Model-independent measurement of the e+e-→ HZ cross section at a future e+e- linear collider using hadronic Z decays

Abstract

A future e+e-$$\mathrm{e}^{+} \mathrm{e}^{-} $$ collider, such as the ILC or CLIC, would allow the Higgs sector to be probed with a precision significantly beyond that achievable at the High-Luminosity LHC. A central part of the Higgs programme at an e+e-$$\mathrm{e}^{+} \mathrm{e}^{-} $$ collider is the model-independent determination of the absolute Higgs couplings to fermions and to gauge bosons. Here the measurement of the e+e-→HZ$$\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{H} \mathrm{Z} $$ Higgsstrahlung cross section, using the recoil mass technique, sets the absolute scale for all Higgs coupling measurements. Previous studies have considered σ(e+e-→HZ)$$\upsigma (\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{H} \mathrm{Z})$$ with Z→ℓ+ℓ-$$\mathrm{Z} \rightarrow {\ell } ^{+} {\ell } ^{-} $$, where ℓ=e,μ$${\ell } = \mathrm{e},,{\upmu } $$. In this paper it is shown for the first time that a near model-independent recoil mass technique can be extended to the hadronic decays of the Z$$\mathrm{Z} $$ boson. Because the branching ratio for Z→qq¯$$\mathrm{Z} \rightarrow \mathrm{q} {\overline{\mathrm{q}}} $$ is approximately ten times greater than for Z→ℓ+ℓ-$$\mathrm{Z} \rightarrow {\ell } ^{+} {\ell } ^{-} $$, this method is statistically more powerful than using the leptonic decays. For an integrated luminosity of 500 fb-1$$\text {fb}^{-1}$$ at a centre-of-mass energy of s=350GeV$$\sqrt{s} =350~\text {GeV} $$ at CLIC, σ(e+e-→HZ)$$\upsigma (\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{H} \mathrm{Z})$$ can be measured to ±1.8%$${\pm }1.8~%$$ using the hadronic recoil mass technique. A similar precision is found for the ILC operating at s=350GeV$$\sqrt{s} =350~\text {GeV} $$. The centre-of-mass dependence of this measurement technique is discussed, arguing for the initial operation of a future linear collider at just above the top-pair production threshold.