Search for Higgs boson pair production in the two bottom quarks plus two photons final state in pp collisions at √s = 13 TeV with the ATLAS detector

Searches are performed for non-resonant and resonant di-Higgs boson production in the bb̅γγ final state. The data set used corresponds to an integrated luminosity of 139 fb⁻¹ of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No excess with respect to background expectations is found and upper limits on the di-Higgs boson production cross sections are set. A 95% confidence level upper limit of 130 fb is set on the pp→HH non-resonant production, where the expected limit is 180 fb. The observed (expected) limit corresponds to 4.1 (5.5) times the cross section predicted by the Standard Model. The observed (expected) limit on the Higgs boson trilinear coupling modifier κλ is extracted to be [-1.5, 6.7] ([-2.4, 7.7]) at 95% confidence level. The constraints on κλ are obtained over an expected hypothesis excluding pp→HH production. For the resonant production of a new hypothetical scalar particle X (X→HH→bb̅γγ), limits on the cross section pp→X→HH are presented for the narrow-width approximation as a function of mX in the range 251 GeV ≤mX≤1000 GeV. The observed (expected) limits on the cross section pp→X→HH range from 610 fb to 47 fb (360-43 fb) over the considered mass range.