Physics Letters B 741 (2015) 111–116
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Gluon fusion contribution to VHj production at hadron colliders
Pankaj Agrawal
a
, Ambresh Shivaji
b,∗
a
Institute of Physics, Sachivalaya Marg, Bhubaneswar, Odisha 751005, India
b
Regional Centre for Accelerator-based Particle Physics, Harish-Chandra Research Institute, Chhatnag Road, Jhusi, Allahabad 211019, India
a r t i c l e i n f o a b s t r a c t
Article history:
Received
30 September 2014
Received
in revised form 2 December 2014
Accepted
8 December 2014
Available
online 12 December 2014
Editor:
G.F. Giudice
Keywords:
LHC
Gluon
fusion
Higgs
One-loop
We study the associated production of an electroweak vector boson and the Higgs boson with a jet
via gluon–gluon fusion. At the leading order, these processes occur at one-loop level. The amplitudes
of these one-loop processes are gauge invariant and finite. Therefore, their contributions towards the
corresponding hadronic cross sections and kinematic distributions can be calculated separately. We
present results for the Large Hadron Collider and its discussed upgrades. We find that the gluon–
gluon
one-loop process gives dominant contribution to the γ Hj production. We observe a destructive
interference effect in the gg → ZHj amplitude. We also find that in the high transverse momentum and
central rapidity region, the ZHj production cross section via gluon–gluon fusion becomes comparable to
the cross section contributions coming from quark–quark and quark–gluon channels.
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/3.0/). Funded by SCOAP
3
.
With the discovery of the Higgs boson [1,2] at the Large Hadron
Collider (LHC), the standard model and its symmetry-breaking
mechanism have been validated. The CMS and ATLAS Collabora-
tions are
measuring its properties.The Higgs boson was discov-
ered
through gg → H production mechanism. Since then signals
of other production mechanisms have also been examined. In par-
ticular,
the associated production of the Higgs boson with an elec-
troweak
boson has been explored [3,4]. To ensure that the discov-
ered
Higgs boson is indeed the standard model Higgs boson, there
is a need to detect as many of its signatures as possible. Further-
more,
since there is no signal that points to new physics beyond
the standard model, there is a need to look for standard model
processes that do not have large but accessible cross sections, and
can be enhanced/modified by new physics effects.
The
LHC and its proposed upgrades provide us an opportunity
to explore two types of processes in more detail: (a) the pro-
cesses
which, in the standard model, begin at the one-loop level
(one-loop being the leading order (LO)); (b) gluon–gluon scatter-
ing
processes. As the centre-of-mass energy increases, the gluon–
gluon
luminosity increases, making many more processes observ-
able.
Study of such relatively rare processes is complementary to
new physics searches at high energy colliders. Thus, the LHC pro-
vides
a unique opportunity for testing many of the standard model
predictions which was not possible at earlier high energy colliders.
*
Corresponding author.
E-mail
addresses: agrawal@iopb.res.in (P. Agrawal), ambreshkshivaji@hri.res.in
(A. Shivaji).
For example, many one-loop gluon–gluon fusion processes are/will
be accessible only at the LHC [5–10]. These gluon fusion one-loop
processes can be studied both in the signal and background cate-
gories.
In
this Letter, we are interested in the gluon–gluon contribution
to the pp → VHj + X hadronic processes, i.e.,
g + g → VHj, (1)
where V is an electroweak vector boson and ‘ j’ stands for a
light-quark, or gluon initiated jet. The amplitude of the process
gg → W
±
Hj is trivially zero due to the electromagnetic charge
conservation. Therefore, V would refer to a photon or a Z boson.
This process occurs at the one-loop via triangle, box, and pen-
tagon
diagrams. Since quarks carry both the electroweak and color
charges, the leading order contribution comes from quark-loop dia-
grams.
The prototype quark-loop diagrams are shown in Fig. 1 [11].
(We have not displayed some of the triangle and bubble diagrams
which do not contribute due to the vanishing color factor.) For the
γ Hj case, only pentagon class of diagrams contribute. The box dia-
grams
with qqH coupling do not contribute because of the Furry’s
theorem. Due to the same reason, the leading order gg → γ H am-
plitude
vanishes. There are a total 24 pentagon diagrams. However,
due to charge conjugation symmetry only 12 of those are inde-
pendent.
The full amplitude is proportional to the symmetric color
factor d
abc
.
In
the ZHj case, box and triangle diagrams also contribute.
Once again there are 12 independent pentagon (PEN) diagrams.
There are two types of box diagrams depending on the nature of
http://dx.doi.org/10.1016/j.physletb.2014.12.021
0370-2693/
© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/). Funded by
SCOAP
3
.
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