Search for four-top-quark production in the single-lepton and opposite-sign dilepton final states in pp collisions at s=13  TeV with the ATLAS detector

Abstract

A search for four-top-quark production, tttt, is presented. It is based on proton-proton collision data with a center-of-mass energy √ s = 13 TeV collected by the ATLAS detector at the Large Hadron Collider during the years 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb −1 . Data are analyzed in both the single-lepton and opposite-sign dilepton channels, characterized by the presence of one or two isolated electrons or muons with hightransverse momentum and multiple jets. A data-driven method is used to estimate the dominant background from top-quark pair production in association with jets. No significant excess above the Standard Model expectation is observed. The result is combined with the previous same-sign dilepton and multilepton searches carried out by the ATLAS Collaboration and an observed (expected) upper limit of 5.3 (2.1) times the four-top-quark Standard Model cross section is obtained at 95% confidence level. Additionally, an upper limit on the anomalous four-top-quark production cross section is set in the context of an effective field theory model.

The emergence of multi-lepton anomalies at the LHC and their compatibility with new physics at the EW scale

“…[1], the ttH and tH BSM production modes discriminate most strongly against the SM prediction of b-jet multiplicity, and this effect can be seen in the data here. A similar (yet very strongly correlated) excess can be seen in the more recent ATLAS results in the search for four-top-quark production [51].…”

A Monte Carlo global analysis of the Standard Model Effective Field Theory: the top quark sector

“…This measurement supersedes previous upper bounds at 8 TeV [147] and 13 TeV [148]. In the case of ATLAS, upper bounds based on the 2015 dataset at 13 TeV were presented in [149] and then updated in [150] from the 2016 dataset. In this analysis we utilise the CMS cross-section measurement of [104].…”

The Ĥ-parameter: an oblique Higgs view

“…Nonetheless, significant progress by the experimental collaborations has been made recently. Both ATLAS and CMS analysed about 36 fb −1 of 13 TeV data each [47,48], with constraints approaching the SM rate. Interestingly, ATLAS reported comparable sensitivities in the combination of single lepton plus opposite-sign dilepton searches when compared to the combination of same-sign dilepton plus three lepton searches.…”