Annotation of ttbar/p20_taujets_note/plots/d0conf_ttbarljets_v19_rvk.dvi, revision 1.1.1.1

1.1       uid12904    1: &; TeX output 2008.02.01:1901&2&=PSfile="d0logo.eps" llx=206 lly=343 urx=406 ury=449 rwi=1000 &o       cmr9DnoteT5234-CONFWۍg+(Ncmbx12Measurementof*gcmmi12n9'XQcmr12(pp  :,!",
                      2: cmsy10!URt$)6܍t>6)in&+jetschannelPύ0K`y
                      3: 
                      4: cmr10The%D$CollabGoration
                      5: (S&j             cmti9URLhttp://www-d0.fnal.gov(Dated:pF:ebruaryT1,2008)mo..Thisnotepresen9tsanewmeasurementof5"             cmmi9pDZp         cmsy9!
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                      6: O=
1:96T:eVusing350$pb-=q%cmsy6Aacmr61
nof|data|collectedwiththeDdetectorbAet9ween|2002and2005.SmW:efoAcusonthenalstate$where70the71WbAosonfromoneofthetopquarksdeca9ysinto70a?0leptonanditsassoAciatedneutrino,$whiletheotherdeca9ysintoaquark-antiquarkpair.e
                      7: W:eaimtoselectthoseev9entsinwhic9hthe$lepton#subsequen9tlydecays"tooneorthreecharged"hadrons,`zeroormoreneutralhadronsandatau$neutrino(thec9hargeconjugateproAcessesareimpliedinalloftheabAo9ve).MTheobserv|rablesignature$th9usconsistsofanarro9wcalorimetershowerwithassoAciatedtrack(s)characteristicofahadronic$taurdeca9y:,fourormorejets,ofwhic9htwoareinitiatedrbybquarksaccompanyingtherW&H'sinthe$topNquarkNdeca9ys,]andalargenetmissingmomen9tuminthetransv9erseplaneduetotheenergetic$neutrino-an9tineutrinoTpairthatleaveUnotraceinthedetectormedia.pThepreliminaryresultforthe$measuredTcrosssectionis:fR(tSaHWtW)=5:1=#+4;cmmi6:38Q#3:5*(statw)=#+0:78Q#0:7(systƻ)1Ľ80:3#(lumij:0)pbOPreliminaryN<ResultsforFJalxl2006Conferences*2&2jt:            cmbx9I.$INTRCODUCTIONThetopquarkistheheaviestfundamentalparticleinnature.5PrecisemeasurementsofitsproGductionrateandotherpropGerties!allowustoperformprecisiontests!ofQCD predictions.!Inaddition,TanydeviationsfromtheStandardMoGdel%(SM)maysignalthe$presenceofnewphysics.U
InthisrespGect,bthedecaysofthetopquarkintothe
                      8: b>
                      9: 
                     10: cmmi10 leptonareespGeciallyinteresting,sincetheNistheheaviestlepton.0Anynon-standard
avor-andmass-depGendentcouplingscouldproGduceDaverysignicanteectinthischannel.[AninterestingexampleisthechargedHiggsbGoson,whichappGearsinextensionsoftheSMHiggssectorto2HDMs(Two-HiggsDoubletMoGdels),) andisrequiredinMSSM(MinimalSupGersymmetricStandardModel)[1&].^SincetheHiggs-fermioncouplingisproportionaltothelatter'smass,Ҕdecaysto=the<heavyleptonwouldbGemuch<morefrequentthan<thosetothelightereand.~ThispromptsustosearchforGH^ٓRcmr7+"ղdecayingFtoleptons.DandCDF0pGerformedsuchsearchesinRunI/[2&,3].ThemeasurementFoftheSMproGcess$presentedhere$isanimportantingredient$toextendingthereachof$suchsearchesinaddition$topGerformingacrucialUUtestoftheStandardMoGdel.TheoreticalGlcomputationsof[ٲ(pWp b
!",
                     11: 
                     12: cmsy10!Zt'#&btr)areconstantlyimproving.HThelatestpublishedNNLOG-crosssectionis6.80.4pb[4&].ThedecaymoGdeto{в+Z        jetshasabranchingfractionof0.15,thesameastheeZ       +jetsandZ      +jetschannels.%However,n|secondaryite'sand'sfromiuleptonicdecaysofa;leptonarediculttodistinguishfromprompt(primary)onesatahadroncollider.     &Hence,Kqinthisanalysisweonlytrytoidentifytheeventsinwhichthesubsequentlydecaystooneorthreechargedhadrons,Szeroormoreneutralhadronsanda& 0ercmmi7(thechargeconjugateproGcesses|!areimplied| inalloftheabove).*These|!account| foronly0.65oftheleptonbranchingratio,soweexpGecttheUUnumbGerofeventstobGelowerthaninthee8+jetsand+jetschannels.This2note1presentstherstmeasurement1ofthet'#&btcrosssectioninthischannel,usingthedatacollectedduringRunIGIbytheDdetector.?Theintegratedluminosityofourdatasamplewas349&[&\23pb^O!cmsy71
y[5&].?Aftercarefuloptimizationofj&triggers,o,ob8jectidenticationjandusinganarticialneuralnetworkforthenaljfull-eventpatternrecognition,o,weareabletoextractthefaintsignalfromtheverylargebackground,!whichisdominatedbymismeasuredQCDevents.!C%IKI.urTHEDDETECTORTheDRunIGIpdetector[6&]iscomprisedofthefollowingmaincompGonents:thecentraltrackingsystem,#theliquid-argon/uraniumUUcalorimeterandthemuonspGectrometer.Thecentraltrackingsystemincludesasiliconmicrostriptracker(SMT)andacentralbGertracker(CFT),bGothloGcatedTinsidea2T!superconductingsolenoidmagnet..rTheSMT!isdesignedtoprovideecienttrackingandvertexingcapabilityatpseudorapiditiesofj[ٸj=ܵ<=۲3.GThesystemhasasix-barrellongitudinalstructure,heachwithasetoffourlayersarrangedaxiallyaroundthebGeampipe,andinterspersedwith16radialdisks.Atypicalpitchof50-80moftheB_SMTB"stripsallowsB^aprecisiondeterminationofthethree-dimensionaltrackimpactB^parameterwithrespGecttothe,primary-vertex,!whichis,thekeycompGonent-ofthelifetimebasedb-jettaggingalgorithms.MTheCFThaseightcoaxial#barrels,eachsuppGortingtwodoubletsofoverlappingscintillatingbGersof0.835mmdiameter,onedoubletbGeingUUparalleltothecollisionaxis,andtheotheralternatingby3^9relativetotheaxis.Thecalorimeterisdividedintoacentralsection(CC)providingcoverageouttoj[ٸj1andtwoendcalorimeters(EC) extending.coverage-toj[ٸjղ4,each-housedinseparatecryostats.
