Physics Letters B 758 (2016) 219–225
Contents lists available at ScienceDirect
Physics Letters B
www.elsevier.com/locate/physletb
Probing compositeness with the CMS eejj & eej data
Tanumoy Mandal
a
, Subhadip Mitra
b
, Satyajit Seth
c,∗
a
Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden
b
Center for Computational Natural Sciences and Bioinformatics, International Institute of Information Technology, Hyderabad 500 032, India
c
PRISMA Cluster of Excellence, Institut für Physik, Johannes Gutenberg-Universität Mainz, 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
6 February 2016
Received
in revised form 3 May 2016
Accepted
7 May 2016
Available
online 11 May 2016
Editor:
G.F. Giudice
Keywords:
LHC
Compositeness
scale
Leptogluon
Exclusion
limits
Quark-lepton compositeness is a well-known beyond the Standard Model (SM) scenario with heavy exotic
particles like leptoquarks (LQs) and leptogluons (LGs) etc. These particles can couple to leptons and jets
simultaneously. In this letter, we use the recent CMS scalar LQ search data in the eejj and eej channels
to probe this scenario. We recast the data in terms of a color octet partner of the SM electron (or a first
generation spin-1/2 LG) that couples to an electron and a gluon via a dimension five operator suppressed
by the quark–lepton compositeness scale (). By combining different production processes of the color
octet electron (e
8
) at the LHC, we use the CMS 8TeV data to obtain a simultaneous bound on and the
mass of the e
8
(M
e
8
). We also study the reach of the 13 TeV LHC to discover the e
8
and interpret the
required luminosity in terms of M
e
8
and .
© 2016 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
The idea of quark–lepton compositeness [1–8] goes along with
our intention to describe nature in terms of its most fundamental
building blocks. As its name suggests, in the models with quark–
lepton
compositeness, the Standard Model (SM) fermions are not
elementary but rather have finer substructures. Similarities be-
tween
the SM lepton and quark sectors (like, both come with three
flavors and behave similarly under the SU(2)
L
× U (1)
Y
gauge sym-
metry
with the same weak coupling) can be explained if they are
assumed to be different bound states of some fundamental con-
stituents.
These fundamental constituents, called preons by Pati
and Salam [1], are charged under some new strong force which
confines them below a certain scale , known as the composite-
ness
scale.
As
we have hadrons in QCD, in this scenario one expects a
host of new exited preonic-condensates. Some of these conden-
sates
would be quite exotic, as they would carry both SU(3)
c
color
charges and lepton numbers, like the bosonic leptoquarks (LQs or
q
’s) that transform as triplets under SU(3)
c
[9–11] or the lep-
togluons
(LGs or
8
’s) that are color-octet fermions [12–17] etc.
Because of their color charges, if these exotic condensates have
TeV-range masses, they would be produced copiously at the Large
*
Corresponding author.
E-mail
addresses: tanumoy.mandal@physics.uu.se (T. Mandal),
subhadip.mitra@iiit.ac.in (S. Mitra), sseth@uni-mainz.de (S. Seth).
Hadron Collider (LHC) making it possible to probe this scenario ex-
perimentally.
The
LHC has already put some constraints on the masses of
scalar LQs decaying to SM quarks and leptons [18–21]. Of these,
we look at the most recent search by CMS, for the first and second
generations of scalar LQs in the jj and the ν
jj channels with
19.7 fb
−1
of integrated luminosity at the 8 TeV LHC [18]. With
pair production, the 95% confidence level (CL) exclusion limit on
the mass of the first (second) generation scalar LQ now stands at
M
q
= 1005 (1080) GeV assuming it always decays to an elec-
tron
(a muon) and a jet. (Note that unless specified otherwise,
we do not distinguish between any particle and its anti-particle.
Hence, an electron here could mean a positron as well.) In the first
generation search, mild excesses of events compared to the SM
background were observed in both the eejj and the eej channels
for M
q
∼ 650 GeV. Currently, these excesses have attracted consid-
erable
attention in the literature. CMS has also performed a dedi-
cated
search for the single productions of the first two generations
of LQs in the j channels [21]. However, unlike the mostly QCD
mediated pair production, the single productions depend strongly
on an unknown coupling λ, the
q
––q coupling. Hence, the exclu-
sion
limits from this search are λ dependent. For the first gener-
ation,
the exclusion limit goes from 895 GeV to 1730 GeV when
λ goes from 0.4 to 1.0 and for the second generation the data ex-
clude
M
q
below 530 GeV for λ = 1.0.
In
this letter, we recast the CMS 8 TeV ee jj [18] and ee j [21]
data
in terms of the first generation spin-1/2 LG carrying unit elec-
http://dx.doi.org/10.1016/j.physletb.2016.05.020
0370-2693/
© 2016 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
.