HEP 101 Detector Basics:

Interac4on of Par4cles with Ma:er February20,2017

D.MarkoffAssociateProfessor,NCCU

Purpose of “Detec4ng” Par4cles? CounthowmanyparCclesthereareIdenCfyparCclesandtheirproperCes–energy,momentum,charge,spinInformaConusedtoreconstructinteracConsandveryshortlivedparCclescreatedinthecollisionorbeamontargetNote–inelementaryparCclephysics,usuallythechargeis±1e,wheree=1.6×10-19CHowever,thechargeisnotoQenthissimplefornuclearsystems,cosmic-rayinteracCons,orheavy-ionphysics.

Whatdoesitmeanto“detect”aparCcle?DirectdetecCon:theparCcleinteractswithamaterialtoproducesomesortofobservablesignal,usually anelectronicsignal(usedtobeanimprintonfilm) then,theelectronicsignalsareprocessed,calibrated,andcomparedtoparCcle‘signatures’for idenCficaConorcalibratedtoindicateenergy,momentum,charge

Indirectmethods:theparCcledoesnotinteractinthematerialandthereconstrucConofanevent requiressome‘missingmass’or‘missingmomentum’andtheparCcleisdeducedusing conservaConofenergyandmomentum

What Par4cles? 17fundamentalparCcles

(includingtheHiggsBoson)Quarks–notseenasfreeparCcles

-combinetoformhadrons (baryons3qandmesons2q)

ParCclesthatdecay‘onthespot’

-mustbereconstructedfromdecaysParCclesmustlivelongenoughtoleaveatrack

inthedetectorofatleast1µmMostpopular:electrone,muonµ,photonγ,

pionsπ,kaonsK,protonp,neutronn

First:ConsidertheStandardModelofFundamentalParCcles

Interac4on Mechanisms

AtomicexcitaCon PhotoelectriceffectAtomicionizaCon ComptonscaceringBremsstrahlung PairproducConMulCplescaceringCerenkovradiaConTransiConradiaCon

ElectromagneCcInteracCons StronginteracConsSecondaryhadronproducConHadronicshowers

ParCclesinteractwiththeelectronsand/orwiththenucleiofthemedium,dependingontheparCcle,charge,energy–interacConthroughthestrong,weakorelectromagneCcinteracCondependingonthetypeofparCcleTheresultoreffectsoftheinteracConareusedto‘detect’theparCcle.

Atomic Excita4ons, Atomic Ioniza4on •  ChargedparCclescanexciteanatomormolecule–thatistomovetheelectrontoahigherenergystate

•  Subsequentde-excitaConordecaysoftheelectronbacktothe‘groundstate’withtheemissionofphotons

•  ThephotonsarecollectedfordetecCon–forexampleaphotomulCpliertube(PMT)thathasaphotocathodematerialthatproduceselectronswhenphotonshitthematerial(photoelectriceffect)

•  ChargedparCclescanionizetheelectrons–liberaCngthemfromtheatomormolecule

•  Liberatedelectrons(“knock-on”electronsorδ-rays)canthenbecollectedasa‘totalcharge’or‘current’.Theseelectronscanfurtherionizeotheratomstoproduceashowereffectoramplifiedsignal.

•  IfthedetecConmechanismcandetermineposiCon,willseetheparCcletrackasindicatedbytheionizaCon

Slowing Down of Heavy Charged Particles (1)

ThelossofenergythroughionizaConrepresentsingeneraltheprincipalmechanismbywhichachargedparCcleissloweddowninthemedium.HowdowequanCfythis“slowingdown”?

StoppingPower=averageenergylossperunit pathlength

Whatdoesthestoppingpowerdependupon?

dxdE

−

• Ioniccharge,ze,ofthechargedparCcle• Velocity/energyoftheparCcle• Sizeofthematerial–N(atoms/volume),Z(atomicnumber),A(atomicweight)

Slowing Down of Heavy Charged Particles (2)

)(2

2

vvZz

dxdE

φN

=−

• Ioniccharge,ze,ofthechargedparCcle• Velocity/energyoftheparCcle• Sizeofthematerial–N(atoms/volume),Z(atomicnumber),A(atomicweight)

CorrecConsincludeforveryhighenergies,effectsfromtheelectricfieldoftheparCcleandfromassuminganinfiniteparCclemass,fromverylowenergies,whenthevelocityoftheparCclecompareswiththeelectronorbitvelocity,internalstructureoftheparCcleincludingspin–theseeffectsarenegligiblewithinabout1%.

Bethe-BlochFormula

NotethatthisexpressionisindependentofthemassoftheheavychargedparCcle.

Stopping Power Plots

NuclearPhysicsforApplica4ons(Prussin)

ProtonstraversingvariousmaterialsC,Al,Sn,Ta,U

Examples MinimumionizaConofmuoninvariousmaterialsisabout1–2MeV/(g/cm2)Foramaterialwithdensityρ=1g/cm3dE/dx=1–2MeV/cmIniron:thickness100cmanddensityρ=7.87g/cm3Wehaveenergylossover1m:ΔE≈1.4MeVg-1cm2*100cm*7.87g/cm3ThusΔE≈1102MeVConcludethata1GeVmuoncantransverse1mofiron!

Proton with p = 1 GeV Target: lead with density ρ = 11.34g/cm3 dE/dx = 2 MeV/(g/cm2) ΔE/Δx≈2MeVg-1cm2*11.34g/cm3=23MeV/cm

ProperintegraCongivesrangeof20cm

Bremstrahlung = Breaking Radiation WhenthevelocityofachargedparCclechanges,electromagneCcradiaConisemiced–acceleratedchargesemitEMwaves,usuallyx-rayorγ-ray

DuetointeracConswithnuclei,parCclesaredeflectedandslowedtherebyemirngbremsstrahlungradiaConTheeffectisstrongthelargertheraCoof(energy/mass)thereforehigh-energyelectronsemitthisradiaConPhotonsaresubsequentlydetectedorenergylost

Bremsstrahlung IonizaCon

Slowing Down of Beta Particles - Electrons

EnergylossbycollisionsandionizaConofmaterial.

collradtot dxdE

dxdE

dxdE

⎟⎠

⎞⎜⎝

⎛−+⎟⎠

⎞⎜⎝

⎛−=⎟⎠

⎞⎜⎝

⎛−

EnergylossbytheemissionofBremsstrahlungradiaCon.

colldxdE

⎟⎠

⎞⎜⎝

⎛− ModifyBethe-BlochformulaforsmallmassandcollisionswithsameparCcle–indisCnguishableparCcles

raddxdE

⎟⎠

⎞⎜⎝

⎛−EmissionofelectromagneCcradiaConarisingfromscaceringintheelectricfieldofthenucleus(orelectrons).ClassicallyunderstoodasradiaConemicedfromanacceleratedcharge.

Magne4c Fields – Change Charged Par4cle Trajectory Measure momentum using the track

WithmagneCcfield–measuremomentum;Useothermeanstomeasurevelocity,sayslowingdownorionizaCon;TogetherdeterminemassoftheparCcle

Bv

BvqEqF!!!!

×+=

qrBprmvqvBF

=

==2

DirecConoftheforceisperpendicularcreaCngcircularmoCon

B -charge

+charge

K0→π+π-π+→µ++νµµ+→e++νe + νµ

Cherenkov Radiation CherenkovradiaConariseswhenachargedparCcleinamaterialmediummovesfasterthanthespeedoflightinthatmedium.

whenvparCcle>c/n wherec=speedoflightinvacuum n=indexofrefracConofthemedium

TheimportanceoftheCerenkoveffectasascienCfictoolliesintheconnecConbetweenparCclespeedandanglebetweenmomentumdirecConandradiaConemission.IftheparCcleislightandβ≈1,thentheangleofemicedradiaConwillprovideinformaCononthemomentumdirecConortrajectoryoftheparCcle.(Goodformuons,electrons,neutrinos.)

nvnc

vttnc

βϑ

1cos ===

Leo–page34

Cherenkov Radiation at a Small Reactor

Averyimpressiveandeeriebluecolor.Imagecanbefoundat::en.wikipedia.org/wiki/Cherenkov_radiaCon

Example: Cerenkov Ring

NeutrinoeventatSuperK

Transi4on Radia4on WhenachargedparCclecrossestheboundarybetweentwomediawithdifferentspeedsoflight(different‘refracCveindex’)electromagneCcradiaConisemicedTheamountofradiaConemicedincreaseswiththeraCoofenergy/mass.ProbabilityofradiaConisproporConaltotheLorentzfactorγ.

Electricdipole ProcessusedtodisCnguishhigh-energyelectronsfromhadrons.InteracConrateissmallsousemanylayersofmaterial.ForelectronsandpositronstheemicedphotonsareinthekeVregion.

Interlude: Interaction Probability ReacConofincidentprojecCleswithrandomlyspacedtrajectoriesontargetnucleithatarethemselvesrandomlydistributed→staCsCcaldescripCon

densitycurrent projectileincident unit nucleus per target areaunit per ratereaction

=σ

WecallthisreacConprobabilitythe“crosssecCon”inunitsofcm2 10-24cm2=1barn(unitsofarea)

Photon Interac4on With Ma:er

µ = n σ = (Ν/V)σistheacenuaConcoefficient(theprobabilityofinteracConperunitlengthforaγ)

Gamma-ray Interactions Photoelectric Absorption

Te=E0-BEe

NuclearPhysicsforApplicaCons,Prussin.

Gamma-ray Interactions Compton Scattering

Energyofscaceredphotonisnotzero;recoilelectronatforwardangles.Maximumenergyforrecoilelectronsapproaches themaximumenergydepositedinthemedium(detector).Notethatheretheelectronsarebound–negligibleeffectforhighenergyphotons.

)cos1(1

2

θ

ν

γγ

γγ

−+=ʹ

==

rE

E

hEcmE

re

2tan)1(cot θφ r+=

CrosssecConcalculatedusingQuantumElectrodynamics(QED)andisknownastheKlein-Nishinaformula.

