Model-independent measurement of the e $$^{{+}}$$ + e $$^{-}$$ - $$\rightarrow $$ → HZ cross section at a future e $$^{{+}}$$ + e $$^{-}$$ - linear collider using hadronic Z decays

Abstract

A future e + 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 − 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 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) with Z → + − , where = e, μ. 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 boson. Because the branching ratio for Z → qq is approximately ten times greater than for Z → + − , this method is statistically more powerful than using the leptonic decays. For an integrated luminosity of 500 fb −1 at a centre-of-mass energy of √ s = 350 GeV at CLIC, σ(e + e − → HZ) can be measured to ±1.8 % using the hadronic recoil mass technique. A similar precision is found for the ILC operating at √ s = 350 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.

Higgs physics at the CLIC electron–positron linear collider

“…The study of the Higgsstrahlung process is central to the precision Higgs physics programme at any future high-energy electron–positron collider [45]. This section presents studies of at with a focus on model-independent measurements of production from the kinematic properties of the Z decay products.…”

“…5.1.2. When all these measurements are taken together, a model-independent measurement of the coupling constant with a precision of can be inferred [45]. …”

“…In contrast, for decays, the selection efficiency shows a stronger dependence on the Higgs decay mode [45]. For example, events consist of four jets and the reconstruction of the boson is complicated by ambiguities in associations of particles with jets and the three-fold ambiguity in associating four jets with the hadronic decays of the and .…”

“…The recoil mass technique can also be used to search for BSM decay modes of the Higgs boson into long-lived neutral “invisible” final states [45]. At an collider, a search for invisible Higgs decays is possible by identification of events with a visible decay and missing energy.…”

Dimension-6 operator analysis of the CLIC sensitivity to new physics

“…In particular, the Higgsstrahlung cross-section has a very strong dependence on energy for the dimension-6 operator coefficientsc W ,c HW andc HB , namely a factor O(100) between 350 GeV and 3 TeV. As an illustration, figure 1 displays the CLIC sensitivities toc HW for various centre-of-mass energies, also including estimates for 250 GeV and 420 GeV [76] that we do not include in our analysis. The horizontal dashed lines denote the corresponding projected experimental errors in the measurements, based on the estimates in section 3 for 1.4 and 3 TeV and the recoil cross-section measurement for the lower energies, and the dots indicate the sensitivities toc HW that could be obtained by CLIC runs at these different energies, assuming that this is the only significant SM EFT effect.…”