Measurement of the single top quark and antiquark production cross sections in the t channel and their ratio in proton-proton collisions at √s =13TeV

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

the

single

top

quark

and

antiquark

production

cross

sections

in

the

t channel

and

their

ratio

in

proton-proton

collisions

at

√

s

=

13 TeV

.

The

CMS

Collaboration



CERN,Switzerland

a

r

t

i

c

l

e

i

n

f

o

a

b

s

t

r

a

c

t

Articlehistory: Received26December2018

Receivedinrevisedform5October2019 Accepted21October2019

Availableonline24October2019 Editor:M.Doser Keywords: CMS Physics Topquark Singletop Crosssection

Measurements of the cross sections for the production ofsingle top quarks and antiquarks in thet channel,andtheirratio,arepresentedforproton-protoncollisionsatacenter-of-massenergyof13 TeV. Thedatasetusedwasrecordedin2016bytheCMSdetectorattheLHCandcorrespondstoanintegrated luminosityof35.9 fb−1_{.Eventswithonemuonorelectronareselected,anddifferentcategoriesofjetand}

b jetmultiplicityandmultivariatediscriminatorsareappliedtoseparatethesignalfromthebackground. Thecrosssectionsforthet-channelproductionofsingletopquarksandantiquarksaremeasuredtobe 130_±1(stat) ±19(syst)pb and77_±1(stat) ±12(syst)pb,respectively,andtheirratiois1.68_±0.02(stat) ±

0.05(syst).Theresultsareinagreementwiththepredictionsfromthestandardmodel.

©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

1. Introduction

Thestudyofsingletopquarkproductionprovidesimportant in-sightinto the electroweakprocesses of thestandard model (SM) of elementary particles and into the structure of the proton. It alsoprovidesaccesstothemagnitudeoftheCabibbo–Kobayashi– Maskawa(CKM)matrixelement

V

tb.Amongtheproduction

chan-nels,the

t-channel

processisthedominantmechanismin proton-proton (pp) collisions at the CERN LHC accounting for approxi-mately70%ofthe totalsingle top quarkproductioncross section at

√

s

=

13 TeV [1]. The t channel has a very distinct signature witha light quark, which is predominantlyproduced inthe for-warddirection,andatopquark.Fig.1illustratestheproductionof asingletopquarkandasingletopantiquark.Theflavorofthe ini-tiallightquark definesthecharge ofthe producedtop quark;up quarksintheinitialstateresultintopquarks,whiledownquarks producetopantiquarks.Theratioofthecrosssectionsofthesetwo processesprovidesinsightintotheinnerstructureoftheprotonas described by theparton distributionfunctions (PDFs). The ATLAS andCMSCollaborations haveperformedseveralmeasurementsof thecrosssectionforsingletopquark productioninthe

t channel

usingLHC datacollected at

√

s

=

7,8, and13 TeV[2–9]. Witha

 _{E-mailaddress:cms-publication-committee-chair@cern.ch.}

Fig. 1. FeynmandiagramsatBornlevelfortheelectroweakproductionofasingle topquark(left)andantiquark(right).Theflavorofthelightquarkintheinitial state—eitherupquark(u)ordownquark(d)—defineswhetheratopquarkortop antiquarkisproduced.

data set corresponding to an integrated luminosity of 35.9 fb−1, theanalysisdescribedinthisletterusesabout18timesmoredata comparedtotheprevious analysisat13 TeV[9] andalsoexploits theelectronfinalstate.

The 13 TeVt-channel single top quark crosssection has been calculated to next-to-leading-order (NLO) accuracy in quantum chromodynamics(QCD)usinghathor 2.1[10,11].Assumingatop quarkmassof172.5 GeVandVtb

=

1,thecalculationyields cross

sectionvaluesof

https://doi.org/10.1016/j.physletb.2019.135042

0370-2693/©2019TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/).Fundedby SCOAP3_.

σ

t-ch,t

=

136

.

0+₋42..19

(

scale

)

±

3

.

5

(

PDF

+

α

S

)

pb

,

σ

_t-ch,¯t

=

81

.

0+₋2_1..₇5

(

scale

)

±

3

.

2

(

PDF

+

α

S

)

pb

,

σ

_t-ch,t+¯t

=

217

.

0+₋6_4..₆6

(

scale

)

±

6

.

2

(

PDF

+

α

S

)

pb

,

(1)

for the t-channel production of single top quarks (

σ

t-ch,t), sin-gle top antiquarks (

σ

_t-ch,¯t), and the sum of both subprocesses (

σ

t-ch,t+¯t), respectively,where

α

S isthe strongcouplingconstant. The cross sections are evaluated in the five-flavor scheme (5FS), wherethe b quarkis described bythe PDF oftheincoming pro-tons. The quoted uncertainties are associated withthe renormal-izationandfactorizationscales, aswell as

α

S atthe massofthe Zboson,andPDFs.ThePDF and

α

S

(

mZ

)

uncertaintieswere

calcu-latedwiththeMSTW200868%confidencelevelNLO[12,13],CT10 NLO [14], and NNPDF2.3 [15] PDF sets, using the PDF4LHC pre-scription[16,17].Apredictionatfullnext-to-next-to-leading-order (NNLO)accuracy [18] isalsoavailableforsingletopquark produc-tioninthe

t channel

at13 TeV.AstheavailableNNLOcalculations consideronlyuncertaintiesfromvariationsintherenormalization andfactorizationscales,theNLO predictionprovidingall required systematicuncertaintysourcesisused insteadinthisanalysisfor the normalization of the signal process. Depending on the PDF set used,the predicted values forthe cross sections forthe two processes andtheir ratio may differ,rendering the measurement sensitivetovariousPDFparameterizations.Usingthecrosssection valuesandthe PDF sets givenabove, the predictedvalue forthe ratio

R

t-ch

=

σ

t-ch,t

/

σ

t-ch,¯t is1

.

68

±

0

.

08,wheretheuncertainty

in-cludescontributions duetovariations ofthe renormalizationand thefactorizationscales,thetopquarkmass,andthePDFand

α

S.

The analysisuses eventscontaining a single isolated muonor electron inthe final state. The muon orelectron originates from the decay of the W boson from the top quark decay, either di-rectly orvia W

→

τ ν

and thefollowing

τ

→ 

ν

decay,where



referstoeitheramuonoranelectron.Themainbackgroundscome fromtheproductionoftopquark-antiquarkpairs

(

t

¯

t

)

andfromthe productionofWbosonsinassociationwithjets(W

+

jets).The sep-arationbetweensignalandbackgroundisachievedusingboosted decisiontrees(BDTs),whichcombinethediscriminatingpowerof several kinematic distributions into a single classifier. The cross sections of t-channel single top quark and single top antiquark production,as well asthe ratio of the two processes, are deter-minedfromafittothedistributionsofthissingleclassifier. 2. TheCMSdetector

The central feature of the CMS apparatus is a superconduct-ing solenoidof6 m internaldiameter, providinga magneticfield of3.8 T.Withinthesolenoidvolume area siliconpixelandstrip tracker,aleadtungstatecrystalelectromagneticcalorimeter(ECAL), andabrass andscintillatorhadron calorimeter,eachcomposedof abarrelandtwoendcapsections.Forwardcalorimetersextendthe pseudorapidity(

η

)coverageprovidedbythebarrelandendcap de-tectors.Muonsaremeasuredintherange

|

η

|

<

2

.

4,withdetection planes made using three technologies: drift tubes, cathode strip chambers, and resistive plate chambers, embedded in the steel flux-return yoke outside the solenoid. The electron momentum is estimatedby combining the energymeasurement in the ECAL withthemomentummeasurementinthetracker.Eventsof inter-est are selected using a two-tiered trigger system [19]. The first level,composedofcustom hardware processors,usesinformation from the calorimeters andmuon detectors to select events. The secondlevel,knownasthehigh-leveltrigger,consistsofafarmof processorsrunningaversionofthefulleventreconstruction soft-wareoptimizedforfastprocessing.Amoredetaileddescriptionof theCMSdetector,togetherwithadefinitionofthecoordinate

sys-tem used andthe relevant kinematic variables, can be found in Ref. [20].

3. Simulationofevents

Signal and background events are simulated to NLO accuracy witheitherthe powheg orthe MadGraph5_amc@nlo [21] Monte Carlo (MC) eventgenerator. The t-channel signal process [22] is simulated with powheg 2.0 [23–25] in the four-flavor scheme (4FS), where b quarks are produced via gluon splitting. This scheme yields a more precise description of the kinematic dis-tributions of t-channel signal eventsthan the 5FS [4,26]. Forthe normalizationofthesignalsamplesthepredictionsderivedinthe 5FS(seeEq. (1))areemployed.Thett background [

¯

27] issimulated using powheg 2.0 andis normalizedto theprediction calculated with top++ 2.0 [28]. The production of single top quarks asso-ciated to W bosons (tW) is simulated with powheg 1.0 in the 5FS [29],normalizedtoapredictionprovidingapproximateNNLO accuracy [30,31].Thevalueofthetopquarkmassinthesimulated samplesis

m

t

=

172

.

