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

Abstract

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, themore » 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.« less

Authors:

d’Enterria, David  ^[1];

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Poldaru, Andres ^[2]; Wojcik, George ^[3]

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+ Show Author Affiliations

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)

Publication Date:

Fri Feb 04 00:00:00 EST 2022

Research Org.:

SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1856255

Grant/Contract Number:  

AC02-76SF00515

Resource Type:

Accepted Manuscript

Journal Name:

European Physical Journal Plus

Additional Journal Information:

Journal Volume: 137; Journal Issue: 2; Journal ID: ISSN 2190-5444

Publisher:

Springer

Country of Publication:

United States

Language:

English

Subject:

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS