The ALICE detector A L Large I Ion C Collider E Experiment Gert-Jan Nooren Bachelor Introduction 10 February 2010
Jan 14, 2016
The ALICE detector
A LLargeIIonCColliderEExperiment
Gert-Jan Nooren
Bachelor Introduction10 February 2010
10 FEB 10 bachelor introThe ALICE detector GJN22
in search of the Quark Gluon Plasma
collide heaviest ions at largest accelerator to make quark-gluon-plasma
10 FEB 10 bachelor introThe ALICE detector GJN326 JUN 09 The ALICE detector GJN3
10 FEB 10 bachelor introThe ALICE detector GJN4
Simulated event
10 FEB 10 bachelor introThe ALICE detector GJN5Fysisch Colloquium 31 maart 2006 5
some signatures of QGP
• thermal photons– black body radiation, however
pions are produced copiously and 0 requires photon detector
• heavy quark production– short lifetimes, only decay detectable
• D0 (cū) ―> K-π+ cτ = 0.1 mm
requires precision vertex detector
π+ cτ = 7.8 mK- cτ = 3.7 m
10 FEB 10 bachelor introThe ALICE detector GJN66
some signatures of QGP
• thermal photons– black body radiation, however
pions are produced copiously and 0 requires photon spectrometer
• heavy quark production– short lifetimes, only decay detectable
• D0 (cū) ―> K-π+ cτ = 0.1 mm
requires secondary vertex detector
• properties of hot dense matter– jet quenching– flow
requires 2π azimuthal coverage
10 FEB 10 bachelor introThe ALICE detector GJN77
general layout of a LHC detector
define point of collision or the vertex measure momentum
– magnetic field– inner tracking system– general tracking device
particle identification– hadron detectors– photon detectors– muon detector
10 FEB 10 bachelor introThe ALICE detector GJN8GJN88
ALICE detector design• Due to high number of particles cannot follow all
– incomplete reconstruction of collision– no ‘hermetic’ detector– subdetectors do not cover full angular ranges
• what we need:– detectors for event characterisation
• spectators -> ZDC• multiplicity -> V0, FMD
– heavy quark detectors• e.g. charm
– J/ψ -> dimuonspectrometer– D0 -> vertex detector
– photons -> PHOS, EMCAL
10 FEB 10 bachelor introThe ALICE detector GJN9GJN9
magnet B = 0.5 T
10 FEB 10 bachelor introThe ALICE detector GJN10GJN1010
The IInner TTracking SSystem
The main tracking device of ALICE is the TPC, butthe ITS is the heart of the ALICE tracking system
– needed to get reasonable momentum resolution at higher pT
– needed to reconstruct secondary vertices– needed to track low momentum particles
• being at the centre:– do not disturb the particles for the outer detectors
• scattering• energy loss / secondary particle production
– cope with high particle density: 104 tracks simultaneously main features
– low mass / radiation thickness– high granularity– all silicon, various techniques
10 FEB 10 bachelor introThe ALICE detector GJN11GJN1111
The IInner TTracking SSystem
all silicon, 6 layers
low mass: 8 % X0
SPD 2.3 %SDD 2.4 %SSD 1.7 %structure 1.3 %
layertype R
[cm]area[m2]
chan-nels
occu-pancy
_R _Z
1 pixels
SPD
4 0.07 3.3 M 2.112 m 100 m
2 8 0.14 6.6 M 0.6
3 drift
SDD
15 0.42 43 k 2.535 m 25 m
4 24 0.89 90 k 1
5 double sided strip SSD
38 2.2 1.1 M 4
20 m 830 m6 43 2.8 1.5 M 3.3
10 FEB 10 bachelor introThe ALICE detector GJN1226 JUN 09 GJN1212
The IInner TTracking SSystempixel, drift, strip
1698 double sided strip sensors73 * 40 mm2 300 um thick768 strips on each side 35 mrad stereo angle
260 silicon drift sensors70 * 70 mm2 300 um thick256 + 256 collection anodes291 + 291 field cathodes
Z
R
R
240 silicon pixel sensors13 * 68 mm2 200 um thick256 * 160 cells5 pixelchips per sensor
E = 600 V/cm
E ~ 200 V/cm
10 FEB 10 bachelor introThe ALICE detector GJN13GJN13
10 FEB 10 bachelor introThe ALICE detector GJN14GJN14
TTime PProjection CChamber
• ionising particle creates free electrons• electric field pulls them towards
endplates with read-out chambers particle track is projected onto endplate• position sensitive detectors record:
– position: R and φ – arrival time– charge
• drift time determines Z
3 D track reconstruction [1 mm]
continuous energy loss measurement [5 %]
slow
EB
φ Z
R
10 FEB 10 bachelor introThe ALICE detector GJN1526 JUN 09 GJN1515
outerField Cage
inner
drift gas90% Ne10% CO2
HV electrode
90 m3
5 m dia/length100 kV
558k channels90 MB/event
ALICE TPC, largest ever
10 FEB 10 bachelor introThe ALICE detector GJN16GJN16
10 FEB 10 bachelor introThe ALICE detector GJN17GJN17
TTransitionRRadiationDDetector
• principle:– radiation is emitted when a fast particle
traverses a EM discontinuity– electron is fast enough to produce X-rays in
the radiator, pion is not
• radiator fibre+foam: many transitions• driftchamber to detect X-ray photons
– also sensitive to charge particles– 2-D read-out
• six layers of these (638 m2)– tracking!
