Speaker
Description
Using the full (139~\mathrm{fb}^{-1}) of (\sqrt{s}=13\ \mathrm{TeV}) (pp) collision data recorded by ATLAS during Run~2, this search looks for a pseudoscalar (a) (CP-odd Higgs boson) produced with a top-quark pair or a single top\,+\,(W) and decaying via (a!\to!b\bar b). Events are selected in the dileptonic final state with exactly two opposite-sign leptons and at least three jets. Two \emph{boosted} signal regions, each requiring one large-(R) (B)-jet, target (m_a!\lesssim!30\ \mathrm{GeV}); two \emph{resolved} regions with three or four small-(R) (b)-jets probe higher masses. No significant excess relative to expectations is observed for (12 \le m_a \le 100\ \mathrm{GeV}). Assuming (\mathrm{BR}(a!\to!b\bar b)=100\%), pseudoscalar masses in the interval (50\text{–}80\ \mathrm{GeV}) are excluded at 95\% CL for a top-Yukawa coupling modifier 0.5; the full mass range is excluded for coupling 1.0.
