Measurement of the ZH cross-section with hadronic Z decays

Abstract

At FCC-ee, the measurement of the total e+e− → ZH cross section is an essential input to the absolute determination of the HZZ coupling and of the trilinear Higss self-coupling. With one million ZH events expected in three years at √s = 240GeV, and 200,000 Higgs events expected at and above the ttbar threshold in five years, the ultimate statistical precision on the production cross section is 0.1% and 0.2%, respectively. If achievable, such a performance would lead to a determination of the Higgs self-coupling κ_λ with a precision better than 10% in a full EFT fit. Traditionally, only the leptonic decays of the Z boson (e+e− and μ+μ−) are used for the cross- section measurement, as they allow the Higgs boson to be tagged with an efficiency independent of the Higgs decay mode. The small Z leptonic branching ratio is expensive in terms of cross- section precision, which become 0.5% and 1% at 240 GeV and 365 GeV, respectively. Such a decay- mode independent tag is more challenging with hadronic Z decays, and needs to be quantified. The requirements on the detector design (hadronic mass and hadronic recoil-mass resolutions) to approach the ultimate statistical precision on the Higgs self-coupling will be studied. As a by-product, this precision will be optimized as a function of the centre-of-mass energy (around 240GeV), to fully benefit from the increase of the ZH cross-section sensitivity to κ_λ (and of the FCC-ee luminosity) at smaller √s values.

• The corresponding Snomass LOI

Bibliography

• Precision Higgs physics at the CEPC Fenfen An et al 2019 Chinese Phys. C 43 043002
• Model-Independent Measurement of the e+e- -> HZ Cross Section at a Future e+e- Linear Collider using Hadronic Z Decays M.A. Thomson, EUr. Phys. J. C (2016). 76

People

Interest from:

• F. Simon, S. Sasikumar (MPI)
• M. Klute et al (MIT)
• Ang Li, G. Bernardi (APC)