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

: 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¯tH and tH
associated production, using 138 fb−1
of data collected in proton-proton collisions at √
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 → τ τ 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. Twodimensional confidence regions are set on κt and 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
Htt
CP | are observed; the parameter
is determined to be |f
Htt
CP | = 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 κ˜t
, while |f
Htt
CP | is
determined to be |f
Htt
CP | = 0.28 with an interval of |f
Htt
CP | < 0.55 at 68% confidence level, in
agreement with the standard model CP-even prediction of |f
Htt
CP | = 0.