Restoring good high energy behaviour in Higgs production via W fusion at the LHC

TL;DR

This paper develops a method using the pinch-technique to isolate and remove anomalous high-energy terms in W-fusion Higgs production at the LHC, restoring proper behaviour and enabling clearer Higgs resonance identification.

Contribution

It introduces a gauge-invariant approach to separate Higgs signal from background in W-fusion processes, improving high-energy behaviour analysis and simplifying calculations.

Findings

Successfully isolates unitarity-violating terms using the pinch-technique.

Restores good high-energy behaviour of the cross section.

Provides a resonant approximation that matches full results well.

Abstract

The W-fusion scattering process W+W- --> ZZ for off-shell W bosons is studied, focusing on the issue of its high-energy behaviour which is known to be anomalous. It is shown that the unitarity violating terms can be isolated and extracted in a well-defined and efficient way using the pinch-technique. This restores the good high energy behaviour of the cross section and, in particular, makes possible the identification of the Higgs resonance in the invariant mass distribution M(ZZ) of the Z pair. The discarded terms, which are proportional to the off-shellness of the W bosons, cancel against similar terms originating from the remaining diagrams for the full physical process f1 f2 --> f1' f2' Z Z. This cancellation ensures the gauge invariance of our result, which therefore constitutes a meaningful separation between signal and background when they both contribute coherently. Equipped with this result, we are able to define a resonant approximation for the process p p --> Z Z + 2 jets + X, which circumvents the problem of good high energy behaviour without having to resort to the lengthy calculation of the complete set of diagrams. In this approximation only the W and Z fusion signal graphs are included, i.e. the ones which contain the Higgs resonance. We have verified that the approximate resonant cross section describes very well the full result not only close to the resonance but also beyond it.