5 GeV.Events withW andZbosonsin

asso-ciation withjetsare simulatedusing MadGraph5_amc@nlo 2.2.2 and the FxFx merging scheme [32]. Predictions calculated with fewz3.1 [33–35] areemployedforthenormalizationofthesetwo processes. For all samples, pythia 8.212 [36] is used to simulate parton shower andhadronization. The underlying event is mod-eled for all samples using the tune CUETP8M1 [37], except for thet

¯

t sample,forwhichthetuneCUETP8M2T4 [38] isused,which providesamoreaccuratedescriptionofthekinematicdistributions ofthetop quark pairandofthejetsint

¯

t events.The parameter-izationofthePDFsusedinallsimulationsisNNPDF3.0NLO[39]. Allofthegeneratedeventsundergoafullsimulationofthe detec-tor response usinga model ofthe CMSdetectorimplemented in Geant4[40].Additionalppinteractionswithinthesameornearby bunch crossing (pileup) are included in the simulation with the samedistributionasobservedindata.

4. Eventselectionandtopquarkreconstruction

Inthisanalysis,thesignatureofthesingletopquark

t-channel

productionprocessconsistsofachargedlepton,aneutrino,which is observed as pT imbalance, a light-quark jet, which is often

produced in the forward direction, and a jet arising from the hadronization of a bottom quark (b jet) fromthe top quark de-cay. A second b jet, arising in the production process via gluon splitting,generallyhasasofter

p

Tspectrumandabroader

η

distri-butioncomparedtotheb jetoriginatingfromthetopquarkdecay, and therefore often escapes detection. The event selection crite-riaarechosenaccordingtothissignatureandeventsmustcontain one muon orelectron candidateand atleast two jets. Events in themuonchannelareselectedonlineusingatriggerthatrequires an isolatedmuonwithpT

>

24 GeV and

|

η

|

<

2

.

4.Intheelectron

channel,atriggerisusedthatrequireselectronswith

p

T

>

32 GeV

and

|

η

|

<

2

.

1.Only eventsforwhich atleastone primary vertex isreconstructedareconsideredintheanalysis.Theprimaryvertex mustbereconstructedfromatleastfourtracksthathavea longi-tudinal distance

|

dz

|

<

24 cm and a radial distance

|

dxy

|

<

2 cm from the interaction point. If more than one primary vertex is foundinanevent,thereconstructedvertexwiththelargestvalue ofsummedphysics-object p2

T istakentobetheprimarypp

inter-actionvertex. Thephysicsobjectsarethejets, clusteredusingthe jetfindingalgorithm [41,42] withthetracksassignedtothevertex asinputs,andtheassociatedmissingtransversemomentum,taken asthenegativevectorsumofthe

p

Tofthosejets.

Theparticle-flow(PF)algorithm [43],whichoptimallycombines information from all subdetectors, is used forthe reconstruction

Fig. 2. Eventyieldsfortherelevantprocessesinallcategoriesafterapplyingthefulleventselectioninthemuon(left)andelectron(right)channels.Theyieldsareshown separatelyforpositively(+)andnegatively(−)chargedmuons(electrons).Theuncertaintiesincludestatisticalandallsystematicuncertainties.Theyieldsareobtainedfrom simulation,exceptfortheQCDmultijetcontribution,whichisderivedfromdata(seeSection5).

of the individual particles. Muon candidates must have at least one hit in the muon detector and at least five hits in the sil-icon tracker. They are then reconstructed by a global fit to the informationfromthe silicontracker andthe muon spectrometer. Selected muons must fulfill the criteria pT

>

26 GeV,

|

η

|

<

2

.

4,

andrelativeisolation, Irel

<

0

.

06.The Irel ofachargedlepton

can-didateiscalculated by summingthe transverse energydeposited byphotonsandchargedandneutralhadronswithinaconeofsize

√

(

η

)

2

+ ( φ)

2

<

0

.

4 (where

φ

istheazimuthalangleinradians) formuonsand0.3forelectrons arounditsdirection,correctedfor contributionsfrompileup [44],relativetoits pT.

Electroncandidatesarereconstructedbyfittingtracksinthe sil-icontracker usingtheGaussian-sum filter [45] and matchingthe trackstoenergyclustersintheECAL.Theelectronidentificationis performedusingninedifferentvariablesandvariousselection cri-teria,includinga requirementontherelative isolation Irel

<

0

.

06.

Electronsare required to have pT

>

35 GeV and

|

η

|

<

2

.

1,while

electrons falling inthe gapbetween theECAL barrelandendcap regions (1

.

44

<

|

η

|

<

1

.

57) are rejected. Events containing addi-tionalmuonswith pT

>

10 GeV and

|

η

|

<

2

.

4 or additional

elec-tronswith pT

>

15 GeV and

|

η

|

<

2

.

5 arerejected. Inbothcases,

thecriteria on thelepton identification andisolation are relaxed (Irel

<

0

.

2 formuons; Irel

<

0

.

18 for electrons intheECAL barrel

andIrel

<

0

.

16 forelectronsintheECALendcaps).LeptonpT- and

η

-dependentscalefactorsareappliedtocorrectfordifferencesin theleptonreconstructionefficienciesbetweendataandsimulation. Jets are clustered using the anti-kT clustering algorithm [41]

witha distanceparameter of 0.4, asimplemented in the FastJet package [42].The effect ofadditionaltracks andcalorimetric en-ergy depositsfrom pileupon the jet momentum is mitigated by discardingtracks identifiedto be originatingfrompileupvertices andapplyinganoffsetcorrection toaccountforremaining contri-butions.Jetenergycorrectionsarederivedfromsimulationtobring themeasuredaverageresponseofjetstothatofparticle-leveljets. Insitumeasurements ofthemomentumbalanceindijet,

γ

+

jet, Z

+

jet, and multijet events are used to account for any residual differencesinthe jetenergyscaleindata andsimulation [46].In this analysis, jets with pT

>

40 GeV and

|

η

|

<

4

.

7 are selected.

The combined secondary vertex algorithm (CSVv2) [47] is used to identify b jets, which are required to have pT

>

40 GeV and

|

η

|

<

2

.

4.Theefficiencytoidentifyjetsfromb quarksisabout40% atthechosen workingpoint,while theprobability tomisidentify jetsfromlightquarksorgluonsasb jetsis0.1%.Correctionstothe simulationareappliedinordertoaccountforthedifferenceinthe b taggingefficiencyindataandsimulation.

TosuppressthebackgroundfromQCDmultijetprocessesinthe electronchannel,eventsmustfulfill pmiss

T

>

30 GeV.Foreventsin

the muon channel thisvariable is not sufficiently well modelled, andarequirementonthetransversemassoftheW bosonis im-posedinstead.ThetransversemassoftheWbosonisdefinedas

mW_T

=



2pT,μpmissT



(

1

−

cos

φ) >

50 GeV

.

(2) Here, pmiss_T isthemagnitudeofthetransverse momentumvector



pmiss_T .Thisvectorisdefinedastheprojectionontotheplane per-pendiculartothebeamaxisofthenegativevectorsumofthe mo-mentaofallreconstructedPFobjectsinanevent.Theenergyscale correctionsappliedtojetsarepropagatedto p



miss

T [48].Theangle

betweenthedirectionsofthemomentumvectorofthemuonand



pmiss_T is

φ

.

The selected events are divided into fourdifferent categories, depending on the number of selected jets and the number of b-tagged jets (njets-mtags). The category with two selected jets, one of which is identified as originating from a bottom quark, i.e., 2jets-1tag category, provides the largest contribution of sig-nal eventsconstituting thesignal category. Events withthree se-lected jets withone ortwo ofthem b-tagged,namely events in the3jets-1tagand3jets-2tagscategories,aredominatedbyt

¯

t pro-duction.Theseserve ascontrol categoriesthat areusedinthe fit toconstrainthecontributionfromthisdominantbackground pro-cess. Besidesthesecategories, afourthcategorycontaining events withtwoselectedjetsandnoidentifiedb jets,the2jets-0tags cat-egory, is defined to validate the estimation of the QCD multijet backgroundcontributionindata.

The numbers of selected events are shown in Fig. 2 for the muonandelectronchannels.Inbothchannels,theeventyieldsare shownseparatelyforeventswithpositivelyandnegativelycharged muons(electrons).Positivelychargedleptonsstemfromtopquarks andnegativelychargedleptonsfromtopantiquarks.The contribu-tionfromtheQCDmultijetbackgroundisdetermineddirectlyfrom dataasdescribed inSection5.Fortheother processes,theevent yieldsarederivedfromsimulation.

The momentum four-vector of the top quark is reconstructed fromthemomenta ofitsdecayproducts:thechargedlepton, the reconstructedneutrino,andtheb jet.Theambiguityofthe assign-mentofone ofthetwob-taggedjetstotheb quarkfromthetop quark decayinthe3jets-2tagscategoryissolved bychoosing the b jetthatleadstoareconstructedtopquarkmassclosertothetop quark massinthesimulation.Inthe3jets-1tag category, two un-taggedjetsexist,ofwhichtheonewiththehighest

|

η

|

isassigned tothelight-quarkjetinforwarddirection.Thetransverse momen-tumof theneutrino,



pT,ν , can beobtained from



pmissT . Assuming

energy-momentumconservationattheW



ν

vertexandsettingthe Wbosonmassto

m

W

=

80

.

4 GeV, thelongitudinalmomentum of

theneutrino,

p

z,ν , canbecalculatedas

pz,ν

=



pz, p2_T,

±

1 p2_T,





2_p2 z,

−

p2T,

(

p2p2T,ν

− 

2

),

(3) where



=

m 2 W 2

+ 

pT,

· 

pT,ν

,

(4) and p2_

=

p2_T,

+

p2_z, denotes the squared momentum of the chargedlepton. Ingeneral, thisprocedure resultsin twopossible solutions for pz,ν , which can haveeither realorcomplex values. If both solutions take real values, the one withthe smallest ab-solute value is chosen [49,50]. In the caseof complex solutions, thetransversecomponentsoftheneutrinomomentumare modi-fiedsuch that thealgebraic discriminant inEq. (3) becomes null, while still fulfilling the constrainton the W boson mass. Ofthe possible solutions for px,ν and py,ν that resolve the problem of thenegativediscriminant,thecoordinatepairthatisclosesttothe correspondingcomponentsofp



miss_T ischosen.

