Measurement of the $W+b$-jet and $W+c$-jet differential production cross sections in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV

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Measurement of the W + b-jet and W + c-jet differential

production cross sections in p¯

p collisions at

√

s = 1.96 TeV

V.M. Abazov, G. Sajot, J. Stark, S. Greder, F. Miconi, I. Ripp-Baudot, G.

Grenier, T. Kurca, P. Lebrun, J.-F. Grivaz, et al.

To cite this version:

V.M. Abazov, G. Sajot, J. Stark, S. Greder, F. Miconi, et al.. Measurement of the W + b-jet and

W + c-jet differential production cross sections in p¯

p collisions at

√

s = 1.96 TeV. Physics Letters B,

Contents lists available atScienceDirect

Physics

Letters

B

www.elsevier.com/locate/physletb

Measurement

of

the

W

+

b-jet

and

W

+

c-jet

differential

production

cross

sections

in

p

p collisions

¯

at

√

s

=

1

.

96 TeV

D0

Collaboration

V.M. Abazov

af

,

B. Abbott

bp

,

B.S. Acharya

z

,

M. Adams

au

,

T. Adams

as

,

J.P. Agnew

ap

,

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,

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,

1

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bc

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at

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z

,

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bd

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at

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bb

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x

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E-mailaddress:gogota.olga@gmail.com(O. Gogota).

http://dx.doi.org/10.1016/j.physletb.2015.02.012

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a_{LAFEX,CentroBrasileirodePesquisasFísicas,RiodeJaneiro,Brazil} b_{UniversidadedoEstadodoRiodeJaneiro,RiodeJaneiro,Brazil} c_{UniversidadeFederaldoABC,SantoAndré,Brazil}

d_{UniversityofScienceandTechnologyofChina,Hefei,People’sRepublicofChina} e_{UniversidaddelosAndes,Bogotá,Colombia}

f_{CharlesUniversity,FacultyofMathematicsandPhysics,CenterforParticlePhysics,Prague,CzechRepublic} g_{CzechTechnicalUniversityinPrague,Prague,CzechRepublic}

h_{InstituteofPhysics,AcademyofSciencesoftheCzechRepublic,Prague,CzechRepublic} i_{UniversidadSanFranciscodeQuito,Quito,Ecuador}

j_{LPC,UniversitéBlaisePascal,CNRS/IN2P3,Clermont,France}

k_{LPSC,UniversitéJosephFourierGrenoble1,CNRS/IN2P3,InstitutNationalPolytechniquedeGrenoble,Grenoble,France} l_{CPPM,Aix-MarseilleUniversité,CNRS/IN2P3,Marseille,France}

m_{LAL,UniversitéParis-Sud,CNRS/IN2P3,Orsay,France} n_{LPNHE,UniversitésParisVIandVII,CNRS/IN2P3,Paris,France} o_{CEA,Irfu,SPP,Saclay,France}

p_{IPHC,UniversitédeStrasbourg,CNRS/IN2P3,Strasbourg,France} q_{IPNL,UniversitéLyon1,CNRS/IN2P3,Villeurbanne,France} r_{UniversitédeLyon,Lyon,France}

s_{III.PhysikalischesInstitutA,RWTHAachenUniversity,Aachen,Germany} t_{PhysikalischesInstitut,UniversitätFreiburg,Freiburg,Germany}

u_{II.PhysikalischesInstitut,Georg-August-UniversitätGöttingen,Göttingen,Germany} v_{InstitutfürPhysik,UniversitätMainz,Mainz,Germany}

w_{Ludwig-Maximilians-UniversitätMünchen,München,Germany} x_{PanjabUniversity,Chandigarh,India}

y_{DelhiUniversity,Delhi,India}

z_{TataInstituteofFundamentalResearch,Mumbai,India} aa_{UniversityCollegeDublin,Dublin,Ireland}

ab_{KoreaDetectorLaboratory,KoreaUniversity,Seoul,RepublicofKorea} ac_{CINVESTAV,MexicoCity,Mexico}

ad_{Nikhef,SciencePark,Amsterdam,TheNetherlands} ae_{RadboudUniversityNijmegen,Nijmegen,TheNetherlands} af_{JointInstituteforNuclearResearch,Dubna,Russia}

ag_{InstituteforTheoreticalandExperimentalPhysics,Moscow,Russia} ah_{MoscowStateUniversity,Moscow,Russia}

ai_{InstituteforHighEnergyPhysics,Protvino,Russia} aj_{PetersburgNuclearPhysicsInstitute,St.Petersburg,Russia}

al_{UppsalaUniversity,Uppsala,Sweden}

am_{TarasShevchenkoNationalUniversityofKyiv,Kiev,Ukraine} an_{LancasterUniversity,LancasterLA14YB,UnitedKingdom} ao_{ImperialCollegeLondon,LondonSW72AZ,UnitedKingdom} ap_{TheUniversityofManchester,ManchesterM139PL,UnitedKingdom} aq_{UniversityofArizona,Tucson,AZ 85721,USA}