                     13: PScintillatorsplaced-bGetweenthe-CC!andECprovideUUsamplingofshowersat1:1<j[ٸj<1:4.Themuonsystem,\coveringj[ٸj<2,\residesbGeyondthecalorimetryandconsistsofthreelayersoftrackingdetectorsand>fscintillatingtriggercounters.j"Movingradially>goutwards,Btherstlayerisplacedinsidethe>g1.8T>`toroidmagnets,andUUthetwoUUfollowinglayersareloGcatedoutsidethemagnets.ThedDetriggerisathree-leveltriggersystem.@Level1isahardwaretrigger,whilelevelse2and3aresoftwaredlters.!C%RIKII.AOBJECTIDENTIFICATIONThe7?mostimpGortantob8jectsforthisanalysisarejets7@andhadronicYleptoncandidates.Jetsarereconstructedusing{an|iterativealgorithm,?Ewhichintegrates|theenergyobserved|inthecalorimeterinaconewithradius&RȲ=
P\n5u
                     14: 
                     15: cmex10pn5fe*f       ˍ`y
                     16: 2+8`
2$8=0:5,where1y?isdetector2rapidityandistheangleintheplanetransversetothebGeamaxis.KThesejetsare=required=tobGeintheducialregionj[ٸj<2:4,Awith=p&T     ε>20GeV/c.iThe=energyofthejetsafterreconstructioniscorrectedUUtorepresentthetruejetenergy[5&].qAnequivqalentcorrectionisderivedforMonteCarloevents. 2&3jײA.
                     17: ^IDP\1.     qTJauN<decaymodesThe%oleptonhasseveraldecaychannels,/=classiedbythenumbGerofchargedparticles(tracks)andEM{clustersassoGciatedUUwithit[7&]:electronUUormuon(߸!e&eKK&Tor!&\&5),BR=35%.singleUUchargedhadron(߸![ٟ^ڵ&5),BR=12%.singleUUchargedhadron+1neutralparticle(i.e.,߸!^&&M!(n[ٟ^0,+8[ٟ^ڲ)&5),BR=38%.3UUchargedhadrons+0neutralhadrons,BR=15%(so-called\3-prong"decays).!C%‰2.    qTJauN<IDvariablesAtD,leptonsareidentiedintheirhadronicmoGdesasnarrow(&R)=20:3cone)jets,isolatedandmatchedtochargedUUtracks.qThe(mostimpGortant)discriminatingvqariablesare[8&]:ProleUU-iErb}Zcmr51O
\cmmi5T+Erb}0Tɉfe$M.9#cmex7P
                     18: L@i<Eb}iύT"Q,whereE^ibT   istheE&Tofthei^th`highestE&TtowerUUinthecluster.OIsolation,rdenedas&h8Eb}(0:5)E(0:3)8ʉfe3+Eb}(0:3);,whereE(RDz)istheenergycontainedinay,ofradiusRͲaroundthe
$calorimeterUUclustercentroid.T*rackisolation,0denedasscalarP=p&T
                     19: Qqofnon-&tracksinay  εconeof0.5aroundthecalorimeterclustercentroid.Using"theseandothervqariables,,threeNeuralNetworks"(NNs)are"trainedtoidentifythreetypGesofDlepton([ٲ-typGe,-typGeUUand3-prong)Thet5outputt4oftheseNNsprovidesasetofthreevqariables(D<x
                     20: 
                     21: cmtt10Dnnout=1,2,3)tobGeusedtoselecttheleptonintheevent.huThetypGesroughlycorrespondtotheVleptondecaymodes.hvType1containsonlyonechargedtrack,typGe2hasHoneIchargedtrackIandoneormoreelectromagneticclustersandtypGe3hasmorethanonetrack(multi-prongdecays).p_HighQvqaluesofNNQcorrespGondtothephysicalrleptons,Qwhilelowonesshouldindicatejetsmisidentiedas&!Dz'sUU(fakes).qF*ormoredetails,seeRef.[8&].!C%~B.
