processes with heavy flavor in ATLAS analyses (including ...

ExperiencewithmodellingofprocesseswithheavyflavorinATLASanalyses(includingcalibra?ons)-

Whatarethekeyissues?PaulThompson

UniversityofBirminghamOnbehalfoftheATLASCollabora?on

OpenDayofHbb/FTAGWorkshopStonyBrookUniversityTuesday5thSeptember2017

HeavyFlavourattheLHC

ModellingeventsusingMonteCarlo(MC)attheLHCinvolves:Matrixelementstoleadingorder(LO)ornext-to-leadingorder(NLO)Highermul?plici?esthroughpartonshower(PS)ormul?-legwitheachmul?plicityatLO.Needtoavoiddoublecoun?ngusingmatchingschemes(CKKW-L,MLLM,FxFxetc.)

PaulThompsonExperiencewithmodellingofprocesseswithheavyflavorinATLASanalyses-Whatarethekeyissues?

HeavyFlavourprovidestes?nggroundforQCD,mul?-scalemZ,mW,pTjetandchallengehowtodealwiththeheavyquarkmass:5Flavourscheme(5FS)allowstoresumlargelogarithmictermsintointheb-quarkPDF4Flavourscheme(4FS)allowstotakecareofmasseffectsbutdoesnotresumanypossiblelargelogs.ChallengingtoproduceinclusiveflavourMCsavoidingoverlapsofHFinMEandPS

5FS 4FS

Inthisshortintroduc?onjustfocusonSMVHbbanalysisandtwoareasnamelyV+HFjetproduc?onandsingletopWt

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V+JetsModellinginRun1

Usedleadingorder4FSSherpav1.4ForbothW+jetsandZ+jetshadmis-modellingsinpTVandΔφjj.Appliedvariousreweightsdependingonbosontypeandnumberofb-tagsExampleshownispTWwith0b-tagsagerapplyingreweightasafunc?onofΔφjjEachmis-modellingledtoreweightplussizeablesystema?cuncertain?esinthecorrec?onsPaulThompsonExperiencewithmodellingofprocesseswithheavyflavorinATLASanalyses-Whatarethekeyissues?

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ATLASMCNotesATLAS(viaitsPhysicsModellingGroup–PMG)con?nuestoprovideup-to-datedocumenta?onoftheATLASMCstatus–exis?ng/plannedmodels/systema?cprescrip?ons.Generallyaimtobein?meforthevariousexperimental-theore?calworkshopsthroughouttheyearsothatcangetfeedbackfromtheore?calcommunity.hkps://twiki.cern.ch/twiki/bin/view/AtlasPublic/MCPublicResultsRecentexamplesofMCnotes:•  ATLASsimula?onofbosonplusjetsprocessesinRun2hkps://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2017-063/•  Mul?-BosonSimula?onfor13TeVATLASAnalyseshkps://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2017-005/

•  Studiesontop-quarkMonteCarlomodellingwithSherpaandMG5_aMC@NLOhkps://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2017-007/•  Modellingofthek̄Handk̄V(V=W,Z)processesfor√s=13TeVATLASanalyseshkps://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2016-005/

PaulThompsonExperiencewithmodellingofprocesseswithheavyflavorinATLASanalyses-Whatarethekeyissues? 4

V+JetsModellinginRun2

Comparisonwithrecent13TeV2015Z+jetsdata(arXiv:1702.05725)Reasonabledescrip?onofdatabylatestNLOmodels:Sherpa2.2MEPS@NLO,NLOforV+0,1,2jets,LOmul?-legupto4.NNLOPDFPowhegMinNLO+Pythia8,withNLOaccuracyforZ+1jetMadGraph5_aMC@NLO+Pythia8usingNLOupto2jetsandFxFxmergingwithPSPaulThompsonExperiencewithmodellingofprocesseswithheavyflavorinATLASanalyses-Whatarethekeyissues?

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Run2V+JetsHFModelling

Canobtainrela?velypurecontrolregionsforW+HFandZ+HFSherpav2.2doesagoodjobofdescribingshapes(noneedforreweights).Fitrequiresadjustmentofpredictednormalisa?ons(seeover)Systema?cuncertain?es:Zbbfromdata,WbbfromMC(dataCRisatlowmBB)PaulThompsonExperiencewithmodellingofprocesseswithheavyflavorinATLASanalyses-Whatarethekeyissues?

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W/ZBackgroundModel


FreeFloa?ngNormalisa?ons

Extrapola?onto0-lepton

Extrapola?onfromW+HFtoSR

Datashowneedforbe>ertheore?calunderstanding-oragreeswithinfulltheore?calerror?–Centralvaluedifferenceisthechoiceofscale,scheme(5FSvs4FS),orderofpQCDorchoiceofmassorPDForfragmenta?onparametersor…?

