Physics Letters B 784 (2018) 223–228
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Cornering sgluons with four-top-quark events
Luc Darmé
a,∗
, Benjamin Fuks
b,c
, Mark Goodsell
b
a
National Centre for Nuclear Research, Ho ˙za 69, 00-681 Warsaw, Poland
b
Laboratoire de Physique Théorique et Hautes Energies (LPTHE), UMR 7589, Sorbonne Université et CNRS, 4 place Jussieu, 75252 Paris Cedex 05, France
c
Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France
a r t i c l e i n f o a b s t r a c t
Article history:
Received
12 June 2018
Received
in revised form 1 August 2018
Accepted
2 August 2018
Available
online 3 August 2018
Editor:
G.F. Giudice
The existence of colour-octet scalar states, often dubbed sgluons, is predicted in many extensions of
the Standard Model of particle physics, such as supersymmetric realisations featuring Dirac gauginos.
Such states have a large pair-production rate at hadron colliders and mainly decay into pairs of jets and
top quarks. Consequently, they represent a primary target for experimental searches for new resonances
in the multijet and multitop channels at the Large Hadron Collider. Adopting a phenomenologically-
motivated
simplified model, we reinterpret the results of a recent experimental search for the four-top-
quark
Standard Model signal, from which we constrain the sgluon mass to be larger than about 1.06 TeV.
We additionally consider how modifications of the existing four-top-quark studies could enhance our
ability to unravel the presence of scalar octets in data.
© 2018 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
.
1. Introduction
Since its discovery as the heaviest particle of the Standard
Model of particle physics, the top quark is considered as an at-
tractive
probe for new physics, in particular at the Large Hadron
Collider (LHC). In many theories extending the Standard Model,
top-quark production at the LHC is indeed expected to be en-
hanced
by contributions originating from the decay of new states
into one or more top quarks. Moreover, as the corresponding Stan-
dard
Model background is usually well understood, top-quark stud-
ies
consist of particularly clean targets for new physics searches,
especially when leptonic top decays are in order.
Whilst
most studies have so far solely focused on single-top and
top-quark pair production, the increased integrated luminosity and
centre-of-mass energy of the LHC Run 2 reinforce the potential role
of new physics probes exhibiting a higher top-quark multiplicity.
Among all interesting processes, there has been a growing experi-
mental
push in measuring the four-top production cross section at
the LHC. The most recent experimental measurement undertaken
by the CMS Collaboration [1],
σ
exp
4t
=16.9
+13.8
−11.4
fb, (1.1)
*
Corresponding author.
E-mail
addresses: luc.darme@ncbj.gov.pl (L. Darmé), fuks@lpthe.jussieu.fr
(B. Fuks),
goodsell@lpthe.jussieu.fr (M. Goodsell).
has been found to agree with the Standard Model expectation [2],
σ
SM
4t
=11.97
+2.15
−2.51
fb , (1.2)
where the latter results include next-to-leading order (NLO) cor-
rections
both in QCD and in the electroweak theory, and where
the error only accounts for scale uncertainties. The theoretical and
(still statistically-limited) experimental precision available today
nevertheless open bright prospects for advancing our knowledge
on new physics from four-top probes, as the room for a signif-
icant
beyond the Standard Model contribution starts to be more
and more reduced.
Many
new physics theories feature heavy coloured resonances
that essentially decay into a pair of top quarks, so that their
pair production could hence yield an enhancement of the four-
top
production cross section. Conversely, the current measurement
of the latter and its confrontation to theoretical predictions in
varied new physics setups could lead to constraints on the corre-
sponding
models. For instance, models with composite top quarks
have historically offered one of the theoretical motivations for
LHC searches in this channel [3–6] and led to early recasting re-
sults [7].
In this work, we focus instead on scenarios featuring
the presence of light scalar or pseudoscalar states lying in the
adjoint representation of the QCD gauge group. Such states are
commonly dubbed sgluons and for instance arise in non-minimal
supersymmetric models [8–18], vector-like confining theories [19]
and
extra-dimensional frameworks [20]. Among those models, the
https://doi.org/10.1016/j.physletb.2018.08.001
0370-2693/
© 2018 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
.