Physics Letters B 773 (2017) 462–469
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Physics Letters B
www.elsevier.com/locate/physletb
Probing Higgs boson couplings in H +γ production at the LHC
Hamzeh Khanpour
a,b
, Sara Khatibi
b
, Mojtaba Mohammadi Najafabadi
b,∗
a
Department of Physics, University of Science and Technology of Mazandaran, P.O.Box 48518-78195, Behshahr, Iran
b
School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), P.O. Box 19395-5531, Tehran, Iran
a r t i c l e i n f o a b s t r a c t
Article history:
Received
24 February 2017
Received
in revised form 19 May 2017
Accepted
4 September 2017
Available
online 7 September 2017
Editor:
G.F. Giudice
In this paper, we examine the potential of Higgs boson production associated with a photon at the LHC to
probe the new physics effects in the framework of the standard model effective field theory. It is shown
that the differential kinematic distributions such as photon transverse momentum and invariant mass of
Higgs + γ in Higgs associated production are powerful variables to explore the coefficients of dimension
six operators. The analysis is performed in the decay channel of Higgs boson into a b
¯
b pair including
the main sources of background processes and a realistic simulation of the detector effects. We provide
constraints at 95% confidence level on the Wilson coefficients of dimension-six operators affecting Higgs
boson plus a photon production. We show to what extent these limits could be improved at the high
luminosity LHC. The effect of these constraints on a well-motivated beyond standard model scenario is
presented.
© 2017 The Author(s). 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
.
1. Introduction
After the discovery of Higgs boson by the LHC experiments [1,
2],
standard model (SM) has been found to be a successful the-
ory
to describe the interactions among the fundamental particles
at the electroweak scale. However, it has some shortcomings which
leads us to construct new models beyond the SM. Various models
such as supersymmetric SM, extra-dimensions, two-Higgs doublet
models etc. have been suggested to solve the SM problems. For in-
stance,
supersymmetric extension of SM provides the possibility to
stabilize the Higgs boson mass from the ultra-violet divergencies
through the contributions of the supersymmetric partners of the
SM particles [3]. Most of these theories lead to some modifications
of the SM parameters. In particular, the Higgs boson couplings
are affected by several extensions of the SM. Nevertheless, all the
experimental measurements done by the LHC experiments are in
agreement with the SM predictions and so far no significant devi-
ation
with respect to the SM expectations have been found [4–7].
As a result, any new degrees of freedom are expected to be well
separated from the SM particles in mass [8,9]. Due to the presence
of several beyond SM scenarios and in some cases similar experi-
mental
signatures, auseful way to search for new physics could be
done in a model independent way. In other words, the new physics
*
Corresponding author.
E-mail
address: mojtaba.mohammadi.najafabadi@cern.ch (M. Mohammadi
Najafabadi).
effects could show up in the effective field theory extension of the
SM which is composed of an infinite series of higher-dimensional
effective operators [10–15]. It is built based on the SM degrees
of freedom and its symmetries and it could be written by adding
new higher than four dimension operators to the Lagrangian of the
SM. The leading contribution of the SM effective Lagrangian comes
from the operators of dimension-six that is based on a complete
and non-redundant operator basis [16–18].
From
the phenomenological point of view, these operators can
affect not only the signal strengths but also the differential distri-
butions
and angular observables as they contain new vertex struc-
tures.
There are many effective operators that are contributing to
Higgs couplings which motivate us to look at all possible Higgs in-
volved
processes at the LHC. Studying all processes in which Higgs
boson is involved such as Higgs + jets production, Higgs associated
production, and processes where Higgs is off-shell is necessary to
provide information of all related new couplings. So far, there have
been many studies for exploring new physics effects in the Higgs
boson sector at the particle colliders in the context of SM effective
field theory [19–53].
At
the LHC, the Higgs production mostly proceeds through
gluon–gluon fusion, vector boson fusion (H + 2 jets) and associ-
ated
production with a Z or a W boson. Higgs boson could also be
produced associated with a pair of top or a single top quark with
production rates substantially less than the gluon–gluon fusion,
vector boson fusion and associated production [54]. In addition to
these processes, Higgs boson can be produced in association with a
http://dx.doi.org/10.1016/j.physletb.2017.09.005
0370-2693/
© 2017 The Author(s). 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
.