TOP-17-009

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TOP-17-009

# Search for standard model production of four top quarks with same-sign and
multilepton final states in proton-proton collisions at $\sqrt{s}=13\TeV$

###### Abstract

A search for standard model production of four top quarks ($\ttbar\ttbar$) is
reported using events containing at least three leptons ($\Pe,\Pgm$) or a
same-sign lepton pair. The events are produced in proton-proton collisions at
a center-of-mass energy of 13at the LHC, and the data sample, recorded in
2016, corresponds to an integrated luminosity of 35.9. Jet multiplicity and
flavor are used to enhance signal sensitivity, and dedicated control regions
are used to constrain the dominant backgrounds. The observed and expected
signal significances are, respectively, 1.6 and 1.0 standard deviations, and
the $\ttbar\ttbar$ cross section is measured to be $16.9^{+13.8}_{-11.4}$fb,
in agreement with next-to-leading-order standard model predictions. These
results are also used to constrain the Yukawa coupling between the top quark
and the Higgs boson to be less than 2.1 times its expected standard model
value at 95% confidence level.

##  0.1 Introduction

In the standard model (SM) the production of four top quarks ($\ttbar\ttbar$)
is a rare process, with representative leading-order (LO) Feynman diagrams
shown in Fig. 1. Many beyond-the-SM (BSM) theories predict an enhancement of
the $\ttbar\ttbar$ cross section, $\sigma(\Pp\Pp\to\ttbar\ttbar$), such as
gluino pair production in the supersymmetry framework [1, 2, 3, 4, 5, 6, 7, 8,
9, 10], the pair production of scalar gluons [11, 12], and the production of a
heavy pseudoscalar or scalar boson in association with a pair in Type II two-
Higgs-doublet models (2HDM) [13, 14, 15]. In addition, a top quark Yukawa
coupling larger than expected in the SM can lead to a significant increase in
$\ttbar\ttbar$ production via an off-shell SM Higgs boson [16]. The SM
prediction for $\sigma(\Pp\Pp\to\ttbar\ttbar$) at $\sqrt{s}=13\TeV$ is
$9.2^{+2.9}_{-2.4}$fb at next-to-leading order (NLO) [17]. An alternative
prediction of $12.2^{+5.0}_{-4.4}$fb is reported in Ref. [16], obtained from a
LO calculation of $9.6^{+3.9}_{-3.5}$fb and an NLO/LO $K$-factor of 1.27 based
on the $14\TeV$ calculation of Ref. [18].

Figure 1: Representative Feynman diagrams for $\ttbar\ttbar$ production at LO
in the SM.

After the decays of the top quarks, the final state contains several jets
resulting from the hadronization of light quarks and b quarks (b jets), and
may contain isolated leptons and missing transverse momentum depending on the
decays of the bosons [19]. Among these final states, the same-sign dilepton
and the three- (or more) lepton final states, considering $\ell=\Pe,\mu$,
correspond to branching fractions in $\ttbar\ttbar$ events of 8 and 1%,
respectively, excluding the small contribution from $\PW\rightarrow\tau\nu$,
which is included in selected events. However, due to the low level of
backgrounds, these channels are the most sensitive to $\ttbar\ttbar$
production in the regime with SM-like kinematic properties. The ATLAS and CMS
Collaborations at the CERN LHC have previously searched for SM $\ttbar\ttbar$
production in $\sqrt{s}=8$ and 13 collisions [20, 21, 22, 23, 24]. The most
sensitive of these results is a re-interpretation of the CMS same-sign
dilepton search for BSM physics at $13~{}$ [23], with an observed (expected)
$\ttbar\ttbar$ cross section upper limit (assuming no SM $\ttbar\ttbar$
signal) of 42 ($27^{+13}_{-8}$)fb at the 95% confidence level (CL).

The previous search is inclusive, exploring the final state with two same-sign
leptons and at least two jets, using an integrated luminosity of 35.9 [23].
The analysis described in this paper is based on the same data set and
improves on the previous search by optimizing the signal selection for
sensitivity to SM $\ttbar\ttbar$ production, by using an improved b jet
identification algorithm, and by employing background estimation techniques
that are adapted to take into account the higher jet and b jet multiplicity
requirements in the signal regions.

##  0.2 Background and signal simulation

Monte Carlo (MC) simulations at NLO are used to evaluate the $\ttbar\ttbar$
signal acceptance and to estimate the background from diboson (, ZZ,
$\PZ\Pgg$, $\PW^{\pm}\PW^{\pm}$) and triboson (, , $\PW\PZ\PZ$, $\PZ\PZ\PZ$,
$\PW\PW\Pgg$, $\PW\PZ\Pgg$) processes, as well as from production of single
top quarks ($\PQt\PZ\PQq$, $\PQt\Pgg$), or produced in association with a
boson ($\ttbar\PW$, $\ttbar\cPZ/\gamma^{*}$, $\ttbar\mbox{H}$). These samples
are generated using the NLO 2.2.2 [17] program with up to one additional
parton in the matrix-element calculation, except for $\PW^{\pm}\PW^{\pm}$
which is generated with up to two additional partons, and the , ZZ and
$\ttbar\mbox{H}$ samples, which are generated with no additional partons with
the powheg box v2 [25, 26] program. The $\ttbar\cPZ/\gamma^{*}$ sample with
$\PZ/\gamma^{*}\rightarrow\ell\ell$ is generated with a dilepton invariant
mass greater than $1\GeV$. The LO generator, scaled to NLO cross sections, is
used to estimate the $\PW\Pgg$ and $\ttbar\Pgg$ processes with up to three
additional partons. Other rare backgrounds, such as production in association
with dibosons ($\ttbar\PW\PW$, $\ttbar\PW\PZ$, $\ttbar\PZ\PZ$, $\ttbar\PW\PH$,
$\ttbar\PZ\PW$, $\ttbar\PH\PH$), triple top quark production ($\ttbar\PQt$,
$\ttbar\PQt\PW$), and $\PQt\PW\PZ$ are generated using LO without additional
partons, and scaled to NLO cross sections [27]. The NNPDF3.0LO (NNPDF3.0NLO)
[28] parton distribution functions (PDFs) are used to generate all LO (NLO)
samples. Parton showering and hadronization, as well as $\PW^{\pm}\PW^{\pm}$
from double-parton-scattering, are modeled by the 8.205 [29] program, while
the MLM [30] and FxFx [31] prescriptions are employed in matching additional
partons in the matrix-element calculations to parton showers in the LO and NLO
samples, respectively. The top quark mass in the generators is set to
$172.5\GeV$. The package [32] is used to model the response of the CMS
detector. Additional proton-proton interactions (pileup) within the same or
nearby bunch crossings are also included in the simulated events.

To improve the MC modeling of the multiplicity of additional jets from
initial-state radiation (ISR), simulated $\ttbar\PW$ and
$\ttbar\cPZ/\gamma^{*}$ events are reweighted based on the number of ISR jets
($N_{\text{jets}}^{\mathrm{ISR}}$). The reweighting is based on a comparison
of the light-flavor jet multiplicity in dilepton events in data and
simulation. The method requires exactly two jets identified as originating
from b quarks in dilepton events, and assumes that all other jets are from
ISR. Weighting factors are obtained as a function of
$N_{\text{jets}}^{\mathrm{ISR}}$ to bring data and MC into agreement. These
weights are then applied, keeping the total cross section constant, to
$\ttbar\PW$ and $\ttbar\cPZ/\gamma^{*}$ MC as a function of the number of jets
not originating from top quark, , or decays. To improve the modeling of the
flavor of additional jets, the simulation is also corrected to account for the
measured ratio of $\ttbar\bbbar/\ttbar\text{jj}$ cross sections reported in
Ref. [33]. More details on these corrections and their uncertainties are
provided in Section 0.6.

##  0.3  The CMS detector and event reconstruction

The central feature of the CMS detector is a superconducting solenoid of 6m
internal diameter, providing a magnetic field of 3.8T. Within the solenoid
volume are a silicon pixel and strip tracker, a lead tungstate crystal
electromagnetic calorimeter (ECAL), and a brass and scintillator hadron
calorimeter (HCAL), each composed of a barrel and two endcap sections. Forward
calorimeters extend the pseudorapidity ($\eta$) coverage provided by the
barrel and endcap detectors. Muons are measured in gas-ionization detectors
embedded in the steel flux-return yoke outside the solenoid. A more detailed
description of the CMS detector, together with a definition of the coordinate
system used and the relevant kinematic variables, can be found in Ref. [34].

Events of interest are selected using a two-tiered trigger system [35]. The
first level (L1), composed of custom hardware processors, uses information
from the calorimeters and muon detectors to select events at a rate of around
100kHz within a time interval of less than 4. The second level, known as the
high-level trigger (HLT), consists of a farm of processors running a version
of the full event reconstruction software optimized for fast processing, and
reduces the event rate to less than 1kHz before data storage.

Events are processed using the particle-flow (PF) algorithm [36], which
reconstructs and identifies each individual particle with an optimized
combination of information from the various elements of the CMS detector. The
energy of photons is directly obtained from the ECAL measurement. The energy
of electrons is determined from a combination of the electron momentum at the
primary interaction vertex as determined by the tracker, the energy of the
corresponding ECAL cluster, and the energy sum of all bremsstrahlung photons
spatially compatible with the electron track [37]. The momentum of muons is
obtained from the curvature of the corresponding track, combining information
from the silicon tracker and the muon system [38]. The energy of charged
hadrons is determined from a combination of their momentum measured in the
tracker and the matching ECAL and HCAL energy deposits, corrected for the
response function of the calorimeters to hadronic showers. The energy of
neutral hadrons is obtained from the corresponding corrected ECAL and HCAL
energies.

Hadronic jets are clustered from neutral PF candidates and charged PF
candidates associated with the primary vertex, using the anti-algorithm [39,
40] with a distance parameter of 0.4. The jet momentum is determined as the
vectorial sum of all PF candidate momenta in the jet. An offset correction is
applied to jet energies to take into account the contribution from pileup. Jet
energy corrections are derived from simulation, and are improved with in situ
measurements of the energy balance in dijet, multijet, +jet and leptonically
decaying Z+jet events [41, 42]. Additional selection criteria are applied to
each event to remove spurious jet-like features originating from isolated
noise patterns in certain HCAL regions. Jets originating from quarks are
identified as b-tagged jets using a deep neural network algorithm [43], with a
working point chosen such that the efficiency to identify a b jet is 55–70%
for a jet transverse momentum () between 20 and 400. The misidentification
rate for a light-flavor jet is 1–2% in the same jet range. The vector is
defined as the projection on the plane perpendicular to the beams of the
negative vector sum of the momenta of all reconstructed PF candidates in an
event [44]. Its magnitude, called missing transverse momentum, is referred to
as . The scalar sum of all jets in an event is referred to as .

##  0.4 Event selection and search strategy

The definitions of objects and the baseline event selection follow closely
those of Refs. [23, 45]. Electron identification is based on a multivariate
discriminant using shower shape and track quality variables, while for muons
it is based on the quality of the geometrical matching between the tracker and
muon system measurements. Isolation and impact parameter requirements are
applied to both lepton flavors, as well as specific selections designed to
improve the accuracy of the charge reconstruction. The combined reconstruction
and identification efficiency is in the range of 45–70% (70–90%) for electrons
(muons), increasing as a function of and converging to the maximum value for
$\pt>$ 60\. The number of leptons ($N_{\ell}$), the number of jets
($N_{\text{jets}}$), and the number of b-tagged jets ($N_{\text{b}}$) are
counted after the application of the basic kinematic requirements summarized
in Table 0.4.