TRD
Electrons
Pions
10 FEB 10 bachelor introThe ALICE detector GJN18GJN18
10 FEB 10 bachelor introThe ALICE detector GJN19GJN19
TTime OOf FFlight
measure traveling time between two detectors– start detector T0
• quartz Cherenkov radiator with fast Photomultiplier -> 37 ps
– stop detector TOF at R= 3.8 m• MultigapResistivePlateChamber -> 40 ps
13 kV
141 m2 of these!
10 FEB 10 bachelor introThe ALICE detector GJN20GJN20
10 FEB 10 bachelor introThe ALICE detector GJN21SAP1EXP21
E.M. cascades
X0
2X0
3X0
bremsstrahlung
annihilation
pair creation
electron
Compton
positron photoncontinues down to ~10 MeV
2Rmoliere
10 FEB 10 bachelor introThe ALICE detector GJN22GJN2222
EElectroMagneticCALCALorimeter
Lead-scintillator sampling calorimeterShashlik fiber geometry Avalanche photodiode readout12288 ‘towers’
10 FEB 10 bachelor introThe ALICE detector GJN23GJN23
10 FEB 10 bachelor introThe ALICE detector GJN24
PHOton Spectrometer• PbWO4 crystals: clear as glass, denser than
steel• Avalanche photodiode read out• Charged particle veto needed: MWPC
• 3854 crystals
10 FEB 10 bachelor introThe ALICE detector GJN25GJN25
photon detectors
granularityPHOS’ better resolution can
separate 2 photons from 0 decay
PHOS EMCAL
depth [X0]
20 20
energy resolution
in plot 10%/√E
width / RM [cm]
2.2/2.2 6/3.2
m0 = 135 MeV/c2
PHOS (9 m2)
10 FEB 10 bachelor introThe ALICE detector GJN26GJN26
10 FEB 10 bachelor introThe ALICE detector GJN27GJN27
HHigh-MMomentumPParticleIIdentificationDDetector
Particle identification at momenta beyond the range of ITS, TPC, TOFRing Imaging Čerenkov detector n = 1.3 ( = 175 nm) > 0.77 p > 1.21 mc
10 FEB 10 bachelor introThe ALICE detector GJN28GJN28
10 FEB 10 bachelor introThe ALICE detector GJN29GJN29
dimuon spectrometer• muon pair produced by decay of J/ψ and Y• front absorber to filter muons >4 GeV/c• dipole 0.7 T, 3 Tm with 5 tracking chambers
• special trigger plus filter to reduce low pT muons from π and K decay
front absorber:10 int 60 X0
carbon, concrete, steel
beam shield:W, Pb, Fe
filter:7 int
Fe
10 FEB 10 bachelor introThe ALICE detector GJN30The ALICE detector GJN30
V0• Two arrays of scintillators on each
side of the interaction point– plastic scintillator– photomultiplier read-out via fibres
• combinations yield triggers:– minimum bias– multiplicity– centrality– beam / gas
V0A (z=3.3 m)
V0C (z=-0.9 m)
delay from interaction point
10 FEB 10 bachelor introThe ALICE detector GJN3126 JUN 09 The ALICE detector GJN31
ZZeroDDegreeCCalorimeter
three types: proton, neutron, EM
ZN ZP ZEM
dimensions [cm3] 7*7*100 12*22*150 7*7*20
absorber
tungsten alloy brass lead
17.6 g/cm3 8.5 g/cm3 11.3 g/cm3
length
251 X0 100 X0 35 X0
8.7 int 8.2 int 1.1 int
10 FEB 10 bachelor introThe ALICE detector GJN32GJN32
trigger
• controls the read-out of subdetectors– prepare detectors– control sequences, like sampling or digitising– busy: if any is not ready, no new trigger is allowed– past-future protection