ar_{UniversityofCaliforniaRiverside,Riverside,CA 92521,USA} as_{FloridaStateUniversity,Tallahassee,FL 32306,USA} at_{FermiNationalAcceleratorLaboratory,Batavia,IL 60510,USA} au_{UniversityofIllinoisatChicago,Chicago,IL 60607,USA} av_{NorthernIllinoisUniversity,DeKalb,IL 60115,USA} aw_{NorthwesternUniversity,Evanston,IL 60208,USA} ax_{IndianaUniversity,Bloomington,IN 47405,USA} ay_{PurdueUniversityCalumet,Hammond,IN 46323,USA} az_{UniversityofNotreDame,NotreDame,IN 46556,USA} ba_{IowaStateUniversity,Ames,IA 50011,USA} bb_{UniversityofKansas,Lawrence,KS 66045,USA} bc_{LouisianaTechUniversity,Ruston,LA 71272,USA} bd_{NortheasternUniversity,Boston,MA 02115,USA} be

UniversityofMichigan,AnnArbor,MI 48109,USA

bf_{MichiganStateUniversity,EastLansing,MI 48824,USA} bg_{UniversityofMississippi,University,MS 38677,USA} bh_{UniversityofNebraska,Lincoln,NE 68588,USA} bi_{RutgersUniversity,Piscataway,NJ 08855,USA} bj_{PrincetonUniversity,Princeton,NJ 08544,USA} bk_{StateUniversityofNewYork,Buffalo,NY 14260,USA} bl_{UniversityofRochester,Rochester,NY 14627,USA} bm_{StateUniversityofNewYork,StonyBrook,NY 11794,USA} bn_{BrookhavenNationalLaboratory,Upton,NY 11973,USA} bo_{LangstonUniversity,Langston,OK 73050,USA} bp_{UniversityofOklahoma,Norman,OK 73019,USA} bq_{OklahomaStateUniversity,Stillwater,OK 74078,USA} br_{BrownUniversity,Providence,RI 02912,USA} bs_{UniversityofTexas,Arlington,TX 76019,USA} bt_{SouthernMethodistUniversity,Dallas,TX 75275,USA} bu_{RiceUniversity,Houston,TX 77005,USA}

bv_{UniversityofVirginia,Charlottesville,VA 22904,USA} bw_{UniversityofWashington,Seattle,WA 98195,USA}

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Articlehistory:

Received18December2014

Receivedinrevisedform4February2015 Accepted5February2015

Availableonline11February2015 Editor:W.-D.Schlatter

We presentameasurementofthecrosssections fortheassociated productionofaW boson withat least oneheavy quarkjet,

b or c,

inproton–antiprotoncollisions.Datacorrespondingto anintegrated luminosity of8.7 fb−1 recordedwith the D0 detectorat the FermilabTevatron p¯p Collider at√s= 1.96 TeV areusedtomeasurethecrosssectionsdifferentiallyasafunctionofthejettransversemomenta intherange 20to150 GeV.Theseresultsare comparedtocalculationsofperturbativeQCDtheoryas wellaspredictionsfromMonteCarlogenerators.

©2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBYlicense (http://creativecommons.org/licenses/by/4.0/).FundedbySCOAP3_.

Measurement of the production cross section of a W boson

in association with a b or c-quark jet provides a stringent test

1 _{VisitorfromAugustanaCollege,SiouxFalls,SD,USA.} 2 _{VisitorfromTheUniversityofLiverpool,Liverpool,UK.} 3 _{VisitorfromDESY,Hamburg,Germany.}

4 _{VisitorfromUniversidadMichoacanadeSanNicolasdeHidalgo,Morelia,} Mex-ico.

5 _{VisitorfromSLAC,MenloPark,CA,USA.}

6 _{VisitorfromUniversityCollegeLondon,London,UK.}

7 _{VisitorfromCentrodeInvestigacionenComputacion–IPN,MexicoCity,Mexico.} 8 _{VisitorfromUniversidadeEstadualPaulista,SãoPaulo,Brazil.}

9 _{Visitorfrom KarlsruherInstitut fürTechnologie (KIT)–Steinbuch Centrefor} Computing(SCC),D-76128Karlsruhe,Germany.

10 _{Visitor from Office ofScience, U.S. Departmentof Energy, Washington, D.C.} 20585,USA.

11 _{VisitorfromAmericanAssociationfortheAdvancementofScience,Washington,} D.C.20005,USA.

12 _{VisitorfromKievInstituteforNuclearResearch,Kiev,Ukraine.} 13 _{VisitorfromUniversityofMaryland,CollegePark,Maryland20742,USA.} 14 _{Visitor from European Organization for Nuclear Research (CERN), Geneva,} Switzerland.

of quantum chromodynamics (QCD). At hadron colliders, the as-sociatedproductionofaheavyquarkwitha W bosoncanalsobe a significantbackgroundtorarestandardmodel(SM)processes,for example,productionoftopquarkpairs[1],asingletopquark [2], anda W bosoninassociationwithaHiggsbosondecayingtotwo

b quarks[3],aswellasfornewphysics processes,e.g., supersym-metricscalartopquarkproduction[4].

