Abstract
We compute the next-to-leading order virtual corrections to the partonic cross-section of the process gg → ZH, in the high-energy and large-mt limits. We use Padé approximants to increase the radius of convergence of the high-energy expansion in {m}_t^2/s , {m}_t^2/t and {m}_t^2/u and show that precise results can be obtained down to energies which are fairly close to the top quark pair threshold. We present results both for the form factors and the next-to-leading order virtual cross-section.
Highlights
Associated ZH production can occur via the loop-induced gluon fusion process
It is important to consider NLO QCD corrections to gg → ZH, requiring the computation of two-loop box-type Feynman diagrams with two different final-state masses and the massive top quark propagating in the loops
In appendix A we present analytic results for the one-particle reducible double-triangle contribution and in appendix B we briefly discuss our treatment of γ5 and the application of projectors to obtain the form factors
Summary
We consider the amplitude for the process g(p1)g(p2) → Z(p3)H(p4) where all momenta are assumed to be incoming. In the box-type diagrams the Higgs boson couples directly to the quark loop, so diagrams involving the bottom quark are suppressed by their Yukawa coupling with respect to diagrams involving the top quark This is not the case for the triangle-type diagrams; here contributions from both the top and bottom quark loops must be considered. The contribution from the reducible double-triangle diagrams to the (differential) partonic cross- section is implemented in the computer program which comes together with ref. For the computation of the one- and two-loop Feynman diagrams (some examples are shown in figure 1) in the high-energy limit, we proceed as follows: after producing the amplitude we perform a Taylor expansion in the Z and Higgs boson masses (since m2Z, m2H m2t ), leaving one- and two-loop integrals which depend only on s, t and mt.
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