Kinematic requirements for leptons and jets.  Object () $\abs{\eta}$ Electrons
$>$20 $<$2.5 Muons $>$20 $<$2.4 Jets $>$40 $<$2.4 b-tagged jets $>$25 $<$2.4

Signal events are selected using triggers that require two leptons with
$\pt>8\GeV$ and $\HT>300\GeV$. The trigger efficiency is greater than 95% for
di-electron ($\Pe\Pe$) and electron-muon ($\Pe\Pgm$) events and about 92% for
di-muon ($\Pgm\Pgm$) events. The baseline selections require $\HT>300\GeV$ and
$\ptmiss>50\GeV$, at least two jets ($N_{\text{jets}}\geq 2$), at least two
b-tagged jets ($N_{\text{b}}\geq 2$), a leading lepton with $\pt>25\GeV$, and
a second lepton of the same charge with $\pt>20\GeV$. To reduce the background
from Drell–Yan with a charge-misidentified electron, events with same-sign
electron pairs with mass below 12are rejected. Events where a third lepton
with larger than 5 (7)for muons (electrons) forms an opposite-sign (OS) same-
flavor pair with mass below 12or between 76 and 106are also rejected. If the
third lepton has $\pt>20\GeV$ and the invariant mass of the pair is between 76
and 106, these rejected events are used to populate a $\ttbar\cPZ$ background
control region (CRZ). The signal acceptance in the baseline region, including
the leptonic boson branching fraction, is approximately 1.5%. After these
requirements, we define eight mutually exclusive signal regions (SRs) and a
control region for the $\ttbar\PW$ background (CRW), based on
$N_{\text{jets}}$, $N_{\text{b}}$, and $N_{\ell}$, as detailed in Table 0.4.
The observed and predicted yields in the control and signal regions are used
to measure $\sigma(\Pp\Pp\to\ttbar\ttbar$), following the procedure described
in Sec. 0.7.

Definitions of the eight SRs and the two control regions for $\ttbar\PW$ (CRW)
and $\ttbar\cPZ$ (CRZ).  $N_{\ell}$ $N_{\text{b}}$ $N_{\text{jets}}$ Region 2
2 $\leq$5 CRW 6 SR1 7 SR2 $\geq$8 SR3 3 5, 6 SR4 $\geq$7 SR5 $\geq$4 $\geq$5
SR6 $\geq$3 2 $\geq$5 SR7 $\geq$3 $\geq$4 SR8 Inverted Z veto CRZ

##  0.5 Backgrounds

The main backgrounds to the $\ttbar\ttbar$ process in the same-sign dilepton
and three- (or more) lepton final states arise from rare multilepton
processes, such as $\ttbar\PW$, $\ttbar\cPZ/\gamma^{*}$, and $\ttbar\mbox{H}$
($\mathrm{H}\to\mathrm{WW}$), and single-lepton or OS dilepton processes with
an additional “nonprompt lepton”. Nonprompt leptons consist of electrons from
conversions of photons in jets and leptons from the decays of heavy- or light-
flavor hadrons. In this category we include also hadrons misidentified as
leptons. The minor background from OS dilepton events with a charge-
misidentified lepton is also taken into account.

Rare multilepton processes are estimated using simulated events. Control
regions are used to constrain the normalization of the $\ttbar\PW$ and
$\ttbar\cPZ$ backgrounds, as described in Section 0.7, while for other
processes the normalization is based on the NLO cross sections referenced in
Section 0.2. Processes such as the associated production of a pair with a pair
of bosons ($\PW$, $\PZ$, ) are grouped into a “$\ttbar\mathrm{VV}$” category.
Associated photon production processes such as $\PW\Pgg$, $\PZ\Pgg$,
$\ttbar\Pgg$, and $\PQt\Pgg$, where an electron is produced in an unidentified
photon conversion, are grouped into a “X” category. All residual processes
with very small contributions, including diboson (, ZZ, $\PW^{\pm}\PW^{\pm}$
from single- and double-parton scattering), triboson (, , $\PW\PZ\PZ$,
$\PZ\PZ\PZ$, $\PW\PW\Pgg$, $\PW\PZ\Pgg$), and rare single top quark
($\PQt\PZ\PQq$, $\PQt\PW\PZ$) and triple top quark processes ($\ttbar\PQt$ and
$\ttbar\PQt\PW$), are grouped into a “Rare” category.

The nonprompt lepton and charge-misidentified lepton backgrounds are estimated
following the methods described in Ref. [23]. For nonprompt leptons, an
estimate referred to as the “tight-to-loose” method defines two control
regions by modifying the lepton identification (including isolation) and event
kinematic requirements, respectively. An “application region” is defined for
every SR by requiring at least one lepton to fail the standard identification
(“tight”) while satisfying a more relaxed one (“loose”). To obtain the
nonprompt lepton background estimate in the corresponding SR, the event yield
in each application region is weighted by a factor of
$\epsilon_{\mathrm{TL}}/(1-\epsilon_{\mathrm{TL}})$ for each lepton failing
the tight requirement. The $\epsilon_{\mathrm{TL}}$ parameter is the
probability that a nonprompt lepton that satisfies a loose lepton selection
also satisfies the tight selection. It is extracted as a function of lepton
flavor and kinematic properties from a “measurement region” that consists of a
single-lepton events with event kinematic properties designed to suppress the
$\PW\to\ell\nu$ contribution.

For charge-misidentified leptons, an OS dilepton control region is defined for
each same-sign dilepton signal region. Its yield is then weighted by the
charge misidentification probability estimated in simulation, which ranges
between $10^{-5}$ and $10^{-3}$ for electrons and is negligible for muons.

##  0.6 Systematic uncertainties

The sources of experimental and theoretical uncertainty for the data and
simulations are summarized in Table 0.6. The uncertainty in the integrated
luminosity is 2.5% [46]. The simulation is reweighted to match the
distribution in the number of pileup collisions per event in data. The
uncertainty in the inelastic cross section propagated to the final yields
provides an uncertainty of at most 6%.

Trigger efficiencies are measured with an uncertainty of 2% in an independent
data sample selected using single-lepton triggers. Lepton-efficiency scale
factors, used to account for differences in the reconstruction and
identification efficiencies between data and simulation, are measured using a
“tag-and-probe” method in data enriched in $\PZ\to\ell\ell$ events [37, 38].
The scale factors are applied to all simulated processes with an uncertainty
per lepton of approximately 3% for muons and 4% for electrons.

The uncertainty in the calibration of the jet energy scale depends on the and
$\eta$ of the jet and results in a 1–15% variation in the event yield in a
given SR. The uncertainty due to the jet energy resolution is estimated by
broadening the resolution in simulation [42], and the resulting effect is a
change of 1–5% in the SR yields. The b tagging efficiency in simulation is
corrected using scale factors determined from efficiencies measured in data
and simulation [47]. The uncertainty in the measured scale factors results in
an overall effect between 1 and 15%, again depending on the SR.

As mentioned in Section 0.2, $\ttbar\PW$ and $\ttbar\cPZ/\gamma^{*}$ simulated
events are reweighted to match the number of additional jets observed in data.
The reweighting factors vary between 0.92 for
$N_{\text{jets}}^{\mathrm{ISR}}=1$ and 0.77 for
$N_{\text{jets}}^{\mathrm{ISR}}\geq 4$. Half of the difference from unity is
taken as a systematic uncertainty in these reweighting factors to cover
differences observed between data and simulation when the factors are used to
reweight simulation in a control sample enriched in single-lepton events.
Uncertainties in the reweighting factors are treated as correlated among
regions. Simulated $\ttbar\PW$ and $\ttbar\cPZ/\gamma^{*}$ events with two b
quarks not originating from top quark decay are also weighted to account for
the CMS measurement of the ratio of cross sections
$\sigma({\ttbar\bbbar})/\sigma({\ttbar\mathrm{jj}})$, which was found to be a
factor of $1.7\pm 0.6$ larger than the MC prediction [33]. In signal regions
requiring four b-tagged jets, where the effect is dominant, this results in a
systematic uncertainty of up to 15% on the total background prediction. In
signal regions requiring three b-tagged jets, the dominant origin of the
additional b-tagged jet is a charm quark from a decay, so the effect is
negligible.

Uncertainties in the renormalization and factorization scales (varied by a
factor of two) and from the choice of PDF [48, 49] affect the number of events
expected (normalization) in the simulated background processes, as well as the
acceptance for the $\ttbar\ttbar$ signal. The effects of these uncertainties
on the relative distribution of events in the signal regions (shape) are also
considered. For the $\ttbar\PW$ and $\ttbar\cPZ/\gamma^{*}$ backgrounds, the
normalization uncertainty is 40%, while for $\ttbar\mbox{H}$ a 50%
normalization uncertainty reflects the signal strength of $1.5\pm 0.5$
measured by CMS [50]. The processes in the Rare category along with X and
$\ttbar\mathrm{VV}$, many of which have never been observed, are expected to
give small contributions to the event yields in the signal regions. We assign
separate 50% normalization uncertainties to each of these three categories.
The shape uncertainty resulting from variations of the renormalization and
factorization scales is as large as 15% for the $\ttbar\PW$,
$\ttbar\cPZ/\gamma^{*}$, and $\ttbar\mbox{H}$ backgrounds, and 10% for the
$\ttbar\ttbar$ signal, while the effect from the PDF is only 1%. For the
signal, the uncertainty in the acceptance from variations of the scales (PDFs)
is 2% (1%). In addition, for the $\ttbar\ttbar$ signal, the scales that
determine ISR and final-state radiation (FSR) in the parton shower are also
varied, resulting in a 6% change in the acceptance and shape variations as
large as 15%.

For nonprompt and charge-misidentified lepton backgrounds, the statistical
uncertainty from the application region depends on the SR considered. The
background from misidentified charge is assigned a systematic uncertainty of
20%, based on comparisons of the expected number of same-sign events estimated
from an OS control sample and the observed same-sign yield in a control sample
enriched in $\PZ\to\Pep\Pem$ events with one electron or positron having a
misidentified charge.

In addition to the statistical uncertainty, the nonprompt lepton background is
assigned an overall normalization uncertainty of 30% to cover variations
observed in closure tests performed with simulated multijet and events. This
uncertainty is increased to 60% for electrons with $\pt>50\GeV$, to account
for trends observed at high in the closure tests. We also include an
uncertainty related to the subtraction of events with prompt leptons (from
electroweak processes with a or boson) in the measurement region, which has an
effect between 1% and 50%, depending on the SR. The prompt lepton
contamination was also checked in the application region, where it was found
to be below 1%.

Experimental uncertainties are treated as correlated among signal regions for
all signal and background processes. Systematic uncertainties in data-driven
estimates and theoretical uncertainties are treated as uncorrelated between
processes, but correlated among signal regions. Statistical uncertainties from
the limited number of simulated events or in the number of events in data
control regions are considered uncorrelated.

Summary of the sources of uncertainty and their effect on signal and
background yields. The first group lists experimental and theoretical
uncertainties in simulated signal and background processes. The second group
lists normalization uncertainties in the estimated backgrounds.  Source
Uncertainty (%) Integrated luminosity 2.5 Pileup 0–6 Trigger efficiency 2
Lepton selection 4–10 Jet energy scale 1–15 Jet energy resolution 1–5 $\cPqb$
tagging 1–15 Size of simulated sample 1–10 Scale and PDF variations 10–15
ISR/FSR (signal) 5–15 $\ttbar\PH$ (normalization) 50 Rare, X,
$\ttbar\mathrm{VV}$ (norm.) 50 $\ttbar\cPZ/\gamma^{*}$, $\ttbar\PW$
(normalization) 40 Charge misidentification 20 Nonprompt leptons 30–60

##  0.7 Results and interpretation

The properties of events in the signal regions (SR 1–8 as defined in Table
0.4) are shown in Fig. 2, where distributions of the main kinematic variables
in the data ($N_{\text{jets}}$, $N_{\text{b}}$, , and ) are compared to SM
background predictions. The $N_{\text{jets}}$ and $N_{\text{b}}$ distributions
for CRW and CRZ are shown in Fig. 3. In both figures we overlay the expected
SM $\ttbar\ttbar$ signal, scaled by a factor of 5. The SM predictions are
generally consistent with the observations, with some possible underestimation
in CRW and CRZ.