The dominant processes contributing to W

+

c-jet produc-tion are qg

→

W c and qq

¯



→

W g followed by g

→

cc.

¯

The production cross section for the first process is sensitive to the quark and gluon parton density functions (PDFs). Since the c–b

quark Cabibbo–Kobayashi–Maskawa matrixelement is very small (

|

Vcb

|

2

≈

0

.

0016)[5],thecontributionofab-quarkinitial statein

the PDF is negligible. Comparing the d-quark and s-quark PDFs, theprobability ofinteractionofagluonwithad-quark isgreater thanthatwithan s-quark,buttheCKMmatrixelementsuppresses

d

→

c transitionssince

|

Vcd

|

2

≈

0

.

04.Asaresult,theexpected

simulationforW

+

c-jetevents,thecontributionfromqg

→

W

+

c

dominates the entire 20

<

pjet_T

<

100 GeV region with the con-tribution from qq

¯



→

W

+

cc events

¯

increasing from about 25% to45% asjet pT increases from 20to 100 GeV. Measurementof

the p

¯

p

→

W

+

c-jet differentialcross section should provide in-formation about the s-quark PDF. This PDF has been measured directlyonlyinfixed targetneutrino–nucleondeepinelastic scat-tering experiments at relatively low momentum transfer Q



15–20 GeV[9–14].Aprobeofthes-quarkPDFattheTevatrontests theuniversalityofs(x,Q2

₎

_{,wherex istheFeynmanvariable[15],}

anditsQCDevolutionuptoQ2

_

₁₀4 _GeV2_.

Thereareonlya fewprevious measurementsofthe W

+

c-jet

crosssectionathadroncolliders,performedbytheD0[6],CDF[16, 17],ATLAS[18],andCMS[19]Collaborations.ThepreviousD0and CDFmeasurementsareinclusive;theCMSandATLAS inclusive re-sultswereaugmentedbydistributionsinthepseudorapidityofthe lepton from W decay. It is importantto note that the measure-ments listed above are performed by requiring opposite electric charges of a soft lepton inside a jet fromsemileptonic charmed hadrondecaywithaleptonfromW decayelsewhereintheevent, and measuring the cross section for “opposite-sign” (OS) minus “same-sign”(SS) events.A requirement ofopposite signs forthe leptonsandsubtractionofeventswiththesamesignssuppresses the sign-symmetric backgrounds as well as W

+

cc events

¯

due to gluon splitting, which become significant at high jet pT. All

measurements are in agreement with the perturbative next-to-leading order (NLO) QCD predictions [20,21] that include contri-butions fromgluonsplitting withintotal theoretical uncertainties of15–30%.

Measurementsof the inclusive W

+

b-jet cross-sections have beenreportedby theCDF[22],D0 [23], andATLAS[24] Collabo-rations.The CDFresultisapproximately3

σ

higherthanthe NLO predictionswhiletheD0andATLAS measurementsagreewiththe theorywithinlarge(30–40%)theoreticaluncertainties.Adominant (



85%)contribution to W

+

b-jet productionat the Tevatronis dueto the qq

¯



→

W

+

g

(g

→

bb)

¯

process while the remaining contributionarisesfromthebq

¯

→

W bq

¯

 process[21],witha neg-ligiblecontributionfromsingletopquarkproduction.

Wepresent,forthefirsttime,measurementsof W

+

c-jet and

W

+

b-jetdifferentialcrosssectionsasafunctionofjet pT,where

no requirement of a soft lepton within a jet is made, and that arethereforesensitivetothegluonsplittingcontributions.TheW

bosoncandidatesareidentifiedinthe

μ

+

ν

decaychannel. ThedatausedinthisanalysiswerecollectedbetweenJuly2006 andSeptember 2011usingthe D0 detectoratthe Fermilab Teva-tron Collider at

√

s

=

1

.

96 TeV, and correspond to an integrated luminosityof8

.

7 fb−1.TheD0detector[25]hasacentraltracking system consisting of a silicon microstrip tracker (SMT) [26] and a centralfibertracker,bothlocatedwithina1.9 Tsuperconducting solenoidalmagnet,whichareoptimizedfortrackingandvertexing atpseudorapidities

|

η

|

<

3 and

|

η

|

<

2

.

5,respectively[27].A liquid argon anduranium calorimeterhas a central section (CC) cover-ingpseudorapidities

|

η

|



1

.

1,andtwoendcalorimeters(EC)that extend coverage to

|

η

|

≈

4

.

2, with all three housed in separate cryostats[28].An outermuonsystemcovering

|

η

|

<

2 consistsof a layer of tracking detectors and scintillation trigger counters in frontof1.8 Tirontoroids,followedbytwosimilarlayersafterthe toroids.Luminosityismeasuredusingplasticscintillatorarrays lo-catedinfrontoftheECcryostats.

