GranularCalorimetersforGeant4Valida3on

DennisWright(SLAC)

IASWorkshop18January2018

Introduc3ontoGeant4

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Geant4Simula3onToolkit• Ageneralpurposeradia3ontransportcodedevelopedoriginallyforuseinHEP

• alsousedextensivelyforspace,medicalandnuclearapplica3ons

• Offersmost,ifnotall,func3onalityrequiredforMonteCarlosimula3ons

• kernel• geometryandnaviga3on• physicsprocesses• GUIandvisualiza3ondrivers

• Flexibleandextensible

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Geant4isaToolkit;YouMust:•  Buildyourownapplica3onusingGeant4components

•  Geant4doesnotprovideamain()

•  Defineyourgeometricalset-up•  materials,volumes

•  Definethephysicsyouneed•  par3cles,physicsprocesses•  produc3onthresholds

•  Definehowaneventstarts•  primarytrackgenera3on

•  Extracttheinforma3onyouneedfromthesimula3on•  Aswellas,amongotherthings

•  visualiza3onofdetectors,trajectories,physicsoutput•  useorextensionoftheUserInterface

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Geant4isaMonteCarloCode:Example

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Geant4isaMonteCarloCode:Example

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Geometry• Largenumberofgeometryprimi3vesavailable

• G4Box,G4Tubs,G4Cons,G4Trd,etc.

• Specificsolids• G4Polycone,G4Hype,…

• Tessellatedsolid• Booleansolids• Userbuildsdetectorbycombining,fillingwithmaterialsandplacingthesesolidsinamothervolume

• certainvolumescanthenbemadesensi3ve

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Physics• InGeant4thereisnotjustoneall-purposesetofphysics

• usermaycustomize

• Geant4offerselectromagne3c,hadronicanddecayphysics

• foralmosteveryphysicsprocess,alterna3vecrosssec3onsetsandphysicsmodelsareoffered

• Usermustvalidatecombina3onhechooses

• Geant4validatesthecomponentsandsomecombina3ons

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EM

HAD

PhysicsLists

Wherephysicsmodelsarecollectedandassignedtopar3clesCustomdesignedforeachapplica3on

Twomaincomponents:Electromagne3candhadronic

Formostcalorimeterapplica3ons“standard”EMphysicsischosen

Maindifferencecomeswithchoiceofhadronicmodels

“Backbone”ofhadroniccomponentFTFP_BERTphysicslist(original)

Inordertogetagreementwithmeasuredshowershapes,transi3onbetweenmodelsischanged(ATLAS)

OtherphysicslistsaddothermodelsQGS,BIC,etc.

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Geant4Valida3onStrategy

ThintargetscaieringdataMostofourvalida3ondependsonthis

Modelsaretunedonit,sinceitmostlytestssingleinterac3ons

Lotsofthiskindofdataavailable,butsignificantgapsincoverage

ThicktargetscaieringdataAtoughertestasitdependsonmul3pleinterac3ons

Dataareojennotasreliableasthintargetduetosystema3cerrors

CalorimeterdatamoststringenttestofallEffec3velythicktarget

Showershapes!

Physicslistsaretunedonthisdata

TestbeamdataVeryusefulcalorimeterdatareliesonsingle-par3cle,mono-energe3cbeamsonsegmentsofcalorimeters

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Geant4isMul3threaded

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Geant4GeneralPaper(2016)

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RecentCalorimeterResults

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EMModels:EnergyLossFluctua3ons

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ALICETPCBenchmarkmeasuresenergydepositin7.5mmgapby1GeV/cincidentprotons

TwoGeant4modelscomparedPAI

Urban

RecentimprovementsinUrbanmodelleadtobeieragreementwithdata

agreementwithmoreprecisePAI

E/p

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HadronicCrossSec3ons

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LHCbAsymmetryMeasurementslookedatamountofan3-maiervs.maierproducedinD+/-decays