The yields from SR 1–8, CRW, and CRZ are combined in a maximum-likelihood fit,
following the procedures described in Ref. [51], to estimate a best-fit cross
section for $\ttbar\ttbar$, the significance of the observation relative to
the background-only hypothesis, and the upper limit on
$\sigma(\Pp\Pp\to\ttbar\ttbar$). The experimental and theoretical
uncertainties described in Section 0.6 are incorporated in the likelihood as
“nuisance” parameters and are profiled in the fit. Nuisance parameters
corresponding to systematic uncertainties are parameterized as log-normal
distributions. The fitted values of the nuisance parameters are found to be
consistent with their initial values within uncertainties. The nuisance
parameters corresponding to the $\ttbar\PW$ and $\ttbar\cPZ/\gamma^{*}$
normalizations are scaled by $1.2\pm 0.3$ and $1.3\pm 0.3$, respectively,
while other background contributions including $\ttbar\mbox{H}$ are scaled up
by $1.1$ or less. The signal and control region results after the maximum-
likelihood fit (post-fit) are shown in Fig. 4, with the fitted $\ttbar\ttbar$
signal contribution added to the background predictions, which are given in
Table 0.7. The $\ttbar\ttbar$ cross section is measured to be
$16.9^{+13.8}_{-11.4}$fb, where the best-fit value of the parameter and an
approximate 68% CL confidence interval are extracted following the procedure
described in Sec. 3.2 of Ref. [52]. The observed and expected significances
relative to the background-only hypothesis are found to be 1.6 and 1.0
standard deviations, respectively, where the expectation is based on the
central value of the NLO SM cross section of $9.2^{+2.9}_{-2.4}$fb [17]. The
observed 95% CL upper limit on the cross section, based on an asymptotic
formulation [53] of the modified frequentist CLs criterion [54, 55], is found
to be 41.7fb. The corresponding expected upper limit, assuming no SM
$\ttbar\ttbar$ contribution to the data, is $20.8^{+11.2}_{-6.9}$fb, showing a
significant improvement relative to the value of 27fb of Ref. [23].

The $\Pp\Pp\to\ttbar\ttbar$ process has contributions from diagrams with
virtual Higgs bosons, as shown in Fig. 1. Experimental information on
$\sigma(\Pp\Pp\to\ttbar\ttbar$) can therefore be used to constrain the Yukawa
coupling, $y_{\PQt}$, between the top quark and the Higgs boson. We constrain
$y_{\PQt}$ assuming that the signal acceptance is not affected by the relative
contribution of the virtual Higgs boson diagrams. As the cross section for the
$\ttbar\mbox{H}$ background also depends on the top quark Yukawa coupling, for
the purpose of constraining $y_{\PQt}$ the fit described above is repeated
with the $\ttbar\mbox{H}$ contribution scaled by the square of the absolute
value of the ratio of the top quark Yukawa coupling to its SM value
($\abs{y_{\PQt}/y_{\PQt}^{\mathrm{SM}}}^{2}$), where
$y_{\PQt}^{\mathrm{SM}}=m_{\PQt}(\sqrt{2}G_{\mathrm{F}})^{1/2}\approx 1$. This
results in a dependence of the measured $\sigma(\Pp\Pp\to\ttbar\ttbar$) on
$\abs{y_{\PQt}/y_{\PQt}^{\mathrm{SM}}}$ which is shown in Fig. 5 and is
compared to its theoretical prediction. The prediction is obtained from the LO
calculation of Ref. [16], with an NLO/LO $K$-factor of 1.27 [18]. The LO
calculation is used instead of the NLO one, as Ref. [16] provides a breakdown
of the contributions to the cross section according to powers of $y_{\PQt}$.
The prediction also includes the uncertainty associated with varying the
renormalization and factorization scales in the LO calculation by a factor of
2. The central, upper and lower values of the theoretical cross section
provide respective 95% CL limits for
$\abs{y_{\PQt}/y_{\PQt}^{\mathrm{SM}}}<2.1$, $<$1.9 and $<$2.4.

Figure 2: Distributions in $N_{\text{jets}}$ (upper left), $N_{\text{b}}$
(upper right), (lower left), and (lower right) in the signal regions (SR 1–8),
before fitting to data, where the last bins include the overflows. The hatched
areas represent the total uncertainties in the SM background predictions,
while the solid lines represent the $\ttbar\ttbar$ signal, scaled up by a
factor of 5, assuming the SM cross section from Ref. [17]. The upper panels
show the ratios of the observed event yield to the total background
prediction. Bins without a data point have no observed events.

Figure 3: Distributions in $N_{\text{jets}}$ and $N_{\text{b}}$ in $\ttbar\PW$
(upper) and $\ttbar\cPZ$ (lower) control regions, before fitting to data. The
hatched area represents the uncertainty in the SM background prediction, while
the solid line represents the $\ttbar\ttbar$ signal, scaled up by a factor of
5, assuming the SM cross section from Ref. [17]. The upper panels show the
ratios of the observed event yield to the total background prediction. Bins
without a data point have no observed events.

Figure 4: Observed yields in the control and signal regions (left, in log
scale), and signal regions only (right, in linear scale), compared to the
post-fit predictions for signal and background processes. The hatched areas
represent the total uncertainties in the signal and background predictions.
The upper panels show the ratios of the observed event yield and the total
prediction of signal and background. Bins without a data point have no
observed events.

The post-fit background, signal, and total yields with their total
uncertainties and the observed number of events in the control and signal
regions in data.  SM background $\ttbar\ttbar$ Total Observed CRZ 31.7 $\pm$
4.6 0.4 $\pm$ 0.3 32.1 $\pm$ 4.6 35 CRW 83.7 $\pm$ 8.8 1.9 $\pm$ 1.2 85.6
$\pm$ 8.6 86 SR1 7.7 $\pm$ 1.2 0.9 $\pm$ 0.6 8.6 $\pm$ 1.2 7 SR2 2.6 $\pm$ 0.5
0.6 $\pm$ 0.4 3.2 $\pm$ 0.6 4 SR3 0.5 $\pm$ 0.3 0.4 $\pm$ 0.2 0.8 $\pm$ 0.4 1
SR4 4.0 $\pm$ 0.7 1.4 $\pm$ 0.9 5.4 $\pm$ 0.9 8 SR5 0.7 $\pm$ 0.2 0.9 $\pm$
0.6 1.6 $\pm$ 0.6 2 SR6 0.7 $\pm$ 0.2 1.0 $\pm$ 0.6 1.7 $\pm$ 0.6 0 SR7 2.3
$\pm$ 0.5 0.6 $\pm$ 0.4 2.9 $\pm$ 0.6 1 SR8 1.2 $\pm$ 0.3 0.9 $\pm$ 0.6 2.1
$\pm$ 0.6 2

Figure 5: The predicted SM value of $\sigma(\Pp\Pp\to\ttbar\ttbar$) [16],
calculated at LO with an NLO/LO $K$-factor of 1.27, as a function of
$\abs{y_{\PQt}/y_{\PQt}^{\mathrm{SM}}}$ (dashed line), compared with the
observed value of $\sigma(\Pp\Pp\to\ttbar\ttbar$) (solid line), and with the
observed 95% CL upper limit (hatched line).

##  0.8 Summary

The results of a search for standard model (SM) production of $\ttbar\ttbar$
at the LHC have been presented, using data from $\sqrt{s}=13\TeV$ proton-
proton collisions corresponding to an integrated luminosity of 35.9, collected
with the CMS detector in 2016. The analysis strategy uses same-sign dilepton
as well as three- (or more) lepton events, relying on jet multiplicity and jet
flavor to define search regions that are used to probe the $\ttbar\ttbar$
process. Combining these regions yields a significance of 1.6 standard
deviations relative to the background-only hypothesis, and a measured value
for the $\ttbar\ttbar$ cross section of $16.9^{+13.8}_{-11.4}$fb, in agreement
with the standard model predictions. The results are also re-interpreted to
constrain the ratio of the top quark Yukawa coupling to its SM value, yielding
$\abs{y_{\PQt}/y_{\PQt}^{\mathrm{SM}}}<2.1$ at 95% confidence level.

###### Acknowledgements.

We thank Qing-Hong Cao, Shao-Long Chen, and Yandong Liu for providing
calculations used in determining a constraint on the top quark Yukawa
coupling. We congratulate our colleagues in the CERN accelerator departments
for the excellent performance of the LHC and thank the technical and
administrative staffs at CERN and at other CMS institutes for their
contributions to the success of the CMS effort. In addition, we gratefully
acknowledge the computing centers and personnel of the Worldwide LHC Computing
Grid for delivering so effectively the computing infrastructure essential to
our analyses. Finally, we acknowledge the enduring support for the
construction and operation of the LHC and the CMS detector provided by the
following funding agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium);
CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and
NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus);
SENESCYT (Ecuador); MoER, ERC IUT, and ERDF (Estonia); Academy of Finland,
MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF
(Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM
(Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS
(Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and
UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC
(Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS, RFBR and RAEP
(Russia); MESTD (Serbia); SEIDI, CPAN, PCTI and FEDER (Spain); Swiss Funding
Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA
(Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United
Kingdom); DOE and NSF (USA). Individuals have received support from the Marie-
Curie program and the European Research Council and Horizon 2020 Grant,
contract No. 675440 (European Union); the Leventis Foundation; the A. P. Sloan
Foundation; the Alexander von Humboldt Foundation; the Belgian Federal Science
Policy Office; the Fonds pour la Formation à la Recherche dans l’Industrie et
dans l’Agriculture (FRIA-Belgium); the Agentschap voor Innovatie door
Wetenschap en Technologie (IWT-Belgium); the Ministry of Education, Youth and
Sports (MEYS) of the Czech Republic; the Council of Science and Industrial
Research, India; the HOMING PLUS program of the Foundation for Polish Science,
cofinanced from European Union, Regional Development Fund, the Mobility Plus
program of the Ministry of Science and Higher Education, the National Science
Center (Poland), contracts Harmonia 2014/14/M/ST2/00428, Opus
2014/13/B/ST2/02543, 2014/15/B/ST2/03998, and 2015/19/B/ST2/02861, Sonata-bis
2012/07/E/ST2/01406; the National Priorities Research Program by Qatar
National Research Fund; the Programa Severo Ochoa del Principado de Asturias;
the Thalis and Aristeia programs cofinanced by EU-ESF and the Greek NSRF; the
Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chulalongkorn University
and the Chulalongkorn Academic into Its 2nd Century Project Advancement
Project (Thailand); the Welch Foundation, contract C-1845; and the Weston
Havens Foundation (USA).

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##  .9 The CMS Collaboration