The W

+

b/c candidate events are chosen by selecting single muonormuon

+

jet signatureswithathree-leveltrigger system. ThetriggerefficiencyhasbeenestimatedusingZ

→

μ

+

μ

−

(

+

jets

)

eventsindata.Thetriggerefficiencyisparametrizedasafunction ofmuon pT and

η

andisonaverage

≈

70%.

Offlineeventselection requiresa reconstructed pp interaction

¯

primaryvertex(PV)thathasatleastthreeassociatedtracksandis locatedwithin60 cmofthecenterofthedetectoralongthebeam direction.ThevertexselectionforW

+

b/c eventsisapproximately 99%efficientasmeasuredinsimulation.

Werequireamuoncandidatetobereconstructed fromhitsin themuonsystemandmatchedtoareconstructedtrackinthe cen-tral tracker [29]. The transverse momentum of the muon must satisfy pμ_T

>

20 GeV, with

|

η

μ

|

<

1

.

7.Muons are required to be spatially isolatedfromother energeticparticles usinginformation from the central tracking detectors and calorimeter [30]. Muons fromcosmicraysarerejectedbyapplyingatimingcriteriononthe hitsinthescintillatorlayers ofthemuon systemandbyapplying restrictionsonthedisplacementofthemuontrackwithrespectto thePV.Themuonreconstructionefficiencyis

≈

90%.

Candidate W

+

jets events are selected by requiring at least one reconstructed jet with pseudorapidity

|

η

jet

_|

_<

₁

_.

_{5 and p}jet

T

>

20 GeV. Jets are reconstructed from energy deposits in the calorimeterusingtheiterativemidpointconealgorithm [31]with aconeofradius R

=



y

2

_{+ φ}

2

₌

₀

_.

_{5[27].Theenergiesofjets}

arecorrectedfordetectorresponse,thepresenceofnoiseand mul-tiple pp interactions

¯

[32].To enrich thesample with W bosons,

eventsare required to havemissingtransverse energy[32]

/

ET

>

25 GeV duetotheneutrinoescapingdetection.Werequirethatthe

W bosoncandidateshaveatransversemass MT

>

40 GeV[33].

Backgrounds forthisanalysisincludeeventsfromthe produc-tionofW

+

light parton jets,Z

/

γ

∗

+

jets,tt,

¯

singletopquark, dibo-son V V (V

=

W

,

Z )andQCDmultijetsinwhichajet is misiden-tifiedasamuon.TheW

+

c andW

+

b signalandthebackground processesexcludingmultijetaresimulatedusingacombinationof alpgen [7]and pythia[8] MC eventgenerators with pythia pro-viding partonshowering andhadronization. We use pythia with CTEQ6L1[34]PDFs. alpgen generatesmulti-partonfinal states us-ingtree-levelmatrixelements(ME).Wheninterfacedwith pythia, itemploystheMLMscheme[7]totreatMEpartonsproducedfrom showeringin pythia.Forthesignalprocess,wealsousethe sherpa MCgenerator[35]thatmatchespartonsfromtheleading-orderME withuptotworealpartonemissionstotheparton-showerjets ac-cordingtotheCKWKmatchingscheme[36].Thegeneratedevents are processed through a geant-based [37] simulation of the D0 detectorgeometryandresponse.Toaccuratelymodeltheeffectsof multiple pp interactions

¯

anddetectornoise, eventsfromrandom

pp crossings

¯

withasimilarinstantaneous luminosityspectrumas indataare overlaidon theMCevents.TheseMC eventsarethen processedusingthesamereconstructioncodeasforthedata.The MCeventsarealsoweighted totakeintoaccountthetrigger effi-ciencyandsmallobserveddifferencesbetweenMCanddatainthe distributionsoftheinstantaneous luminosityandofthe z

coordi-nateofthepp collision

¯

vertex.

The V

+

jets processesarenormalizedtothetotalinclusiveW

and Z -boson cross sections calculated atNNLO (next-to-next-to-leading order) [38]. The Z -boson pT distribution is modeled to

matchthe distributionobservedin data[39],takingintoaccount the dependence on the number of reconstructed jets. To repro-duce the W -boson pT distribution in simulated events, we use

theproductofthemeasured Z -bosonpT spectrumtimestheratio

of W to Z -bosonpT distributionsatNLO[39,40].TheNLO

+

NNLL

(next-to-next-to-leading log) calculations are used to normalize

tt production

¯

[41],whilesingletopquarkproductionisnormalized toNNLOpredictions[42].TheNLO W W ,W Z ,and Z Z production

theisolationrequirements.Toreducethecontributionfromtt pro-

¯

ductionthatincreaseswithjet pT,werestrictthescalarsumofall

thejet pT values(HT)tobelessthan175 GeV.Thisrequirement

reducesthett fraction

¯

bya factor1.5–2,dependingonjet pT,and

hassignalefficiencygreaterthan95%exceptinthehighestPT bin whereit fallsto 82%. Thett fraction

¯

after the HT cut varies

be-tween5and20%withincreasingjetpT.