5. ModelingandnormalizationoftheQCDmultijetbackground BecauseofthetheoreticallychallengingsimulationofQCD mul-tijetprocesses,thisbackgroundcontributionissuppressedasmuch aspossibleandtheremainingcontaminationismodeledfromdata. As described in Section 4, requirements on mW_T or pmiss_T are ap-pliedontheeventsinthemuonandelectronchannelstosuppress eventsfromQCDmultijetproduction.Differentvariableshavebeen chosenforthetwochannelsas

m

W

T isfoundtobebettermodeled

comparedto

p

miss

T inthemuonchannelandviceversainthe

elec-tronchannel.Thesevariablesprovidethehighestseparationpower between QCD multijet events and other processes, including the

t-channel single top quark production, for the respective lepton finalstate.TheremainingQCDcontributionismodeled with sam-ples ofeventsderived from sidebandregions indata enriched in QCDmultijetevents.Thesesidebandregionsaredefinedby invert-ing the muon or electron isolation requirements, whileall other selection criteria described in Section 4 remain the same. As no reliable prediction forthe QCD contributionto the selected data isavailable, thenormalizationforthe QCDmodeling samplesare estimated from data. For that purpose, the same variables that are used to suppress this backgroundcontributions are explored by fitting their distributions over the entire range. A maximum likelihoodfit isperformedon themW

T or p

miss

T distribution using

twoprobabilitydensityfunctions,onefortheQCDmultijetprocess andoneforallother non-QCDprocesses.Thelatterdistributionis obtainedbyaddingthedifferentnon-QCDcontributionsfrom sim-ulation, including the t-channel signal, according to their theory predictions, while the former is modeled using events from the sidebandregionsdescribed above.The fitisperformedseparately in the 2jets-1tag and the 3jets-1tag categories. The contribution fromQCDmultijeteventstothe3jets-2tagscategoryisonlyminor andisneglected.TovalidatetheQCDestimationprocedure,thisfit isalsoperformedinthe2jets-0tagscategory,asignal-depleted cat-egorythatprovidesanumberofbackgroundeventsofthissource larger by factors of 10 and 28for the muon and electron chan-nel,respectively.Theentirerangeofthedistributionsisfittedand theresultingyieldsoftheQCDmultijetcontributionarethenused inthesignal regions inwhichtherequirements

m

W

T

>

50 GeV or pmiss_T

>

30 GeV are applied. In this extrapolation,an uncertainty of50%isapplied tocoveralleffects fromvariations intheshape andrate of thisbackground process. Fig. 3 showsthe fitted mW T

and

p

miss

T distributionsinthe2jets-1tag,3jets-1tag,and2jets-0tags

categories. Goodagreementbetweentheresultsofthefitandthe dataisfoundinthelow-mW_T andlow-pmiss_T regions,where signifi-cantcontributionsfromtheQCDmultijetbackgroundareexpected. Thissimpletwo-templatefitisdesignedtogiveareliableestimate of theQCD multijet contributionandis not expectedto describe alsothetailsofthefitteddistributionswiththesameaccuracy. 6. Signalextraction

BDTalgorithms,implementedinthe tmva package [51] are em-ployed to combine multiple variables into single discriminators, andthus enhance theseparation betweensignal andbackground processes.Kinematic variablesthat aresuitable todistinguish the single top quark t-channel signal process from the main back-groundcontributionsare usedfortheBDT training.Eachofthese variables isrequiredto be modeledreasonablyin thesimulation. The list of variables used fordiscrimination can be found in Ta-ble 1. The five most important variables are the light-quark jet

|

η

|

,thereconstructedtopquarkmass,whichhashigh discrimina-tionpoweragainstbackgroundprocesseswherenotopquarksare produced,theinvariant massofthedijetsystemconsistingofthe light-quarkjetandtheb-taggedjetfromthetopquarkdecay,the distancein the

η

–

φ

plane (

R) betweenthe chargedleptonand theb jet,andthecosineoftheanglebetweenthechargedlepton andthelight-quarkjetintherestframeofthetopquark(cos

θ

∗). Figs. 4 and5show the distributions ofthesefive input variables fromdatacomparedtothesimulation.

The BDTsare trainedinthe 2jets-1tag category,separately for muonsandelectrons.Thelepton

|

η

|

and

m

W

T distributionsareonly

considered ineventswithmuons,whilethe pmiss_T variableisonly usedintheelectron sample.Thesamplesofsimulatedsignaland backgroundevents,aswell astheQCD multijetsamplefrom side-band data,arenormalizedaccordingtotherespectivepredictions, with each sample split into two parts. One half is used for the training, while the other half serves for validation purposes and theactualmeasurement.ThetrainedBDTsarethenappliedtothe 2jets-1tag,3jets-1tag,and3jets-2tagscategories,separatelyforthe twodifferentflavorsandchargesofthelepton.

A maximum likelihood fit is performed simultaneously on twelvedifferentBDToutputdistributions(twoleptoncharges,two leptonflavors,three

njets-mtags

categories).Byincludingthe cate-gorieswiththreeselectedjetsinthefit,thet

¯

t background,which dominates these categories, is constrained. In this fit, the back-groundratesare determined byintroducing nuisanceparameters, while the signal rate is a free parameter of the fit. The results of the fit are the cross sections for the productionof single top quarks (

σ

t-ch,t)andantiquarks (

σ

t-ch,¯t).The ratioofthetwo cross

sectionscanbecalculatedfromthesetworesultspropagatingtheir uncertainties to the ratio using the covariance matrix of the fit. However, amoreelegant andstraightforward wayofproperly ac-countingforthecorrelationsbetweentheuncertaintiesinthetwo cross sections is used by repeating the fit with one of the two cross sectionsreplaced by their ratio.This way,potential cancel-lations ofuncertainties are taken into account directly in the fit anddo not need tobe calculated afterwards. Thefitted distribu-tions ofthe BDToutput distributions areshowninFigs. 6and7. To verify the quality of the fit, for each distribution, the pull is alsoshown.Thepullisdefinedasthedifferencebetweenthe dis-tribution in data and the fitted one, divided by the uncertainty

=

√

2_data

−

2_fit,where

data isthePoissonuncertainty inthe

data and

fit is the uncertainty of the fit,including the

statisti-cal component and all uncertainties that have been included as nuisance parameters. As a cross-check, thisfit is also performed

Fig. 3. Outcomeofthemaximumlikelihoodfit tothemW

T distributionofeventswithmuons(left)andtothe p miss

T distributionforeventswithelectrons(right)inthe

2jets-1tag(upperrow),3jets-1tag(middlerow),andthe2jets-0tags(lowerrow)categories.TheQCDbackgroundtemplateisextractedfromthesidebandregionindata.For thefit,onlystatisticaluncertaintiesareconsidered.

Fig. 4. ThethreemostdiscriminatinginputvariablesforthetrainingoftheBDTsinthemuonchannel(left)andintheelectronchannel(right):theabsolutevalueofthe pseudorapidityofthelight-quarkjet,themassofthereconstructedtopquark,themassofthelight-quarkjetandtheb-taggedjetassociatedtothetopquarkdecay.The variablesareorderedbytheirimportance.Thesimulationisnormalizedtothetotalnumberofeventsindata.Theshadedarescorrespondtothequadraticsumofstatistical andsystematicuncertaintiesinthesimulationbeforeperformingthefit.Alsoshownistherelativedifferencebetweenthedistributionsindataandsimulationinthelower panels.

Table 1

InputvariablesfortheBDTs.ThevariablesmW

T andlepton|η|areonlyusedinthetrainingofeventswitha

muon,whilepmissT isonlyconsideredasinputforeventswithanelectron.

Variable Description

Light-quark jet|η| Absolutevalueofthepseudorapidityofthelight-quarkjet Top quark mass Invariantmassofthetopquarkreconstructedfromthelepton,the

neutrino,andtheb-taggedjetassociatedtothetopquarkdecay Dijet mass Invariantmassofthelight-quarkjetandtheb-taggedjetassociatedtothe

topquarkdecay

R (lepton, b jet) R betweenthemomentumvectorsoftheleptonandtheb-taggedjet associatedwiththetopquarkdecay

cosθ∗ Cosineoftheanglebetweentheleptonandthelight-quarkjetintherest frameofthetopquark

Jet pTsum Scalarsumofthetransversemomentaofthelight-quarkjetandthe

b-taggedjetassociatedtothetopquarkdecay

mW

T TransversemassoftheWboson

pmiss

T Missingmomentuminthetransverseplaneoftheevent

R (light jet, b jet) R betweenthemomentumvectorsofthelight-quarkjetandthe b-taggedjetassociatedtothetopquarkdecay

Lepton|η| Absolutevalueofthepseudorapidityoftheselectedlepton W boson|η| AbsolutevalueofthepseudorapidityofthereconstructedWboson Light-quark jet mass Invariantmassofthelight-quarkjet

Fig. 5. ThefourthandfifthmostdiscriminatinginputvariablesforthetrainingoftheBDTsinthemuonchannel(left)andintheelectronchannel(right):the R between

themomentumvectorsoftheleptonandtheb-taggedjetassociatedwiththetopquarkdecay,thecosineoftheanglebetweentheleptonandthelight-quarkjetintherest frameofthetopquark.Thesimulationisnormalizedtothetotalnumberofeventsindata.Theshadedarescorrespondtothequadraticsumofstatisticalandsystematic uncertaintiesinthesimulationbeforeperformingthefit.Alsoshownistherelativedifferencebetweenthedistributionsindataandsimulationinthelowerpanels.

