Measuring the electron Yukawa coupling via resonant s-channel Higgs production at FCC-ee

Journal Article · Fri Feb 04 00:00:00 EST 2022 · European Physical Journal Plus

DOI:https://doi.org/10.1140/epjp/s13360-021-02204-2· OSTI ID:1856255

d’Enterria, David ^[1]; Poldaru, Andres ^[2]; Wojcik, George ^[3]

---

1. European Organization for Nuclear Research (CERN), Geneva (Switzerland)
2. Ludwig Maximilian Univ. of Munich, Munich (Germany)
3. SLAC National Accelerator Lab., Menlo Park, CA (United States)

The Future Circular Collider (FCC-ee) offers the unique opportunity of studying the Higgs Yukawa coupling to the electron, \(y_\mathrm {e}\), via resonant s-channel production, \(\mathrm {e^+e^-}\rightarrow \mathrm {H}\), in a dedicated run at \(\sqrt{s} = m_\mathrm {H}\). The signature for direct Higgs production is a small rise in the cross sections for particular final states, consistent with Higgs decays, over the expectations for their occurrence due to Standard Model (SM) background processes involving \(\mathrm {Z}^*\), \(\gamma ^*\), or t-channel exchanges alone. Performing such a measurement is remarkably challenging for four main reasons. First, the low value of the e\(^\pm \) mass leads to a tiny \(y_\mathrm {e}\) coupling and correspondingly small cross section: \(\sigma _\mathrm {ee\rightarrow H} \propto m_\mathrm {e}^2 = 0.57\) fb accounting for initial-state \(\gamma \) radiation. Second, the \(\mathrm {e^+e^-}\) beams must be monochromatized such that the spread of their centre-of-mass (c.m.) energy is commensurate with the narrow width of the SM Higgs boson, \(\varGamma _\mathrm {H} = 4.1\) MeV, while keeping large beam luminosities. Third, the Higgs mass must also be known beforehand with a few-MeV accuracy in order to operate the collider at the resonance peak, \(\sqrt{s} = m_\mathrm {H}\). Last but not least, the cross sections of the background processes are many orders-of-magnitude larger than those of the Higgs decay signals. A preliminary generator-level study of 11 Higgs decay channels using a multivariate analysis, which exploits boosted decision trees to discriminate signal and background events, identifies two final states as the most promising ones in terms of statistical significance: \(\mathrm {H}\rightarrow gg\) and \(\mathrm {H}\rightarrow \mathrm {W}\mathrm {W}^*\!\rightarrow \ell \nu \) + 2 jets. For a benchmark monochromatization with 4.1-MeV c.m. energy spread (leading to \(\sigma _\mathrm {ee\rightarrow H} = 0.28\) fb) and 10 ab\(^{-1}\) of integrated luminosity, a \(1.3\sigma \) signal significance can be reached, corresponding to an upper limit on the e\(^\pm \) Yukawa coupling at 1.6 times the SM value: |y_e| < 1.6|y_e^SM| at 95% confidence level, per FCC-ee interaction point per year. Directions for future improvements of the study are outlined.

• Research Organization: SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1856255
• Journal Information: European Physical Journal Plus, Journal Name: European Physical Journal Plus Journal Issue: 2 Vol. 137; ISSN 2190-5444
• Publisher: Springer
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS