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

Abstract

We analyze the prospects of probing the C P -odd itilde{kappa}overline{t}gamma 5th 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 tilde{kappa} . 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 tilde{kappa} . We project future sensitivity to the signal in pp → t(→ ℓ\U0001d708b)h(→ b overline{b} )j. We also propose novel C P -odd observables for top quark pair production in association with the Higgs, pp → t overline{t} h, with semileptonically decaying tops and h → b overline{b} , 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 tilde{kappa} ∼ 0.1 at the high-energy LHC with 2\U0001d70e confidence.