Measurement of the $H\to \gamma \gamma $ and $H\to Z{Z}^{\ast }\to 4\ell $ cross-sections in pp collisions at $\sqrt{s}=13.6$ TeV with the ATLAS detector

The inclusive Higgs boson production cross-section is measured in the di-photon and the $Z{Z}^{\ast }\to 4\ell $ decay channels using 31.4 and 29.0 fb ${}^{-1}$ of pp collision data respectively, collected with the ATLAS detector at a centre-of-mass energy of $\sqrt{s}=13.6$ $\text{TeV}$ . To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the channel's detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are ${\sigma }_{\text{fid},\gamma \gamma }=$ ${76}_{-13}^{+14}$ fb, and ${\sigma }_{\text{fid},4\ell }=$ $2.80\phantom{\rule{0.166667em}{0ex}}±\phantom{\rule{0.166667em}{0ex}}0.74$ fb, in agreement with the corresponding Standard Model predictions of $67.6±3.7$ fb and $3.67±0.19$ fb. Assuming Standard Model acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of $\sigma \left(pp\to H\right)={67}_{-11}^{+12}$ pb and $46±12$ pb at 13.6 $\text{TeV}$ from the di-photon and $Z{Z}^{\ast }\to 4\ell $ measurements respectively. The two measurements are combined into a total cross-section measurement of $\sigma \left(pp\to H\right)=58.2±8.7$ pb, to be compared with the Standard Model prediction of $\sigma {\left(pp\to H\right)}_{\text{SM}}=59.9±2.6$ pb.