Fig. 6. TheBDToutputdistributionsinthe2jets-1tagcategory(upperrow),the3jets-1tagcategory(middlerow),andthe3jets-2tagscategory(lowerrow)forpositively chargedmuons(leftcolumn)andelectrons(rightcolumn).Thedifferentprocessesarescaledtothecorrespondingfitresults.Theshadedareascorrespondtotheuncertainties afterperformingthefit.Ineachfigure,thepullisalsoshown.

Fig. 7. BDToutputdistributionsinthe2jets-1tagcategory(upperrow),the3jets-1tagcategory(middlerow),andthe3jets-2tagscategory(lowerrow)fornegativelycharged muons(leftcolumn)andelectrons(rightcolumn).Thedifferentprocessesarescaledtothecorrespondingfitresults.Theshadedareascorrespondtotheuncertaintiesafter performingthefit.Ineachfigure,thepullisalsoshown.

separately foreach lepton flavor. The obtainedvaluesare consis-tentwithintheiruncertaintiescomparedtothemainresultsinthe combinedmuonandelectronchannel.

7. Systematicuncertainties

Several sources of systematic uncertainties are considered in the analysis, either asnuisance parameters inthe fit to the BDT distributions (profiled uncertainties) or asnonprofiled uncertain-ties.Whilemostuncertaintysources,likepurelyexperimentalones and uncertainties in the rates and the modeling of the back-grounds,can be profiled in the fit,this is not possible forthose uncertaintysourcesthat arerelatedtothemodelingofthesignal process. As theresults forthe signal cross sectionsare given for the full phase space, the analysis contains an extrapolation from thephasespaceoftheselecteddataset,inwhichtheactual mea-surement takes place, to the full phase space, using predictions fromthesignalsimulationabouttheshapesoftherelevant distri-butionsoutsidethemeasuredarea.Hence,theuncertaintiesinthe modelingofthesignalprocessapplynotonlytothephasespaceof theselecteddatasetbuttothefullphasespaceandshould there-forenotgetconstrainedfromthefitinthisreducedphasespace. Theirimpactisdeterminedbyrepeatingtheanalysisusingvaried templates according to the systematic uncertainty sources under studyin thefit instead ofthe nominaltemplates. The larger ab-soluteshiftintheparameter ofinterest,eithercausedby“down” or“up”variationofthesystematicsourceunderstudy,istakenas symmetricuncertaintyinbothdirections.Inthefollowing,the dif-ferentuncertaintysources that are consideredin theanalysisare brieflydescribed.Theyaregroupedincategoriesofrelatedsources. It is indicated whetherthe uncertainty sources are implemented viashapemorphing(“shape”)orvianormalization(“rate”).

Nonprofiled uncertainties

•

Signal modeling (shape): The following uncertainty sources coverpotentialmismodelingofthesingletopquark

t-channel

signalprocess.Theyarenotconsideredasnuisanceparameters in the fit but evaluated by repeating the full analysis using samples ofsimulated signal events that feature variations in themodeling parameters coveringthe systematicuncertainty sourcesunderstudy.

– Renormalizationand factorization scales (shape): The uncer-tainties caused by variations in the renormalization and factorization scales (

μ

R

/

μ

F) are considered by applying

weights [52], corresponding to simultaneously doubled or halved renormalization and factorization scales with the nominalvalue set to172.5 GeV, onthe BDT output distri-butions.

– Matching

of matrix element and parton shower (shape): The

pa-rameter

h

damp

=

1

.

581₋+00..658585mt (with

m

t

=

172

.

5 GeV) [38],

which controls the matching between the matrix-element level calculation andthe parton shower (ME-PS matching) andregulatesthehigh-pTradiationinthesimulation,is

var-iedwithinitsuncertainties.

– Partonshower scale (shape): The renormalizationscalesofthe initial-stateandfinal-statepartonshower(PS)arevariedby factors oftwo andone half withthe nominalvalue set to 172.5 GeV.

– Signal

PDFs (shape): The

impact due to the choice of PDFs is studied by replacing the nominal signal templates with reweighteddistributionsderivedfromtheeigenvector varia-tionsofNNPDF3.0NLO [39].Thefullenvelopeofthe eigen-vectorvariationsisused.

•

Integrated luminosity (rate): The relative uncertaintyinthe in-tegratedluminosityisdetermined tobe

±

2

.

5% [53].This

un-certainty is addedto the totaluncertainties of themeasured crosssections.

Profiled uncertainties

•

Jet energy scale (shape): All reconstructedjetfour-momentaare simultaneously variedinsimulationaccordingto the pT- and

η

-dependent uncertainties in the jet energyscale (JES) [54]. In total,26differentuncorrelatedJESuncertaintysources are considered.Thesevariationsarealsopropagatedto pmiss_T .

•

Jet energy resolution (shape): To account for the difference in thejetenergyresolution(JER)betweendataandsimulation,a dedicated smearingisapplied tothe simulatedjets [54],and theresolutionsarevariedwithintheiruncertainties.

•

Unclustered energy (shape): The contributionsofunclusteredPF candidates to pmiss

T are varied within their respectiveenergy

resolutions [55].

•

b tagging

(shape): The

scale factors thatare usedto calculate the efficiency corrections of the CSVv2 b tagging algorithm are variedup anddownwithin theiruncertainties [47]. From theseupanddownvaried scalefactors,up anddown shifted efficiencycorrectionsare calculatedandappliedtothe simu-lation.

•

Muon and electron efficiencies (shape): The efficiencies of the leptonidentificationandisolation,ofthetriggerpaths,andof the detectorresponse aredetermined witha“tag-and-probe” method [56] from Drell–Yan events falling into the Z boson masswindow. The efficiencycorrectionfactors arevaried ac-cordingtothe

p

T- and

η

-dependentuncertainties.

•

Pileup (shape): The uncertaintyinthe averageexpected num-berofpileupinteractionsispropagatedasasystematic uncer-taintytothismeasurementbyvaryingthetotalinelasticcross sectionby

±

4

.

6% [57].

•

QCD background normalization (rate): As describedinSection5, anuncertaintyof

±

50% isappliedtotheQCDbackground esti-matetocoveralleffectsfromvariationsintheshapeandrate ofthisprocess.

•

Limited size of samples of simulated events (shape): The limited number of available simulated events is considered by per-formingthefitusingtheBarlow–Beestonmethod [58].

•

t

¯

t backgroundmodeling (shape) and normalization (rate): Multiple

systematiceffectsonthet

¯

t backgroundpredictionarestudied: the influence of the parton shower scale and of the match-ing betweenthe NLO calculation andtheparton shower, the impact of variations in the initial- andfinal-state radiation— dependingonthechoiceof

α

S—andtheeffectofuncertainties inthemodelingoftheunderlyingevent.Dedicatedt

¯

t simula-tionsamplesareusedtostudyeacheffectindividually,where the corresponding parameters are varied within their uncer-tainties. To account for the uncertainty in the prediction of theinclusivet

¯

t crosssection,arateuncertaintyof

±

6%is ap-plied [59].

•

Top quark pT (shape): In differential measurementsofthe top

quark pT int

¯

t events,thepredicted pT spectrum isfound to

beharder thantheobservedspectrum [60,61].Toaccountfor this mismodeling, the results derived using the default sim-ulation fort

¯

t arecompared to theresults usingsimulated t

¯

t events that are reweighted according to the observed differ-ence betweendata and simulation.This results in one-sided variationsofthenominaltemplate.

•

tW background normalization (rate): To account forthe uncer-tainty in the cross section of tW production and to cover a possible additional systematicuncertainty arising from the procedurewhichdealswiththeoverlapwiththet

¯

t processat

NLO, a rateuncertainty of

±

11%, corresponding to the most precise measurement [62],isapplied.Oneadditionalrate un-certainty isincludedinthefittoaccountfortheimpactfrom thechoiceofPDFsandtheirspecificvariation(

±

4%).To deter-minetheinfluenceofpossiblemismodelingofthetWprocess, thenominalsampleiscomparedtosamplesgeneratedwitha partonshowerscaleshiftedby

±

1 standarddeviation.

•

W

/

Z

+

jets background normalization (rate): To takethe uncer-taintyinthecrosssectionsoftheW

+

jetsandZ

+

jets contribu-tions intoaccount,aswellaspossibleeffectsduetoselecting heavy-flavored jets, individual rateuncertainties of

±

10% are applied.Byemployingtheseuncertainties,afullevaluationof uncertaintysourcesfortheseprocessesisachieved,aswell as aconsistenttreatmentamongthedifferentbackground contri-butions.

•

Renormalization and factorization scales (shape): For the back-groundcontributionsfromt

¯

t,tW,andW

/

Z

+

jets production, the uncertainties causedby variations in therenormalization andfactorizationscales (

μ

R

/

μ

F) are consideredby

reweight-ing [52] the BDT output distributions according to simulta-neously doubled or halved renormalization andfactorization scales. In the case of the t

¯

t and tW processes, the nominal value ofthescales issetto172.5 GeV,whiledynamic scales, definedas



m2_W/Z

+ (

pW_T/Z

)

2,areusedforW

/

Z

+

jets produc-tion.Thisuncertaintyisestimatedforeachprocessseparately.