Yerevan Physics Institute, Yerevan, Armenia
A.M. Sirunyan, A. Tumasyan Institut für Hochenergiephysik, Wien, Austria
W. Adam, F. Ambrogi, E. Asilar, T. Bergauer, J. Brandstetter, E. Brondolin, M.
Dragicevic, J. Erö, A. Escalante Del Valle, M. Flechl, M. Friedl, R.
Frühwirth1, V.M. Ghete, J. Grossmann, J. Hrubec, M. Jeitler1, A. König, N.
Krammer, I. Krätschmer, D. Liko, T. Madlener, I. Mikulec, E. Pree, N. Rad, H.
Rohringer, J. Schieck1, R. Schöfbeck, M. Spanring, D. Spitzbart, A. Taurok, W.
Waltenberger, J. Wittmann, C.-E. Wulz1, M. Zarucki Institute for Nuclear
Problems, Minsk, Belarus
V. Chekhovsky, V. Mossolov, J. Suarez Gonzalez Universiteit Antwerpen,
Antwerpen, Belgium
E.A. De Wolf, D. Di Croce, X. Janssen, J. Lauwers, M. Van De Klundert, H. Van
Haevermaet, P. Van Mechelen, N. Van Remortel Vrije Universiteit Brussel,
Brussel, Belgium
S. Abu Zeid, F. Blekman, J. D’Hondt, I. De Bruyn, J. De Clercq, K. Deroover,
G. Flouris, D. Lontkovskyi, S. Lowette, I. Marchesini, S. Moortgat, L.
Moreels, Q. Python, K. Skovpen, S. Tavernier, W. Van Doninck, P. Van Mulders,
I. Van Parijs Université Libre de Bruxelles, Bruxelles, Belgium
D. Beghin, B. Bilin, H. Brun, B. Clerbaux, G. De Lentdecker, H. Delannoy, B.
Dorney, G. Fasanella, L. Favart, R. Goldouzian, A. Grebenyuk, A.K. Kalsi, T.
Lenzi, J. Luetic, T. Maerschalk, A. Marinov, T. Seva, E. Starling, C. Vander
Velde, P. Vanlaer, D. Vannerom, R. Yonamine, F. Zenoni Ghent University,
Ghent, Belgium
T. Cornelis, D. Dobur, A. Fagot, M. Gul, I. Khvastunov2, D. Poyraz, C. Roskas,
S. Salva, D. Trocino, M. Tytgat, W. Verbeke, N. Zaganidis Université
Catholique de Louvain, Louvain-la-Neuve, Belgium
H. Bakhshiansohi, O. Bondu, S. Brochet, G. Bruno, C. Caputo, A. Caudron, P.
David, S. De Visscher, C. Delaere, M. Delcourt, B. Francois, A. Giammanco, M.
Komm, G. Krintiras, V. Lemaitre, A. Magitteri, A. Mertens, M. Musich, K.
Piotrzkowski, L. Quertenmont, A. Saggio, M. Vidal Marono, S. Wertz, J. Zobec
Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brazil
W.L. Aldá Júnior, F.L. Alves, G.A. Alves, L. Brito, G. Correia Silva, C.
Hensel, A. Moraes, M.E. Pol, P. Rebello Teles Universidade do Estado do Rio de
Janeiro, Rio de Janeiro, Brazil
E. Belchior Batista Das Chagas, W. Carvalho, J. Chinellato3, E. Coelho, E.M.
Da Costa, G.G. Da Silveira4, D. De Jesus Damiao, S. Fonseca De Souza, L.M.
Huertas Guativa, H. Malbouisson, M. Melo De Almeida, C. Mora Herrera, L.
Mundim, H. Nogima, L.J. Sanchez Rosas, A. Santoro, A. Sznajder, M. Thiel, E.J.
Tonelli Manganote3, F. Torres Da Silva De Araujo, A. Vilela Pereira
Universidade Estadual Paulista a, Universidade Federal do ABC b, São Paulo,
Brazil
S. Ahujaa, C.A. Bernardesa, T.R. Fernandez Perez Tomeia, E.M. Gregoresb, P.G.
Mercadanteb, S.F. Novaesa, Sandra S. Padulaa, D. Romero Abadb, J.C. Ruiz
Vargasa Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy
of Sciences, Sofia, Bulgaria
A. Aleksandrov, R. Hadjiiska, P. Iaydjiev, M. Misheva, M. Rodozov, M. Shopova,
G. Sultanov University of Sofia, Sofia, Bulgaria
A. Dimitrov, L. Litov, B. Pavlov, P. Petkov Beihang University, Beijing, China
W. Fang5, X. Gao5, L. Yuan Institute of High Energy Physics, Beijing, China
M. Ahmad, J.G. Bian, G.M. Chen, H.S. Chen, M. Chen, Y. Chen, C.H. Jiang, D.
Leggat, H. Liao, Z. Liu, F. Romeo, S.M. Shaheen, A. Spiezia, J. Tao, C. Wang,
Z. Wang, E. Yazgan, T. Yu, H. Zhang, J. Zhao State Key Laboratory of Nuclear
Physics and Technology, Peking University, Beijing, China
Y. Ban, G. Chen, J. Li, Q. Li, S. Liu, Y. Mao, S.J. Qian, D. Wang, Z. Xu, F.
Zhang5 Tsinghua University, Beijing, China
Y. Wang Universidad de Los Andes, Bogota, Colombia
C. Avila, A. Cabrera, L.F. Chaparro Sierra, C. Florez, C.F. González
Hernández, J.D. Ruiz Alvarez, M.A. Segura Delgado University of Split, Faculty
of Electrical Engineering, Mechanical Engineering and Naval Architecture,
Split, Croatia
B. Courbon, N. Godinovic, D. Lelas, I. Puljak, P.M. Ribeiro Cipriano, T.
Sculac University of Split, Faculty of Science, Split, Croatia
Z. Antunovic, M. Kovac Institute Rudjer Boskovic, Zagreb, Croatia
V. Brigljevic, D. Ferencek, K. Kadija, B. Mesic, A. Starodumov6, T. Susa
University of Cyprus, Nicosia, Cyprus
M.W. Ather, A. Attikis, G. Mavromanolakis, J. Mousa, C. Nicolaou, F. Ptochos,
P.A. Razis, H. Rykaczewski Charles University, Prague, Czech Republic
M. Finger7, M. Finger Jr.7 Universidad San Francisco de Quito, Quito, Ecuador
E. Carrera Jarrin Academy of Scientific Research and Technology of the Arab
Republic of Egypt, Egyptian Network of High Energy Physics, Cairo, Egypt
Y. Assran8,9, S. Elgammal9, A. Mahrous10 National Institute of Chemical
Physics and Biophysics, Tallinn, Estonia
S. Bhowmik, R.K. Dewanjee, M. Kadastik, L. Perrini, M. Raidal, A. Tiko, C.
Veelken Department of Physics, University of Helsinki, Helsinki, Finland
P. Eerola, H. Kirschenmann, J. Pekkanen, M. Voutilainen Helsinki Institute of
Physics, Helsinki, Finland
J. Havukainen, J.K. Heikkilä, T. Järvinen, V. Karimäki, R. Kinnunen, T.
Lampén, K. Lassila-Perini, S. Laurila, S. Lehti, T. Lindén, P. Luukka, T.
Mäenpää, H. Siikonen, E. Tuominen, J. Tuominiemi Lappeenranta University of
Technology, Lappeenranta, Finland
T. Tuuva IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France
M. Besancon, F. Couderc, M. Dejardin, D. Denegri, J.L. Faure, F. Ferri, S.
Ganjour, S. Ghosh, A. Givernaud, P. Gras, G. Hamel de Monchenault, P. Jarry,
I. Kucher, C. Leloup, E. Locci, M. Machet, J. Malcles, G. Negro, J. Rander, A.
Rosowsky, M.Ö. Sahin, M. Titov Laboratoire Leprince-Ringuet, Ecole
polytechnique, CNRS/IN2P3, Université Paris-Saclay, Palaiseau, France
A. Abdulsalam11, C. Amendola, I. Antropov, S. Baffioni, F. Beaudette, P.
Busson, L. Cadamuro, C. Charlot, R. Granier de Cassagnac, M. Jo, S. Lisniak,
A. Lobanov, J. Martin Blanco, M. Nguyen, C. Ochando, G. Ortona, P. Paganini,
P. Pigard, R. Salerno, J.B. Sauvan, Y. Sirois, A.G. Stahl Leiton, T. Strebler,
Y. Yilmaz, A. Zabi, A. Zghiche Université de Strasbourg, CNRS, IPHC UMR 7178,
F-67000 Strasbourg, France
J.-L. Agram12, J. Andrea, D. Bloch, J.-M. Brom, M. Buttignol, E.C. Chabert, N.
Chanon, C. Collard, E. Conte12, X. Coubez, F. Drouhin12, J.-C. Fontaine12, D.
Gelé, U. Goerlach, M. Jansová, P. Juillot, A.-C. Le Bihan, N. Tonon, P. Van
Hove Centre de Calcul de l’Institut National de Physique Nucleaire et de
Physique des Particules, CNRS/IN2P3, Villeurbanne, France
S. Gadrat Université de Lyon, Université Claude Bernard Lyon 1, CNRS-IN2P3,
Institut de Physique Nucléaire de Lyon, Villeurbanne, France
S. Beauceron, C. Bernet, G. Boudoul, R. Chierici, D. Contardo, P. Depasse, H.
El Mamouni, J. Fay, L. Finco, S. Gascon, M. Gouzevitch, G. Grenier, B. Ille,
F. Lagarde, I.B. Laktineh, M. Lethuillier, L. Mirabito, A.L. Pequegnot, S.
Perries, A. Popov13, V. Sordini, M. Vander Donckt, S. Viret, S. Zhang Georgian
Technical University, Tbilisi, Georgia
A. Khvedelidze7 Tbilisi State University, Tbilisi, Georgia
I. Bagaturia14 RWTH Aachen University, I. Physikalisches Institut, Aachen,
Germany
C. Autermann, L. Feld, M.K. Kiesel, K. Klein, M. Lipinski, M. Preuten, C.
Schomakers, J. Schulz, M. Teroerde, B. Wittmer, V. Zhukov13 RWTH Aachen
University, III. Physikalisches Institut A, Aachen, Germany
A. Albert, D. Duchardt, M. Endres, M. Erdmann, S. Erdweg, T. Esch, R. Fischer,
A. Güth, T. Hebbeker, C. Heidemann, K. Hoepfner, S. Knutzen, M. Merschmeyer,
A. Meyer, P. Millet, S. Mukherjee, T. Pook, M. Radziej, H. Reithler, M.
Rieger, F. Scheuch, D. Teyssier, S. Thüer RWTH Aachen University, III.
Physikalisches Institut B, Aachen, Germany
G. Flügge, B. Kargoll, T. Kress, A. Künsken, T. Müller, A. Nehrkorn, A.
Nowack, C. Pistone, O. Pooth, A. Stahl15 Deutsches Elektronen-Synchrotron,
Hamburg, Germany
M. Aldaya Martin, T. Arndt, C. Asawatangtrakuldee, K. Beernaert, O. Behnke, U.
Behrens, A. Bermúdez Martínez, A.A. Bin Anuar, K. Borras16, V. Botta, A.
Campbell, P. Connor, C. Contreras-Campana, F. Costanza, C. Diez Pardos, G.
Eckerlin, D. Eckstein, T. Eichhorn, E. Eren, E. Gallo17, J. Garay Garcia, A.
Geiser, J.M. Grados Luyando, A. Grohsjean, P. Gunnellini, M. Guthoff, A. Harb,
J. Hauk, M. Hempel18, H. Jung, M. Kasemann, J. Keaveney, C. Kleinwort, I.
Korol, D. Krücker, W. Lange, A. Lelek, T. Lenz, J. Leonard, K. Lipka, W.
Lohmann18, R. Mankel, I.-A. Melzer-Pellmann, A.B. Meyer, M. Missiroli, G.
Mittag, J. Mnich, A. Mussgiller, E. Ntomari, D. Pitzl, A. Raspereza, M.
Savitskyi, P. Saxena, R. Shevchenko, N. Stefaniuk, G.P. Van Onsem, R. Walsh,
Y. Wen, K. Wichmann, C. Wissing, O. Zenaiev University of Hamburg, Hamburg,
Germany
R. Aggleton, S. Bein, V. Blobel, M. Centis Vignali, T. Dreyer, E. Garutti, D.
Gonzalez, J. Haller, A. Hinzmann, M. Hoffmann, A. Karavdina, R. Klanner, R.
Kogler, N. Kovalchuk, S. Kurz, T. Lapsien, D. Marconi, M. Meyer, M. Niedziela,
