Aad G.Abbott B.Abeling K.Abicht N. J.Abidi S. H.Aboulhorma A.Abramowicz H.Abreu H.Abulaiti Y.Abusleme Hoffman A. C.Acharya B. S.Bourdarios C. AdamAdamczyk L.Adamek L.Addepalli S. VAddison M. J.Adelman J.Adiguzel A.Adye T.Affolder A. A.Afik Y.Agaras M. N.Agarwala J.Aggarwal A.Agheorghiesei C.Ahmad A.Ahmadov F.Ahmed W. S.Ahuja S.Ai X.Aielli G.Aikot A.Tamlihat M. AitAitbenchikh B.Aizenberg IAkbiyik M.Akesson T. P. A.Akimov A. VAkiyama D.Akolkar N. N.2025-05-192025-05-192023/11/282470-0010http://dx.doi.org/10.1103/PhysRevD.108.092007https://publicacionesabiertas.userena.cl/handle/123456789/290A search for a new pseudoscalar a-boson produced in events with a top-quark pair, where the a-boson decays into a pair of muons, is performed using root s=13 TeV pp collision data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb(-1). The search targets the final state where only one top quark decays to an electron or muon, resulting in a signature with three leptons e mu mu and mu mu mu. No significant excess of events above the Standard Model expectation is observed and upper limits are set on two signal models: pp -> tta and pp -> tt with t -> H(perpendicular to)b, H-perpendicular to -> W(perpendicular to)a, where a ->mu mu, in the mass ranges 15 GeV<72 GeV and 120 GeV <= m(H +/-)<= 160 GeV.PLUS PLUSArticle