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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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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EMModels:EnergyLossFluctua3ons
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ALICETPCBenchmarkmeasuresenergydepositin7.5mmgapby1GeV/cincidentprotons
TwoGeant4modelscomparedPAI
Urban
RecentimprovementsinUrbanmodelleadtobeieragreementwithdata
agreementwithmoreprecisePAI
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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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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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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