Z boson mass reconstruction Caroline Steiblin Prof. Al Goshaw Dr. Andrea Bocci Duke University 1.
Detector Basics: Interacon of Parcles with...
Transcript of Detector Basics: Interacon of Parcles with...
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