•

Background PDFs (shape): By reweighting distributions derived from the eigenvector variations of NNPDF3.0 NLO [39], the impact due to the choice of PDFs is studied for the t

¯

t and W

/

Z

+

jets background processes. The full envelope of the eigenvector variations is used. The variations in the back-ground PDFs are treatedas uncorrelatedto the variations in the signal PDFs, because the dominant contributions to the signalPDFsstemfromupanddownquarks,whereasthe back-groundPDFsaredominatedbygluons.

Theby far largestcontributionto theselected dataset comes from the t

¯

t background. To understand this background as well as possible, the fit is performed simultaneously in different

njets-mtags categories.Asaconsequence,nuisanceparametersfor systematicuncertainties that can causemigrations of events be-tween the different categories, like the t

¯

t modeling and the jet reconstructionuncertainties,getconstrainedbythefit.Theimpact ofthe individual systematic uncertainties on the measured cross sectionsandtheir ratioare listed inTable 2.Fornonprofiled un-certainties,thechangeoftheresultduetotherespectivevariation islisted.Theimpactofeachprofileduncertaintyisdefinedasthe shiftintheparameterofinterestthat isinduced byrepeatingthe fitwiththecorrespondingnuisanceparameterfixedateitherone standarddeviationaboveorbelowitspost-fitvalue,withallother nuisanceparameters treatedas usual. Ofthe two resultingshifts always thelarger one istakenasthe impact.For Table2 several nuisanceparametersaregroupedtogetherbyaddingtheirimpacts inquadrature.

Thedominantuncertaintiesforthecrosssectionmeasurements come from variations of the parton shower scale and from the matchingbetweenthematrixelementandthepartonshower em-ployedinthesignalmodeling.Thevariousuncertaintiesaffectthe twocrosssection measurementsinacorrelated way,whichleads toasignificantreductionoftheir impactwhencalculatingthe ra-tio. The strength of the cancellation depends on the correlation oftherespectiveuncertainties andtheir impactonthe twocross sections.Forinstance,thenonprofiled signal modeling uncertain-tiesare highlycorrelatedbetweenthetwo crosssectionsandthe onlyremaining uncertaintycontribution in the ratiocomes from thedifferencesinthe size oftheimpacts on theindividual cross

Table 2

Estimatedrelativeimpactofuncertaintiesinpercentofthemeasuredcrosssections orcrosssectionratio.

Rt-ch/Rt-ch σ/σ(t) σ/σ(¯t)

Nonprofiled uncertainties

μR/μFscale t channel 1.5 6.1 5.0

ME-PS scale matching t channel 0.5 7.1 7.8

PS scale t channel 0.9 10.1 9.6 PDF t channel 3.0 3.1 5.8 Luminosity – 2.5 2.5 Profiled uncertainties JES 0.9 1.5 1.8 JER 0.2 <0.1 0.2 Unclustered energy <0.1 0.1 0.2 b tagging 0.1 1.1 1.2

Muon and electron efficiencies 0.2 0.8 0.6

Pileup 0.1 0.9 1.0

QCD bkg. normalization <0.1 0.1 0.1

MC sample size 2.5 2.2 3.2

t¯t bkg. model and normalization 0.2 0.6 0.6

Top quark pT <0.1 <0.1 <0.1

tW bkg. normalization 0.1 0.5 0.6

W/Z+jets bkg. normalization 0.3 0.6 0.9

μR/μFscale t¯t, tW, W/Z+jets 0.1 0.2 0.3

PDF t¯t, W/Z+jets <0.1 0.2 0.2

sections.Thedominantuncertaintycontributionsintheratio mea-surementaretheuncertaintyduetothechoiceofthePDFsetfor the

t-channel

signalmodelandtheuncertaintyduetothesizeof thesimulationsamples.

8. Results

The measured cross sections for the t-channel production of singletopquarksandantiquarksare

σ

t-ch,t

=

130

±

1 (stat)

±

4 (prof)

±

18 (sig-mod)

±

3 (lumi) pb

=

130

±

1 (stat)

±

19 (syst) pb

=

130

±

19 pb

,

σ

t-ch,¯t

=

77

±

1 (stat)

±

2 (prof)

±

11 (sig-mod)

±

2 (lumi) pb

=

77

±

1 (stat)

±

12 (syst) pb

=

77

±

12 pb

.

Here, the uncertainty sources that are profiled in the fit, are la-beled as “prof”, the uncertainties on the signal modeling are la-beled as“sig-mod”, andtheuncertaintyduetotheintegrated lu-minosity measurement is labeled as “lumi”. The total systematic uncertaintyisobtainedby addingthe threeuncertainty contribu-tions inquadrature.Adding the

σ

t-ch,tand

σ

t-ch,¯t results,the total

crosssectionisfoundtobe

σ

t-ch,t+¯t

=

207

±

2 (stat)

±

6 (prof)

±

29 (sig-mod)

±

5 (lumi) pb

=

207

±

2 (stat)

±

31 (syst) pb

=

207

±

31 pb

,

wherethestatisticaluncertainties aretreatedasuncorrelatedand thesystematicuncertainties ascorrelatedbetweenthe

σ

t-ch,t and

σ

t-ch,¯t measurements. The total crosssection is used to calculate

theabsolutevalueoftheCKMmatrixelement

V

tb.Neglecting

|

Vtd

|

and

|

Vts

|

astheyaresignificantlysmallerthan

|

Vtb

|

,andassuming

thatthetopquarkexclusivelydecaystoab quarkandaWboson, leadsto

Fig. 8. ComparisonofthemeasuredRt-ch(centraldashedline)withtheNLO pre-dictionsfromdifferentPDFsets,provided byLHAPDF6.2.1 [65]:NNPDF3.0 [39], NNPDF3.1 [66],CT14 [67],ABMP16 [68,69],MMHT2014 [70],HERAPDF2.0 [71].The hathor5FScalculationisusedwiththenominalvaluesforthetopquarkpolemass and

α

SsettothebestvaluesofeachPDFset.Theuncertaintybarsforthedifferent

PDFsetsincludetheuncertaintyduetothefactorizationandrenormalizationscales, theuncertaintyinthetopquarkpolemass,andthecombinedinternalPDF+αS

un-certainty.Forthemeasurement,thestatisticalandtotaluncertaintiesareindicated individuallybytheinnerandouteruncertaintybars.

|

fLVVtb

| =



σ

_t-ch,t+¯t

σ

theo t-ch,t+¯t

,

withthepredictedSMvalue

σ

theo

t-ch,t+¯t

=

217

.

0

+6.6

−4.6(scale)

±

6

.

2

(

PDF

+

α

S

)

pb [10,11,16] assuming

|

Vtb

|

=

1.The anomalousform

fac-tor fLVtakesthepossiblepresenceofananomalousWtbcoupling

intoaccount,with fLV

=

1 forthecaseinwhichtheWtb

interac-tion is a left-handed weak SM coupling and fLV

=

1 for physics

beyondtheSM [63].Themeasuredcrosssectiontranslatesto

|

fLVVtb

| =

0

.

98

±

0

.

07 (exp)

±

0

.

02 (theo)

.

Thefirstuncertaintyconsidersalluncertaintiesofthecrosssection measurement, while the second uncertainty is derived from the uncertaintyofthetheoreticalSMprediction.Assumingthe unitar-ityoftheCKMmatrix,alower limitof0.82isdeterminedinthe Feldman–Cousinsunifiedapproach [64] for

|

Vtb

|

at95%confidence

level.

Theratioofthecrosssectionsfortheproductionofsingletop quarksandantiquarksinthe

t channel

ismeasuredas

Rt-ch

=

1

.

68

±

0

.

02 (stat)

±

0

.

02 (prof)

±

0

.

05 (sig-mod)

=

1

.

68

±

0

.

02 (stat)

±

0

.

05 (syst)

=

1

.

68

±

0

.

06

.

Themeasuredratioiscomparedtothepredictionsusingdifferent PDF sets asshown in Fig.8. Good agreement betweenthe mea-surementandmostpredictionsisfound.

9. Summary

Eventswithone muon orelectronandmultiplejetsinthe fi-nalstateareusedtomeasurethecrosssectionsforthe

t-channel

production of single top quarks and antiquarks, and their ratio. Themeasuredcrosssectionsare130

±

1(stat)

±

19(syst) pb forthe productionofsingle topquarks,77

±

1(stat)

±

12(syst) pb forthe productionofsingletopantiquarks,and207

±

2(stat)

±

31(syst) pb forthetotal production.The latterresultisused tocalculatethe absolutevalueoftheCabibbo–Kobayashi–Maskawamatrixelement

|

fLVVtb

|

=

0

.

98

±

0

.

07(exp)

±

0

.

02(theo),includingan anomalous

form factor fLV. The measured ratio of the cross sections of the

two processes Rt-ch

=

1

.

68

±

0

.

02(stat)

±

0

.

05(syst) is compared to recentpredictions usingdifferentpartondistributionfunctions (PDFs)to describethe innerstructure ofthe proton.Good agree-mentwithmostPDF setsisfoundwithintheuncertainties ofthe measurement.

