This process is calculable at leading LO, at next-to-leading order NLO, and at next-to-next-to-leading order NNLO.

These processes represent the production of a Standard Model Higgs boson that
decays either into a bottom quark pair (nproc=111), a pair of tau’s (nproc=112), a
W^{+}W^{-} pair that further decays leptonically (nproc=113) a W^{+}W^{-} pair where the
W^{-} decays hadronically (nproc=114,115) or a ZZ pair (nproc=116-118) . In
addition, the loop-level decays of the Higgs into a pair of photons (nproc=119) and
the Zγ decay are included (nproc=120,121).

For the case of W^{+}W^{-} process nproc=115 gives the contribution of radiation
from the hadronically decaying W^{-}. Process 114 may be run at NLO with the
option todk, including radiation in the decay of the hadronically decaying
W^{-}. ^{1}
For the case of a ZZ decay, the subsequent decays can either be into a pair of muons
and a pair of electrons (nproc=116), a pair of muons and neutrinos (nproc=117) or a
pair of muons and a pair of bottom quarks (nproc=118).

At LO the relevant diagram is the coupling of two gluons to the Higgs via a top quark loop. This calculation is performed in the limit of infinite top quark mass, so that the top quark loop is replaced by an effective operator. This corresponds to the effective Lagrangian,

(1) |

where v is the Higgs vacuum expectation value and G_{μν}^{a} the gluon field
strength tensor. The calculation may be performed at NLO, although radiation
from the bottom quarks in the decay of processes 111 and 118 is not yet
included.

When removebr is true in processes 111,112,113,118, the Higgs boson does not decay.

Process 119 implements the decay of the Higgs boson into two photons via loops of top quarks and W-bosons. The decay is implemented using the formula Eq.(11.12) from ref. [1]. When removebr is true in process 119 the Higgs boson does not decay.

Processes 120 and 121 implement the decay of the Higgs boson into an
lepton-antilepton pair and a photon. As usual the production of a charged
lepton-antilepton pair is mediated by a Z∕γ^{*} (process 120) and the production of
three types of neutrinos ∑
ν by a Z-boson (process 121). These processes are
implemented using a generalization of the formula of [2]. (Generalization to take
into account off-shell Z-boson and adjustment of the sign of C_{2} in their
Eq.(4)).

nplotter_ZZlept.f is the default plotting routine.

[1] R.K. Ellis, W.J. Stirling and B.R. Webber, QCD and collider physics, Camb. Monogr. Part. Phys. Nucl. Phys. Cosmol. 8 (1996) 1.

[2] A. Djouadi, V. Driesen, W. Hollik and A. Kraft, The Higgs photon - Z boson coupling revisited, Eur. Phys. J. C1 (1998) 163 [hep-ph/9701342].