Physics Letters B 750 (2015) 407–410
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
ZZ production at the LHC: Fiducial cross sections and distributions in
NNLO QCD
Massimiliano Grazzini
a,∗,1
, Stefan Kallweit
b
, Dirk Rathlev
a
a
Physik-Institut, Universität Zürich, CH-8057 Zürich, Switzerland
b
PRISMA Cluster of Excellence, Institute of Physics, Johannes Gutenberg University, D-55099 Mainz, Germany
a r t i c l e i n f o a b s t r a c t
Article history:
Received
31 July 2015
Received
in revised form 17 September
2015
Accepted
22 September 2015
Available
online 26 September 2015
Editor:
G.F. Giudice
We consider QCD radiative corrections to the production of four charged leptons in the ZZ signal
region at the LHC. We report on the complete calculation of the next-to-next-to-leading order (NNLO)
corrections to this process in QCD perturbation theory. Numerical results are presented for
√
s = 8 TeV,
using typical selection cuts applied by the ATLAS and CMS Collaborations. The NNLO corrections increase
the NLO fiducial cross section by about 15%, and they have a relatively small impact on the shape of
the considered kinematical distributions. In the case of the distribution of the two Z candidates, the
computed corrections improve the agreement of the theoretical prediction with the CMS data.
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
The production of Z -boson pairs at the Large Hadron Collider
(LHC) provides an important test of the electroweak (EW) sector of
the Standard Model (SM) at the TeV scale. Small deviations in the
observed rates or in the kinematical distributions could be a sig-
nal
of new physics, possibly in the form of anomalous couplings.
At the same time, ZZ production is an irreducible background
for Higgs boson production and new-physics searches. Particu-
larly
important are the off-shell effects below the ZZ threshold,
relevant for the Higgs signal region in the four-lepton channel.
Various measurements of ZZ hadroproduction have been carried
out at the Tevatron and the LHC (for some recent results see
Refs. [1–7]).
From
the theory side the first NLO predictions for on-shell
ZZ production were obtained long ago [8,9]. The leptonic decays
of the Z bosons were included, initially neglecting spin correla-
tions
in the virtual contributions [10]. The computation of the
relevant one-loop helicity amplitudes [11] enabled the first com-
plete
NLO calculations [12,13], including spin correlations and off-
shell
effects. The loop-induced gluon-fusion production channel,
which formally contributes only at the next-to-next-to-leading or-
der
(NNLO), was computed in Refs. [14,15]. The corresponding
*
Corresponding author.
E-mail
address: grazzini@physik.uzh.ch (M. Grazzini).
1
On leave of absence from INFN, Sezione di Firenze, Sesto Fiorentino, Florence,
Italy.
leptonic decays were taken into account in Refs. [16–18]. NLO pre-
dictions
for ZZ production including the gluon-induced contribu-
tion,
the leptonic decays with spin correlations and off-shell effects
were presented in Ref. [19]. The NLO QCD corrections to on-shell
ZZ + jet production were discussed in Refs. [20,21], and approx-
imate
NNLO predictions obtained by merging NLO results for ZZ
and
ZZ + jet production were presented in Ref. [22]. The EW cor-
rections
to ZZ production were obtained in Ref. [23]. Adecisive
step forward was carried out in Ref. [24] where the inclusive NNLO
cross
section for on-shell ZZ production was presented. This calcu-
lation
was based on the evaluation of the two-loop amplitude for
on-shell ZZ production. Later, the two-loop helicity amplitudes for
all the vector-boson pair production processes were presented [25,
26].
This computation paves the way to the consistent inclusion
of the leptonic decays and off-shell effects in the NNLO computa-
tion.
In
this Letter we carry out this step by considering ZZ produc-
tion
at NNLO including the leptonic decays of the vector bosons
together with spin correlations and off-shell effects. Contributions
from Zγ
∗
and γ
∗
γ
∗
production as well as from pp → Z/γ
∗
→
4 leptons topologies are also consistently included with all inter-
ference
terms. Our calculation allows us to apply arbitrary cuts on
the final-state leptons and the associated QCD radiation. Here we
present selected numerical results for pp → 4leptons at the LHC
in NNLO QCD, using the typical cuts that are applied in the exper-
imental
ZZ analyses.
http://dx.doi.org/10.1016/j.physletb.2015.09.055
0370-2693/
© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.