                     22: ^TheSecondaryVertexTaggingAlgorithmTheFµt'#&bt
inalFstatecontainsFtwoFµb-jets,IwhilejetsinQCDFandW+jetseventsForiginatemostoftenfromlightquarksoregluons.:RequiringatdleastonejetintheeventetobGeb-taggedisthereforeaverypGowerfulemethoddofbackgroundrejection._Theb-taggingalgorithmusedinthismeasurementisasecondaryvertextaggingalgorithm(SVT),whichexplicitly4reconstructsverticesthataredisplacedfromtheprimaryvertex.ZdInthettingproGcedure, theSVT
                     23: usesonlygoGodqualitytracksthathaveanimpactparametersignicance>3.hAlso,&onlysecondaryverticeswhicharedisplacedJfromKtheprimaryvertexintheplanetransversetothebGeamlinebymorethan7standarddeviationsareconsideredUUinthismeasurement.E':
                     24: 
                     25: cmti10Ea.
                     26: 8bE-taggingeciency
                     27: &ItTisSknown[9&]thattheb-tagging,TwhenapplieddirectlytoMonteCarlo,TgivesTaneciencythatgishigherthandata.%Inordertoaccountforg thisfactor,kSVTghasbGeenparameterizedont7ferYɍt0!侵D+jetsgMCgand+jetsWdatatoXcomputethecorrectionfactor,
                     28: whichscalestheMC-derivedeciency*.$Asaresult,
                     29: weobtaintheMCftaggingprobabilityandthedata-correctedone[9&].HItcanbGenotedthatthedata-correctedeciencyisindeednoticeablyUU(30%)lowerUUthanwhatwewouldexpGectbyapplyingtheSVTdirectlytoMC.Eb.
                     30: 8cE-taggingeciency
                     31: &An`assumption`ismadethatthecorrectionfactorobtainedbydividingthesemi-leptonicb-taggingeciencyindatatotheoneinMCalsoiscorrectforcjets.H      HencetheMC-obtainedinclusivec-taggingeciencyUUismultipliedbythisfactorinordertoestimatethec-taggingprobability*.$2&4]YC9T:ABLETI:Bac9kgroundsources,relev|rantforthe7+8jetsanalysis.pThebranchingfractionintohadronicShasbAeenapplied0/37ff&ffff&ff&Y&Bac9kground<Description&fCrossTSectionΉff&&WW+8jjjj׽!ƻ&qjjjjôhasTiden9ticalsignaturetothesignal&1Խ18Tpb
                     32: &Z Z=
ƹ+8jjj׽!&jjjbSleptonTisusuallyfoundasajet&۠2.6Tpb&W&HZ5!ƻ&qjjneedsTt9woextrajets(canbAegluonemission)&۠0.2Tpb&W&HWک!ƻ&qjjČneedsTt9woextrajet(canbAegluonemission)&۠0.5Tpb&singleTtopSsmallTcrosssection,buthasbjets&۠0.5Tpb&QCDan9yT4-jeteventthatdoAesn'thavearealSleptoninit&ӝ>100Tn9bΉff&ffff&(.Ec.
                     33: 8Lightkjettaggingeciency
                     34: &Thevb-tagvfakeratefromlightquarksiscomputedbymeasuringthenegativetagrate.vItisdenedbytherateofappGearanceofsecondaryverticeswithanegativedecaylengthsignicance.vItisassumedg~thatthelightquarkshaveanequalchancetoproGduceasecondaryvertexwithpGositiveandnegativedecaylengthƵsignicanceƶ(duetoniteresolutioneects)whiletheheavy
avorƶjetscanonlyproGduceaSVƘwithpGositivedecayRlengthRsignicance.pHowever,SFthisisRnotquitetrueandaspGecialscalingfactor(SF&hf   ݧ)isintroGducedtocorrectforthefractionofheavy
avorsamongthejetswithanegativedecaylengthsignicance.hAnothercorrectionisfortheUUpresenceoflonglivedparticlesinlightjets(SF&l
                     35: `l).qBothfactorsarederivedfromMonteCarlo.!C%ELIV.xBACCKGROUNDSTwomaindistinctivefeaturesofthesignaldeterminewhichbackgroundsareimpGortant.InordertobGerelevqant,theproGcessmusthaveahigh(>3)numbGerofjetsaswellasasizeable(>15GeV)6qȵE&TL.MTAllofthecandidateproGcessesareUUlistedinT*ableIV.qThecrosssectionslistedincludethebranchingfractionsintowleptons.W*e.canconcludethatthetwo.dominantbackgroundsourcesareQCD.{(\fake&!Dz")andW&c+4jets.dThesetwosourceswere&takenintoaccountinthisanalysis.wQCD&isderivedfromthedata,-,whileMonteCarlosimulationisusedforW&c+jets.This|simulation|utilizesevents|generatedatp!fe3荵s=1:96T*eV|withtheALPGEN1.2[10
                     36: ]matrixelementgenerator,assumingatopmassof175GeV/c^2\andthepartondistributionfunctionsetCTEQ6.1M[11
                     37: ].[NTheseeventsarethenproGcessedtthroughF-
                     38: 
                     39: cmcsc10FPythias6.2[12
                     40: ].$Thispackqagetakestintoaccountthegluonradiationsandfragmentationeectsand)also*pGerformstheshortlivedparticledecays,eexceptforbhadronsandleptons.=EvtGen[13
                     41: ]isusedtomoGdelthedecays'of'bhadrons.bIòleptonsaredecayed'usingT*auola[14
                     42: ].bThegeneratedevents'arethenproGcessedthroughafullFgeantBj[15
