Top Yukawa coupling measurement with indefiniteCPHiggs ine+e−→tt¯

Abstract

We consider the issue of the top quark Yukawa coupling measurement in a model-independent and general case with the inclusion of CP violation in the coupling. Arguably the best process to study this coupling is the associated production of the Higgs boson along with a tt pair in a machine like the International Linear Collider (ILC). While detailed analyses of the sensitivity of the measurementassuming a Standard Model (SM)-like coupling is available in the context of the ILC-conclude that the coupling could be pinned down to about a 10% level with modest luminosity, our investigations show that the scenario could be different in the case of a more general coupling. The modified Lorentz structure resulting in a changed functional dependence of the cross section on the coupling, along with the difference in the cross section itself leads to considerable deviation in the sensitivity. Our studies of the ILC with center-of-mass energies of 500 GeV, 800 GeV, and 1000 GeV show that moderate CP mixing in the Higgs sector could change the sensitivity to about 20%, while it could be worsened to 75% in cases which could accommodate more dramatic changes in the coupling. Detailed considerations of the decay distributions point to a need for a relook at the analysis strategy followed for the case of the SM, such as for a modelindependent analysis of the top quark Yukawa coupling measurement. This study strongly suggests that a joint analysis of the CP properties and the Yukawa coupling measurement would be the way forward at the ILC and that caution must be exercised in the measurement of the Yukawa couplings and the conclusions drawn from it.

Laboratory-frame observables for probing the top-Higgs boson interaction

“…Note, on the other hand, that tth production can be studied very precisely at a future linear collider such as the ILC [75]. Sufficiently high rates for this process are possible at such colliders [76][77][78][79][80][81][82] and can therefore be used to extract CP information [83][84][85][86][87][88][89][90][91] by exploiting angular correlations and/or polarization of the top pair.…”

Probing the type-II seesaw mechanism through the production of Higgs bosons at a lepton collider

“…For the earlier discussions on Higgs triplet model at a linear collider, see [40][41][42][43]. For the other SM and BSM searches at CLIC and other linear colliders, see [38,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58] for Higgs physics and effective field theory, [59][60][61][62][63] for different BSM scenarios, and [64][65][66][67][68][69][70] for seesaw and radiative neutrino mass model searches. For the discussion on probing dark-sector at e + e − collider, see [71,72].…”

Probing CP violation in e + e − production of the Higgs boson and toponia

“…As well, there have also appeared many papers devoted to find optimized CP observables at hadron colliders [31][32][33][34][35][36][37][38][39] and lepton colliders [40][41][42][43][44]. The simplest one requires the reconstruction of the top-and anti-top-quark momenta from their decay products which is difficult to be measured accurately even at lepton colliders.…”

“…In this paper, we study the density matrix for the e + e − production of the Higgs boson and toponia analytically, and propose new CP-odd observables for the measurement of the CP property of the Higgs boson at the ILC with √ s = 500 GeV [43][44][45][46][47]. In this energy region, the strong-interaction Coulomb force is known to be important to calculate the total production rate.…”