Identification ofb and c jetsis crucial for thismeasurement. OncetheinclusiveW

+

jets sampleisselected,atleastonejetis requiredtobetaggable,i.e.itmustcontainatleasttwotrackseach withatleastone hit in theSMT, pT

>

1 GeV forthehighest-pT

track and pT

>

0

.

5 GeV for the next-to-highest pT track. These

criteriaensuresufficientinformationtoclassifythejetasa heavy-flavor candidateandhavea typical efficiencyofabout90%. Light partonjets(those resultingfromlightquarks orgluons)are sup-pressedusingadedicatedartificialneuralnetwork(b-NN)[44]that exploits the longer lifetimes of heavy-flavor hadrons relative to their lightercounterparts. Theinputsto theb-NN includeseveral characteristicquantitiesofthejetandassociatedtrackstoprovide a continuous output value that tends towards one forb jets and zeroforthelightjets. Theb-NN inputvariablesprovidingmostof thediscriminationarethenumberofreconstructedsecondary ver-tices(SV) inthejet,theinvariant massofchargedparticletracks associatedwiththeSV(MSV),thenumberoftracksusedto

recon-structtheSV,thetwo-dimensionaldecaylengthsignificanceofthe SV inthe plane transverseto the beam, a weighted combination of the tracks’transverse impact parameter significances, andthe probability that the tracks associatedwith the jet originate from the pp interaction

¯

vertex, whichisreferred to asthejet lifetime probability(JLIP).Thejetisrequiredtohaveab-NNoutputgreater than 0.5.Forjet pT inarangebetween 20and150 GeVthis

se-lectionis (36–47)%efficient forb-jets and(8–11)% efficientforc

jets with relative systematic uncertainties of (4.2–6.5)% for both theb jetsandc jets.Thesystematicuncertaintyisobtainedfroma comparisonoftheheavyflavortaggingefficienciesindataandMC asdescribedin[44].Only0.2–0.4%oflightjetsaremisidentifiedas heavy-flavorjetsandcomprise7%to15%ofthefinalsample,with alarger fractionatlower jet pT. Inaddition totheb-NN output,

weobtainfurtherinformationbycombiningtheMSVandJLIP

vari-ables,which providegood discrimination betweenb,c, andlight quarkjetsduetotheir differentmasses[45,46].Weformasingle variablediscriminant

D

MJL

=

1₂

(M

SV

/(

5 GeV

)

−

ln

(

JLIP

)/

20

)

[45]

andrequire

D

MJL

>

0

.

1 toremovepoorlyreconstructedeventsand

reduce the number of light-jet events. The efficiency for signal eventstopassthisselectionis98%forb-jetsand97%forc-jets.

Afterallselectionrequirements,5260eventsremaininthedata sample. Wemeasure the fractionof W

+

c and W

+

b events in theselectedsample byperforming abinned maximumlikelihood fit to the observed datadistribution of the

D

MJL discriminant in

binsofjet pT,asshowninFig. 1forthebin30

<

pjetT

<

40 GeV.

Thetemplatesfor W

+

b and W

+

c jetsaretakenfromthe sim-ulation.Expectedcontributionsfromthebackgroundprocessesare subtracted fromthe

D

MJL distribution indata before the fit.The

ratioof the W

+

light parton jets to W

+

all jet flavors has been estimated using alpgen

+

pythia MC events taking into account thedata-to-MCcorrectionfactorsasdescribedinRef.[44],andhas been crosschecked in datausing looser cutson b-NN output in therangefrom0.15–0.3.

The fractions of W

+

b and W

+

c events after subtraction of background contribution are shown inFig. 2 as a function of jet pT. The relative uncertainties on the fractions obtained from

the fit range within (7–13)% for W

+

b and(6–11)% for W

+

c.

Thisincludes theuncertaintydue to W

+

b and W

+

c template

shapes,studiedinapreviousanalysis[47].Thecontributionsfrom thebackgroundeventsarevariedwithinuncertaintiesontheir

pre-Fig. 1. (Coloronline.)DistributionoftheDMJLdiscriminantafterallselection crite-ria(includingb-NNoutput

>

0.5)forarepresentativebinof30

<

pjetT <40 GeV. Thecontributionsfrombackgroundeventsare subtractedfromdatabeforethefit. Thedistributionsforthec-jetandb-jettemplates(withstatisticaluncertainties)are shownnormalizedtotheirrespectivefittedfractions.

Fig. 2. (Coloronline.)Theb- andc-jetfractions(theirtotalsumisnormalizedto 1.0)versusjetpT withtotaluncertaintyfromtheDMJLfit.

dicted crosssections,andtheseuncertainties arepropagated into theextractedsignalfractions.Theuncertaintyduetothelight par-tonjetstemplateshapeistakenfromRef.[46].Theoverallrelative uncertainties on the subtracted backgroundsrange within (4–6)% forW

+

b and(3–4)%forW

+

c.

