Abstract
We perform a preliminary study of the ability of the Higgs decay to four leptons to shed light on the top quark Yukawa couplings. In particular we examine whether the $h\to 4\ell$ `golden channel' is sensitive to the $CP$ properties of the top quark couplings to the Higgs boson. We show that kinematic distributions are sensitive to interference of the next-to-leading order electroweak corrections with the tree level $ZZ$ contribution. This translates into a sensitivity to the top quark Yukawa couplings such that meaningful constraints on their $CP$ properties can begin to be obtained once $\sim 300$ fb$^{-1}$ of data has been collected at $\sim 14$ TeV, with significant improvements at higher luminosity or with a higher energy hadron collider. This makes the $h\to4\ell$ channel a useful probe of the top quark Yukawa couplings that is qualitatively different from already established searches in $h\to V\gamma$ two body decays, $tth$, and $gg\to h$. We also briefly discuss other potential possibilities for probing the top Yukawa $CP$ properties in $h\to2\ell\gamma$ and $\ell^+\ell^-\to h Z, h\gamma$.
Highlights
The observation of a Higgs-like resonance with mass near 125 GeV [1,2] completes the standard model (SM) and opens up a vast new research program in studying its detailed properties in order to determine whether it is the SM Higgs
It has been established that its couplings to ZZ are dominantly CP even [3,4], but CP is violated in Nature, so if there is physics beyond the SM (BSM), some Higgs couplings may not conserve CP
We have demonstrated that the h → 4l golden channel can be a useful probe of the top Yukawa at the LHC and future colliders
Summary
The observation of a Higgs-like resonance with mass near 125 GeV [1,2] completes the standard model (SM) and opens up a vast new research program in studying its detailed properties in order to determine whether it is the SM Higgs. We perform an initial feasibility study to explore whether the golden channel can be used as a probe of the Higgs top quark Yukawa coupling and perhaps uncover CP violation To do this we utilize the parameter extraction framework developed in [56,64,66,67,68,74] to study effective Higgs couplings and adapt it to include the leading contributions from top quark (and W) loop effects. The differential distributions for the many kinematic observables in h → 4l [56,64,66,67] give us a probe into detailed properties of these effective couplings It was demonstrated in [66,68] that golden channel measurements are surprisingly sensitive to the effective couplings of the Higgs boson to Zγ and γγ pairs. This allows us to treat this part of the amplitude which does not depend on the top Yukawa as part of the SM “background” to our top Yukawa “signal.”
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