March 3, 2008 E. Scapparone INSTR08 1
Particle identification in ALICE
E. Scapparone(INFN/CERN) on behalf of the ALICE Collaboration INSTR08, March 3, 2008
Outline- Experimental layout and status of the main subdetectors;
- Detector performance;
- Example of ALICE phsycs potential.
March 3, 2008 E. Scapparone INSTR08 22
ALICE: A Large Ion Collider Experiment at CERN-LHC
Size: 16 x 26 meters
Weight: 10,000 tonnes
p-p (L=1031 cm-2 s-1), Pb-Pb (L= 1027 cm-2 s-1)
March 3, 2008 E. Scapparone INSTR08 3
Life in Pb-Pb interactionswas never easy….
NA49
At RHIC became harder…..
ALICE simulated central event !
..also more difficult @ RHIC
STAR
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• 6 layers, three technologies (keep occupancy at a few % for max multiplicity)
• SPD: silicon pixels (0.2 m2, two layers, 9.8 M channels)
• SDD: silicon drift (1.3 m2, two layers, 133 k channels) • SSD: double-sided silicon strips (4.9 m2, two layers, 2.6 M channels)
Rout=43.6 cm
SPD
SSD
SDD
ITS(Inner Tracking System)
Lout=97.6 cm
Material Budget: ≤ 1% X0 per layer !
March 3, 2008 E. Scapparone INSTR08 5
Challenge: track densities at r = 4 cm (1st layer): up to 100 / cm2
SPD (0.2 m2)Cell size (rz : 50 m x 425 µm space resolution(r) : 12 mspace resolution(z): 100 m
ITS
SDD (1.3 m2)cell size (r,z): 294 x 150 m2space resolution (r, z) : 35 mspace resolution(z): 23 m
SSD (4.9 m2)cell size (r,z): 95 x 4200 m2space resolution (r): 20 mspace resolution (z); 830 m
40
m m
75 mm42 m
m6 chips
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Inner Tracking System~ 10 m2 Si detectors, 6 layers
Pixels, Drift, double sided Strips
Strips
SSD
Drift
SDD
Pixels
Inner Silicon Tracker
Pixels
SPD
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TPC
SSD/SDD
SPD
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• Optimized for dN/dη ≈ 8000• l = 5 m, Ø = 5.6m, 88 m3,
570,000 channels x 500 time bins, • up to 80 Mbytes/event (after 0
suppression)• Features:
• lightweight: 3% X0 total material for perpendicular tracks
• novel digital electronics (ALTRO)• highly integrated, digital shaping; tail
cancellation;0-suppression; Baseline restoration
• Powerful laser calibration system
TPC
Drift gas:Ne (86) / CO2 (9.5) / N2 (4.5)
σ(dE/dx) ≈ 5.5 to 6.5 %, depending on multiplicity (measurements and simulations)
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ALICE TPC: 5 years construction
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Cosmics recorded in TPC@ALICE
Commissioning with Cosmics and Laser tracksSpatial resolution and Electronics noise in experiment according to specifications
Status: installed and being commissioned
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• e/ separation in central barrel p>1 GeV/c
• fast trigger for high momentum particles (hadrons, electrons)+ tracking
• 540 detectors ~ 760m2
• 18 super modules
• length: 7m
• X/X0 ~ 22 %
• 28 m3 Xe/CO2 (85/15)
• 1.2 million channels
Transition Radiation Detector (TRD)
Status: partially installed; being commissioned
TRD
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TRD - Signal Generation & Processing
Ave
rag
e p
uls
e h
eig
th (
mV
)
e-) = 90 %
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TRD Installation
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TOF requirements:
Large array to cover the ALICE barrel (~150 m2)Time resolution σ < 100 ps High efficiency, ε > 95%High segmentation: few thousands of particles per unit of rapidity expected in Pb-Pb collision at s = 5.5 TeV/nucleon pair
ALICE choice: a detector based on MRPC, segmented in ~157,000 channels, (3.5 x 2.5) cm2 area
√
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TOF
2 crates /side
157248 pads, total sensitive area: ~150 m2
18 Supermodules, each made of 5 modules: 2 external (19 strips), 2 intermediate (19 strips), 1 central (15 strips)
7.4 m
Readout performed bytwo VME Crates/Side
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Cross section of a double-stack MRPC strip
2 rows of 48 readout pads (3.5 x 2.5 cm2)
Active strip length = 120 cm
Differential signal to FEA card
10 gaps 250 m
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Test beam of single strips E
ffic
ien
cy
Tim
e re
solu
tio
n(
ps)ε > 99.9 %
average ~ 50 ps
Gas mixture: C2F4H2(90%) – SF6 (5%) – C4H10(5%)
Similar results obtained when strips are inserted inside the modules