221 cmE e−γ

RadiaConDetectors,DelaneyandFinch

Gamma-ray Interactions Pair Production

Conversionofaphotontoanelectron-positronpair.

MeV 02.12

electron)or (nucleus2 =>

++== −+

cmE

TEEhE

eγ

γ ν

+−→ eeγ

TheprobabilityofpairproducCon(crosssecCon)increaseswithhigherphotonenergyandwithhighernuclearatomicnumber,Z.

Gamma-ray Interactions Total Attenuation Coefficient

Photoelectriceffect

ComptonScacering

PairproducCon

Total–darkline

TotalphotonabsorpConcrosssecConforlead.

TechniquesforNuclearandParCclePhysicsExperiments,Leo

Summary – Electromagne4c Interac4ons

Par4cle “Showers” ElectromagneCcShower

highenergyelectronsandphotonscancausetheseelectromagneCcshowersofradiaConbysuccessivebremsstrahlungandpairproducCon–energydepositedintothedetectorthencollectedtoprovideinformaConaboutthetotalenergyoftheparCcle

HadronicProducCon–HadronicShower

stronglyinteracCngparCclescanproducenewparCclesbythestronginteracCon(scaceringanddecays)whichinturncanproducemoreparCcles…..Createsthehadronicshower.

‘Calorimeter’Detector•  adestrucCvemethodofmeasuringaparCcle’senergy–putenoughmaterialintothepathof the

parCcletoforcetheformaConofelectromagneCcorhadronicshowers•  DesignthelengthofthecalorimetersothattheparCclewilleventuallyloseallofitsenergyinthe

material•  EnergydepositedinthecalorimetergivesameasureoftheoriginalparCcleenergy

Calorimeters – Detectors PuSng Material Interac4ons to Use

Calorimeter–enoughmaterialinthepathoftheparCcletocreateelectromagneCcorhadronicshowersorbothNeeddetecConschemetoconvertradiaConemicedtoanelectronicsignal

TotalAbsorpConCalorimeter•  Depthofthecalorimetersufficienttocontainor‘detect’showersoriginaCngfromtheparCcle–notethese

secondaryparCcleswillhavelowerenergies•  Depthmeasuredin‘radiaConlengths’forelectromagneCcshowersandin‘nuclearabsorpConlengths’forhadronic

showers(inverselyproporConaltothetotalcrosssecConforinteracCon)•  Mostmoderncalorimetersare‘samplingcalorimeters’withseparatelayersofhigh-densitymaterial(absorber)to

forceshowerdevelopmentandsensiCvelayerstodetecttheresulCngparCclesfromtheshower•  TotalvisiblepathlengthofshowerparCclesisproporConaltothetotalenergydepositedinthecalorimeter•  SegmentaConallowsmeasurementsofposiConsandenergydeposit•  EnergydistribuConasafuncConofanglerelaCvetotheforwarddirecConoraxisofdetectormaterialisdifferent

forhadronicandelectromagneCcshowers–usethisinformaContoseparatethetwotypes•  AbsorbermaterialsincludeU,W,Pb,FeCu•  SensiCvemediumincludescinCllator,siliconsolidstatedetecCon,liquidargon

PMT – Convert Scin4lla4on Light/Photons to Electronic Signal

Apply What You Learned Review the slides and informa4on

Youhavea‘trackingdetector’madeofascinCllatormaterialthatemitslightaQerexcitaConWhichparCclesdoyouexpecttoleavetracksinthisdetector?photon,electron,proton,neutrino,muon,chargedkaon,neutralkaon,chargedpion

Youhavea‘hadroniccalorimeter’madeof…..Thatproduceshardonicshowers

WhichparCclesdoyouexpecttoproducehadronicshowersinthisdetector?photon,electron,proton,neutrino,muon,chargedkaon,neutralkaon,chargedpion

Youhavean‘electromagneCccalorimeter’madeupof……

WhichparCclesdoyouexpecttoproducehadronicshowersinthisdetector?photon,electron,proton,neutrino,muon,chargedkaon,neutralkaon,chargedpion

Bibliography • Radia4onDetectorsbyC.F.G.DelaneyandE.C.Finch

ClarendonPress,1992• TechniquesforNuclearandPar4clePhysicsExperimentsbyW.R.Leo

Springer-Verlag,1987• DetectorsforPar4cleRadia4onbyK.Kleinknecht

CambridgeUniversityPress,1998• NuclearPhysicsforApplica4onsbyS.G.Prussin

Wiley,2007OthersincludingRadia4onDetec4onbyG.Knoll,

ThePhysicsofPar4cleDetectorsbyD.Green“ThePhysicsofParCcleDetectors”LectureNotesErikaGarur“ParCclePhysicsInstrumentaCon”WernerRiegler,CERN“ParCcleDetectors”HorstWahl,Quarknetlecture,June2002“PhysicsofParCcleDetecCon”ClausGrupen,UniversityofSiegen

hcp://www.hep.physik.uni-siegen.de/grupen (verydetailed)PassageofParCclesThroughMacer–Chapter30(Bischel,Groom,Klien)

hcp://pdg.lbl.gov/2013/reviews/rpp2012-rev-passage-parCcles-macer.pdf