Errorsonflavourra?ostakenfromcomparisonofmodelsAsispTV,mbbshape(S)uncertaintyinW+jets

Freefloa?nguncertain?es

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V+JetsHFModellingRun1Data(revisited)

Modelsfromoriginalpaper:Zbbcentralvalueslower,althoughagreewithinuncertain?esComparisonwithSherpaMEPS@NLO(hkp://arxiv.org/abs/arXiv:1612.04640)alsoreasonable.V+HeavyFlavourdataanalysesfromRun2willbevitaltocon?nuestudies… 8

SingleTop(Wt)

SingletopWtandt-channelcontributesbackgroundtothe1-leptonchannel:Systema?cerrorsonmbbandpTVshapeses?matedfromcomparingMCmodelswithdifferentimplementa?onsofME,partonshowermodelling/fragmenta?onWtatNLOhassingly-resonantanddoublyresonantcontribu?ons(interfereswithLOkbar)Powheg+Pythia6usedinVHbbanalysiswithDiagramRemoval1(DR1)whichsetsMdr=0Interferencees?matedusingDiagramSubtrac?on(DS)UncertaintytakenfromlargestdifferencesandforWtcomesfromDSMadGraph5aMC@NLOalsoimplementsDR1andassessesinterferenceusingalterna?veDR2


Singlyresonant(sr) Doublyresonant(dr)

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SingleTop(Wt)

Generatorcomparisonfordileptonselec?on:ForleadingjetpTsimilarpredic?onforDR1Powheg+Pythia6andDR1MG5_aMC@NLO+HPPAlsosimilarinterferencees?matebetweenDSPowheg+Pythia6andDR2MG5_aMC@NLO+HPPInterferenceeffectsvisibleinleadingjetpTbutnotleadingjeteta


hkps://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PUBNOTES/ATL-PHYS-PUB-2016-020/

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ATLASMCNote

KeyIssues(summary)•  MonteCarlogeneratorsvitalforunderstandingmodellingofimportant

backgroundstonewphysicsandimprovingourunderstandingofunderlyingQCDaswellasparametertuning

•  FocussingonVHbbissues:V+HFandsingletopsystema?csaskeyissues


•  DoweunderstandthelikelyV+HFscalefactordifferenceof~1.2?Shouldwebeconcernedorisitreasonablewithinthetheore?caluncertain?es(Note:>barSF~1)?

•  Weusemul?-leg5FSupto2jetsatNLOwithB-hadronfilter(3jets@NLOtakestoolong)•  FortheW+HFsystema?cuncertain?esweuseMCmodelcomparisons•  Candevelopmentsin4FSincludingWbb+j@NLObeusedtohelptoreducethiserror?•  CanweboostourHFsta?s?csmoredirectlyand/orimproveourVbbjprecision?

•  Thesingletopsystema?cerrorcontributesasmuchaserrorsfrommoredominantbackgrounds

•  LargestuncertaintyisfromWtandkbarinterferenceeffects•  Isitpossibletohavetheinterferencecalcula?on(andthereforesmallererrors)

accountedforinoursimula?ons?

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Backup


V+jetsModellinginRun2•  UpdatedRun2modelsoriginallytunedonpublished7/8TeVRun-Idata,seehowthey

compareat13TeV5FSModelsusedbyATLAS:•  MadGraph5+Pythia8.LeadingorderinMEupto4jets,PSbeyond.Differentfinalstate

parametertunings“A”and“B”andmovefromLOtoNLOPDF•  Sherpav2.2NLOforV+0,1,2jets,LOmul?-legupto4jets,PSforhighermul?plici?es.

•  AlsousedAlpgenin4FSwithoverlapbetweenHFandLFsamplesremoved•  [email protected]+0,1,2jetsandPSbeyond•  AndalsoPowhegMiNLOwithNLOforV+1jet

NowhaveRun2ATLASSMV+jetsmeasurement(inclusive-notyetHF)…

Sample W, 7 TeV W, 13 TeV Z, 7 TeV Z, 13 TeV� [pb] k-fac � [pb] k-fac � [pb] k-fac f � [pb] k-fac f

NNLO 10455 - 20080 - 964 - - 1906 - -Sherpa 2.1 11270 0.928 22108 0.9083 1150 0.912 1.08 2290 0.9013 1.08Sherpa 2.2 10600 0.986 - - 1080 0.981 1.08 - - -

MadGraph+Pythia8 A 8290 1.26 16707 1.21 827 1.287 1.10 1710 1.239 1.10MadGraph+Pythia8 B 8960 1.17 17880 1.123 907 1.17 1.10 1840 1.15 1.10


ImpactofSystema?csonμ


MonteCarloStatsdespiteflavourfilteringandpTVslicing

Signalmodellingdominatedbyextrapola?onfromhighpTVtofullphasespaceandshoweringPythia8vsHerwig7.Doesn’taffectsignificance

Backgroundmodel,allcontributesimilarlevelWillimproveaswecollectmoredatabuttheore?calprogresscrucialtooSurprisingthatsingletopcontributes(seeover)

Systema?callyLimited

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TopBackgroundModel


Freefloa?nguncertain?es

Extrapola?onuncertain?esanalogoustoW/Z

Note:Theoryagreeswithdatawithinerrors

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processes with heavy flavor in ATLAS analyses (including ...

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