Showedaprobleminourcrosssec3onskaonasymmetrybecametoosmall

pionasymmetryOK

Problemduetoerrorinkaon-nuclearcrosssec3onsfixedin10.1

JetEnergyScaleUnexpecteddifferencebetweenFTFP_BERTand

QGSP_BERTphysicslistswasduetotransi3onregion

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ShowerDepthandHadronicModels

ExampleofhowthintargettuningcandivergefromcalorimeterdataCon3nuousFTFmodelimprovementthroughGeant4version10.3accordingtothintargetdata

V9.3:good(fortuitous?)agreement

V9.6:significantlyworse

V10.1:gepngbeieragain

V10.4:?

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GranularCalorimetersandGeant4

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Problem:Hadron-NuclearPhysics

•  Atmediumandlowenergies(<20GeV)simula3onofhadron-nuclearinterac3onsleavessomethingtobedesired•  models(factoroftwoerrorsconsideredgood!)•  crosssec3ons(somewhatbeierbuts3llproblemsatlower

energies)

•  Highenergymodelsarebeier,but..•  s3llasignificantnumberoffreeparameters

•  Howcanwedobeier?•  improvethetheory•  gotodata-drivenmodels

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Needed:SingleInterac3ons

•  Widerangeofnucleartargets•  oratleastafewspreadoverawiderangeofA

•  Ini3alstate•  nearlymono-energe3cprojec3le•  goodpar3cleID•  well-definedini3aldirec3on

•  Finalstate•  mul3plicity•  angulardistribu3on•  goodpar3cleID

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Problem:ThinTargetandThickTargetValida3onsOjenDisagree

•  Werelyheavilyonthin-targetdatatotunemodels•  morecontroloverincidentbeam,target•  usuallysingleinterac3on•  morereliablethanthicktarget

•  However,improvingagreementwiththin-targetdataojenreducesagreementwiththicktargetorcalorimeterdata•  latelythecasewithFTF(energyresponse,showershapes)•  butalsowithBer3ni(shieldingexperiments)

•  Reasons?•  modelsarefaulty•  measureddoubledifferen3alcrosssec3onsdonotcoverenough

phasespace

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ForwardScaiering:AClue?

•  HARPdata(above)goesto12.9,10.0,7.1and4.3degrees•  characterofspectrumchangesgoingtosmallangles•  couldthisaccountforpartoftheproblemconnec3ngthinand

thicktargetdata–overes3ma3ngtheforwardscaiering?

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GranularCalorimetersCanHelp

Isolatedhadronicinterac3onsNumberoftracksAngulardistribu3onsTargetNeutraltracks?Recoilnucleus?Forthefirst3mewehaveobservablesotherthanthe“bulk”valuesfromconven3onalcalorimeters

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WhatElseCanGranularCalorimetersGiveUs?

•  Cantheyactasmodernday“bubblechambers”?•  Forwardanglehadronicscaiering•  lookslikeanglesdownto0degreesmaybepossible•  impossibleformostthintargetexperiments(limitedbybeam/

targetgeometry)•  HARPdataabigimprovement,butnotenough

•  Lowmomentumsecondaries•  whatissmallestenergysecondarythatcanbeseen?•  whataboutneutralhadrons?

•  CanEMandhadronicvertexesbecleanlyseparated?

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SimplifiedCalorimeter

•  AGeant4toolforregressiontes3ng•  compareoneGeant4versionagainstanother•  alterphysicsmodelparametersandobservechanges(quickly)•  severalsta3s3caltestsused(χ2,K.S.,etc.)

