Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb−1 of pp collisions at s=13TeV with the ATLAS experiment

Search for new physics in top quark production with additional leptons in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV using effective field theory

“…This is indicative of the complex interplay between all 16 WCs. Exploring the 16D hypersurface provides a unique handle on the WCs, which was not previously utilized in single parameter analyses such as [16,[19][20][21][22][23][24][25][26][27].…”

“…Focusing on multilepton final states leads to unique challenges that have not been encountered by previous LHC analyses employing EFT methods to search for new physics associated with top quark production [16,[18][19][20][21][22][23][24][25][26][27]. First, multilepton final states receive contributions from multiple processes, and it is not possible to isolate high-purity samples from each contribution.…”

Flavor Constraints from Unitarity and Analyticity

“…For example, although Brðτ → 3eÞ ≲ 10 −8 is weaker than Brðμ → 3eÞ ≲ 10 −12 , as ðm τ =m μ Þ 4 ∼ 10 5 it probes a slightly higher scale. Similarly, as ðm t =m μ Þ 4 ∼ 10 13 , flavor-changing neutral current decays of the top are likely to be particularly sensitive probes [40][41][42]. Beyond the dimension-8 qualifier, traditionally promising avenues for establishing BSM flavor violation such as neutral meson mixing remain sensitive [43,44].…”

Automated EW corrections with isolated photons: t$$ \overline{t} $$γ, t$$ \overline{t} $$γγ and tγj as case studies

“…15 Therefore, results in this section are new not only for what concerns NLO EW corrections but also at NLO QCD accuracy. We remind the reader that the CMS collaboration has already found the evidence for tγj production [100], and searches in the context of flavour-changing neutral currents have been performed for this process by the ATLAS collaboration [101].…”