Weapplycorrectionstothemeasurednumberofsignalevents to account forthedetectorandkinematicacceptances and selec-tionefficienciesusingsimulatedsamplesofW

+

b(c)-jetevents.In thesecalculations,weapplythefollowingselectionsattheparticle level:atleastoneb(c)-jetwithpb_T(c)-jet

>

20 GeV,

|

η

b(c)-jet

_|

_<

₁

_.

_5,

a muon with pμ_T

>

20 GeV and

|

η

μ

_|

_<

₁

_.

_{7, and a neutrinowith} pν_T

>

25 GeV.Inthefollowing,wequote ourcrosssection results forthisrestrictedphasespaceasafiducialcrosssection.

The acceptanceisdefinedbythe selectionrequirementsin jet and muon transverse momenta and pseudorapidities. Correction factors to account for small differences between jet-pT and

ra-pidity spectrain dataandsimulation are estimated, and usedas weights tocreateadata-likeMCsample. Thedifferencesbetween acceptance correctionsobtained withstandard and correctedMC samplesare takenasa systematicuncertaintyofup to3% atlow jet pT. An additional systematic uncertainty of up to 4% is due

Fig. 3. (Coloronline.)SimilartoFig. 1butforeventsselectedwithb-NNoutput

>0.3.Thisalternativeselectionisusedasacross-checkofthemainresults.

20

<

pjet_T

<

150 GeV theproductofacceptanceandmuonselection efficiencyvarieswithin(50–65)%witharelativesystematic uncer-taintyof(3–5)%.Thesystematicuncertaintyonthemuonselection efficiencyis about2% andis obtainedfrom a comparisonof the muonefficiencies in Z

→

μμ

eventsin dataandMC. Uncertain-tiesonb-jetidentificationaredeterminedinsimulationsanddata byusingb-jet-enrichedsamples[44]andareabout(2–5)%perjet. The integrated luminosity is known to a precision of 6

.

1% [48]. Bysummingthe uncertaintiesinquadratureweobtaina final to-tal systematicuncertainty on the cross section measurements of (11–18)%dependingonjet pT andfinalstate.

Tocheckthestabilityoftheresults,theW

+

b-jetandW

+

c-jet

crosssectionshavebeenremeasuredusingalooserb-NNselection,

b-NNoutput

>

0

.

3,andwiththelightpartonjetfractionincluded asan additional fit parameter, thus increasing the data statistics andthebackgroundfractions.Thefractionsofb- andc-jetsare ob-tainedfromthemaximumlikelihood fitofthelight, b- andc-jet

templatesto

D

MJL distributionindataasshowninFig. 3.Wealso

varythedefaultHT cutby

±

15 GeV andremeasurethecross

sec-tions.Inbothcross-checks,thedefaultandnewcrosssectionsare foundtobeinagreementwithinuncertaintiesthatincludethe cor-relationbetweenthetwomeasurements.

InFigs. 4 and5andTables 1 and2,wepresenttheW

+

b-jet

and W

+

c-jet differential productioncross sections times W

→

μν

branching fraction for the fiducial phase space defined by

pμ_T

>

20 GeV,

|

η

μ

_|

_<

₁

_.

_{7, pν}

T

>

25 GeV, and with at least one

b(c)-jetwithpjet_T

>

20 GeV and

|

η

jet

_|

_<

₁

_.

_{5.Thecrosssectionsare}

presenteddifferentiallyinfive pjet_T binsintheregion20–150 GeV. The data points are plotted at the value of p_Tjet for which the value of a smooth function describing the cross section equals theaveraged crosssection inthe bin[49]. Thecross sectionsare comparedtopredictionsfromNLO QCD[43]andtwoMC genera-tors, sherpa and alpgen.TheNLO predictionsaremadeusingthe MSTW2008 [50] and CT10 [51] PDF sets. We calculate the NLO QCDpredictionusing mcfm withcentralvaluesofrenormalization and fragmentation scales

μ

r

=

μ

f

=

MW and with the b-quark

andc-quarkmassesmb

=

4

.

75 GeV andmc

=

1

.

5 GeV,respectively.

Uncertaintiesareestimatedby varying

μ

r and

μ

f independently

byafactoroftwoineachdirection.

TheNLO predictionsare correctedfornon-perturbativeeffects such as parton-to-hadron fragmentation and multiple parton in-teractions. The latter are evaluated using sherpa and pythia MC samplesgenerated usingtheir defaultsettings [8,35]. The overall corrections vary within a factor of 0.80–1.1 with an uncertainty of



5% assignedto account forthe difference betweenthe two MC generators.The ratios ofdataover the NLO QCD calculations

Fig. 4. (Coloronline.)TheW+b-jetdifferentialproductioncrosssectiontimesW→

μνbranchingfractionasafunctionofjetpT.Theuncertaintiesonthedatapoints includestatisticalandsystematiccontributionsaddedinquadrature.The measure-mentsarecomparedtotheNLOQCDcalculations[43]usingtheMSTW2008PDF set[50](solidline).Thepredictionsfrom sherpa[35]and alpgen[7]areshownby thedottedanddashedlines,respectively.

