Order $v^4$ corrections to Higgs boson decay into $J/\psi + \gamma$

The process $H \to J/\psi + \gamma$, where $H$ is the Higgs particle, provides a way to probe the size and the sign of the Higgs-charm coupling. In order to improve the theoretical control of the decay rate, we compute order $v^4$ corrections to the decay rate based on the nonrelativistic QCD factorization formalism. The perturbative calculation is carried out by using automated computer codes. We also resum logarithms of the ratio of the masses of the Higgs boson and the $J/\psi$ to all orders in the strong coupling constant $\alpha_s$ to next-to-leading logarithmic accuracy. In our numerical result for the decay rate, we improve the theoretical uncertainty, while our central value is in agreement with previous studies within errors. We also present numerical results for $H \to \Upsilon(nS) + \gamma$ for $n=1,2$, and 3, which turn out to be extremely sensitive to the Higgs bottom coupling.