Paper detail

Inclusive production of Higgs boson in the two-photon channel at the LHC within $k_{t}$-factorization approach and with the Standard Model couplings

We calculate differential cross sections for Higgs boson and/or two-photon production from intermediate (virtual) Higgs boson within the formalism of $k_t$-factorization. The off-shell $g^* g^* \to H$ matrix elements are used. We compare results obtained with infinite top fermion (quark) mass and with finite mass taken into account. The latter effect is rather small. We compare results with different unintegrated gluon distributions from the literature. Two methods are used. In the first method first Higgs boson is produced in the $2 \to 1$ $g g \to H$ $k_t$-factorization approach and then isotropic decay with the Standard Model branching fraction is performed. In the second method we calculate directly two photons coupled to the virtual Higgs boson. The results of the two methods are compared and differences are discussed. The results for two photons from the Higgs boson are compared with recent ATLAS collaboration data. In contrast to a recent calculation the leading order $g g \to H$ contribution is rather small compared to the ATLAS experimental data ($γγ$ transverse momentum and rapidity distributions) for all unintegrated gluon distributions from the literature. We include also higher-order contribution $g g \to H (\to γγ) g$, $g g \to g H g$ and the contribution of the $W^+ W^-$ and $Z^0 Z^0$. The $gg\to Hg$ mechanism gives similar cross section as the $gg\to H$ mechanism. We argue that there is almost no double counting when adding $gg\to H$ and $gg\to Hg$ contributions due to different topology of Feynman diagrams. The final sum is comparable with the ATLAS two-photon data. We discuss uncertainties related to both the theoretical approach and existing UGDFs.