Abstract
A search for standard model production of four top quarks (mathrm {t}overline{mathrm {t}} mathrm {t}overline{mathrm {t}} ) is reported using events containing at least three leptons (mathrm {e}, mathrm {mu }) or a same-sign lepton pair. The events are produced in proton–proton collisions at a center-of-mass energy of 13,text {TeV} at the LHC, and the data sample, recorded in 2016, corresponds to an integrated luminosity of 35.9,text {fb}^{-1}. 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 mathrm {t}overline{mathrm {t}} mathrm {t}overline{mathrm {t}} cross section is measured to be 16.9^{+13.8}_{-11.4},text {fb}, 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.
Highlights
Introduction9.6+−33..95 fb and an nepxret-dtioc-tlieoandifnogr order (NLO)/LO K -factor of 1.27 based on the 14 TeV calculation of Ref. [18]
Background and signal simulationMonte Carlo (MC) simulations at nepxret-dtioc-tlieoandifnogr order (NLO) are used to evaluate the tttt signal acceptance and to estimate the back- 140 Page 2 of 24Eur
The yields from SR 1–8, control region for the ttW background (CRW), and CRZ are combined in a maximum-likelihood fit, following the procedures described in Ref. [51], to estimate a best-fit cross section for tttt, the significance of the observation relative to the background-only hypothesis, and the upper limit on σ
Summary
9.6+−33..95 fb and an NLO/LO K -factor of 1.27 based on the 14 TeV calculation of Ref. [18]. After the decays of the top quarks, the final state contains several jets resulting from the hadronization of light quarks and b quarks (b jets), and may contain isolated leptons and missing transverse momentum depending on the decays of the W bosons [19]. Among these final states, the same-sign dilepton and the three- (or more) lepton final states, considering = e, μ, correspond to branching fractions in tttt events of 8 and 1%, respectively, excluding the small contribution from W → τ ν, which is included in selected events. The analysis described in this paper is based on the same data set and improves on the previous search by optimizing the signal selection for sensitivity to SM tttt production, by using an improved b jet identification algorithm, and by employing background estimation techniques that are adapted to take into account the higher jet and b jet multiplicity requirements in the signal regions
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