Search for production of four top quarks in final states with same-sign or multiple leptons in proton–proton collisions at $$\sqrt{s}=13$$ $$\,\text {TeV}$$

Abstract

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.

LHC bounds on colored scalars

“…The decay width into gluons can be neglected compared to the decays into top and bottom quarks because it is a loop process with only top and bottom quarks in the loop. The dependence of the resulting limits with η U and η D follows the same [73] and [75]. trend as before: the higher the value of |η U /η D |, the better the constraint.…”

“…In the event generation we have used the Particle Distribution Functions (PDF) set NNPDF23_nlo_ as_0119 of the package LHAPDF_6.1.6 [79]. The centre-of-mass energy has been fixed to √ s = 13 TeV, while the experimental data had an integrated luminosity of 36.1 fb −1 for the ATLAS data [72][73][74] and 137 fb −1 for the CMS data [75]. Furthermore, we have estimated the theoretical uncertainties varying the values of the renormalisation and factorisation scales by a factor between 1/2 and 2.…”

“…The experimental bounds are taken from Refs. [73] and [75]. inside its perturbative unitarity region.…”

“…[70], where the single and pair production of neutral scalars was studied. The recent release of high-luminosity experimental searches for massive resonances decaying into heavy quarks [72][73][74][75] makes now possible to improve those bounds. In this work we focus on the associated production of neutral and charged scalars with heavy quarks that was not considered in previous analyses.…”

Topic model for four-top at the LHC

“…There exists also in the literature many works that point out four-top as a sensitive channel to test heavy NP and/or Effective Field Theory effects [14][15][16][17][18]. However, since it is a very populated final state and with many different possible channels, its reconstruction is inefficient and therefore its measurement [19,20] is carried on mainly through signal regions which are compared to Monte Carlo (MC) predictions. Although MC-predictions have reached a complex level of development, including Next to Leading Order (NLO) matrix level calculations for four-top production, there are still many measurements of four-top signal and backgrounds which require renormalizations to data in control regions which still need further understanding.…”