D. Nowatschin, F. Pantaleo15, T. Peiffer, A. Perieanu, C. Scharf, P. Schleper,
A. Schmidt, S. Schumann, J. Schwandt, J. Sonneveld, H. Stadie, G. Steinbrück,
F.M. Stober, M. Stöver, H. Tholen, D. Troendle, E. Usai, A. Vanhoefer, B.
Vormwald Institut für Experimentelle Kernphysik, Karlsruhe, Germany
M. Akbiyik, C. Barth, M. Baselga, S. Baur, E. Butz, R. Caspart, T. Chwalek, F.
Colombo, W. De Boer, A. Dierlamm, N. Faltermann, B. Freund, R. Friese, M.
Giffels, M.A. Harrendorf, F. Hartmann15, S.M. Heindl, U. Husemann, F.
Kassel15, S. Kudella, H. Mildner, M.U. Mozer, Th. Müller, M. Plagge, G. Quast,
K. Rabbertz, M. Schröder, I. Shvetsov, G. Sieber, H.J. Simonis, R. Ulrich, S.
Wayand, M. Weber, T. Weiler, S. Williamson, C. Wöhrmann, R. Wolf Institute of
Nuclear and Particle Physics (INPP), NCSR Demokritos, Aghia Paraskevi, Greece
G. Anagnostou, G. Daskalakis, T. Geralis, A. Kyriakis, D. Loukas, I. Topsis-
Giotis National and Kapodistrian University of Athens, Athens, Greece
G. Karathanasis, S. Kesisoglou, A. Panagiotou, N. Saoulidou, E. Tziaferi
National Technical University of Athens, Athens, Greece
K. Kousouris University of Ioánnina, Ioánnina, Greece
I. Evangelou, C. Foudas, P. Gianneios, P. Katsoulis, P. Kokkas, S. Mallios, N.
Manthos, I. Papadopoulos, E. Paradas, J. Strologas, F.A. Triantis, D.
Tsitsonis MTA-ELTE Lendület CMS Particle and Nuclear Physics Group, Eötvös
Loránd University, Budapest, Hungary
M. Csanad, N. Filipovic, G. Pasztor, O. Surányi, G.I. Veres19 Wigner Research
Centre for Physics, Budapest, Hungary
G. Bencze, C. Hajdu, D. Horvath20, Á. Hunyadi, F. Sikler, V. Veszpremi, G.
Vesztergombi19 Institute of Nuclear Research ATOMKI, Debrecen, Hungary
N. Beni, S. Czellar, J. Karancsi21, A. Makovec, J. Molnar, Z. Szillasi
Institute of Physics, University of Debrecen, Debrecen, Hungary
M. Bartók19, P. Raics, Z.L. Trocsanyi, B. Ujvari Indian Institute of Science
(IISc), Bangalore, India
S. Choudhury, J.R. Komaragiri National Institute of Science Education and
Research, Bhubaneswar, India
S. Bahinipati22, P. Mal, K. Mandal, A. Nayak23, D.K. Sahoo22, N. Sahoo, S.K.
Swain Panjab University, Chandigarh, India
S. Bansal, S.B. Beri, V. Bhatnagar, R. Chawla, N. Dhingra, A. Kaur, M. Kaur,
S. Kaur, R. Kumar, P. Kumari, A. Mehta, J.B. Singh, G. Walia University of
Delhi, Delhi, India
Ashok Kumar, Aashaq Shah, A. Bhardwaj, S. Chauhan, B.C. Choudhary, R.B. Garg,
S. Keshri, A. Kumar, S. Malhotra, M. Naimuddin, K. Ranjan, R. Sharma Saha
Institute of Nuclear Physics, HBNI, Kolkata, India
R. Bhardwaj, R. Bhattacharya, S. Bhattacharya, U. Bhawandeep, S. Dey, S. Dutt,
S. Dutta, S. Ghosh, N. Majumdar, A. Modak, K. Mondal, S. Mukhopadhyay, S.
Nandan, A. Purohit, A. Roy, S. Roy Chowdhury, S. Sarkar, M. Sharan, S. Thakur
Indian Institute of Technology Madras, Madras, India
P.K. Behera Bhabha Atomic Research Centre, Mumbai, India
R. Chudasama, D. Dutta, V. Jha, V. Kumar, A.K. Mohanty15, P.K. Netrakanti,
L.M. Pant, P. Shukla, A. Topkar Tata Institute of Fundamental Research-A,
Mumbai, India
T. Aziz, S. Dugad, B. Mahakud, S. Mitra, G.B. Mohanty, N. Sur, B. Sutar Tata
Institute of Fundamental Research-B, Mumbai, India
S. Banerjee, S. Bhattacharya, S. Chatterjee, P. Das, M. Guchait, Sa. Jain, S.
Kumar, M. Maity24, G. Majumder, K. Mazumdar, T. Sarkar24, N. Wickramage25
Indian Institute of Science Education and Research (IISER), Pune, India
S. Chauhan, S. Dube, V. Hegde, A. Kapoor, K. Kothekar, S. Pandey, A. Rane, S.
Sharma Institute for Research in Fundamental Sciences (IPM), Tehran, Iran
S. Chenarani26, E. Eskandari Tadavani, S.M. Etesami26, M. Khakzad, M.
Mohammadi Najafabadi, M. Naseri, S. Paktinat Mehdiabadi27, F. Rezaei
Hosseinabadi, B. Safarzadeh28, M. Zeinali University College Dublin, Dublin,
Ireland
M. Felcini, M. Grunewald INFN Sezione di Bari a, Università di Bari b,
Politecnico di Bari c, Bari, Italy
M. Abbresciaa,b, C. Calabriaa,b, A. Colaleoa, D. Creanzaa,c, L. Cristellaa,b,
N. De Filippisa,c, M. De Palmaa,b, F. Erricoa,b, L. Fiorea, G. Iasellia,c, S.
Lezkia,b, G. Maggia,c, M. Maggia, G. Minielloa,b, S. Mya,b, S. Nuzzoa,b, A.
Pompilia,b, G. Pugliesea,c, R. Radognaa, A. Ranieria, G. Selvaggia,b, A.
Sharmaa, L. Silvestrisa,15, R. Vendittia, P. Verwilligena INFN Sezione di
Bologna a, Università di Bologna b, Bologna, Italy
G. Abbiendia, C. Battilanaa,b, D. Bonacorsia,b, L. Borgonovia,b, S. Braibant-
Giacomellia,b, R. Campaninia,b, P. Capiluppia,b, A. Castroa,b, F.R. Cavalloa,
S.S. Chhibraa,b, G. Codispotia,b, M. Cuffiania,b, G.M. Dallavallea, F.
Fabbria, A. Fanfania,b, D. Fasanellaa,b, P. Giacomellia, C. Grandia, L.
Guiduccia,b, S. Marcellinia, G. Masettia, A. Montanaria, F.L. Navarriaa,b, A.
Perrottaa, A.M. Rossia,b, T. Rovellia,b, G.P. Sirolia,b, N. Tosia INFN Sezione
di Catania a, Università di Catania b, Catania, Italy
S. Albergoa,b, S. Costaa,b, A. Di Mattiaa, F. Giordanoa,b, R. Potenzaa,b, A.
Tricomia,b, C. Tuvea,b INFN Sezione di Firenze a, Università di Firenze b,
Firenze, Italy
G. Barbaglia, K. Chatterjeea,b, V. Ciullia,b, C. Civininia, R.
D’Alessandroa,b, E. Focardia,b, P. Lenzia,b, M. Meschinia, S. Paolettia, L.
Russoa,29, G. Sguazzonia, D. Stroma, L. Viliania INFN Laboratori Nazionali di
Frascati, Frascati, Italy
L. Benussi, S. Bianco, F. Fabbri, D. Piccolo, F. Primavera15 INFN Sezione di
Genova a, Università di Genova b, Genova, Italy
V. Calvellia,b, F. Ferroa, F. Raveraa,b, E. Robuttia, S. Tosia,b INFN Sezione
di Milano-Bicocca a, Università di Milano-Bicocca b, Milano, Italy
A. Benagliaa, A. Beschib, L. Brianzaa,b, F. Brivioa,b, V. Cirioloa,b,15, M.E.
Dinardoa,b, S. Fiorendia,b, S. Gennaia, A. Ghezzia,b, P. Govonia,b, M.
Malbertia,b, S. Malvezzia, R.A. Manzonia,b, D. Menascea, L. Moronia, M.
Paganonia,b, K. Pauwelsa,b, D. Pedrinia, S. Pigazzinia,b,30, S. Ragazzia,b, T.
Tabarelli de Fatisa,b INFN Sezione di Napoli a, Università di Napoli ’Federico
II’ b, Napoli, Italy, Università della Basilicata c, Potenza, Italy,
Università G. Marconi d, Roma, Italy
S. Buontempoa, N. Cavalloa,c, S. Di Guidaa,d,15, F. Fabozzia,c, F. Fiengaa,b,
A.O.M. Iorioa,b, W.A. Khana, L. Listaa, S. Meolaa,d,15, P. Paoluccia,15, C.
Sciaccaa,b, F. Thyssena INFN Sezione di Padova a, Università di Padova b,
Padova, Italy, Università di Trento c, Trento, Italy
P. Azzia, N. Bacchettaa, L. Benatoa,b, A. Bolettia,b, R. Carlina,b, A.
Carvalho Antunes De Oliveiraa,b, P. Checchiaa, M. Dall’Ossoa,b, P. De Castro
Manzanoa, T. Dorigoa, U. Dossellia, F. Gasparinia,b, U. Gasparinia,b, A.
Gozzelinoa, S. Lacapraraa, P. Lujan, M. Margonia,b, A.T. Meneguzzoa,b, N.
Pozzobona,b, P. Ronchesea,b, R. Rossina,b, F. Simonettoa,b, E. Torassaa, M.
Zanettia,b, P. Zottoa,b, G. Zumerlea,b INFN Sezione di Pavia a, Università di
Pavia b, Pavia, Italy
A. Braghieria, A. Magnania, P. Montagnaa,b, S.P. Rattia,b, V. Rea, M.
Ressegottia,b, C. Riccardia,b, P. Salvinia, I. Vaia,b, P. Vituloa,b INFN
Sezione di Perugia a, Università di Perugia b, Perugia, Italy
L. Alunni Solestizia,b, M. Biasinia,b, G.M. Bileia, C. Cecchia,b, D.
Ciangottinia,b, L. Fanòa,b, P. Laricciaa,b, R. Leonardia,b, E. Manonia, G.
Mantovania,b, V. Mariania,b, M. Menichellia, A. Rossia,b, A. Santocchiaa,b, D.
Spigaa INFN Sezione di Pisa a, Università di Pisa b, Scuola Normale Superiore
di Pisa c, Pisa, Italy
K. Androsova, P. Azzurria,15, G. Bagliesia, T. Boccalia, L. Borrello, R.
Castaldia, M.A. Cioccia,b, R. Dell’Orsoa, G. Fedia, L. Gianninia,c, A.
Giassia, M.T. Grippoa,29, F. Ligabuea,c, T. Lomtadzea, E. Mancaa,c, G.
Mandorlia,c, A. Messineoa,b, F. Pallaa, A. Rizzia,b, A. Savoy-Navarroa,31, P.
Spagnoloa, R. Tenchinia, G. Tonellia,b, A. Venturia, P.G. Verdinia INFN
Sezione di Roma a, Sapienza Università di Roma b, Rome, Italy
L. Baronea,b, F. Cavallaria, M. Cipriania,b, N. Dacia, D. Del Rea,b, E. Di
Marcoa,b, M. Diemoza, S. Gellia,b, E. Longoa,b, F. Margarolia,b, B.
Marzocchia,b, P. Meridiania, G. Organtinia,b, R. Paramattia,b, F. Preiatoa,b,
S. Rahatloua,b, C. Rovellia, F. Santanastasioa,b INFN Sezione di Torino a,
Università di Torino b, Torino, Italy, Università del Piemonte Orientale c,
Novara, Italy
N. Amapanea,b, R. Arcidiaconoa,c, S. Argiroa,b, M. Arneodoa,c, N. Bartosika,
R. Bellana,b, C. Biinoa, N. Cartigliaa, F. Cennaa,b, M. Costaa,b, R.
Covarellia,b, A. Deganoa,b, N. Demariaa, B. Kiania,b, C. Mariottia, S.
Masellia, E. Migliorea,b, V. Monacoa,b, E. Monteila,b, M. Montenoa, M.M.
Obertinoa,b, L. Pachera,b, N. Pastronea, M. Pelliccionia, G.L. Pinna
Angionia,b, A. Romeroa,b, M. Ruspaa,c, R. Sacchia,b, K. Shchelinaa,b, V.
Solaa, A. Solanoa,b, A. Staianoa, P. Traczyka,b INFN Sezione di Trieste a,
Università di Trieste b, Trieste, Italy
S. Belfortea, M. Casarsaa, F. Cossuttia, G. Della Riccaa,b, A. Zanettia
Kyungpook National University, Daegu, Korea