The statistical uncertainty plays only a minor role for the achievedprecisionofthemeasurements,whicharelimitedbythe systematic uncertainties in the modeling of the signal process. Deeperunderstandingoftheseeffectsandimprovedproceduresto estimate the uncertaintyare thereforecrucial tofurther decrease thesystematicuncertainty.Becauseofthecancellationof system-atic effects when measuring the ratio of cross sections Rt-ch, its precision,reportedinthisletter,issignificantlyimprovedwith re-spectto theresultsofprevious measurements.Thevalue of Rt-ch canbeusedtotestthepredictionsfromdifferentPDFsetsfortheir compatibilitywiththedata.

Acknowledgements

WecongratulateourcolleaguesintheCERNaccelerator depart-ments for the excellent performance of the LHC and thank the technical andadministrativestaffs atCERNand atother CMS in-stitutes for their contributions to the success of the CMS effort. Inaddition,wegratefullyacknowledgethecomputingcentersand personneloftheWorldwideLHCComputingGridfordeliveringso effectively thecomputinginfrastructure essentialto our analyses. Finally, we acknowledge the enduring support for the construc-tion andoperationofthe LHCandtheCMSdetectorprovided by the followingfundingagencies: BMBWFandFWF(Austria);FNRS and FWO (Belgium); CNPq, CAPES,FAPERJ, FAPERGS, andFAPESP (Brazil); MES (Bulgaria); CERN; CAS, MOST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); SENESCYT(Ecuador);MoER,ERCIUT,andERDF(Estonia);Academy ofFinland,MEC,andHIP(Finland);CEAandCNRS/IN2P3(France); BMBF, DFG, and HGF (Germany); GSRT (Greece); NKFIA (Hun-gary);DAEandDST(India);IPM(Iran);SFI(Ireland);INFN (Italy); MSIP andNRF (Republicof Korea);MES(Latvia); LAS(Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, andUASLP-FAI(Mexico);MOS(Montenegro);MBIE(NewZealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna);MON,ROSATOM,RAS,RFBR,andNRCKI(Russia);MESTD (Serbia);SEIDI,CPAN,PCTI,andFEDER(Spain);MoSTR (SriLanka); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR, and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU andSFFR (Ukraine); STFC (United Kingdom);DOEand NSF (USA).

Individuals have received support from the Marie-Curie pro-gramandtheEuropeanResearchCouncilandHorizon2020Grant, contract No. 675440 (European Union); the Leventis Founda-tion; 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’A-griculture (FRIA-Belgium); the Agentschap voor Innovatie door Wetenschap en Technologie (IWT-Belgium); the F.R.S.-FNRS and FWO (Belgium) under the “Excellence of Science – EOS” – be.h projectn. 30820817;the MinistryofEducation,YouthandSports (MEYS) of the Czech Republic; the Lendület (“Momentum”) Pro-gram and the János Bolyai Research Scholarship of the Hun-garian Academy of Sciences, the New National Excellence Pro-gram ÚNKP, the NKFIA research grants 123842, 123959, 124845, 124850, and 125105 (Hungary); the Council of Science and In-dustrial Research,India;theHOMING PLUSprogramofthe Foun-dation for Polish Science, cofinanced from European Union, Re-gional 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-bis2012/07/E/ST2/01406;theNationalPriorities Re-search Program by Qatar National Research Fund; the Programa Estatal de Fomento de la Investigación Científica y Técnica de ExcelenciaMaríade Maeztu,grantMDM-2015-0509 andthe Pro-grama Severo Ochoa del Principado de Asturias; the Thalis and Aristeiaprograms cofinancedbyEU-ESF andtheGreek NSRF;the Rachadapisek Sompot Fund for Postdoctoral Fellowship, Chula-longkornUniversity andthe ChulalongkornAcademicintoIts 2nd CenturyProjectAdvancementProject(Thailand);TheWelch Foun-dation,contractC-1845;andtheWestonHavensFoundation(USA). References

[1] U.Husemann,Top-quarkphysics:statusandprospects,Prog.Part.Nucl.Phys. 95(2017)48,https://doi.org/10.1016/j.ppnp.2017.03.002.

[2] ATLASCollaboration,Measurementofthet-channelsingletop-quark produc-tioncrosssection in pp collisionsat√s=7 TeVwith the ATLASdetector, Phys. Lett. B 717 (2012) 330, https://doi.org/10.1016/j.physletb.2012.09.031, arXiv:1205.3130.

[3] ATLAS Collaboration,Comprehensive measurementsoft-channelsingle top-quarkproductioncrosssectionsat√s=7 TeVwiththeATLASdetector,Phys. Rev.D90(2014)112006,https://doi.org/10.1103/PhysRevD.90.112006,arXiv: 1406.7844.

[4] ATLASCollaboration,Fiducial,totalanddifferentialcross-sectionmeasurements oft-channelsingletop-quarkproductioninpp collisionsat8TeVusingdata collectedbytheATLASdetector,Eur.Phys.J.C77(2017)531,https://doi.org/ 10.1140/epjc/s10052-017-5061-9,arXiv:1702.02859.

[5] ATLAS Collaboration, Measurement ofthe inclusivecross-sections ofsingle top-quarkandtop-antiquarkt-channelproduction in pp collisionsat √s=

13 TeVwiththeATLASdetector,J.HighEnergyPhys.04(2017)086,https:// doi.org/10.1007/JHEP04(2017)086,arXiv:1609.03920.

[6] CMSCollaboration,Measurementofthet-channelsingletopquarkproduction crosssectioninppcollisionsat√s=7 TeV,Phys.Rev.Lett.107(2011)091802,

https://doi.org/10.1103/PhysRevLett.107.091802,arXiv:1106.3052.

[7] CMSCollaboration,Measurementofthesingle-top-quarkt-channelcross sec-tioninpp collisionsat√s=7 TeV,J.HighEnergyPhys.12(2012)035,https:// doi.org/10.1007/JHEP12(2012)035,arXiv:1209.4533.

[8] CMSCollaboration, Measurementof thet-channel single-top-quark produc-tion cross section and ofthe |Vtb| CKM matrix element in pp collisions

at √s=8 TeV,J. HighEnergyPhys. 06(2014)090,https://doi.org/10.1007/ JHEP06(2014)090,arXiv:1403.7366.

[9] CMSCollaboration,Crosssectionmeasurementoft-channelsingletopquark production inpp collisions at √s=13 TeV, Phys. Lett.B 772(2017)752,

https://doi.org/10.1016/j.physletb.2017.07.047,arXiv:1610.00678.

[10] M. Aliev, H. Lacker, U. Langenfeld, S.-O. Moch, P. Uwer, M. Wiedermann, HATHOR: HAdronic Top and Heavy quarks crOss section calculatoR, Com-put. Phys. Commun. 182(2011) 1034, https://doi.org/10.1016/j.cpc.2010.12. 040,arXiv:1007.1327.

[11] P.Kant,O.M.Kind,T.Kintscher,T.Lohse,T.Martini,S.Molbitz,P.Rieck,P.Uwer, HatHorforsingletop-quarkproduction:updatedpredictionsanduncertainty estimatesforsingletop-quarkproductioninhadroniccollisions,Comput.Phys. Commun.191(2015)74,https://doi.org/10.1016/j.cpc.2015.02.001,arXiv:1406. 4403.

[12] A.D.Martin,W.J.Stirling,R.S.Thorne,G.Watt,PartondistributionsfortheLHC, Eur.Phys.J.C63(2009)189,https://doi.org/10.1140/epjc/s10052-009-1072-5, arXiv:0901.0002.

[13] A.D.Martin,W.J.Stirling,R.S.Thorne,G.Watt,Uncertaintieson

α

Singlobal

PDFanalysesandimplicationsforpredictedhadroniccrosssections,Eur.Phys. J. C 64 (2009) 653, https://doi.org/10.1140/epjc/s10052-009-1164-2, arXiv: 0905.3531.

[14] H.-L.Lai,M.Guzzi,J.Huston,Z.Li,P.M.Nadolsky,J.Pumplin,C.P.Yuan,New partondistributionsforcolliderphysics,Phys.Rev.D82(2010)074024,https:// doi.org/10.1103/PhysRevD.82.074024,arXiv:1007.2241.

[15] R.D.Ball,V.Bertone,S.Carrazza,C.S.Deans,L.D.Debbio,S.Forte,A.Guffanti, N.P.Hartland,J.I.Latorre,J.Rojo,M.Ubiali,PartondistributionswithLHCdata, Nucl.Phys.B867(2013)244,https://doi.org/10.1016/j.nuclphysb.2012.10.003, arXiv:1207.1303.

[16]M.Botje,J.Butterworth,A.Cooper-Sarkar,A.deRoeck,J.Feltesse,S.Forte,A. Glazov,J.Huston,R.McNulty,T.Sjöstrand,R.Thorne,ThePDF4LHCworking groupinterimrecommendations,arXiv:1101.0538,2011.

[17]S.Alekhin,etal.,ThePDF4LHCWorkingGroupInterimReport,arXiv:1101.0536, 2011.

[18] E.L.Berger,J.Gao,C.P.Yuan,H.X.Zhu,NNLOQCDcorrectionstot-channel sin-gletop-quarkproduction anddecay,Phys.Rev.D94(2016)071501,https:// doi.org/10.1103/PhysRevD.94.071501,arXiv:1606.08463.

[19] CMS Collaboration, The CMStrigger system, J. Instrum. 12 (2017) P01020,

https://doi.org/10.1088/1748-0221/12/01/P01020,arXiv:1609.02366. [20] CMSCollaboration,TheCMSexperimentattheCERNLHC,J.Instrum.3(2008)

S08004,https://doi.org/10.1088/1748-0221/3/08/S08004.

