Speaker
Prof.
Matthias Neubert
(Johannes Gutenberg University Mainz)
Description
We present a detailed analysis of the rare exclusive Higgs-boson decays into a single vector meson and a photon and investigate the possibility of using these processes to probe the light-quark Yukawa couplings. We work with an effective Lagrangian with modified Higgs couplings to account for possible new-physics effects in a model-independent way. The $h\to V\gamma$ decay rate is governed by the destructive interference of two amplitudes, one of which involves the Higgs coupling to the quark anti-quark pair inside the vector meson. We derive this amplitude at next-to-leading order in $\alpha_s$ using QCD factorization, including the resummation of large logarithmic corrections and accounting for the effects of flavor mixing. The high factorization scale $\mu\sim m_h$ ensures that our results are rather insensitive to poorly known hadronic parameters. The second amplitude arises from the loop-induced effective $h\gamma\gamma^*$ and $h\gamma Z^*$ couplings, where the off-shell gauge boson converts into the vector meson. We devise a strategy to eliminate theoretical uncertainties related to this amplitude to almost arbitrary precision. This opens up the possibility to probe for ${\cal O}(1)$ modifications of the $c$- and $b$-quark Yukawa couplings and ${\cal O}(30)$ modifications of the $s$-quark Yukawa coupling in the high-luminosity LHC run. In particular, we show that measurements of the ratios $\mbox{Br}(h\to\Upsilon(nS)\,\gamma)/\mbox{Br}(h\to\gamma\gamma)$ and $\mbox{Br}(h\to b\bar b)/\mbox{Br}(h\to\gamma\gamma)$ can provide complementary information on the real and imaginary parts of the $b$-quark Yukawa coupling. More accurate measurements would be possible at a future 100\,TeV proton-proton collider.
Author
Prof.
Matthias Neubert
(Johannes Gutenberg University Mainz)
