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

ATLASATLAS

See http://pdg.lbl.gov/atlas/index.html

See http://cmsinfo.cern.ch/Welcome.html/

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– ……