• select interesting events– adjust datastream to available bandwidth– reduces data volume for analysis
• input from key detectors– T0 and V0: time and position of interaction– ZDC: centrality– pixels– Muontrigger– PHOS and EMCAL: photons
10 FEB 10 bachelor introThe ALICE detector GJN33GJN33
Trigger, DAQ and HLT
1.25 GB/s to mass storage, 1 PB/y
25 GB/s
why HHighLLevelTTrigger?• even with good trigger all subdetectors produce 25 GB/s• processorfarm can reconstruct events refined selection
10 FEB 10 bachelor introThe ALICE detector GJN34GJN34
tracking
tracking from 0.1 to 100 GeV/c– small material budget: < 10% X0 vertex end of TPC
• main tracking subdetectors– ITS 6 layers
• ~30 um 6 cm < R < 45 cm
• stand-alone tracking at low pT
– TPC continuous• ~1 mm 85 cm < R < 247 cm
– TRD 6 layers• ~1 mm 2.9 m < R < 3.7 m
10 FEB 10 bachelor introThe ALICE detector GJN35
ITS performance
Beam spot at 2.36 TeV
ITS measures primary vertex with ~ 100 m resolution (only rough alignment)
10 FEB 10 bachelor introThe ALICE detector GJN36GJN36
• determine momentum in B field• bonus: charge
• determine mass via by measuring β and γ:– energy loss via Bethe-Bloch
36
techniques for PParticle IDIDentification
Bqrp
cmp 0
10 FEB 10 bachelor introThe ALICE detector GJN37
energy loss signals
ITS
900 GeV p+p data
ITS (SDD + SSD)
TPC
10 FEB 10 bachelor introThe ALICE detector GJN38GJN38
• determine momentum in B field• bonus: charge
• determine mass via by measuring β and γ:– energy loss via Bethe-Bloch ITS, TPC– beta
• Time of flight• Čerenkov
– gamma: transition radiation
38
techniques for PParticle IDIDentification
Bqrp
cmp 0
10 FEB 10 bachelor introThe ALICE detector GJN39
velocity signals from TOF
velocity = v/c
Protons
Kaons
Pions
all plots:
preliminary calibration & alignment !
p+p @ 900 GeV
10 FEB 10 bachelor introThe ALICE detector GJN40GJN40
• determine momentum in B field• bonus: charge
• determine mass via by measuring β and γ:– energy loss via Bethe-Bloch ITS, TPC– beta
• Time of flight TOF• Čerenkov HMPID
– gamma: transition radiation TRD• neutral particles
– exclude charged particles, then measure energy PHOS, EMCAL– via decay into charged particles
• short lived particles via decay to measured particles– J/ψ via dimuonspectrometer– others via displaced vertex
40
techniques for PParticle IDIDentification
Bqrp
cmp 0
10 FEB 10 bachelor introThe ALICE detector GJN41
Decay examples
PDG: 497.6 MeV
K0s
PDG: 1115.7 MeV
p
PDG: 1019.5 MeV
All from ~300k p+p events @ 900 GeV – Physics analysis ongoing
PDG: 1115.7 MeV
p
Λ cτ = 7.9 cm K0 cτ = 2.7 cm
10 FEB 10 bachelor introThe ALICE detector GJN42GJN42
First interactions 11th September
.. then, on 19 Sep …
Circulating beam 2 on 11 Sep:stray particle interacts in SPD
ITS has 7 tracks reconstructed with
common vertex
first alignment and calibration is ok
ALICE is ready for beam
10 FEB 10 bachelor introThe ALICE detector GJN43
High-multiplicity event
10 FEB 10 bachelor introThe ALICE detector GJN44GJN44