                     43: ]BksimulationoftheDdetectorprovidingtrackingBjhits,F3calorimetercellenergyandmuonhitinformation.Multiple       interactions      areaddedtoalleventsaccording        toaPoissondistributionwithameanthatisdeterminedfromtheaverageinstantaneousluminosity*.b]Thesamereconstructionandob8jectIDisappliedtodataandMonteCarloevents.qTheUUsignal(t'#&btr)MonteCarloispreparedinthesameway*.V.>EVENTSELECTIONF*orthisanalysis,$Gweusedthedatacollectedwitha4-jettrigger,$Gwhichrequired4jetcandidateswithj[ٸj<3:6andE&TL>10GeV}usingasimpleconealgorithm.aThistriggerwasdesignedfortheall-hadronictopdecaymoGdeandworks!well!forourpurpGoses,,AsinceanenergetichadronicCòleptonisalways!foundasajetcandidate.`TheeciencyofthistriggerhadbGeenparametrizedandcross-checkedondataandisappliedasaweightingfactortotheMonteCarloevents.TheUUanalysisproGcedureinvolvedUUseveralstages:Preselectionqg(sectionqhV&A).Atleast4jetsand6E&T      signicance>3arerequired.653,727eventsqgareselectedintheUUdata,withapredictionof109.97.3t'#&btDzevents,UUforaS:B1:6,000.IDzcutsz(sectionV&B).nAtleastonegoGodzTleptonzcandidateandatleastonetightSVTztagarezrequired.oW*ealsorequired2jetswithj[ٸj<2:4andp&T     ε>20GeV/c.K216eventsareselectedinthedata,~9.30.6t'#&bt~amongthemUUareexpGected.qS:B1:58.T*opGological&NN(sectionV&D).5VAsequenceoftwofeed-forward&NN'shave&bGeentrainedandapplied.5VTheoptimalcuto<onthesecondNNo5hasbGeenfoundtobe0.6.|Withthisnalcut,uweobtained13eventsindatawith4.90.3UUt'#&btDzamongthemexpGected.qS:B1:2.5.8 2&5x@#FIG.T1:p6|rE&T:signicanceforQCD-dominateddata(blac9k),WW+8jets(blue)andtVۍ &%t!ƻ7+jets(red).îT:ABLE]IAI:Preselectionresults.WSho9wnarethetotalacceptances(includingpreselection)andthenumbAerofeventsscaledto
                     44: 349??23pb-=1
1(nosystematicuncertain9tiesexceptforthisluminosit9yerrorareincluded).^TheALPGEN?samplesgenerationcutsTaredescribAedin[16       ?].pAnestimateofQCDbac9kgroundnotincluded.1~)(=ff&ffff&ff&Y(#Tpassed)/(total#)&KR,Tpb&l#TpassedscaledΉff&!ndata653,727/17M&̤Y653,727
                     45: 􍍑tSaHWt!ƻ7+8jets:K6,141/10,878&:z0.821T0.004&
B109.93T7.26
                     46: W&Hbbjj׽!T&+8bbjj:K2,321/11,576&:z0.222T0.044&ĭ@9.98T2.08ֻW&Hccjj׽!T&+8ccjj:K2,289/10,995&:z0.527T0.059&]A24.77T3.22JW&Hcjjj׽!T&+8cjjj:K2,169/10,435&<$0.920T0.087&]A42.23T4.87W&Hjjjj׽!T&+8jjjj:K2,683/11,920&?x14.14T1.3&C720.33T81.48Ήff&ffff&()|The$1WbackgroundhasbGeenmodeledusing$0ALPGEN#MonteCarlosimulation,Wwhile$0QCD#backgroundestimateswereextractedfromthedata    usingtheproGceduredescribedinsectionV&C.]XInorderto  optimizetheselectionwealsousedxtheyt'#&btMonteCarloandnormalizedittoknown(eithertheoreticalorcomputedbyALPGEN)bvqalues.T}IntheendweUUappliedthisoptimalselectiontomeasuretheactualt'#&btDzcrosssectioninthedata.!8E԰A.
                     47: ^PreselectionThee?totalnumbGere>ofe?eventsrecordedbye>ourtriggerinthis349pb^1!datasetis17million.Themaingoalofpreselectionwastoreducethisdataset,&whileimpGosingthemostobviousandstraightforwardrequirementsthatcharacterizeUUthesignalsignature.qSuchcharacteristicfeaturesincludethefollowing:@ۍMoGderateUU6qȵE&T        arisingfromboththeWvertexandwdecay*.fAtUUleast4jetsmustbGepresent.AtUUleast1wleptonand2bjetsarepresent.@ڍ6qȵE&TsignicanceK[17
                     48: ]LisdenedasmeasureofthelikelihoGodofL6qȵE&T~arisingfromLphysicalsources,       Iratherthan
uc-tuationsHinGdetectormeasurements.*These
uctuationsarepredictedfrommeasuringandparametrizingtheob8jectresolutionsinthedata.AscanbGeobservedinFig.1,acutonthisvqariableprovestobGeaneectivewaytoreducetheUUdataset.qAcutof3wasusedforpreselection.Nowweneedtoscaletheoriginal10KeventsoftheMCsampleto349pb^1
                     49: t.<pThetotalt'#&bt5Ucrosssectionis6.8pb[4&].T*akingintoaccountthebranchingfractiontothehadronic~C+\|jetsmoGde,theeectivecrosssectioncomesouttoUUbGe:M|M/BqRDz(߸!hadrons%N:)8&BRDz(t'#&btc!Z+jets)&[ٲ(t'#&btr)=0:65&0:15&6:8=0:66UUpbTheGrelativeH
avorfractionsHoftheW
                     50: V+4jetsproGcessweretakenHfromALPGENsimulationasHratiosofthesimulatedcrossYsections.~ItwasYthennormalizedtothemeasuredtotalvqalueof4.52.2pb[18
                     51: ].~T*ableIGIshowstheresultsoftheUUpreselectionforbGothdataandthebackgrounds.qB.
