Virtual corrections to gg → ZH via a transverse momentum expansion

Abstract

We compute the next-to-leading virtual QCD corrections to the partonic cross section of the production of a Higgs boson in association with a Z boson in gluon fusion. The calculation is based on the recently introduced method of evaluating the amplitude via an expansion in terms of a small transverse momentum. We generalize the method to the case of different masses in the final state and of a process not symmetric in the forward-backward direction exchange. Our analytic approach gives a very good approximation (better than percent) of the partonic cross section in the center of mass energy region up to ∼ 750 GeV, where at the LHC ∼ 98% of the total hadronic cross section is concentrated.

Array programming with NumPy

“…However, approximations of the integrals in certain limits can often be easier to calculate and nonetheless sufficiently accurate for phenomenological purposes. Prominent examples are inclusive Higgs production in gluon fusion at N 3 LO in the large-m t expansion, with [1] and without [2] the threshold approximation, b-quark effects in H+jet production [3,4], the high-energy expansion in Higgs-boson pair production [5,6,7], gg → ZZ [8] and gg → ZH [9] production, combined threshold plus large-m t expansions in gg → HH [10], gg → ZZ [11] and gg → ZH [12], or expansions in the limit of small external masses [13].…”

Gluon Fusion Production at NLO: Merging the Transverse Momentum and the High-Energy Expansions

“…As discussed in refs. [18,19], not only the p T but also the masses of the external particles are understood as small parameters. Since these are all treated on the same footing with respect to the large scales set by ŝ and m t , we can write the general expression for a p T -expanded form factor F in the amplitude in terms of a scaling parameter x…”

“…ii) The evaluation via an expansion in the transverse momentun, p T , of the final-state particles [18,19]. Here, ŝ and m t are assumed to be the large energy scale while m H , m Z and p T , that can be traded for t, are considered to be the small ones.…”

“…The key point of our analysis is to extend the fixed-order results both in the p T expansion [18,19] and in the HE expansion [21,22] up to or beyond their border of validity, i.e. t 4m 2 t , in order to merge the two analytic approximations.…”

Anomalous couplings in associated $VH$ production with Higgs decay to massive $b$ quarks at NNLO in QCD

“…Approximate results for the O(α 3 s ) contributions due to gg → ZH suggest that these can be quite large [30,31] and should be included for reliable predictions despite being formally subleading. In the recent past, significant effort went into their computation [32][33][34][35], using either numerical methods or phenomenologically-motivated analytic approximations. Strategies to extract the gg → ZH contribution from experimental data have been investigated in Ref.…”