Central-edge asymmetry as a probe of Higgs-top coupling in $t\bar{t}h$ production at LHC

TL;DR

This paper introduces a new asymmetry observable, $A_{CE}$, to probe CP violation in the Higgs-top coupling during $t\bar{t}h$ production at the LHC, demonstrating its effectiveness in distinguishing CP phases and scalar vs pseudo-scalar interactions.

Contribution

The study proposes the central-edge asymmetry $A_{CE}$ as a novel probe for CP violation in Higgs-top interactions, utilizing jet substructure techniques to enhance detection at the LHC.

Findings

Achieves 5σ significance for $t\bar{t}h$ detection at high luminosity.

$A_{CE}$ effectively discriminates CP phases with distinct asymmetry values.

Scalar and pseudo-scalar interactions can be distinguished at 95% C.L. at HL-LHC.

Abstract

The Higgs-top coupling plays a central role in the hierarchy problem and the vacuum stability of the Standard Model (SM). We propose a central-edge asymmetry ($A_{CE}$) to probe the CP violating Higgs-top coupling in dileptonic channel of $t\bar{t}h(\to b\bar{b})$ production at the LHC. We demonstrate that the CP-violating Higgs-top coupling can affect the central-edge asymmetry through distorting $\Delta y_{\ell^+\ell^-}$ distribution because of the contribution of new top charge asymmetric term. Since $\Delta y_{\ell^+\ell^-}$ distribution is frame-independent and has a good discrimination even in boosted regime, we use the jet substructure technique to enhance the observability of the dileptonic channel of $t\bar{t}h$ production. We find that (1) the significance of dileptonic channel of $t\bar{t}h$ production can reach $5\sigma$ for CP phase $\xi=0,\pi/4,\pi/2$ when the luminosity ${\cal L}=795,993,1276$ fb$^{-1}$ at 14 TeV LHC. (2) the central-edge asymmetry $A_{CE}$ show a good discrimination power of CP phase of $t\bar{t}h$ interaction, which are -40.26\%, -26.60\%, -9.47\% for $\xi=0$, $\pi/4$, $ \pi/2$ respectively and are hardly affected by the event selections. Besides, by performing the binned-$\chi^2$ analysis of $\Delta y_{\ell^+\ell^-}$ distribution, we find that the scalar and pseudo-scalar interactions can be distinguished at 95\% C.L. level at 14 TeV HL-LHC.