                     52: ^ResultsoftheIDcutsThe&next'stepwastoapplytherequirementof&!Dz-andb-tagging.F
T*ableIGII&showstheselectioncriteriathatweapplytodataandMCpandT*ableIVshowstheresultingselectioneciencies.ZTableVshowsthebreakdownoftheseeventsbGetweentype2and3V(type1isdisregardedduetoitssmallcontributiontothesignalandlargebackground).MuItcan
bGe
    notedthattheS:Batthisstageis1:58,~whichistoGosmall.YInsectionV&DwewilldescribGethetopGologicalNNusedUUtoenhancethesignalcontent.AtUUthispGoint,weusetheseIDalgorithmstodene3subsamplesoutoftheoriginalpreselecteddatasample:@ۍThe\signal"sample-requireatleast1ϟleptonwithN&Nq>Z0:95andatleastoneSVTtag(asintableIGII).ThisUUisthemainsampleusedforthemeasurement.qItcontains268events.Q2&6T:ABLE      IAII:b-taggingandID.IntheMC,w9eusetheb-taggingcertiedparameterizationratherthanactualb-tagging,that
                     53: is,Uw9eappliedtheb-taggingweight.
W:ealsousedthetriggeringweightascomputedbythetriggereciencyparameterization. &iff&ffff&ff&Ydata&
1taggingMC
                     54: kF1ȴwithj@Lj<2:4andp&&mTJ>20GeV/c&hF1ȴwithj@Lj<2:4andp&&mTJ>20GeV/c»F1SVT&3T&r7ig@LWeight&,&bT&agPr7obgF2jetswithj@Lj<2:4andp&&mTJ>20GeV/c&dF2jetswithj@Lj<2:4andp&&mTJ>20GeV/cΉff&ffff&RîT:ABLEIV:b-taggingandIDresults.&GSho9wnarethetotalacceptances(includingpreselection)andthenumbAerofevents
                     55: scaledTto349pb-=1  .pAnestimateofQCDbac9kgroundisnotincluded.0)(=ff&ffff&ff&YH(#Tpassed)/(total#)&>3Acceptance&l#TpassedscaledΉff&!ndatam216/653,727&9216
                     56: 􍍑tSaHWt!ƻ7+8jetsٹ524.0/6141&40.0480T0.0020&
B9.320T0.620
                     57: W&Hbbjj׽!T&+8bbjj
ع54.5/2321&40.0150T0.0024&
B0.012T0.002ֻW&Hccjj׽!T&+8ccjj
ع13.3/2289&40.0039T0.0012&
B0.034T0.005JW&Hcjjj׽!T&+8cjjj]׹8.0/2169&40.0025T0.0010&
B0.160T0.020W&Hjjjj׽!T&+8jjjj]׹3.3/2683&40.0009T0.0006&
B0.860T0.100Ήff&ffff&()The\fvetosample"-Sameselection,butinsteadofN&N&o>o0:95,0o<NN&o<o0:5wasrequiredforgleptoncandidates\andno\events\with\goGod"\(N&N3>0:8)~rleptonswereallowed.Thissampleisused\forthetopGologicalNNUUtraining.qItcontains21,022events.TheD\bCveto"sample-atleast1
                     58: leptonwithN&N>p0:95,ԿbutNO)SVT*tags.ThissampleistobGeusedfortheUUQCDprediction.qItcontains4,642events.+C%ZC.
                     59: ^QCDmoKdelingThedierencebGetweenthetotalnumbGeroft'#&bt]andW$eventsanddatahastobGeaccountedforbyQCD-initiatedevents,+wheregah.candidateisajet,mistakenlyidentiedhasa.lepton.Inordertoestimatethisbackgroundcontribution,UUthefollowingstrategywasemployed.W*estartedwiththe\bveto"sample.EThissampleisdominatedbymultijeteventsinwhichajetismisidentiedasJahadronic&!Dz.R Sincethelcandidatesherearereallyjets,%wecanJsimplydividevsp&T
                     60: ~distributionsofthecandidatesbythesamedistributionsforjetsbinbybintoparameterizethe<Mfakerate.^-Inordertoreducethiseectand'minimizethestatisticaluncertainty*,we'pGerformeda2Dttothis(distribution.=ThistwasthenusedfortheQCD,prediction.HTheTdistributionsinN-andUp&T
                     61: ?
                     62: haveTbGeenseparatelyttedwithA([ٲ)andBq(p&TL).HThevqalidityofusingthenormalizedproGductofthesetwoeciencycurveshasbGeencheckedusingclosuretests.jTheresultofthisproGcedureWcanbeobservedinFig.@2.F*orWtypGeV3leptoncandidatesthe0:85:<j[ٸj:<1:1Wregionwasexcludedfromthe&tduetothepGoor&performanceoftheIDNeuralNetinthisregion.:Thenal2DparameterizationofthefakeUUrate(normalizedproGductof.andp&T  ts)isshowninFig.q3.!C%1.  qComputingN<theQCDfractionW*eassumethatprobabilityforajettofakeaAdleptonissimplyF&c([;&p&TL)=A()Bq(p&TL)._ThentheprobabilitythatatUUleastoneofthejetsintheeventUUwillfakeawcanbGecomputedasthefollowing:kT:ABLE$V:$b-taggingand,ID$resultspAert9ypeafter$thewGcut(asexplainedinsectionV&C).JJSho9wnarethenumbAer$ofevents
                     63: predictedTinsignalandobserv9edinthedata.pAnestimateofQCDbackgroundisnotincluded.!
