to an integrated luminosity of 35.9 fb −1 , and a center-of-mass energy of 13 TeV. The properties of the events are consistent with expectations from standard model processes, and no excess yield is observed. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos, squarks, and same-sign top quarks, as well as top-quark associated production of a heavy scalar or pseudoscalar boson decaying to top quarks, and on the standard model production of events with four top quarks. The observed lower mass limits are as high as 1500 GeV for gluinos, 830 GeV for bottom squarks. The excluded mass range for heavy (pseudo)scalar bosons is 350-360 (350-410) GeV. Additionally, model-independent limits in several topological regions are provided, allowing for further interpretations of the results. IntroductionFinal states with two leptons of same charge, denoted as same-sign (SS) dileptons, are produced rarely by standard model (SM) processes in proton-proton (pp) collisions. Because the SM rates of SS dileptons are low, studies of these final states provide excellent opportunities to search for manifestations of physics beyond the standard model (BSM). Over the last decades, a large number of new physics mechanisms have been proposed to extend the SM and address its shortcomings. Many of these can give rise to potentially large contributions to the SS dilepton signature, e.g., the production of supersymmetric (SUSY) particles [1,2], SS top quarks [3,4], scalar gluons (sgluons) [5,6], heavy scalar * e-mail: cms-publication-committee-chair@cern.ch bosons of extended Higgs sectors [7,8], Majorana neutrinos [9], and vector-like quarks [10].In the SUSY framework [11][12][13][14][15][16][17][18][19][20], the SS final state can appear in R-parity conserving models through gluino or squark pair production when the decay of each of the pairproduced particles yields one or more W bosons. For example, a pair of gluinos (which are Majorana particles) can give rise to SS charginos and up to four top quarks, yielding signatures with up to four W bosons, as well as jets, b quark jets, and large missing transverse momentum (E miss T ). Similar signatures can also result from the pair production of bottom squarks, subsequently decaying to charginos and top quarks.While R-parity conserving SUSY models often lead to signatures with large E miss T , it is also interesting to study final states without significant E miss T beyond what is produced by the neutrinos from leptonic W boson decays. For example, some SM and BSM scenarios can lead to the production of SS or multiple top quark pairs, such as the associated production of a heavy (pseudo)scalar, which subsequently decays to a pair of top quarks. This scenario is realized in Type II two Higgs d...

A search for WW production from double-parton scattering processes using same-charge electron-muon and dimuon events is reported, based on proton-proton collision data collected at a center-of-mass energy of 13 TeV. The analyzed data set corresponds to an integrated luminosity of 77.4 fb −1 , collected using the CMS detector at the LHC in 2016 and 2017. Multivariate classifiers are used to discriminate between the signal and the dominant background processes. A maximum likelihood fit is performed to extract the signal cross section. This leads to the first evidence for WW production via double-parton scattering, with a significance of 3.9 standard deviations. The measured inclusive cross section is 1.41 ± 0.28 (stat) ± 0.28 (syst) pb.

A search is presented for τ slepton pairs produced in proton-proton collisions at a center-of-mass energy of 13 TeV. The search is carried out in events containing two τ leptons in the final state, on the assumption that each τ slepton decays primarily to a τ lepton and a neutralino. Events are considered in which each τ lepton decays to one or more hadrons and a neutrino, or in which one of the τ leptons decays instead to an electron or a muon and two neutrinos. The data, collected with the CMS detector in 2016 and 2017, correspond to an integrated luminosity of 77.2 fb −1. The observed data are consistent with the standard model background expectation. The results are used to set 95% confidence level upper limits on the cross section for τ slepton pair production in various models for τ slepton masses between 90 and 200 GeV and neutralino masses of 1, 10, and 20 GeV. In the case of purely left-handed τ slepton production and decay to a τ lepton and a neutralino with a mass of 1 GeV, the strongest limit is obtained for a τ slepton mass of 125 GeV at a factor of 1.14 larger than the theoretical cross section.