[21] J. Alwall, R. Frederix,S. Frixione, V.Hirschi, F.Maltoni, O. Mattelaer, H.S. Shao, T. Stelzer,P. Torrielli, M. Zaro, The automated computation of tree-levelandnext-to-leadingorderdifferentialcrosssections,andtheirmatching to partonshower simulations,J. HighEnergy Phys. 07(2014)079, https:// doi.org/10.1007/JHEP07(2014)079,arXiv:1405.0301.

[22] S.Alioli,P.Nason, C.Oleari,E.Re,NLOsingle-topproductionmatchedwith showerinPOWHEG:s- andt-channelcontributions,J.HighEnergyPhys.09 (2009)111,https://doi.org/10.1088/1126-6708/2009/09/111,arXiv:0907.4076. [23] P.Nason,AnewmethodforcombiningNLOQCD withshowerMonteCarlo

algorithms,J.HighEnergyPhys.11(2004)040,https://doi.org/10.1088/1126 -6708/2004/11/040,arXiv:hep-ph/0409146.

[24] S.Frixione,P.Nason,C.Oleari,MatchingNLOQCDcomputationswithparton showersimulations:thePOWHEGmethod,J.HighEnergyPhys.11(2007)070,

https://doi.org/10.1088/1126-6708/2007/11/070,arXiv:0709.2092.

[25] S.Alioli, P. Nason, C.Oleari,E. Re,A general framework for implementing NLOcalculationsinshowerMonteCarloprograms:thePOWHEGBOX,J.High Energy Phys. 06(2010)043,https://doi.org/10.1007/JHEP06(2010)043,arXiv: 1002.2581.

[26] R.Frederix,E.Re,P.Torrielli,Single-topt-channelhadroproductioninthe four-flavourschemewithPOWHEGandaMC@NLO,J.HighEnergyPhys.09(2012) 130,https://doi.org/10.1007/JHEP09(2012)130,arXiv:1207.5391.

[27] S.Alioli,S.-O.Moch,P.Uwer,Hadronictop-quarkpair-productionwithonejet andpartonshowering,J.HighEnergyPhys.01(2012)137,https://doi.org/10. 1007/JHEP01(2012)137,arXiv:1110.5251.

[28] M.Czakon,A.Mitov,Top++:aprogramforthecalculationofthetop-pair cross-sectionathadroncolliders,Comput.Phys.Commun.185(2014)2930,https:// doi.org/10.1016/j.cpc.2014.06.021,arXiv:1112.5675.

[29] E.Re,Single-topWt-channelproductionmatchedwithpartonshowersusing thePOWHEGmethod,Eur.Phys.J.C71(2011)1547,https://doi.org/10.1140/ epjc/s10052-011-1547-z,arXiv:1009.2450.

[30] N.Kidonakis,Two-loopsoftanomalousdimensionsforsingletopquark asso-ciatedproductionwithaW- orH-,Phys.Rev.D82(2010)054018,https:// doi.org/10.1103/PhysRevD.82.054018,arXiv:1005.4451.

[31]N.Kidonakis, Topquarkproduction,in:Proceedings,HelmholtzInternational Summer SchoolonPhysicsofHeavyQuarksand Hadrons,(HQ2013),JINR, Dubna,Russia,July15–28,2013,2013,p. 139,arXiv:1311.0283.

[32] R.Frederix, S. Frixione, Merging meetsmatching in MC@NLO, J. High En-ergyPhys.12(2012)061,https://doi.org/10.1007/JHEP12(2012)061,arXiv:1209. 6215.

[33] R.Gavin, Y.Li,F.Petriello,S. Quackenbush, FEWZ2.0:acodefor hadronic Z production at next-to-next-to-leadingorder, Comput.Phys. Commun.182 (2011)2388,https://doi.org/10.1016/j.cpc.2011.06.008,arXiv:1011.3540. [34] R.Gavin,Y.Li,F.Petriello,S.Quackenbush,WphysicsattheLHCwithFEWZ

2.1,Comput.Phys.Commun.184(2013)208,https://doi.org/10.1016/j.cpc.2012. 09.005,arXiv:1201.5896.

[35] Y. Li, F.Petriello, Combining QCD and electroweak corrections to dilepton production inFEWZ,Phys.Rev.D86(2012)094034,https://doi.org/10.1103/ PhysRevD.86.094034,arXiv:1208.5967.

[36] T.Sjöstrand, S.Ask,J.R. Christiansen,R.Corke, N.Desai,P.Ilten,S.Mrenna, S.Prestel,C.O.Rasmussen,P.Z.Skands,AnintroductiontoPYTHIA8.2, Com-put.Phys.Commun.191(2015)159,https://doi.org/10.1016/j.cpc.2015.01.024, arXiv:1410.3012.

[37] CMSCollaboration,Eventgeneratortunesobtainedfromunderlyingeventand multipartonscatteringmeasurements,Eur.Phys. J.C76(2016)155,https:// doi.org/10.1140/epjc/s10052-016-3988-x,arXiv:1512.00815.

[38] CMSCollaboration,Investigationsoftheimpactofthepartonshowertuningin Pythia8inthemodellingoftt at√s=8 and13TeV,CMSPhys.Anal.Summ. CMS-PAS-TOP-16-021(2016),http://cds.cern.ch/record/2235192.

[39] R.D.Ball,etal.,NNPDFCollaboration,PartondistributionsfortheLHCRunII, J.HighEnergyPhys.04(2015)040,https://doi.org/10.1007/JHEP04(2015)040, arXiv:1410.8849.

[40] S.Agostinelli,et al., (GEANT4), Geant4—asimulation toolkit,Nucl. Instrum. Methods, Sect. A 506 (2003) 250, https://doi.org/10.1016/S0168-9002(03) 01368-8.

[41] M.Cacciari,G.P.Salam,G.Soyez,Theanti-kTjetclusteringalgorithm,J.High

Energy Phys. 04(2008)063,https://doi.org/10.1088/1126-6708/2008/04/063, arXiv:0802.1189.

[42] M.Cacciari,G.P.Salam,G.Soyez,FastJetusermanual,Eur.Phys.J.C72(2012) 1896,https://doi.org/10.1140/epjc/s10052-012-1896-2,arXiv:1111.6097. [43] CMSCollaboration, Particle-flowreconstructionand globaleventdescription

withtheCMSdetector,J.Instrum.12(2017)P10003,https://doi.org/10.1088/ 1748-0221/12/10/P10003,arXiv:1706.04965.

[44] CMSCollaboration,PerformanceoftheCMSmuondetectorandmuon recon-structionwithproton-protoncollisionsat√s=13 TeV,J.Instrum.13(2018) P06015,https://doi.org/10.1088/1748-0221/13/06/P06015,arXiv:1804.04528. [45] W.Adam,R.Frühwirth,A.Strandlie,T.Todorov, Reconstructionofelectrons

withtheGaussian-sumfilterintheCMStrackerattheLHC,J.Phys.G31(2005) 9,https://doi.org/10.1088/0954-3899/31/9/N01,arXiv:physics/0306087. [46] CMSCollaboration,JetenergyscaleandresolutionintheCMSexperimentin

ppcollisionsat8TeV,J.Instrum.12(2017)P02014,https://doi.org/10.1088/ 1748-0221/12/02/P02014,arXiv:1607.03663.

[47] CMSCollaboration,Identificationofheavy-flavourjetswiththeCMSdetectorin ppcollisionsat13TeV,J.Instrum.13(2018)P05011,https://doi.org/10.1088/ 1748-0221/13/05/P05011,arXiv:1712.07158.

[48] CMSCollaboration,Performanceofmissingenergyreconstructionin13TeVpp collisiondatausingtheCMSdetector,CMSPhys.Anal.Summ. CMS-PAS-JME-16-004(2016),http://cds.cern.ch/record/2205284.

[49] V.M.Abazov,etal.,D0Collaboration,Observationofsingletop-quark produc-tion,Phys.Rev.Lett.103(2009)092001, https://doi.org/10.1103/PhysRevLett. 103.092001,arXiv:0903.0850.

[50] T.Aaltonen,etal.,CDFCollaboration,Firstobservationofelectroweaksingle topquarkproduction,Phys. Rev.Lett.103(2009)092002,https://doi.org/10. 1103/PhysRevLett.103.092002,arXiv:0903.0885.

[51]J.Therhaag,A.Hoecker,P.Speckmeyer,E.vonToerne,H.Voss,TMVA—toolkit for multivariatedata analysis,in: Proceedings,Int’l Conf. onComputational Methods in Science and Engineering, 2009, ICCMSE2009, vol. 1504, 2012, p. 1013.

[52]A.Kalogeropoulos,J.Alwall,TheSysCalccode:atooltoderivetheoretical sys-tematicuncertainties,arXiv:1801.08401,2018.

[53] CMSCollaboration,CMSluminosity measurementsforthe 2016datataking period,CMSPhys.Anal.Summ.CMS-PAS-LUM-17-001(2017),https://cds.cern. ch/record/2257069.

[54] CMSCollaboration,Determinationofjetenergycalibrationandtransverse mo-mentumresolution inCMS,J. Instrum.6(2011) P11002,https://doi.org/10. 1088/1748-0221/6/11/P11002,arXiv:1107.4277.

