Post on 10-Jan-2016
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HEP ExperimentsHEP Experiments
Detectors and their TechnologiesDetectors and their Technologies
Sascha Marc SchmelingSascha Marc SchmelingCERNCERN
OverviewOverview Introduction and ConceptsIntroduction and Concepts
Properties of ParticlesProperties of Particles– Are they measurable?Are they measurable?– If yes, how?If yes, how?
HEP Detectors @CERNHEP Detectors @CERN– Main Sub-DetectorsMain Sub-Detectors– InfrastructureInfrastructure
Studying InteractionsStudying Interactions
by scatteringby scattering
by annihilationby annihilation
and the production of new particlesand the production of new particles
all interactions are produced inall interactions are produced in– Colliding Beam Experiments orColliding Beam Experiments or– Fixed Target ExperimentsFixed Target Experiments
Ideal Detectors?Ideal Detectors?
In an ideal detector, one could record the full In an ideal detector, one could record the full interaction, capture and measure all interaction, capture and measure all properties of all emerging particles, and by properties of all emerging particles, and by this reconstruct the complete event.this reconstruct the complete event.
This would give us the power to compare This would give us the power to compare the interaction directly to theoretical the interaction directly to theoretical predictions without most uncertainties.predictions without most uncertainties.
Particle PropertiesParticle Properties Which properties does a particle have?Which properties does a particle have?
– energyenergy– momentummomentum– chargecharge– massmass– life timelife time– spinspin– decay modesdecay modes
And which of those are measurable?And which of those are measurable?
Particle PropertiesParticle Properties
Which properties can we derive?Which properties can we derive?
Particle PropertiesParticle Properties
chargecharge
lifetimelifetime
Measuring Particle Measuring Particle PropertiesProperties
momentummomentum
velocityvelocity
time of flighttime of flight energyenergy
calorimetercalorimeter
Measurement PrinciplesMeasurement Principles Measurement occurs via the interaction (again…) Measurement occurs via the interaction (again…)
of a particle with the detector (material)of a particle with the detector (material)– creation of a measureable signalcreation of a measureable signal
IonisationIonisation
Excitation/ScintillationExcitation/Scintillation
Change of the particle trajectoryChange of the particle trajectory– curving in a magnetic field, energy losscurving in a magnetic field, energy loss
– scattering, change of direction, absorptionscattering, change of direction, absorption
p
e-
p
e-
pp
Which particles can be detected?Which particles can be detected?
Charged ParticlesCharged Particles
Neutral ParticlesNeutral Particles
Different particle types interact very Different particle types interact very differently with the detector material.differently with the detector material.
A Typical Detector ConceptA Typical Detector Concept
Interaction point
Precision vertex detector
trackingdetector
Magneticspectrometer
Electro
mag
netic calo
rime
ter
Had
ron
ic calo
rimeter
Mu
on
detecto
rs
IngredientsIngredientsTra
ckin
g Sub
syst
emEle
ctro
mag
netic
Calor
imet
erHad
roni
c Cal
orim
eter
Muo
nSys
tem
Passage of ParticlesPassage of Particles ElectronsElectrons
PhotonsPhotons
HadronsHadrons
MuonsMuons
MesonsMesons
Tracking DetectorsTracking Detectors
measure the tracks of emerging particlesmeasure the tracks of emerging particles determinedetermine
– charge andcharge and– momentummomentum
in connection with a magnetic fieldin connection with a magnetic field tracks are reconstructed from measured tracks are reconstructed from measured
space-pointsspace-points
do not use dense
material!
How do tracking detectors work?How do tracking detectors work?
two main flavorstwo main flavors– ionization detectorsionization detectors
Geiger-Müller counterGeiger-Müller counter MWPCMWPC TPCTPC silicon detectorssilicon detectors
– scintillation detectorsscintillation detectors
Multi-Wire Proportional Chamber
Time Projection Chamber
t = 0
Ionization CountersIonization Counters
+ HV
signal
cathode
Anode Wire
Gas-filled tubeGas-filled tube
---
--
+++
++- -
---
+ +++
+
t = t1
TrackingTracking
Realization:Realization:wire chamberwire chamber
(MWPC)(MWPC)Nobel prize: G.Charpak, 1992Nobel prize: G.Charpak, 1992
Anode wiresAnode wires
Cathode: pads or wiresCathode: pads or wires
x
y
MWPCMWPCITC (ALEPH)
Inner Tracking Chamber
Time Projection ChamberTime Projection Chamber
Gas-filled cylinderGas-filled cylinder
Anode Wires
MWPC
gives r,
MWPC
gives r,
E
B
- --
-
--
++
+
+
++
- -- - - - -
z = vdrift tz = vdrift t
TPCTPC
ALICE TPC sector detail
ALEPH TPCALEPH TPC
LimitationsLimitations Precision limited by wire distancePrecision limited by wire distance
Error on space point d cannot be reduced arbitrarily!
