Probing the C P nature of the top quark Yukawa at hadron colliders

Abstract

We analyze the prospects of probing the C P -odd iκ˜ t¯ γ5th interaction at the LHC and its projected upgrades, the high-luminosity and high-energy LHC, directly using associated on-shell Higgs boson and top quark or top quark pair production. To this end we first construct a C P -odd observable based on top quark polarization in Wb → th scattering with optimal linear sensitivity to κ˜. For the corresponding hadronic process pp → thj we present a method of extracting the phase-space dependent weight function that allows to retain close to optimal sensitivity to κ˜. We project future sensitivity to the signal in pp → t(→ ℓ𝜈b)h(→ bb¯)j. We also propose novel C P -odd observables for top quark pair production in association with the Higgs, pp → tt¯ h, with semileptonically decaying tops and h → bb¯ , that rely solely on measuring the momenta of leptons and b-jets from the decaying tops without having to distinguish the charge of the b-jets. Among the many possibilities we single out an observable that can potentially probe κ˜ ∼ 0.1 at the high-energy LHC with 2𝜎 confidence.