                     64: nff&ffff&ff&YJT9ypAeT2&֜T9ypAeT3
                     65: !data&Zb91&@71
                     66: 􍍑=tSaHWt!ƻ7+8jetsj5.61T0.37&2.81T0.18Wک!ƻ&+8jetsj0.93T0.04&0.32T0.01Ήff&ffff&f2&7)|{Ycmr8(a)  TÎyp<re2t-(b)       TÎyp<re3t8t1@FIG.T2:pFitofthegandp&T:distributionsoftheSfak9erate.[
                     67: (a)       TÎyp<re22Dt
                     68: (b)        TÎyp<re32DFitG@oFIG.T3:pThe2Dcom9binedt(ingandp&T)oftheSfakerate.W1P&ev@Lentв=18QjU(1F&c(p1ɍjTL;&[ٟ^j)):lByUUsummingupsuchprobabilitiesoverthetaggeddata,weobtaintheQCDbackgroundestimate.Using.theresults-describGedintheprevioussection,"#wegetN&QC}D7=*71:131:56.forthetypGe2andN&QC}D7=77:46>?0:80forthe(typGe3,3Gwhichagreeswiththeobserveddata(inT*ableV)fairlywell.rOnecanalsoobserve(seeWAppGendix)WthatthepredicteddistributionsofthemaintopGologicalvqariables(sectionV&D)areinfairlygoGodagreementUUwithwhatisobservedinthedata. 粍D.
                     69: ^TopKologicalNNSimilarlyGtoHtheall-jetsanalysis[5&],wedene2neuralnetworksG(NN)+(theMultiLayerGPerceptron[19
                     70: ]GprogramwasUUused).qThetwoNNscontain'1.3UUtopGological(aplanarity*,sphericityandcentrality)and2energy-based(H&T        andpfe3荵sZ)vqariables.'2.theUUoutputoftherstNN,WandtmasslikelihoGods,UUp&T     anddecaylengthsignicanceofthebjets.lTheUUkinematicandtopGologicalvqariablesusedare:H&T    -UUthescalarsumofalljet'sp&T(andwleptoncandidates).SphericityأandآAplanarity[5&]آ-thesevqariablesareformedfromtheeigenvqaluesofthenormalizedMomentumT*ensorpofothejetsintheevent./ThesearepexpGectedtobGehigherinthetoppaireventsthanpinatypicalQCDevent.Centrality*,UUdenedasH&&mT&7feWQH&&mEha,whereH&E
                     71: ²issumofenergiesofthejets.)ˍT*op$and$W$&masslikelihoGod-a$^2|s-likevqariable.aZL`텍     /M&3j#m&t        /ŭfemʟ&t*,`0ݱ26ֲ+&T`텍     kM&2j#M&&mW        kŭfe$gx̴&&mW.`4ݱ29m,-wherem&tV;&M&W   ;&t;&W<are$topandCW5masses(175GeVand80GeV4respGectively)Dandresolutionvqalues(45GeVand10GeVrespGectively)[5&].M&3jtandUUM&2jareinvqariantmassescompGosedofthejetcombinations,soastominimizeL.p&T    andUUlifetimesignicanceoftheleadingb-taggedjet.lMany~ofthesevqariables(forinstancethemasslikelihoGod~and~aplanarity)areonlydenedforeventswith2ormorejets.pThusQwerequire2jetswithp&T        ε>20GeV/cQandj[ٸj<2:5.pPlotsofsomeofthesevqariables,RwhichalsoservesasanUUadditionalcheckUUoftheagreementbGetweenthedataandprediction,areincludedintheappGendix.The5resultofapplyingthese5NN5todataisshowninFig.g<4.The5maximumsignal5signicanceisusedtodeterminetheoptimalNN{cut.8oThesignalsignicanceisdenedasEN&&mS&7fe$Ti捍pɟW      noN&&mS+N&&mB*R\,whereN&S    bandN&B
                     72: yaretheexpGectednumbersof
bgsignalandbackgroundeventsrespGectivelyandisshowninFig.=5.ThissignicancereachesitsmaximumatN&N3>0:9forΐbGothtype2and3.DTherefore,thisselectionisusedfortheΏcrosssectionmeasurement.TheresultsaresummarizedinUUT*ableVI.|[2&8*:t
                     73: (a)       TÎyp<re2+&2cmmi8lep-ton
                     74: (b)        TÎyp<re2lep-ton(zo<romed)P
                     75: (c)        TÎyp<re3lep-ton
                     76: (d)        TÎyp<re3lep-ton(zo<romed)\KFIG.y4:"ResultofapplyingthexNNWcut.޻tVۍ &%tW,BW\andQCDVareplottedincremen9tallyinordertocomparewiththen9umbAeryof
                     77: ev9entsobservedindata.0Errorbarsincludeonlystatisticaluncertain9ties.0ܻR(tVۍ &%tW)=5:54pbisassumed.0Therigh9tplotonlysho9wsTtheentriesathighv|raluesofNNcut.;E.̍
                     78: d(a)       dTÎyp<re&2
                     79: yc(b)        ycTÎyp<re&3,Z4lFIG.T5:ptVۍ &%t!ƻ7+8jetssignalsignicance.U󍍒DVI.SYSTEMATICUNCERTAINTIESTheBmostAimpGortantsystematiceects(exceptfortheb-tagging,FwhichistreatedindepGendently)aresummarizedinT*able_VIGI.=uMostofthemareassociatedwithuncertaintiesonthecorrespondingquantities(Jet^EnergyScale,PrimaryV*ertex,'Branching
RatioandTriggersimulation).^TheQCDsystematicscomesmainlyfromtheerrorofthe2Dtofthe3nU5fakerate.fzTheW*!&!duncertaintycomes3mfromtwosources:`theuncertaintyof3mthecrosssectionvqalueandtheconservqativeUUestimateoftheerrorassoGciatedwiththemethodthatweusedformodelingthisbackground. nDA.