Fig. 5. (Coloronline.)TheW+c-jetdifferentialproductioncrosssectiontimesW→

μνbranchingfractionasafunctionofjetpT.Theuncertaintiesonthedatapoints includestatisticalandsystematiccontributionsaddedinquadrature.The measure-mentsarecomparedtotheNLOQCDcalculations[43]usingtheMSTW2008PDF set[50](solidline).Thepredictionsfrom sherpa[35]and alpgen[8]areshownby thedottedanddashedlines,respectively.

andofthevarioustheoreticalpredictionstotheNLOQCD calcula-tionsarepresentedinFigs. 6 and7.ThemeasuredW

+

b-jetcross sectionsaresystematically abovethe NLOQCD predictionsforall jet pT bins.The W

+

c-jetdata agreewiththeNLO QCD

predic-tions atsmall pT but disagree at higher pT as the contribution

fromqq

¯



→

W

+

g

(g

→

cc)

¯

eventsincreases.

In addition to measuring the W

+

b-jet and W

+

c-jet cross-sections, we calculate the ratio

σ

(W

+

c)/

σ

(W

+

b) in jet pT

bins.Inthisratio,manyexperimentalsystematicuncertainties can-cel. Also, theory predictionsof the ratioare less sensitive to the scale uncertainties and effects from missing higher-order terms thatimpactthenormalizationsofthecrosssections.Theremaining uncertainties are caused by largely anti-correlated uncertainties comingfromthefittingofc-jet andb-jet DMJL templates todata,

Table 1

TheW+b-jetproductioncrosssectionstimesW→μνbranchingfraction,dσ/dpjetT,togetherwithstatisticaluncertainties(δstat)andtotalsystematicuncertainties(δsyst). Thecolumn

δ

totshowstotalexperimentaluncertaintyobtainedbyadding

δ

statand

δ

systinquadrature.Thelastthreecolumnsshowtheoreticalpredictionsobtainedusing NLOQCDwithMSTWPDFset,andtwoMCeventgenerators, sherpa and alpgen.

pjetT bin (GeV) p jet

T (GeV) dσ/dp jet T (pb/GeV)

Data δstat(%) δsyst(%) δtot(%) NLO QCD sherpa alpgen 20–30 24.3 9.6×10−2 _{2.4 17.8 18.0 6} .5×10−2 ₃ .9×10−2 ₃ .9×10−2 30–40 34.3 4.0×10−2 _{2.9 13.6 13.9 3.0×10}−2 _2.0×10−2 _2.0×10−2 40–50 44.3 2.5×10−2 _{3.6 14.4 14.8 1.6×10}−2 _1.1×10−2 _1.1×10−2 50–70 57.2 1.2×10−2 _{3.4 15.2 15.6 7.4×10}−3 _5.5×10−3 _5.2×10−3 70–150 81.7 2.2×10−3 _{4.5 17.7 18.3 1.4×10}−3 _1.0×10−3 _9.3×10−4 Table 2

TheW+c-jetproductioncrosssectionstimesW→μνbranchingfraction,dσ/dpTjet,togetherwithstatisticaluncertainties(δstat)andtotalsystematicuncertainties(δsyst). Thecolumn

δ

totshowstotalexperimentaluncertaintyobtainedbyadding

δ

statand

δ

systinquadrature.Thelastthreecolumnsshowtheoreticalpredictionsobtainedusing NLOQCDwithMSTWPDFset,andtwoMCeventgenerators, sherpa and alpgen.

pjet_T bin (GeV) pjet_T (GeV) dσ/dpjetT (pb/GeV)

Data δstat(%) δsyst(%) δtot(%) NLO QCD sherpa alpgen 20–30 24.2 4.1×10−1 _{3.7 17.0 17.4 4.1×10}−1 _2.1×10−1 _2.4×10−1 30–40 34.2 2.6×10−1 _{4.6 11.0 11.9 1.8×10}−1 _9.2×10−2 _1.1×10−1 40–50 44.2 1.5×10−1 _{5.8 11.9 13.2 9.2×10}−2 _4.6×10−2 _5.9×10−2 50–70 57.0 8.4×10−2 _{5.3 12.1 13.2 3.9×10}−2 _2.0×10−2 _2.6×10−2 70–150 80.7 1.3×10−2 _{6.9 15.6 17.1 6} .1×10−3 ₃ .1×10−3 ₃ .8×10−3

Fig. 6. (Coloronline.)TheratioofW+b-jetproductioncrosssectionstoNLO pre-dictionswiththeMSTW2008PDFset[50]fordataandtheoreticalpredictions.The uncertaintiesonthedataincludebothstatistical(innererrorbar)andtotal uncer-tainties(fullerrorbar).Alsoshownarethe uncertaintiesonthetheoreticalQCD scales.TheratioofNLOQCDpredictionswithCT10[51]tothoseobtainedwith MSTW2008aswellasthepredictionsgivenby sherpa[35]and alpgen[7]arealso presented.

