ATLAS collaboration (2882 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCantrill, RobertCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseDo Valle Wemans, AndréFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroLopes, LourencoMachado Miguens, JoanaMaio, AméliaManeira, JoséMarques, CarlosOnofre, AntónioPalma, AlbertoPedro, RutePina, João AntonioPinto, BelmiroSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042015-02-26http://dx.doi.org/10.1103/PhysRevLett.114.081802http://hdl.handle.net/10400.26/26617<p>Searches are performed for resonant and nonresonant Higgs boson pair production in the <inline-formula><mml:math display="inline"><mml:mi>γ</mml:mi><mml:mi>γ</mml:mi><mml:mi>b</mml:mi><mml:mover accent="true"><mml:mi>b</mml:mi><mml:mo accent="true" stretchy="false">¯</mml:mo></mml:mover></mml:math></inline-formula> final state using <inline-formula><mml:math display="inline"><mml:mrow><mml:mn>20</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:msup><mml:mrow><mml:mi>fb</mml:mi></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math></inline-formula> of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. A 95% confidence level upper limit on the cross section times branching ratio of nonresonant production is set at 2.2 pb, while the expected limit is 1.0 pb. The difference derives from a modest excess of events, corresponding to 2.4 standard deviations from the background-only hypothesis. The limit observed in the search for a narrow <inline-formula><mml:math display="inline"><mml:mi>X</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>h</mml:mi><mml:mi>h</mml:mi></mml:math></inline-formula> resonance ranges between 0.7 and 3.5 pb as a function of the resonance mass.</p>engjournal article2019-02-04