[55] CMSCollaboration,PerformanceoftheCMSmissingtransversemomentum re-constructioninppdataat√s=8 TeV,J.Instrum.10(2015)P02006,https:// doi.org/10.1088/1748-0221/10/02/P02006,arXiv:1411.0511.

[56] CMSCollaboration,MeasurementsofinclusiveW andZ crosssectionsinpp collisionsat√s=7 TeV,J.HighEnergyPhys.01(2011)080,https://doi.org/10. 1007/JHEP01(2011)080,arXiv:1012.2466.

[57] CMSCollaboration,Measurementoftheinelasticproton-protoncrosssection at √s=13 TeV,J.HighEnergyPhys.07(2018)161,https://doi.org/10.1007/ JHEP07(2018)161,arXiv:1802.02613.

[58] R.Barlow,C.Beeston,FittingusingfiniteMonteCarlosamples,Comput.Phys. Commun.77(1993)219,https://doi.org/10.1016/0010-4655(93)90005-W.

[59] M.Czakon,P.Fiedler,A.Mitov,Totaltop-quarkpair-productioncrosssectionat hadroncollidersthrough O(α4

S),Phys.Rev.Lett.110(2013)252004,https:// doi.org/10.1103/PhysRevLett.110.252004,arXiv:1303.6254.

[60] CMSCollaboration, Measurementofdifferentialcrosssectionsfortopquark pairproductionusingthelepton+jetsfinalstateinproton-protoncollisionsat 13TeV,Phys.Rev.D95(2017)092001,https://doi.org/10.1103/PhysRevD.95. 092001,arXiv:1610.04191.

[61] CMSCollaboration,Measurementofnormalizeddifferentialtt crosssectionsin thedileptonchannelfromppcollisionsat√s=13 TeV,J.HighEnergyPhys. 04(2018)060,https://doi.org/10.1007/JHEP04(2018)060,arXiv:1708.07638. [62] CMS Collaboration, Measurement of the production cross section for

sin-gletopquarksinassociationwithWbosonsinproton-protoncollisionsat

√

s=13 TeV, J. High Energy Phys. 10 (2018) 117, https://doi.org/10.1007/ JHEP10(2018)117,arXiv:1805.07399.

[63] J.A.Aguilar-Saavedra,AMinimalsetoftopanomalouscouplings,Nucl.Phys. B812(2009)181,https://doi.org/10.1016/j.nuclphysb.2008.12.012,arXiv:0811. 3842.

[64] G.J.Feldman,R.D.Cousins,Aunifiedapproachtotheclassicalstatistical anal-ysis ofsmallsignals, Phys. Rev. D57 (1998)3873, https://doi.org/10.1103/ PhysRevD.57.3873,arXiv:physics/9711021.

[65] A. Buckley, J. Ferrando,S. Lloyd, K. Nordström, B. Page, M. Rüfenacht, M. Schönherr,G.Watt,LHAPDF6:partondensityaccessintheLHCprecisionera, Eur.Phys.J.C75(2015)132,https://doi.org/10.1140/epjc/s10052-015-3318-8, arXiv:1412.7420.

[66] R.D.Ball,etal.,NNPDFCollaboration,Partondistributionsfromhigh-precision colliderdata,Eur.Phys.J.C77(2017)663,https://doi.org/10.1140/epjc/s10052 -017-5199-5,arXiv:1706.00428.

[67] S. Dulat, T.-J. Hou, J. Gao, M. Guzzi, J. Huston,P. Nadolsky, J. Pumplin, C. Schmidt,D.Stump,C.P.Yuan,Newpartondistributionfunctionsfromaglobal analysisofquantumchromodynamics,Phys.Rev.D93(2016)033006,https:// doi.org/10.1103/PhysRevD.93.033006,arXiv:1506.07443.

[68] S.Alekhin,J.Blümlein,S.-O.Moch,R.Placakyte,Partondistributionfunctions, αs,andheavy-quarkmassesfor LHCRunII,Phys.Rev.D96(2017)014011, https://doi.org/10.1103/PhysRevD.96.014011,arXiv:1701.05838.

[69] S.Alekhin,J.Blümlein,S.-O.Moch,NLOPDFsfromtheABMP16fit,Eur.Phys.J. C78(2018)477,https://doi.org/10.1140/epjc/s10052-018-5947-1,arXiv:1803. 07537.

[70] L.A.Harland-Lang,A.D.Martin,P.Motylinski,R.S.Thorne,Partondistributions intheLHCera:MMHT2014PDFs,Eur.Phys.J.C75(2015)204,https://doi. org/10.1140/epjc/s10052-015-3397-6,arXiv:1412.3989.

[71] ZEUSandH1Collaborations,CombinedmeasurementandQCDanalysisofthe inclusivee±pscatteringcrosssectionsatHERA,J.HighEnergyPhys.01(2010) 109,https://doi.org/10.1007/JHEP01(2010)109,arXiv:0911.0884.

TheCMSCollaboration

A.M. Sirunyan,

A. Tumasyan

YerevanPhysicsInstitute,Yerevan,Armenia

W. Adam,

F. Ambrogi,

E. Asilar,

T. Bergauer,

J. Brandstetter,

M. Dragicevic,

J. Erö,

A. Escalante Del Valle,

M. Flechl,

R. Frühwirth

1

,

V.M. Ghete,

J. Hrubec,

M. Jeitler

1

,

N. Krammer,

I. Krätschmer,

D. Liko,

T. Madlener,

I. Mikulec,

N. Rad,

H. Rohringer,

J. Schieck

1

,

R. Schöfbeck,

M. Spanring,

D. Spitzbart,

A. Taurok,

W. Waltenberger,

J. Wittmann,

C.-E. Wulz

1

,

M. Zarucki

InstitutfürHochenergiephysik,Wien,Austria

V. Chekhovsky,

V. Mossolov,

J. Suarez Gonzalez

InstituteforNuclearProblems,Minsk,Belarus

E.A. De Wolf,

D. Di Croce,

X. Janssen,

J. Lauwers,

M. Pieters,

H. Van Haevermaet,

P. Van Mechelen,

N. Van Remortel

S. Abu Zeid,

F. Blekman,

J. D’Hondt,

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

VrijeUniversiteitBrussel,Brussel,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,

N. Postiau,

E. Starling,

L. Thomas,

C. Vander Velde,

P. Vanlaer,

D. Vannerom,

Q. Wang

UniversitéLibredeBruxelles,Bruxelles,Belgium

T. Cornelis,

D. Dobur,

A. Fagot,

M. Gul,

I. Khvastunov

2

,

D. Poyraz,

C. Roskas,

D. Trocino,

M. Tytgat,

W. Verbeke,

B. Vermassen,

M. Vit,

N. Zaganidis

GhentUniversity,Ghent,Belgium

H. Bakhshiansohi,

O. Bondu,

S. Brochet,

G. Bruno,

C. Caputo,

P. David,

C. Delaere,

M. Delcourt,

A. Giammanco,

G. Krintiras,

V. Lemaitre,

A. Magitteri,

K. Piotrzkowski,

A. Saggio,

M. Vidal Marono,

S. Wertz,

J. Zobec

UniversitéCatholiquedeLouvain,Louvain-la-Neuve,Belgium

F.L. Alves,

G.A. Alves,

M. Correa Martins Junior,

G. Correia Silva,

C. Hensel,

A. Moraes,

M.E. Pol,

P. Rebello Teles

CentroBrasileirodePesquisasFisicas,RiodeJaneiro,Brazil

E. Belchior Batista Das Chagas,

W. Carvalho,

J. Chinellato

3

,

E. Coelho,

E.M. Da Costa,

G.G. Da Silveira

4

,

D. De Jesus Damiao,

C. De Oliveira Martins,

S. Fonseca De Souza,

H. Malbouisson,

D. Matos Figueiredo,

M. Melo De Almeida,

C. Mora Herrera,

L. Mundim,

H. Nogima,

W.L. Prado Da Silva,

L.J. Sanchez Rosas,

A. Santoro,

A. Sznajder,

M. Thiel,

E.J. Tonelli Manganote

3

,

F. Torres Da Silva De Araujo,

A. Vilela Pereira

UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil

S. Ahuja

a

,

C.A. Bernardes

a

,

L. Calligaris

a

,

T.R. Fernandez Perez Tomei

a

,

E.M. Gregores

b

,

P.G. Mercadante

b

,

S.F. Novaes

a

,

SandraS. Padula

a

a_{UniversidadeEstadualPaulista,SãoPaulo,Brazil} b_{UniversidadeFederaldoABC,SãoPaulo,Brazil}

A. Aleksandrov,

R. Hadjiiska,

P. Iaydjiev,

A. Marinov,

M. Misheva,

M. Rodozov,

M. Shopova,

G. Sultanov

InstituteforNuclearResearchandNuclearEnergy,BulgarianAcademyofSciences,Sofia,Bulgaria

A. Dimitrov,

L. Litov,

B. Pavlov,

P. Petkov

UniversityofSofia,Sofia,Bulgaria

W. Fang

5

,

X. Gao

5

,

L. Yuan

BeihangUniversity,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

6

,

A. Spiezia,

J. Tao,

Z. Wang,

E. Yazgan,

H. Zhang,

S. Zhang

6

,

J. Zhao

InstituteofHighEnergyPhysics,Beijing,China

Y. Ban,

G. Chen,

A. Levin,

J. Li,

L. Li,

Q. Li,

Y. Mao,

S.J. Qian,

D. Wang

StateKeyLaboratoryofNuclearPhysicsandTechnology,PekingUniversity,Beijing,China

Y. Wang