D.H. Kim, G.N. Kim, M.S. Kim, J. Lee, S. Lee, S.W. Lee, C.S. Moon, Y.D. Oh, S.
Sekmen, D.C. Son, Y.C. Yang Chonnam National University, Institute for
Universe and Elementary Particles, Kwangju, Korea
H. Kim, D.H. Moon, G. Oh Hanyang University, Seoul, Korea
J.A. Brochero Cifuentes, J. Goh, T.J. Kim Korea University, Seoul, Korea
S. Cho, S. Choi, Y. Go, D. Gyun, S. Ha, B. Hong, Y. Jo, Y. Kim, K. Lee, K.S.
Lee, S. Lee, J. Lim, S.K. Park, Y. Roh Seoul National University, Seoul, Korea
J. Almond, J. Kim, J.S. Kim, H. Lee, K. Lee, K. Nam, S.B. Oh, B.C. Radburn-
Smith, S.h. Seo, U.K. Yang, H.D. Yoo, G.B. Yu University of Seoul, Seoul,
Korea
H. Kim, J.H. Kim, J.S.H. Lee, I.C. Park Sungkyunkwan University, Suwon, Korea
Y. Choi, C. Hwang, J. Lee, I. Yu Vilnius University, Vilnius, Lithuania
V. Dudenas, A. Juodagalvis, J. Vaitkus National Centre for Particle Physics,
Universiti Malaya, Kuala Lumpur, Malaysia
I. Ahmed, Z.A. Ibrahim, M.A.B. Md Ali32, F. Mohamad Idris33, W.A.T. Wan
Abdullah, M.N. Yusli, Z. Zolkapli Centro de Investigacion y de Estudios
Avanzados del IPN, Mexico City, Mexico
Reyes-Almanza, R, Ramirez-Sanchez, G., Duran-Osuna, M. C., H. Castilla-Valdez,
E. De La Cruz-Burelo, I. Heredia-De La Cruz34, Rabadan-Trejo, R. I., R. Lopez-
Fernandez, J. Mejia Guisao, A. Sanchez-Hernandez Universidad Iberoamericana,
Mexico City, Mexico
S. Carrillo Moreno, C. Oropeza Barrera, F. Vazquez Valencia Benemerita
Universidad Autonoma de Puebla, Puebla, Mexico
J. Eysermans, I. Pedraza, H.A. Salazar Ibarguen, C. Uribe Estrada Universidad
Autónoma de San Luis Potosí, San Luis Potosí, Mexico
A. Morelos Pineda University of Auckland, Auckland, New Zealand
D. Krofcheck University of Canterbury, Christchurch, New Zealand
P.H. Butler National Centre for Physics, Quaid-I-Azam University, Islamabad,
Pakistan
A. Ahmad, M. Ahmad, Q. Hassan, H.R. Hoorani, A. Saddique, M.A. Shah, M.
Shoaib, M. Waqas National Centre for Nuclear Research, Swierk, Poland
H. Bialkowska, M. Bluj, B. Boimska, T. Frueboes, M. Górski, M. Kazana, K.
Nawrocki, M. Szleper, P. Zalewski Institute of Experimental Physics, Faculty
of Physics, University of Warsaw, Warsaw, Poland
K. Bunkowski, A. Byszuk35, K. Doroba, A. Kalinowski, M. Konecki, J.
Krolikowski, M. Misiura, M. Olszewski, A. Pyskir, M. Walczak Laboratório de
Instrumentação e Física Experimental de Partículas, Lisboa, Portugal
P. Bargassa, C. Beirão Da Cruz E Silva, A. Di Francesco, P. Faccioli, B.
Galinhas, M. Gallinaro, J. Hollar, N. Leonardo, L. Lloret Iglesias, M.V.
Nemallapudi, J. Seixas, G. Strong, O. Toldaiev, D. Vadruccio, J. Varela Joint
Institute for Nuclear Research, Dubna, Russia
A. Baginyan, A. Golunov, I. Golutvin, V. Karjavin, V. Korenkov, G. Kozlov, A.
Lanev, A. Malakhov, V. Matveev36,37, V.V. Mitsyn, P. Moisenz, V. Palichik, V.
Perelygin, S. Shmatov, V. Smirnov, N. Voytishin, B.S. Yuldashev38, A. Zarubin,
V. Zhiltsov Petersburg Nuclear Physics Institute, Gatchina (St. Petersburg),
Russia
Y. Ivanov, V. Kim39, E. Kuznetsova40, P. Levchenko, V. Murzin, V. Oreshkin, I.
Smirnov, D. Sosnov, V. Sulimov, L. Uvarov, S. Vavilov, A. Vorobyev Institute
for Nuclear Research, Moscow, Russia
Yu. Andreev, A. Dermenev, S. Gninenko, N. Golubev, A. Karneyeu, M. Kirsanov,
N. Krasnikov, A. Pashenkov, D. Tlisov, A. Toropin Institute for Theoretical
and Experimental Physics, Moscow, Russia
V. Epshteyn, V. Gavrilov, N. Lychkovskaya, V. Popov, I. Pozdnyakov, G.
Safronov, A. Spiridonov, A. Stepennov, V. Stolin, M. Toms, E. Vlasov, A.
Zhokin Moscow Institute of Physics and Technology, Moscow, Russia
T. Aushev, A. Bylinkin37 National Research Nuclear University ’Moscow
Engineering Physics Institute’ (MEPhI), Moscow, Russia
R. Chistov41, M. Danilov41, P. Parygin, D. Philippov, S. Polikarpov, E.
Tarkovskii P.N. Lebedev Physical Institute, Moscow, Russia
V. Andreev, M. Azarkin37, I. Dremin37, M. Kirakosyan37, S.V. Rusakov, A.
Terkulov Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State
University, Moscow, Russia
A. Baskakov, A. Belyaev, E. Boos, V. Bunichev, M. Dubinin42, L. Dudko, A.
Gribushin, V. Klyukhin, N. Korneeva, I. Lokhtin, I. Miagkov, S. Obraztsov, M.
Perfilov, V. Savrin, P. Volkov Novosibirsk State University (NSU),
Novosibirsk, Russia
V. Blinov43, D. Shtol43, Y. Skovpen43 State Research Center of Russian
Federation, Institute for High Energy Physics of NRC "Kurchatov
Institute", Protvino, Russia
I. Azhgirey, I. Bayshev, S. Bitioukov, D. Elumakhov, A. Godizov, V. Kachanov,
A. Kalinin, D. Konstantinov, P. Mandrik, V. Petrov, R. Ryutin, A. Sobol, S.
Troshin, N. Tyurin, A. Uzunian, A. Volkov University of Belgrade, Faculty of
Physics and Vinca Institute of Nuclear Sciences, Belgrade, Serbia
P. Adzic44, P. Cirkovic, D. Devetak, M. Dordevic, J. Milosevic Centro de
Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid,
Spain
J. Alcaraz Maestre, I. Bachiller, M. Barrio Luna, M. Cerrada, N. Colino, B. De
La Cruz, A. Delgado Peris, C. Fernandez Bedoya, J.P. Fernández Ramos, J. Flix,
M.C. Fouz, O. Gonzalez Lopez, S. Goy Lopez, J.M. Hernandez, M.I. Josa, D.
Moran, A. Pérez-Calero Yzquierdo, J. Puerta Pelayo, I. Redondo, L. Romero,
M.S. Soares, A. Triossi, A. Álvarez Fernández Universidad Autónoma de Madrid,
Madrid, Spain
C. Albajar, J.F. de Trocóniz Universidad de Oviedo, Oviedo, Spain
J. Cuevas, C. Erice, J. Fernandez Menendez, I. Gonzalez Caballero, J.R.
González Fernández, E. Palencia Cortezon, S. Sanchez Cruz, P. Vischia, J.M.
Vizan Garcia Instituto de Física de Cantabria (IFCA), CSIC-Universidad de
Cantabria, Santander, Spain
I.J. Cabrillo, A. Calderon, B. Chazin Quero, E. Curras, J. Duarte Campderros,
M. Fernandez, J. Garcia-Ferrero, G. Gomez, A. Lopez Virto, J. Marco, C.
Martinez Rivero, P. Martinez Ruiz del Arbol, F. Matorras, J. Piedra Gomez, T.
Rodrigo, A. Ruiz-Jimeno, L. Scodellaro, N. Trevisani, I. Vila, R. Vilar
Cortabitarte CERN, European Organization for Nuclear Research, Geneva,
Switzerland
D. Abbaneo, B. Akgun, E. Auffray, P. Baillon, A.H. Ball, D. Barney, J.
Bendavid, M. Bianco, A. Bocci, C. Botta, T. Camporesi, R. Castello, M. Cepeda,
G. Cerminara, E. Chapon, Y. Chen, D. d’Enterria, A. Dabrowski, V. Daponte, A.
David, M. De Gruttola, A. De Roeck, N. Deelen, M. Dobson, T. du Pree, M.
Dünser, N. Dupont, A. Elliott-Peisert, P. Everaerts, F. Fallavollita, G.
Franzoni, J. Fulcher, W. Funk, D. Gigi, A. Gilbert, K. Gill, F. Glege, D.
Gulhan, P. Harris, J. Hegeman, V. Innocente, A. Jafari, P. Janot, O.
Karacheban18, J. Kieseler, V. Knünz, A. Kornmayer, M.J. Kortelainen, M.
Krammer1, C. Lange, P. Lecoq, C. Lourenço, M.T. Lucchini, L. Malgeri, M.
Mannelli, A. Martelli, F. Meijers, J.A. Merlin, S. Mersi, E. Meschi, P.
Milenovic45, F. Moortgat, M. Mulders, H. Neugebauer, J. Ngadiuba, S.
Orfanelli, L. Orsini, L. Pape, E. Perez, M. Peruzzi, A. Petrilli, G.
Petrucciani, A. Pfeiffer, M. Pierini, D. Rabady, A. Racz, T. Reis, G.
Rolandi46, M. Rovere, H. Sakulin, C. Schäfer, C. Schwick, M. Seidel, M.
Selvaggi, A. Sharma, P. Silva, P. Sphicas47, A. Stakia, J. Steggemann, M.
Stoye, M. Tosi, D. Treille, A. Tsirou, V. Veckalns48, M. Verweij, W.D. Zeuner
Paul Scherrer Institut, Villigen, Switzerland
W. Bertl${}^{\textrm{\textdagger}}$, L. Caminada49, K. Deiters, W. Erdmann, R.
Horisberger, Q. Ingram, H.C. Kaestli, D. Kotlinski, U. Langenegger, T. Rohe,
S.A. Wiederkehr ETH Zurich - Institute for Particle Physics and Astrophysics
(IPA), Zurich, Switzerland
M. Backhaus, L. Bäni, P. Berger, L. Bianchini, B. Casal, G. Dissertori, M.
Dittmar, M. Donegà, C. Dorfer, C. Grab, C. Heidegger, D. Hits, J. Hoss, G.
Kasieczka, T. Klijnsma, W. Lustermann, B. Mangano, M. Marionneau, M.T.
Meinhard, D. Meister, F. Micheli, P. Musella, F. Nessi-Tedaldi, F. Pandolfi,
J. Pata, F. Pauss, G. Perrin, L. Perrozzi, M. Quittnat, M. Reichmann, D.A.
Sanz Becerra, M. Schönenberger, L. Shchutska, V.R. Tavolaro, K. Theofilatos,
M.L. Vesterbacka Olsson, R. Wallny, D.H. Zhu Universität Zürich, Zurich,
Switzerland
T.K. Aarrestad, C. Amsler50, M.F. Canelli, A. De Cosa, R. Del Burgo, S.
Donato, C. Galloni, T. Hreus, B. Kilminster, D. Pinna, G. Rauco, P. Robmann,
D. Salerno, K. Schweiger, C. Seitz, Y. Takahashi, A. Zucchetta National
Central University, Chung-Li, Taiwan
V. Candelise, Y.H. Chang, K.y. Cheng, T.H. Doan, Sh. Jain, R. Khurana, C.M.
Kuo, W. Lin, A. Pozdnyakov, S.S. Yu National Taiwan University (NTU), Taipei,
Taiwan
Arun Kumar, P. Chang, Y. Chao, K.F. Chen, P.H. Chen, F. Fiori, W.-S. Hou, Y.
Hsiung, Y.F. Liu, R.-S. Lu, E. Paganis, A. Psallidas, A. Steen, J.f. Tsai
Chulalongkorn University, Faculty of Science, Department of Physics, Bangkok,
Thailand
B. Asavapibhop, K. Kovitanggoon, G. Singh, N. Srimanobhas Çukurova University,
Physics Department, Science and Art Faculty, Adana, Turkey
A. Bat, F. Boran, S. Damarseckin, Z.S. Demiroglu, C. Dozen, E. Eskut, S.