above. Experimental resultsas well as theoretical predictions for the ratios are presented in Table 3 and Fig. 8. The systematic uncertainties onthe ratiovarywithin (11–17)%.Theoretical scale uncertainties,estimatedbyvaryingtherenormalizationand factor-izationscalesbyafactoroftwointhesamewayforthe

σ

(W

+

b)

and

σ

(W

+

c)predictions, are alsosignificantly reduced. Specifi-cally,residual scale uncertainties are typically(0.5–4.6)% forNLO QCD,whichindicates a muchsmallerdependenceoftheratioon the higher-order corrections. The ratio

σ

(W

+

c)/

σ

(W

+

b) for

p_Tjet

>

30 GeV isreasonablyconsistentwiththeoreticalpredictions exceptfor sherpa.

Insummary,wehaveperformedthe firstmeasurementofthe differentialcrosssectionasafunctionofpjet_T fortheW

+

b-jetand

W

+

c-jet final stateswith W

→

μν

decayat

√

s

=

1

.

96 TeV, in

Fig. 7. (Coloronline.)TheratioofW+c-jetproductioncrosssectionstoNLO pre-dictionswiththeMSTW2008PDFset[50]fordataandtheoreticalpredictions.The uncertaintiesonthedataincludebothstatistical(innererrorbar)andtotal uncer-tainties(fullerrorbar).AlsoshownaretheuncertaintiesonthetheoreticalQCD scales.TheratioofNLOQCDpredictionswith CT10[51]tothoseobtainedwith MSTW2008aswellasthepredictionsgivenby sherpa[35]and alpgen[7]arealso presented.

a restrictedphasespaceof pμ_T

>

20 GeV,

|

η

μ

_|

_<

₁

_.

_{7, pν}

T

>

25 GeV

and with b(c) jets with the pT range 20

<

pjetT

<

150 GeV and

|

η

jet

_|

_<

₁

_.

_{5. These are the first measurements of W}

₊

_{b/c cross}

sections that are sensitive to the gluon splitting processes. The measured W

+

b-jetcrosssectionishigherthanthepredictionsin all pT bins andissuggestive ofmissinghigherordercorrections.

Themeasured W

+

c-jetcrosssection agreeswithNLOprediction forthelow pjet_T (20–30 GeV),butdisagreestowardshigh pjet_T .The disagreementmaybe duetomissinghigherordercorrectionsand an underestimatedcontribution fromgluon splitting g

→

cc also

¯

Table 3

Theσ(W+c)/σ(W+b)crosssectionratioinbinsofc(b)-jetpT togetherwithstatisticaluncertainties(δstat),totalsystematicuncertainties(δsyst).Thecolumn

δ

totshows totalexperimentaluncertaintyobtainedbyadding

δ

stat and

δ

syst inquadrature.Thelastthreecolumnsshow theoreticalpredictionsobtainedusingNLOQCDwiththe MSTW2008PDFset,andtwoMCeventgenerators, sherpa and alpgen.

pjetT bin (GeV) p jet

T (GeV) Ratioσ(W+c)/σ(W+b)

Data δstat(%) δsyst(%) δtot(%) NLO QCD sherpa alpgen

20–30 24.3 4.3 2.9 13.3 13.6 6.2 5.4 6.2

30–40 34.3 6.6 3.6 12.7 13.2 6.1 4.7 5.7

40–50 44.3 6.1 4.6 13.9 14.7 5.8 4.2 5.4

50–70 57.1 7.2 4.2 13.8 14.4 5.3 3.7 4.9

70–150 81.2 5.7 5.4 17.5 18.3 4.5 3.0 4.1

Fig. 8. TheratiooftheW+c-jettoW+b-jetproductioncrosssectionsfordataand theoryasafunctionofjetpT.Theuncertaintiesonthepointsindataincludeboth statistical(innerline)andthefulluncertainties(theentireerrorbar).Predictions givenbyNLOQCDwiththeMSTW2008PDFset[50], sherpa[35]and alpgen[7]

arealsoshown.

Acknowledgements

WethankJohnCampbellforusefuldiscussionsandpredictions with mcfm.Wethankthestaffs atFermilabandcollaborating in-stitutions,andacknowledgesupportfromtheDOEandNSF(USA); CEA and CNRS/IN2P3 (France); MON, NRC KI, and RFBR (Rus-sia);CNPqandFAPERJ(Brazil);DAEandDST(India);COLCIENCIAS (Colombia); CONACYT (Mexico); NRF (Korea); FOM (The Nether-lands);STFCandTheRoyalSociety(UK);MSMT(CzechRepublic); BMBFandDFG(Germany);SFI(Ireland);SwedishResearchCouncil (Sweden);CASandCNSF(China);andMESU(Ukraine).

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/

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/

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/

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/

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/

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