                     80: ^b-taggingTheeectsofuncertaintiesintaggingbjetsaretakenintoaccountbyvqaryingthesystematicandstatisticaluncertaintiesontheMC1taggingweights.V^TheresultingeectofalloftheerrorsourcesonthenalnumbGerissummarizedUUintableVIGII,UUalongwiththetotalbIDsystematicuncertaintyUU(quotedintableVIGI). neQVIKI.^{CRCOSSSECTIONTheUUcrosssectionisdenedas"=)&N,umber&of&sig@Lnal&h&eventsK);feymJ"(tU)ȱ&JtV)&BW=R ,(tU)ȱ&Jt!+jgets)&Luminosity~Ȳ.qTheresultsarethefollowing:;&!Dz+jetsUUtypGe2(singleprong)crosssection:kpn@[ٲ(t7ferYɍtr)=3:63䍑0+4:7203:50 1(stat)䍑0+0:4900:48(syst;)80:240(lumiq)pb;҄gT:ABLEVI:ThenalresultsummaryaftertheNN>ƹ0:9cut.(tVۍ &%tW)isthetotalsignalacceptance.Uncertain9tiesarestatistical
                     81: only:.,xMخff&ffff&ff&nChannelNN-=obs{=BUzi           cmex9ŖLdt;&pb-=1B{Bac9kgroundsQ)&h#ff&^؉"(tVۍ &%tW)T(%)&sT(7pb)&6s8+bΉff&Y
                     82: 1&+jetsTt9ypAe2VV5xK0.1~349.3RWک!ƻ&&0.60T0.03&Yh1.57T0.01&A3.83+0:468Q0:51&6.84+0:468Q0:51
                     83: Yfak9es&2.41T0.09&+jetsTt9ypAe3VV5xK0.1~349.3RWک!ƻ&&0.27T0.01&Yh0.73T0.01&A1.80+0:228Q0:23&4.39+0:228Q0:23Yfak9es&2.33T0.09Ήff&ffff&       ˠ2&9񍟜
                     84: }ӂT:ABLETVIAI:Systematicuncertain9tiesonR(tVۍ &%tW)(inpb).6&kff&ffff&ff&Y-Channel&Pr+jetsXtÎyp<re2&Tr+jetsXtÎyp<re3
                     85: HJetXEnergyScale&
:ޟ&q0:27;+0:30&D&q0:69;+0:53!PrimaryXVJertex&        7&q+0:037;0:036&&q+0:095;0:093.H*MCXStat&
:ޟ&q+0:25;0:22&D&q+0:65;0:581TJrigger&&q0:020;+0:0025&GI&q0:069;+0:0056BrancÎhingXRatio& 7&q+0:074;0:071&D&q+0:19;0:18QCDXfakÎerateParameterization&
:ޟ&q+0:17;0:17&D&q+0:34;0:34-Wک!ƻ&&
:ޟ&q+0:19;0:19&D&q+0:19;0:19Ήff&ffff&T:ABLETVIAII:b-taggingsystematicssources;?kff&ffff&ff&Y.Channel:r+jetsXtÎyp<re2&Wr+jetsXtÎyp<re3
                     86: ub-tagging&t0ncmsy50:13;+0:076&q&t0:26;+0:41bc-taggingTy&t0:20;+0:16&q&t0:48;+0:60(=l-tagging9&t0:0051;+0:0051&
                     87: y&t0:014;+0:014GlSF&hf&t0:00036;+0:00036&<9&t0:00094;+0:0009412SF&ll&t0:00036;+0:00036&<9&t0:00094;+0:00094Tb-tagging(data)Y&t0:091;+0:094&q&t0:24;+0:25iTb-tagging(MC)Ty&t+0:11;0:10&q&t+0:28;0:25Mtaggabilit9yY&t0:048;+0:049&q&t0:13;+0:13Ήff&ffff&2˵&!Dz+jetsUUtypGe3(multi-prong)crosssection:l'?[ٲ(t7ferYɍtr)=9:39䍑0+10:1007:49$(stat)䍑0+1:2501:18 1(syst;)80:610(lumiq)pb:The1combinedcrosssectionwasestimatedbyminimizingthesumofthenegativelog-likelihoGod1functions(con-structedfromaPoissondistributionusingthenumbGerofobservedeventsand\hypGothetically"observedeventsasthePoissonmean)foreachchannel.UUThefunctionalformofthelikelihoGodfunctionwasthesameashasbGeenusedfortheeUUchannel[20
                     88: ].qThecombinedcrosssectionyieldsn@[ٲ(t7ferYɍtr)=5:05䍑0+4:3103:46 1(stat)䍑0+0:6800:67(syst;)80:330(lumiq)pb:!C%JiVIKII.ߓSUMMARYThis-notepresents,themeasurementof[ٲ(t'#&btr),bytheDcollabGoration,intheRun2aoftheF*ermilabTevqatron.WThedecayb9channelstudiedinvolvesonehadronicallydecayingb8lepton,er2bjets,2lightjetsand6CE&TL.sThetriggerandthecorrespGondingUU349823pb^1ɲdatasetweresharedwiththeall-jetschannel[5&].The/mainchallengewastorejecttheoverwhelmingQCD
background,whileatthesametimepropGerlyhandlingthephysical    Wײ+&I4jirreduciblebackground.SXInordertoachievethisgoal,KaNN-basedϲIDandSVTb-taggingalgorithmwasemployed.Inaddition,ItherelevqanttopGologicalvqariableswerecombinedintoaNNtrainedtodierentiatethesignal>fromQCD.=Thesingleandtripleprongedleptonchannelswere>treatedasindepGendentchannels>andthencombined.TheUUcrosssectionwasmeasuredtobGen@[ٲ(t7ferYɍtr)=5:05䍑0+4:3103:46 1(stat)䍑0+0:6800:67(syst;)80:330(lumiq)pb:Thisresultisinagreementwiththetheoreticallypredictedvqalueof6.80.4pb[4&]aswellasotherDandCDFmeasurementsUU[5&,16
UW].
