Abstract
Abstract Gluon-induced contributions to the associated production of a Higgs and a Z boson are calculated with NLO accuracy in QCD. They constitute a significant contribution to the cross section for this process. The perturbative correction factor (K-factor) is calculated in the limit of infinite top-quark and vanishing bottom-quark masses. The qualitative similarity of the results to the well-known ones for the gluon-fusion process gg → H allows to conclude that rescaling the LO prediction by this K-factor leads to a reliable NLO result and realistic error estimate due to missing higher-order perturbative effects. We consider the total inclusive cross section as well as a scenario with a boosted Higgs boson, where the Higgs boson’s transverse momentum is restricted to values p T,H > 200 GeV. In both cases, we find large correction factors K ≈ 2 in most of the parameter space.
Highlights
The leading-order (LO) cross section for this process can be written as a convolution of the cross section for the Drell-Yan process pp → V ∗ with the decay rate for V ∗ → HV, where V ∗ denotes an off-shell gauge boson of momentum k: σHV,DY(pp → HV ) =
The next-to-leading order (NLO) EW corrections have been evaluated in ref. [12] for the total HV cross sections, where they amount to −(5−10)%, and in ref. [13] for differential distributions as part of the HAWK Monte Carlo program, which fully includes all decays and off-shell effects of the weak boson V = W, Z
As suggested in ref. [14], NLO EW and Drell-Yan-like next-to-next-to-leading order (NNLO) QCD corrections can be conveniently combined in factorized form, where the EW corrections modify the QCD prediction by a relative correction factor that is rather insensitive to the parton luminosities
Summary
At LO and in covariant Rξ gauge, the Feynman diagrams contributing to the gluon-induced Higgs-strahlung process can be divided into three types, shown in figure 2: 1. Box diagrams for gg → HZ: Only massive quarks run in the loop due to the proportionality to the respective Yukawa coupling. Box diagrams for gg → HZ: Only massive quarks run in the loop due to the proportionality to the respective Yukawa coupling Note, that these graphs tend to zero in the heavy-quark limit. It is interesting to note that only the longitudinal part of the Z-boson propagator contributes, while all contributions of the transverse part vanish This consequence of the Landau-Yang theorem [17, 18] can be used at NLO to facilitate the calculation significantly, as will be described below. Triangle diagrams for gg → G0 → HZ: Only the massive-quark loops contribute here, where G0 is the would-be Goldstone boson partner to the Z boson The graphs are both proportional to the respective Yukawa coupling and to the third component of the weak isospin of the quark and tend to a constant in the heavy-quark limit. We have rederived the LO cross section with the full dependence on the top- and bottom-quark masses as a basic ingredient of our NLO calculation
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