Abstract
We consider top-quark mass effects in the Higgs-interference contribution to $Z$-boson pair production in gluon fusion. While this production mechanism is formally of next-to-next-to leading order, its contribution is numerically important above the top threshold $M_{ZZ}^2=4m_t^2$. This region is essential to constrain the width of the Higgs boson and good control over the top-quark mass dependence is crucial. We determine the form factors that are relevant for the interference contribution at two-loop order using a method based on a conformal mapping and Pad\'e approximants constructed from the expansions of the amplitude for large top mass and around the top threshold.
Highlights
A direct measurement of the Higgs boson width ΓH is not possible at the LHC or even the envisioned generation of collider experiments
Indirect constraints can be obtained at the LHC by studying the process pp → H → ZZð→ 4lÞ on the Higgs boson peak where the cross section depends on the combination g2Hggg2HZZ=ΓH and off the peak where the measurement of the cross section constrains the product g2Hggg2HZZ of the effective Higgs boson-gluon coupling gHgg and the Higgs boson-Z boson coupling gHZZ, as proposed in [1–3]
With the exception of the vector form factor jFðV2VÞ i for small transverse momenta, we find that the Padeapproximation based on the large-mass expansion (LME) alone does not yield a realistic reconstruction of the top-quark mass effects of the form factors
Summary
A direct measurement of the Higgs boson width ΓH is not possible at the LHC or even the envisioned generation of collider experiments. The latest studies from the LHC experiments give an upper limit of 14.4 MeV at 95% C.L. from the ZZ final state at ATLAS [7] and the value 3.2þ−22..28. MeV from the combination of VV final states in CMS [8], close to the SM prediction ΓSHM 1⁄4 4.10 Æ 0.06 MeV [9].
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