Girgis, G. Gokbulut, Y. Guler, I. Hos51, E.E. Kangal52, O. Kara, A. Kayis
Topaksu, U. Kiminsu, M. Oglakci, G. Onengut53, K. Ozdemir54, S. Ozturk55, A.
Polatoz, U.G. Tok, H. Topakli55, S. Turkcapar, I.S. Zorbakir, C. Zorbilmez
Middle East Technical University, Physics Department, Ankara, Turkey
G. Karapinar56, K. Ocalan57, M. Yalvac, M. Zeyrek Bogazici University,
Istanbul, Turkey
E. Gülmez, M. Kaya58, O. Kaya59, S. Tekten, E.A. Yetkin60 Istanbul Technical
University, Istanbul, Turkey
M.N. Agaras, S. Atay, A. Cakir, K. Cankocak, Y. Komurcu Institute for
Scintillation Materials of National Academy of Science of Ukraine, Kharkov,
Ukraine
B. Grynyov National Scientific Center, Kharkov Institute of Physics and
Technology, Kharkov, Ukraine
L. Levchuk University of Bristol, Bristol, United Kingdom
F. Ball, L. Beck, J.J. Brooke, D. Burns, E. Clement, D. Cussans, O. Davignon,
H. Flacher, J. Goldstein, G.P. Heath, H.F. Heath, L. Kreczko, D.M. Newbold61,
S. Paramesvaran, T. Sakuma, S. Seif El Nasr-storey, D. Smith, V.J. Smith
Rutherford Appleton Laboratory, Didcot, United Kingdom
K.W. Bell, A. Belyaev62, C. Brew, R.M. Brown, L. Calligaris, D. Cieri, D.J.A.
Cockerill, J.A. Coughlan, K. Harder, S. Harper, J. Linacre, E. Olaiya, D.
Petyt, C.H. Shepherd-Themistocleous, A. Thea, I.R. Tomalin, T. Williams, W.J.
Womersley Imperial College, London, United Kingdom
G. Auzinger, R. Bainbridge, P. Bloch, J. Borg, S. Breeze, O. Buchmuller, A.
Bundock, S. Casasso, M. Citron, D. Colling, L. Corpe, P. Dauncey, G. Davies,
A. De Wit, M. Della Negra, R. Di Maria, A. Elwood, Y. Haddad, G. Hall, G.
Iles, T. James, R. Lane, C. Laner, L. Lyons, A.-M. Magnan, S. Malik, L.
Mastrolorenzo, T. Matsushita, J. Nash, A. Nikitenko6, V. Palladino, M.
Pesaresi, D.M. Raymond, A. Richards, A. Rose, E. Scott, C. Seez, A.
Shtipliyski, S. Summers, A. Tapper, K. Uchida, M. Vazquez Acosta63, T.
Virdee15, N. Wardle, D. Winterbottom, J. Wright, S.C. Zenz Brunel University,
Uxbridge, United Kingdom
J.E. Cole, P.R. Hobson, A. Khan, P. Kyberd, I.D. Reid, L. Teodorescu, S. Zahid
Baylor University, Waco, USA
A. Borzou, K. Call, J. Dittmann, K. Hatakeyama, H. Liu, N. Pastika, C. Smith
Catholic University of America, Washington DC, USA
R. Bartek, A. Dominguez The University of Alabama, Tuscaloosa, USA
A. Buccilli, S.I. Cooper, C. Henderson, P. Rumerio, C. West Boston University,
Boston, USA
D. Arcaro, A. Avetisyan, T. Bose, D. Gastler, D. Rankin, C. Richardson, J.
Rohlf, L. Sulak, D. Zou Brown University, Providence, USA
G. Benelli, D. Cutts, M. Hadley, J. Hakala, U. Heintz, J.M. Hogan, K.H.M.
Kwok, E. Laird, G. Landsberg, J. Lee, Z. Mao, M. Narain, J. Pazzini, S.
Piperov, S. Sagir, R. Syarif, D. Yu University of California, Davis, Davis,
USA
R. Band, C. Brainerd, R. Breedon, D. Burns, M. Calderon De La Barca Sanchez,
M. Chertok, J. Conway, R. Conway, P.T. Cox, R. Erbacher, C. Flores, G. Funk,
W. Ko, R. Lander, C. Mclean, M. Mulhearn, D. Pellett, J. Pilot, S. Shalhout,
M. Shi, J. Smith, D. Stolp, K. Tos, M. Tripathi, Z. Wang University of
California, Los Angeles, USA
M. Bachtis, C. Bravo, R. Cousins, A. Dasgupta, A. Florent, J. Hauser, M.
Ignatenko, N. Mccoll, S. Regnard, D. Saltzberg, C. Schnaible, V. Valuev
University of California, Riverside, Riverside, USA
E. Bouvier, K. Burt, R. Clare, J. Ellison, J.W. Gary, S.M.A. Ghiasi Shirazi,
G. Hanson, J. Heilman, G. Karapostoli, E. Kennedy, F. Lacroix, O.R. Long, M.
Olmedo Negrete, M.I. Paneva, W. Si, L. Wang, H. Wei, S. Wimpenny, B. R. Yates
University of California, San Diego, La Jolla, USA
J.G. Branson, S. Cittolin, M. Derdzinski, R. Gerosa, D. Gilbert, B. Hashemi,
A. Holzner, D. Klein, G. Kole, V. Krutelyov, J. Letts, M. Masciovecchio, D.
Olivito, S. Padhi, M. Pieri, M. Sani, V. Sharma, S. Simon, M. Tadel, A.
Vartak, S. Wasserbaech64, J. Wood, F. Würthwein, A. Yagil, G. Zevi Della Porta
University of California, Santa Barbara - Department of Physics, Santa
Barbara, USA
N. Amin, R. Bhandari, J. Bradmiller-Feld, C. Campagnari, A. Dishaw, V. Dutta,
M. Franco Sevilla, L. Gouskos, R. Heller, J. Incandela, A. Ovcharova, H. Qu,
J. Richman, D. Stuart, I. Suarez, J. Yoo California Institute of Technology,
Pasadena, USA
D. Anderson, A. Bornheim, J. Bunn, J.M. Lawhorn, H.B. Newman, T. Q. Nguyen, C.
Pena, M. Spiropulu, J.R. Vlimant, R. Wilkinson, S. Xie, Z. Zhang, R.Y. Zhu
Carnegie Mellon University, Pittsburgh, USA
M.B. Andrews, T. Ferguson, T. Mudholkar, M. Paulini, J. Russ, M. Sun, H.
Vogel, I. Vorobiev, M. Weinberg University of Colorado Boulder, Boulder, USA
J.P. Cumalat, W.T. Ford, F. Jensen, A. Johnson, M. Krohn, S. Leontsinis, T.
Mulholland, K. Stenson, K.A. Ulmer, S.R. Wagner Cornell University, Ithaca,
USA
J. Alexander, J. Chaves, J. Chu, S. Dittmer, K. Mcdermott, N. Mirman, J.R.
Patterson, D. Quach, A. Rinkevicius, A. Ryd, L. Skinnari, L. Soffi, S.M. Tan,
Z. Tao, J. Thom, J. Tucker, P. Wittich, M. Zientek Fermi National Accelerator
Laboratory, Batavia, USA
S. Abdullin, M. Albrow, M. Alyari, G. Apollinari, A. Apresyan, A. Apyan, S.
Banerjee, L.A.T. Bauerdick, A. Beretvas, J. Berryhill, P.C. Bhat, G.
Bolla${}^{\textrm{\textdagger}}$, K. Burkett, J.N. Butler, A. Canepa, G.B.
Cerati, H.W.K. Cheung, F. Chlebana, M. Cremonesi, J. Duarte, V.D. Elvira, J.
Freeman, Z. Gecse, E. Gottschalk, L. Gray, D. Green, S. Grünendahl, O.
Gutsche, J. Hanlon, R.M. Harris, S. Hasegawa, J. Hirschauer, Z. Hu, B.
Jayatilaka, S. Jindariani, M. Johnson, U. Joshi, B. Klima, B. Kreis, S.
Lammel, D. Lincoln, R. Lipton, M. Liu, T. Liu, R. Lopes De Sá, J. Lykken, K.
Maeshima, N. Magini, J.M. Marraffino, D. Mason, P. McBride, P. Merkel, S.
Mrenna, S. Nahn, V. O’Dell, K. Pedro, O. Prokofyev, G. Rakness, L. Ristori, B.
Schneider, E. Sexton-Kennedy, A. Soha, W.J. Spalding, L. Spiegel, S. Stoynev,
J. Strait, N. Strobbe, L. Taylor, S. Tkaczyk, N.V. Tran, L. Uplegger, E.W.
Vaandering, C. Vernieri, M. Verzocchi, R. Vidal, M. Wang, H.A. Weber, A.
Whitbeck, W. Wu University of Florida, Gainesville, USA
D. Acosta, P. Avery, P. Bortignon, D. Bourilkov, A. Brinkerhoff, A. Carnes, M.
Carver, D. Curry, R.D. Field, I.K. Furic, S.V. Gleyzer, B.M. Joshi, J.
Konigsberg, A. Korytov, K. Kotov, P. Ma, K. Matchev, H. Mei, G. Mitselmakher,
K. Shi, D. Sperka, N. Terentyev, L. Thomas, J. Wang, S. Wang, J. Yelton
Florida International University, Miami, USA
Y.R. Joshi, S. Linn, P. Markowitz, J.L. Rodriguez Florida State University,
Tallahassee, USA
A. Ackert, T. Adams, A. Askew, S. Hagopian, V. Hagopian, K.F. Johnson, T.
Kolberg, G. Martinez, T. Perry, H. Prosper, A. Saha, A. Santra, V. Sharma, R.
Yohay Florida Institute of Technology, Melbourne, USA
M.M. Baarmand, V. Bhopatkar, S. Colafranceschi, M. Hohlmann, D. Noonan, T.
Roy, F. Yumiceva University of Illinois at Chicago (UIC), Chicago, USA
M.R. Adams, L. Apanasevich, D. Berry, R.R. Betts, R. Cavanaugh, X. Chen, O.
Evdokimov, C.E. Gerber, D.A. Hangal, D.J. Hofman, K. Jung, J. Kamin, I.D.
Sandoval Gonzalez, M.B. Tonjes, H. Trauger, N. Varelas, H. Wang, Z. Wu, J.
Zhang The University of Iowa, Iowa City, USA
B. Bilki65, W. Clarida, K. Dilsiz66, S. Durgut, R.P. Gandrajula, M.
Haytmyradov, V. Khristenko, J.-P. Merlo, H. Mermerkaya67, A. Mestvirishvili,
A. Moeller, J. Nachtman, H. Ogul68, Y. Onel, F. Ozok69, A. Penzo, C. Snyder,
E. Tiras, J. Wetzel, K. Yi Johns Hopkins University, Baltimore, USA
B. Blumenfeld, A. Cocoros, N. Eminizer, D. Fehling, L. Feng, A.V. Gritsan, P.
Maksimovic, J. Roskes, U. Sarica, M. Swartz, M. Xiao, C. You The University of
Kansas, Lawrence, USA
A. Al-bataineh, P. Baringer, A. Bean, S. Boren, J. Bowen, J. Castle, S.
Khalil, A. Kropivnitskaya, D. Majumder, W. Mcbrayer, M. Murray, C. Rogan, C.
Royon, S. Sanders, E. Schmitz, J.D. Tapia Takaki, Q. Wang Kansas State
University, Manhattan, USA
A. Ivanov, K. Kaadze, Y. Maravin, A. Mohammadi, L.K. Saini, N. Skhirtladze
Lawrence Livermore National Laboratory, Livermore, USA
F. Rebassoo, D. Wright University of Maryland, College Park, USA
A. Baden, O. Baron, A. Belloni, S.C. Eno, Y. Feng, C. Ferraioli, N.J. Hadley,
S. Jabeen, G.Y. Jeng, R.G. Kellogg, J. Kunkle, A.C. Mignerey, F. Ricci-Tam,
Y.H. Shin, A. Skuja, S.C. Tonwar Massachusetts Institute of Technology,
Cambridge, USA
D. Abercrombie, B. Allen, V. Azzolini, R. Barbieri, A. Baty, G. Bauer, R. Bi,
S. Brandt, W. Busza, I.A. Cali, M. D’Alfonso, Z. Demiragli, G. Gomez Ceballos,
M. Goncharov, D. Hsu, M. Hu, Y. Iiyama, G.M. Innocenti, M. Klute, D.
Kovalskyi, Y.-J. Lee, A. Levin, P.D. Luckey, B. Maier, A.C. Marini, C. Mcginn,
C. Mironov, S. Narayanan, X. Niu, C. Paus, C. Roland, G. Roland, J. Salfeld-
Nebgen, G.S.F. Stephans, K. Sumorok, K. Tatar, D. Velicanu, J. Wang, T.W.
Wang, B. Wyslouch University of Minnesota, Minneapolis, USA
A.C. Benvenuti, R.M. Chatterjee, A. Evans, P. Hansen, J. Hiltbrand, S.
Kalafut, Y. Kubota, Z. Lesko, J. Mans, S. Nourbakhsh, N. Ruckstuhl, R. Rusack,
