Search for $\gamma$H production and constraints on the Yukawa couplings of light quarks to the Higgs boson

A search for $\gamma$H production is performed with data from the CMS experiment at the LHC corresponding to an integrated luminosity of 138 fb${}^{-1}$ at a proton-proton center-of-mass collision energy of 13 TeV. The analysis focuses on the topology of a boosted Higgs boson recoiling against a high-energy photon. The final states of H $\to$ $\mathrm{b}\bar{\mathrm{b}}$ and H $\to$ 4$\mathrm{\ell }$ are analyzed. This study examines effective HZ$\gamma$ and H$\gamma \gamma$ anomalous couplings within the context of an effective field theory. In this approach, the production cross section is constrained to be ${\sigma }_{\gamma \text{H}}$ $<$ 16.4 fb at 95% confidence level (CL). Simultaneous constraints on four anomalous couplings involving HZ$\gamma$ and H$\gamma \gamma$ are provided. Additionally, the production rate for H $\to$ 4$\mathrm{\ell }$ is examined to assess potential enhancements in the Yukawa couplings between light quarks and the Higgs boson. Assuming the standard model values for the Yukawa couplings of the bottom and top quarks, the following simultaneous constraints are obtained: ${\kappa }_{\text{u}}$ = (0.0 $\pm$ 1.5) $\times$ 10${}^3$, ${\kappa }_{\text{d}}$ = (0.0 ${}_{-6.8}^{+6.7}$) $\times$ 10${}^2$, ${\kappa }_{\text{s}}$ = 0 ${}_{-32}^{+30}$, and ${\kappa }_{\text{c}}$ = 0.0 ${}_{-2.8}^{+2.3}$. This rules out the hypothesis that up- or down-type quarks in the first or second generation have the same Yukawa couplings as those in the third generation, with a CL greater than 95%.