Search for CP violation in t$$ \overline{\textrm{t}} $$H and tH production in multilepton channels in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

Abstract

The charge-parity (CP) structure of the Yukawa interaction between the Higgs (H) boson and the top quark is measured in a data sample enriched in the t$$ \overline{\textrm{t}} $$ t ¯ H and tH associated production, using 138 fb−1 of data collected in proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV by the CMS experiment at the CERN LHC. The study targets events where the H boson decays via H → WW or H → ττ and the top quarks decay via t → Wb: the W bosons decay either leptonically or hadronically, and final states characterized by the presence of at least two leptons are studied. Machine learning techniques are applied to these final states to enhance the separation of CP -even from CP -odd scenarios. Two-dimensional confidence regions are set on κt and $$ \overset{\sim }{\kappa } $$ κ ~ t, which are respectively defined as the CP -even and CP -odd top-Higgs Yukawa coupling modifiers. No significant fractional CP -odd contributions, parameterized by the quantity |$$ {f}_{CP}^{\textrm{Htt}} $$ f CP Htt | are observed; the parameter is determined to be |$$ {f}_{CP}^{\textrm{Htt}} $$ f CP Htt | = 0.59 with an interval of (0.24, 0.81) at 68% confidence level. The results are combined with previous results covering the H → ZZ and H → γγ decay modes, yielding two- and one-dimensional confidence regions on κt and $$ \overset{\sim }{\kappa } $$ κ ~ t, while |$$ {f}_{CP}^{\textrm{Htt}} $$ f CP Htt | is determined to be |$$ {f}_{CP}^{\textrm{Htt}} $$ f CP Htt | = 0.28 with an interval of |$$ {f}_{CP}^{\textrm{Htt}} $$ f CP Htt | < 0.55 at 68% confidence level, in agreement with the standard model CP -even prediction of |$$ {f}_{CP}^{\textrm{Htt}} $$ f CP Htt | = 0.

Probing the CP structure of the top quark Yukawa at the future muon collider

“…h → γγ [29], h → b b [30], multi-lepton final state [31]. The combined analyses of th and t th from LHC Run I [32] and Run II data [29,33] suggest that the CP phase should be within the range of |ξ| < 43 • at 95% CL, and a pure CP odd coupling is excluded at 3.9σ.…”

Single-Top Quark Physics at the LHC: From Precision Measurements to Rare Processes and Top Quark Properties

“…The tH processes, together with the t tH process, can also be used to set constraints on a CP-odd top quark Yukawa coupling. Such measurements were performed by ATLAS with the H → γγ [104] and H → b b [105] channels, and at CMS with the H → γγ [106] and multilepton [107] channels. Since the t tH process has a larger cross-section than the tH processes, most of the sensitivity will come from the former, and these measurements will not be described here.…”