Model-independent measurement of the e [equation] e [equation] [equation] HZ cross section at a future e [equation] e [equation] linear collider using hadronic Z decays

摘要

A future (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 (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 (mathrm{e}^{+} mathrm{e}^{-} ightarrow 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 (upsigma (mathrm{e}^{+} mathrm{e}^{-} ightarrow mathrm{H} mathrm{Z})) with (mathrm{Z} ightarrow {ell } ^{+} {ell } ^{-} ), where ({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 (mathrm{Z} ) boson. Because the branching ratio for (mathrm{Z} ightarrow mathrm{q} {overline{mathrm{q}}} ) is approximately ten times greater than for (mathrm{Z} ightarrow {ell } ^{+} {ell } ^{-} ), this method is statistically more powerful than using the leptonic decays. For an integrated luminosity of 500?( ext {fb}^{-1}) at a centre-of-mass energy of (sqrt{s} =350~ ext {GeV} ) at CLIC, (upsigma (mathrm{e}^{+} mathrm{e}^{-} ightarrow mathrm{H} mathrm{Z})) can be measured to ({pm }1.8~%) using the hadronic recoil mass technique. A similar precision is found for the ILC operating at (sqrt{s} =350~ ext {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.