                     89: Ǡ2&10j)@AcCknowledgmentsW*evthankvthestasatF*ermilabandcollabGoratinginstitutions,~andacknowledgevsuppGortfromtheDOEvandNSF(USA);1CEAandCNRS/IN2P3(F*rance);FASI,RosatomandRFBR(Russia);CAPES,0CNPq,hFAPERJ,FAPESPand/FUNDUNESP(Brazil);<DAEand0DST(India);Colciencias/(Colombia);CONACyT(Mexico);KRFand/KOSEF(Korea);CONICETandUBACyT(Argentina);FOM(TheNetherlands);PP*ARC(UnitedKingdom);MSMT(CzechRepublic);yCRCbProgram,سCFI,NSERCandW*estGridPro8ject(Canada);yBMBFcandDFG(Germany);xSFI(Ireland);ResearchUUCorpGoration,AlexandervonHumbGoldtF*oundation,andtheMarieCurieProgram.r.@)0  f&z&@=`򎷹[1]RAJ.TA.Coarasa,J.Guasc9h,andJ.Sola,RepAortNo.UAB-FT-451,1999,hep-ph/9903212.
                     90: [2]RAD.TAcostaet.N<al.,Ph9ys.Rev.D62,012004(2000).[3]RADirectTSearc9hforChargedHiggsBosonsintVۍ &%tloevents,DNote4357.[4]RAN.TKidonakis,R.V:ogt,Ph9ys.Rev.D68,114014(2003).[5]RAMeasuremen9tTofthetVۍ &%t!ƻal&9l4q8jetsproAductioncrosssection,usingSecondaryV:ertexTagging,DNote4879-CONF.[6]RAV.M.TAbazo9v,etN<al.(D0CollabAoration),\TheupgradedD0detector,"Nucl.Instrum.andMethodsA565,463(2006).[7]RAS.TEidelmanetN<al.(P9articleDataGroup),Phys.Lett.B592,1(2004)and2005upAdate.[8]RADTSIDcertication,DNote4773.[9]RADTSecondaryV:ertexb-taggercertication,DNote4796.[10]RAM.L.TManganoetN<al.,JHEP0307,001(2003),hep-ph/0206293.[11]RAJ.TPumplin,D.R.Stump,J.Huston,H.L.Lai,P:.Nadolsky,W.K.Tung,hep-ph/0201195.[12]RAT.TSj`ostrandetal.,LUTP01-21,hep-ph/0108264.[13]RAGߤN          cmtt9Ghttp://c9harm.physics.ucsb.edu/pAeople/lange/EvtGen/[14]RAS.TJadac9h,Z.W:as,R.Decker,J.H.Kuehn,Comp.Phys.Commun.,361(1993)(CERNTH-6793preprint).[15]RAR.TBrunandF.Carminati,CERNProgramLibraryLongW:riteupW50131993.[16]RAMeasuremen9tpNofthepOttbarcrosssectioninthelepton+jetsc9hannelatؽp%؉aHO|(s"=)g1:96&T:eVp7(topAological),DNotes4667andRA4662.[17]RA6|rE&TkxSignicanceTAlgorithminRunIAIdata,DNote4254[18]RAMeasuremen9tJofW&H-=
!?e-=Gބ+Inclusiven-jetCrossSectionswithCDFIDataatT:ev|ratronRunIAI,http://www-RAcdf.fnal.go9v/physics/new/qcd/wjets/WjetffgTyana/Wjetffgana.psT.[19]RAh9ttp://schwind.home.cern.ch/schwind/MLPt.htmlT.[20]RAC.Clemen9tVvetal.,fT:opquarkVuproAductioncrosssectioninthelepton+trac9kchannelusingVusecondaryvertexb-tagging,fDRANoteT5011.!C%ˮAppKendixA:KinematicDistributionsFIG.6:2ofthe5inputv|rariablesofthersttopAologicalNNbeforetheNNcut(t9ype2).kTheKolmogoro9v-Smirnov(KS)probabilitiesTaresho9wn,indicatingthequalityoftheagreement.$@h4*FIG.T7:pTheresultingoutputofthesecond(nal)NN(St9ypAe2).2&11x@h4*FIG.T8:pTheresultingoutputofthesecond(nal)NN(St9ypAe3).&;&
                     91: GߤN           cmtt9F-
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