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

Journal Article · 15 May 2024 · Journal of High Energy Physics (Online)

DOI: https://doi.org/10.1007/jhep05(2024)176 · OSTI ID:2438325

Cassidy, Morgan E. ^[1]; Dong, Zhongtian  ^[2]; Kong, Kyoungchul  ^[2]; Lewis, Ian M.  ^[2]; Zhang, Yanzhe ^[3]; Zheng, Ya-Juan  ^[4]

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1. University of Kansas, Lawrence, KS (United States); University of Pittsburgh, PA (United States); University of Kansas
2. University of Kansas, Lawrence, KS (United States)
3. University of Kansas, Lawrence, KS (United States); University of Massachusetts, Amherst, MA (United States)
4. University of Kansas, Lawrence, KS (United States); Iwate University (Japan)

We study the top-Higgs coupling with a CP violating phase ξ at a future multi-TeV muon collider. We focus on processes that are directly sensitive to the top quark Yukawa coupling: $$t$$$\overline{t}$$$$h$, $tbhμν$, and $$t$$$\overline{t}$$$$h$$v$$$\overline{v}$$ with $$h$$ → $$b$$$\overline{b}$$ and semileptonic top decays. At different energies, different processes dominate the cross section, providing complementary information. At and above an energy of $$\mathcal{O}$$(10) TeV, vector boson fusion processes dominate. As we show, in the Standard Model there is destructive interference in the vector boson fusion processes $$t$$$\overline{t}$$$$h$$v$$$\overline{v}$$ and $tbhμν$ between the top quark Yukawa and Higgs-gauge boson couplings. A CP-violating phase changes this interference, and the cross section measurement is very sensitive to the size of the CP-violating angle. Although we find that the cross sections are measured to $$\mathcal{O}$$(50%) statistical uncertainty at 1σ, a 10 and 30 TeV muon collider can bound the CP-violating angle |ξ| ≲ 9.0° and |ξ| ≲ 5.4°, respectively. However, cross section measurements are insensitive to the sign of the CP-violating angle. To determine that the coupling is truly CP violating, observables sensitive to CP-violation must be measured. We find in the $$t$$$\overline{t}$$$$h$ process the azimuthal angle between the $$t$$ + $$\overline{t}$$ plane and the initial state muon+Higgs plane shows good discrimination for ξ = ±0.1π.

• Research Organization: University of Kansas, Lawrence, KS (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP); National Science Foundation (NSF); JSPS KAKENHI
• Grant/Contract Number: SC0017988; SC0024407
• OSTI ID: 2438325
• Journal Information: Journal of High Energy Physics (Online), Journal Name: Journal of High Energy Physics (Online) Journal Issue: 5 Vol. 2024; ISSN 1029-8479
• Publisher: Springer NatureCopyright Statement
• Country of Publication: United States
• Language: English