•  Geometryisaboxcontaininglayersofabsorbersandac3vematerials•  canchoosenumber,thicknessandmaterialoflayersto

approximaterealcalorimeters•  canalsochooselateralshowerbinsize•  thereisenoughdetailtomakemeaningfulcomparisonstoreal

data

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SimplifiedCalorimeter•  AllLHCcalorimetermaterialcombina3onsaresupported•  Fe-Scint,Cu-Scint,Cu-LAr,W-LAr,Pb-Scint,Pb-LAr,PbWO4

•  Par3cletypestested:•  π+/-,K+/-,KL0,p,n,e-

•  Beamenergiesused:•  1,2,…,10,20,30,40,50,60,80,100,120,150,180,200,250,

300,1000GeV

•  Observables:•  totalenergydepositallac3velayers•  totalenergydepositwholecalorimeter•  energydepositineachac3velayer(longitudinalshowerprofile)•  energydepositineachradialbin(lateralshowerprofile)

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ASimplifiedCalorimeterforCalice

•  Newefforttoextendsimplifiedcalorimeterstohighlygranulardetectors•  KatalinNikolics,WitoldPokorski(CERN)

•  Achallenge•  howmuchsimplifica3oncanbemadewithoutsacrificingtoo

muchdetailedresponse?•  firsttargetcouldbeSiWECALàmostdetailedshowershapes•  maybeDHCALeventually?

•  Goodopportunitytotunemodelparametersandgetfast

turn-aboundonangulardistribu3ons,numberoftracks,etc.

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CalorimetersandBeierHadronicModels•  Geant4EMphysicsalreadyingoodshape

•  sufficientlywellunderstoodthatwecanaiributechangesinshowershapetohadronicmodels

•  usewidthanddepthofshowertochoosemodelsandtransi3onrange

•  FTFvs.QGS•  FTFisamorephenomenologicalmodel•  QGSmoretheory-based,andisvalidathigherenergies

•  Ber3ni•  measuringnumberofhadronicsecondariesiscrucial•  numberofsecondariesasafunc3onofincidentenergy

•  Precompound/deexcita3on•  canweiden3fynuclearfragments?

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Ber3niCascade(LowtoMediumEnergy)•  Dependsonfree-spacehadron-nucleoncrosssec3ons

embeddedinnuclearmedium•  thousandsofpar3alcrosssec3onsasfunc3onofenergyandfinalstate

mul3plicity•  someofthesewell-measured,manynot•  usemeasuredfinalstatenumberoftrackstoconstrainpoorly

measuredpar3clecrosssec3ons(amongothernuclearparameters)

•  Onlyhavegoodangulardistribu3onsfortwo-bodyfinalstates•  n-bodystatesrelyonphasespace•  isolateafewlowmul3plicityfinalstates,parameterizemodelangular

distribu3onsfor3-,4-body,thenfitcalorimeterdata

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Ber3niPar3alp-pCrossSec3ons

Finalstatemul3plicitycrosssec3ons(2-9)

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3-bodyfinalstatecrosssec3ons

FTF/QGSModels(HighEnergy)•  BothFTFandQGSmodelsonmuchbeiertheore3calfoo3ngthan

Ber3ni•  buttheys3llhaveanumberoffreeparameters•  coarse-grainedcalorimetersgavebeenessen3alintuningthese•  canfine-graineddetectorsdatahelp?

•  Cans3lllearnsomethingfromtrackmul3plicity•  besthadronfragmenta3onfunc3ontouses3llunknown->effects

mul3plicity•  asinBer3ni,embeddedhadron-nucleonreac3onss3llimportant•  nuclearphysicslessrelevant

•  Probablynotmuchfromangulardistribu3ons–tooforward•  cantracksberesolvedat>20GeV?

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Summary•  Geant4hasbeenandcon3nuestobeusedbyallHEPexperiments

•  feedbackfromtest-beamsandcalorimetershasbeenessen3alfortuningofGeant4models

•  Whilecoarse-grainedcalorimeterdatahasbeenuseful,detailedmodeltuninghasdependedonthintargetdata•  singleinterac3onassumed•  butdiscrepancieswiththicktargetdataseen

•  Granularcalorimetersholdthepromiseofsingleinterac3ondatainathick-targetenvironment•  finalstatemul3plicity•  angulardistribu3on•  detailedmodeltuningpossible

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