J. Turkewitz, M.A. Wadud University of Mississippi, Oxford, USA
J.G. Acosta, S. Oliveros University of Nebraska-Lincoln, Lincoln, USA
E. Avdeeva, K. Bloom, D.R. Claes, C. Fangmeier, F. Golf, R. Gonzalez Suarez,
R. Kamalieddin, I. Kravchenko, J. Monroy, J.E. Siado, G.R. Snow, B. Stieger
State University of New York at Buffalo, Buffalo, USA
J. Dolen, A. Godshalk, C. Harrington, I. Iashvili, D. Nguyen, A. Parker, S.
Rappoccio, B. Roozbahani Northeastern University, Boston, USA
G. Alverson, E. Barberis, C. Freer, A. Hortiangtham, A. Massironi, D.M. Morse,
T. Orimoto, R. Teixeira De Lima, T. Wamorkar, B. Wang, A. Wisecarver, D. Wood
Northwestern University, Evanston, USA
S. Bhattacharya, O. Charaf, K.A. Hahn, N. Mucia, N. Odell, M.H. Schmitt, K.
Sung, M. Trovato, M. Velasco University of Notre Dame, Notre Dame, USA
R. Bucci, N. Dev, M. Hildreth, K. Hurtado Anampa, C. Jessop, D.J. Karmgard, N.
Kellams, K. Lannon, W. Li, N. Loukas, N. Marinelli, F. Meng, C. Mueller, Y.
Musienko36, M. Planer, A. Reinsvold, R. Ruchti, P. Siddireddy, G. Smith, S.
Taroni, M. Wayne, A. Wightman, M. Wolf, A. Woodard The Ohio State University,
Columbus, USA
J. Alimena, L. Antonelli, B. Bylsma, L.S. Durkin, S. Flowers, B. Francis, A.
Hart, C. Hill, W. Ji, T.Y. Ling, B. Liu, W. Luo, B.L. Winer, H.W. Wulsin
Princeton University, Princeton, USA
S. Cooperstein, O. Driga, P. Elmer, J. Hardenbrook, P. Hebda, S. Higginbotham,
A. Kalogeropoulos, D. Lange, J. Luo, D. Marlow, K. Mei, I. Ojalvo, J. Olsen,
C. Palmer, P. Piroué, D. Stickland, C. Tully University of Puerto Rico,
Mayaguez, USA
S. Malik, S. Norberg Purdue University, West Lafayette, USA
A. Barker, V.E. Barnes, S. Das, S. Folgueras, L. Gutay, M. Jones, A.W. Jung,
A. Khatiwada, D.H. Miller, N. Neumeister, C.C. Peng, H. Qiu, J.F. Schulte, J.
Sun, F. Wang, R. Xiao, W. Xie Purdue University Northwest, Hammond, USA
T. Cheng, N. Parashar, J. Stupak Rice University, Houston, USA
Z. Chen, K.M. Ecklund, S. Freed, F.J.M. Geurts, M. Guilbaud, M. Kilpatrick, W.
Li, B. Michlin, B.P. Padley, J. Roberts, J. Rorie, W. Shi, Z. Tu, J. Zabel, A.
Zhang University of Rochester, Rochester, USA
A. Bodek, P. de Barbaro, R. Demina, Y.t. Duh, T. Ferbel, M. Galanti, A.
Garcia-Bellido, J. Han, O. Hindrichs, A. Khukhunaishvili, K.H. Lo, P. Tan, M.
Verzetti The Rockefeller University, New York, USA
R. Ciesielski, K. Goulianos, C. Mesropian Rutgers, The State University of New
Jersey, Piscataway, USA
A. Agapitos, J.P. Chou, Y. Gershtein, T.A. Gómez Espinosa, E. Halkiadakis, M.
Heindl, E. Hughes, S. Kaplan, R. Kunnawalkam Elayavalli, S. Kyriacou, A. Lath,
R. Montalvo, K. Nash, M. Osherson, H. Saka, S. Salur, S. Schnetzer, D.
Sheffield, S. Somalwar, R. Stone, S. Thomas, P. Thomassen, M. Walker
University of Tennessee, Knoxville, USA
A.G. Delannoy, J. Heideman, G. Riley, K. Rose, S. Spanier, K. Thapa Texas A&M
University, College Station, USA
O. Bouhali70, A. Castaneda Hernandez70, A. Celik, M. Dalchenko, M. De Mattia,
A. Delgado, S. Dildick, R. Eusebi, J. Gilmore, T. Huang, T. Kamon71, R.
Mueller, Y. Pakhotin, R. Patel, A. Perloff, L. Perniè, D. Rathjens, A.
Safonov, A. Tatarinov Texas Tech University, Lubbock, USA
N. Akchurin, J. Damgov, F. De Guio, P.R. Dudero, J. Faulkner, E. Gurpinar, S.
Kunori, K. Lamichhane, S.W. Lee, T. Libeiro, T. Mengke, S. Muthumuni, T.
Peltola, S. Undleeb, I. Volobouev, Z. Wang Vanderbilt University, Nashville,
USA
S. Greene, A. Gurrola, R. Janjam, W. Johns, C. Maguire, A. Melo, H. Ni, K.
Padeken, P. Sheldon, S. Tuo, J. Velkovska, Q. Xu University of Virginia,
Charlottesville, USA
M.W. Arenton, P. Barria, B. Cox, R. Hirosky, M. Joyce, A. Ledovskoy, H. Li, C.
Neu, T. Sinthuprasith, Y. Wang, E. Wolfe, F. Xia Wayne State University,
Detroit, USA
R. Harr, P.E. Karchin, N. Poudyal, J. Sturdy, P. Thapa, S. Zaleski University
of Wisconsin - Madison, Madison, WI, USA
M. Brodski, J. Buchanan, C. Caillol, D. Carlsmith, S. Dasu, L. Dodd, S. Duric,
B. Gomber, M. Grothe, M. Herndon, A. Hervé, U. Hussain, P. Klabbers, A.
Lanaro, A. Levine, K. Long, R. Loveless, V. Rekovic, T. Ruggles, A. Savin, N.
Smith, W.H. Smith, D. Taylor, N. Woods †: Deceased
1: Also at Vienna University of Technology, Vienna, Austria
2: Also at IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France
3: Also at Universidade Estadual de Campinas, Campinas, Brazil
4: Also at Federal University of Rio Grande do Sul, Porto Alegre, Brazil
5: Also at Université Libre de Bruxelles, Bruxelles, Belgium
6: Also at Institute for Theoretical and Experimental Physics, Moscow, Russia
7: Also at Joint Institute for Nuclear Research, Dubna, Russia
8: Also at Suez University, Suez, Egypt
9: Now at British University in Egypt, Cairo, Egypt
10: Now at Helwan University, Cairo, Egypt
11: Also at Department of Physics, King Abdulaziz University, Jeddah, Saudi
Arabia
12: Also at Université de Haute Alsace, Mulhouse, France
13: Also at Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State
University, Moscow, Russia
14: Also at Ilia State University, Tbilisi, Georgia
15: Also at CERN, European Organization for Nuclear Research, Geneva,
Switzerland
16: Also at RWTH Aachen University, III. Physikalisches Institut A, Aachen,
Germany
17: Also at University of Hamburg, Hamburg, Germany
18: Also at Brandenburg University of Technology, Cottbus, Germany
19: Also at MTA-ELTE Lendület CMS Particle and Nuclear Physics Group, Eötvös
Loránd University, Budapest, Hungary
20: Also at Institute of Nuclear Research ATOMKI, Debrecen, Hungary
21: Also at Institute of Physics, University of Debrecen, Debrecen, Hungary
22: Also at Indian Institute of Technology Bhubaneswar, Bhubaneswar, India
23: Also at Institute of Physics, Bhubaneswar, India
24: Also at University of Visva-Bharati, Santiniketan, India
25: Also at University of Ruhuna, Matara, Sri Lanka
26: Also at Isfahan University of Technology, Isfahan, Iran
27: Also at Yazd University, Yazd, Iran
28: Also at Plasma Physics Research Center, Science and Research Branch,
Islamic Azad University, Tehran, Iran
29: Also at Università degli Studi di Siena, Siena, Italy
30: Also at INFN Sezione di Milano-Bicocca; Università di Milano-Bicocca,
Milano, Italy
31: Also at Purdue University, West Lafayette, USA
32: Also at International Islamic University of Malaysia, Kuala Lumpur,
Malaysia
33: Also at Malaysian Nuclear Agency, MOSTI, Kajang, Malaysia
34: Also at Consejo Nacional de Ciencia y Tecnología, Mexico city, Mexico
35: Also at Warsaw University of Technology, Institute of Electronic Systems,
Warsaw, Poland
36: Also at Institute for Nuclear Research, Moscow, Russia
37: Now at National Research Nuclear University ’Moscow Engineering Physics
Institute’ (MEPhI), Moscow, Russia
38: Also at Institute of Nuclear Physics of the Uzbekistan Academy of
Sciences, Tashkent, Uzbekistan
39: Also at St. Petersburg State Polytechnical University, St. Petersburg,
Russia
40: Also at University of Florida, Gainesville, USA
41: Also at P.N. Lebedev Physical Institute, Moscow, Russia
42: Also at California Institute of Technology, Pasadena, USA
43: Also at Budker Institute of Nuclear Physics, Novosibirsk, Russia
44: Also at Faculty of Physics, University of Belgrade, Belgrade, Serbia
45: Also at University of Belgrade, Faculty of Physics and Vinca Institute of
Nuclear Sciences, Belgrade, Serbia
46: Also at Scuola Normale e Sezione dell’INFN, Pisa, Italy
47: Also at National and Kapodistrian University of Athens, Athens, Greece
48: Also at Riga Technical University, Riga, Latvia
49: Also at Universität Zürich, Zurich, Switzerland
50: Also at Stefan Meyer Institute for Subatomic Physics (SMI), Vienna,
Austria
51: Also at Istanbul Aydin University, Istanbul, Turkey
52: Also at Mersin University, Mersin, Turkey
53: Also at Cag University, Mersin, Turkey
54: Also at Piri Reis University, Istanbul, Turkey
55: Also at Gaziosmanpasa University, Tokat, Turkey
56: Also at Izmir Institute of Technology, Izmir, Turkey
57: Also at Necmettin Erbakan University, Konya, Turkey
58: Also at Marmara University, Istanbul, Turkey
59: Also at Kafkas University, Kars, Turkey
60: Also at Istanbul Bilgi University, Istanbul, Turkey
61: Also at Rutherford Appleton Laboratory, Didcot, United Kingdom
62: Also at School of Physics and Astronomy, University of Southampton,
Southampton, United Kingdom
63: Also at Instituto de Astrofísica de Canarias, La Laguna, Spain
64: Also at Utah Valley University, Orem, USA
65: Also at Beykent University, Istanbul, Turkey
66: Also at Bingol University, Bingol, Turkey
67: Also at Erzincan University, Erzincan, Turkey
68: Also at Sinop University, Sinop, Turkey
69: Also at Mimar Sinan University, Istanbul, Istanbul, Turkey
70: Also at Texas A&M University at Qatar, Doha, Qatar
71: Also at Kyungpook National University, Daegu, Korea