Search for Higgs boson pair production in the two bottom quarks plus two photons final state in $pp$ collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ with the ATLAS detector

Searches are performed for nonresonant and resonant di-Higgs boson production in the $b\overline{b}\gamma \gamma $ final state. The dataset used corresponds to an integrated luminosity of $139\text{}\text{}{\mathrm{fb}}^{-1}$ 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 above the expected background is found and upper limits on the di-Higgs boson production cross sections are set. A 95% confidence-level upper limit of 4.2 times the cross section predicted by the Standard Model is set on $pp\to HH$ nonresonant production, where the expected limit is 5.7 times the Standard Model predicted value. The expected constraints are obtained for a background hypothesis excluding $pp\to HH$ production. The observed (expected) constraints on the Higgs boson trilinear coupling modifier ${\kappa }_{\lambda }$ are determined to be $\left[-1.5,6.7\right]$ $\left(\left[-2.4,7.7\right]\right)$ at 95% confidence level, where the expected constraints on ${\kappa }_{\lambda }$ are obtained excluding $pp\to HH$ production from the background hypothesis. For resonant production of a new hypothetical scalar particle $X$ ($X\to HH\to b\overline{b}\gamma \gamma $), limits on the cross section for $pp\to X\to HH$ are presented in the narrow-width approximation as a function of ${m}_{X}$ in the range $251\text{}\text{}\mathrm{GeV}\le {m}_{X}\le 1000\text{}\text{}\mathrm{GeV}$. The observed (expected) limits on the cross section for $pp\to X\to HH$ range from 640 fb to 44 fb (391 fb to 46 fb) over the considered mass range.