Uncertainties on space points Uncertainties on track origin andmomentum
Step forward:Step forward:Silicon Microstrip DetectorsSilicon Microstrip Detectors
Now precision limited by strip distance 10 - 100 m
Now precision limited by strip distance 10 - 100 m
Creation of electron-hole pairs by ionising particle
Creation of electron-hole pairs by ionising particle
Same principle as gas counters
Silicon wafers, doped
0.2 - 0.3 mm
Silicon Microstrip detectors...Silicon Microstrip detectors...
ALEPH VDET
OPAL VDET
Future ATLAS tracking detector
Increase in precisionIncrease in precision
0 1cmx
=Beam crossing point
Mean Lifetime of tau =290 x 10-15 sec !! --> c = 87 m !?
Scintillation DetectorsScintillation Detectors
Photomultiplier: converts light into electronic signal
Scintillatingmaterial
Scintillatingmaterial
PM
Total reflection
Put many fibers close to each other--> make track visible
CalorimetersCalorimeters
Basic principle:Basic principle:– In the interaction of a particle with dense In the interaction of a particle with dense
material all/most of its energy is converted into material all/most of its energy is converted into secondary particles and/or heatsecondary particles and/or heat. .
– These secondary particles are recordedThese secondary particles are recorded eg. Number, energy, density of secondarieseg. Number, energy, density of secondaries this is this is proportional toproportional to the initial energy the initial energy
Electromagnetic ShowersElectromagnetic Showers
Block of Matter,e.g. lead
Lead atom
How to measure the secondary particles?How to measure the secondary particles? 1. With 1. With sampling calorimeterssampling calorimeters::
Dense blocks, such as leadDetectors, such as wire chambers,
or scintillators
Sandwich structure !
Total amount of signalsregistered is proportionalto incident energy.
But has to be calibrated with beams of known energy!
Sandwich structure !
Total amount of signalsregistered is proportionalto incident energy.
But has to be calibrated with beams of known energy!
Sampling CalorimetersSampling Calorimeters
ALEPH ECAL
pions electron
muonsphotons
How to measure the secondary particles?How to measure the secondary particles? 2. With 2. With homogenous calorimetershomogenous calorimeters, such as, such as crystal crystal
calorimeterscalorimeters::
signal
photons
Photo diode
Crystal (BGO, PbWO4,…)
Hadronic calorimetersHadronic calorimeters Hadronic particles (protons, neutrons, pions) can traverse Hadronic particles (protons, neutrons, pions) can traverse
the electromagnetic calorimeters. They can also interact via the electromagnetic calorimeters. They can also interact via nuclear reactions nuclear reactions !!
Usually: Put again a sampling calorimeter after the ECALUsually: Put again a sampling calorimeter after the ECAL
Dense blocks, such as iron, uraniumDetectors, such as wire chambers,
or scintillators
Sandwich structure !
Total amount of signalsregistered is proportionalto incident energy. Same energy lost in nuclear excitations!
Has to be calibrated with beams of known energy!
Sandwich structure !
Total amount of signalsregistered is proportionalto incident energy. Same energy lost in nuclear excitations!
Has to be calibrated with beams of known energy!
ALEPH ALEPH
iron
Particle IdentificationParticle Identification Basic principles:Basic principles:
– via different interaction with matter via different interaction with matter (see previous transparencies)(see previous transparencies)
– by measuring the mass from the decay productsby measuring the mass from the decay products
– by measuring the velocity and by measuring the velocity and independently (!)independently (!) the the momentummomentum
– Observables Observables sensitive to velocitysensitive to velocity are are
mean energy loss mean energy loss
Cherenkov radiationCherenkov radiation
Mean Energy LossMean Energy Loss
Particles which traverse a gas loose energy, Particles which traverse a gas loose energy, e.g. e.g. by ionizationby ionization
EElost lost amount of ionizationamount of ionization size of signals on wiressize of signals on wires
Elost / path length = func( particle-velocity v/c )
Elost / path length = func( particle-velocity v/c ) Bethe-Bloch formula
Note : if plotted as a function of v and not p all the bands would lie on top of each other!
Note : if plotted as a function of v and not p all the bands would lie on top of each other!
Cherenkov RadiationCherenkov Radiation
Particles which in a Particles which in a given medium travel given medium travel faster than the speed faster than the speed of light in that mediumof light in that medium emit radiation: emit radiation:
Cherenkov radiationCherenkov radiationv
1
nvsin 0cc
v
1
nvsin 0cc
c0 = speed of light in vacuum
Cherenkovlight
wavefront
HEP Experiments @CERNHEP Experiments @CERN All these concepts have been put together and realized in All these concepts have been put together and realized in
large detector systemslarge detector systems
Examples at Examples at LEPLEP– ALEPH , OPAL , L3 , DELPHIALEPH , OPAL , L3 , DELPHI
Fixed TargetFixed Target– NA48NA48
Future experiments at LHCFuture experiments at LHC– ATLAS, CMS, LHCb, ALICEATLAS, CMS, LHCb, ALICE
InfrastructureInfrastructure
experiments are not only detectorsexperiments are not only detectors
you needyou need– possibilities to control the detectorspossibilities to control the detectors– possibilities to take the data out and record itpossibilities to take the data out and record it– possibilities to analyze the recorded datapossibilities to analyze the recorded data– ……