lice the alice detector a largeioncolliderexperiment gert-jan nooren bachelor introduction 10...

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


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


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


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


magnet B = 0.5 T


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


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


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


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


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 GJN21SAP1EXP21

E.M. cascades

X0

2X0

3X0

bremsstrahlung

annihilation

pair creation

electron

Compton

positron photoncontinues down to ~10 MeV

2Rmoliere


EElectroMagneticCALCALorimeter

Lead-scintillator sampling calorimeterShashlik fiber geometry Avalanche photodiode readout12288 ‘towers’


PHOton Spectrometer• PbWO4 crystals: clear as glass, denser than

steel• Avalanche photodiode read out• Charged particle veto needed: MWPC

• 3854 crystals


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)


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


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


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


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


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


ITS performance

Beam spot at 2.36 TeV

ITS measures primary vertex with ~ 100 m resolution (only rough alignment)


• 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


energy loss signals

ITS

900 GeV p+p data

ITS (SDD + SSD)

TPC



• determine mass via by measuring β and γ:– energy loss via Bethe-Bloch ITS, TPC– beta

• Time of flight• Čerenkov

– gamma: transition radiation

38


Bqrp

cmp 0


velocity signals from TOF

velocity = v/c

Protons

Kaons

Pions

all plots:

preliminary calibration & alignment !

p+p @ 900 GeV



• 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


Bqrp

cmp 0


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


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


High-multiplicity event

lice the alice detector a largeioncolliderexperiment gert-jan nooren bachelor introduction 10...

Documents

alice tracking

alice detector designdue

inner tracking systempixel

decay detectabled0 c

fmdheavy quark detectorse

high particle density

high number of particles

vertex detectorphotons