A search for electroweak $t\bar{t}Wj$ production in multileptonic final states at $\sqrt{s}=13$ TeV with the ATLAS detector and bounds on effective field theory operators

Abstract

A search is presented for the electroweak production of a top quark pair in association with a $W$ boson and at least one additional jet, known as the $t\bar{t}W{j}_{\mathrm{EW}}$ process. This process has embedded within it a $tW$-scattering vertex, which is probed directly for the first time. The collision data were collected with the ATLAS detector during Run 2 of the LHC and correspond to an integrated luminosity of 140 $\mathrm{f}{\mathrm{b}}^{-1}$ at $\sqrt{s}=13$~TeV. The search uses same-charge pairs of electrons and muons together with jets, of which at least one is $b$-tagged. The properties of the most forward jet relative to the rest of the event are used to discriminate the electroweak $t\bar{t}W{j}_{\text{EW}}$ production process from its strong $t\bar{t}W$ production counterpart. A measured (expected) 95% CL upper limit on the cross section is set at ${\sigma }_{t\bar{t}W{j}_{\mathrm{EW}}}<251$~fb (230 fb), to be compared with the expected SM cross section of 47.7 fb. Limits are set on the SM Effective Field Theory (EFT) operators $O_{Ht}$ and $O_{HQ}^{(1)}$, which modify the electroweak couplings of the top quark through contributions to the $tW$-scattering vertex. The interpretation acts as a case study to emphasize the importance of energy-dependent sensitivity, multi-process and multi-operator EFT contributions.

51 pages in total, author list starting page 34, 11 figures, 6 tables, submitted to Phys. Rev. D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2019-18/