Snowmass White Paper: Prospects of CP-violation measurements with the Higgs boson at future experiments

Abstract

The search for CP violation in interactions of the Higgs boson with either fermions or bosons provides attractive reference measurements in the Particle Physics Community Planning Exercise (a.k.a. "Snowmass"). Benchmark measurements of CP violation provide a limited and well-defined set of parameters that could be tested at the proton, electron-positron, photon, and muon colliders, and compared to those achieved through study of virtual effects in electric dipole moment measurements. We review the current status of these CP -sensitive studies and provide projections to future measurements. ContentsI. Introduction II. Framework of the Higgs CP study for Snowmass III. Prospects of Higgs CP measurements at a photon collider IV. Prospects of Higgs CP measurements at a muon collider A. Muon collider at the H boson pole B. High-energy muon collider V. Prospects of Higgs CP measurements at a hadron collider A. Gluon fusion process at a hadron collider B. The Hγγ and HZγ couplings at a hadron collider C. The HZZ and HW W couplings at a hadron collider D. The Ht t coupling at a hadron collider E. The H → τ + τ − process at a hadron collider VI. Prospects of Higgs CP measurements at an electron-positron collider A. The V H process at an electron-positron collider B. The VBF process at an electron-positron collider C. The t tH process at an electron-positron collider D. The H → τ + τ − and other decay processes at an electron-positron collider VII. Comparison to EDM measurements VIII. Summary A. Recent updates of the studies at a hadron collider B. Recent updates of the studies at an electron-positron collider C. EDM constraints References

Probing Higgs CP properties at the CEPC in the $$e^{+} e^{-} \rightarrow Z H \rightarrow l^{+} l^{-}H$$ using optimal variables

“…Several future lepton colliders, including the International Linear Collider (ILC) [13], the e + e − Future Circular Collider (FCC-ee) [14], the Compact Linear Collider (CLIC) [15], and the Circular Electron-Positron Collider (CEPC) [16], have been proposed with the capability of precise measurement of Higgs boson parameters. There are plenty of approaches to the Higgs CP measurements at the future lepton colliders by using different probes, like the VH process, the t t H process, the VBF process and the H → τ + τ − process [17]. For example, the VBF process, an ongoing study of the Z -fusion process at 1.4 TeV CLIC and 1 TeV ILC are mentioned in Ref [18].…”

Laboratory-frame tests of quantum entanglement in $H \to WW$

“…are non-vanishing. CP-violating effects in the SM arise beyond the LO but are at the level of 10 −5 [22], so CP conservation is an excellent approximation. If CP is broken in the H → V 1 V 2 decay due to effects beyond the SM, additional terms appear…”

Determination of Higgs CPV mixing angle in ZZ-fusion at 1.4 TeV CLIC

“…Determination of the Higgs CPV mixing angle in ZZ-fusion at 1.4 TeV CLIC N. Vukasinović 10 −2 [12]. According to [12], there are no predictions for CPV mixing angle determination in vector boson fusion at 𝑒 − 𝑒 + colliders, where the CPV effect is much weaker, calling for a precision of 10 −5 for the CPV factor f 𝐻𝑉𝑉 CP ,…”