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M = p ((t2 c2 /L2 )-1)1/2
σTOF = 80 ps ; B = 0.5 T
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10 SMs installed ; next 4 SMs to be installed next week; being
commissioned
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December 2007 cosmic run
Event display of a muon crossing the TOF detector
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• Proximity Focused RICH• 11 m2 active detector area• 7 modules• - 0.6< η < 0.6; Δφ = 58 deg • CsI Photocathode read by
16100 pads• Threshold momentum =
1.21* (Particle Mass)
• PID optimization for 1 GeV < p < 6 GeV
High Momentum Particle Identifier: HMPID
March 3, 2008 E. Scapparone INSTR08 2222HMPID (Sept ’06)
HMPID: Installed; being commissioned
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Example of a high multiplicity event as seen by the HMPID
dN/d=6000
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5 stations of high granularity pad tracking chambers, over 1 million channels
Complex absorber/small angle shield system (~10 I)
to minimize background(90 cm from vertex)
RPC Trigger Chambers
MUON spectrometer set-up
0.7 T, bending power 3 Tm 4 MW power, 800 tons World’s largest warm dipole
Trigger pt cut on single : ~1 GeV/c
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Lepton Acceptance
ATLAS & CMS present a large lepton acceptance ||<2.4
ALICE combines muonic and electronic channels
- covers the low pT region (quarkonia)
- covers the forward region 2.5<<4.0
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Charged Particle Identification
ITS
kaons
pions
protons
dE/d
x (M
IP u
nits
) TPC
All known PID techniques used in ALICE
dE/dx = 6.8% at dN/dy=8000 (5.5% for isolated tracks)
HADRON-ID 3 separation power
P(GeV/c)P(GeV/c)
dE/d
x (M
IP u
nits
)
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Combined PID Performance
Efficiency/Contamination
Kaon PID (the most difficult case...)
ITSTPC
TOF(*)(120 ps)
p (GeV/c) p (GeV/c) p (GeV/c)
(C : CK : Cp = 0.75 : 0.15 : 0.1)
Higher efficiency & Lower contamination wrt individual detectors
p (GeV/c)
Combined PID ITS & TPC & TOF
(*) very conservative
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Extension of PID to higher momenta combining the dE/dX of TRD and TPC
Combine TPC and TRD dE/dx capabilities (similar number of samples/track) to get statistical ID in the relativistic rise region
8<p<10GeV/c
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Open Charm Detection in Hadronic DecaysOpen Charm Detection in Hadronic Decays
Mass 1.864 GeV/c2 c=124 m
~0.55 D0K-+ accepted/event important also for J/ normalization
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SpectraSpectra
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Finally …
• ALICE is becoming reality after almost 15 years in the making • 2nd Commissioning run is going on this week.• Further commissioning running until first beams, scheduled for
summer 2008• All systems on track for taking first pp collisions• ALICE is the general purpose Heavy Ion experiment, designed to
address the very rich, expected physics program: particle id will
play a central role in this challenging physics.
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RISERVE
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GIF results
No ageing effect measured at PS
Working voltage = 13 kV
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GIF results: No current increase
Source on
Source off
Source on
Source off
I (A)Flow = 1.4 cm3/s
The gas going to the chamber 2 was bubbled through water for some
time of the exposure
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Ageing study:
Total charge = 14 mC/cm2
Charge/event = 2 pC
7 *109 events /cm2 @ 50 Hz/cm2
T=1.4 108 sec = 1620 days Pb-Pb run
Time(min)
two MRPC strips irradiated at GIF
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ALICE is taking shape All large structures are installed and integration
of detector subsystems will start in AugustThe ALICE Collaboration looks forward to first
operation of LHC for the expected and the unexpected…
ConclusionConclusion
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PHOton Spectrometer: PHOS
• PbO4W- crystal calorimeter for Photons, neutral mesons, 1 to > 100GeV
• Crystals: 2.2*2.2 cm2 , 20 X0, APD R/O Operated at – 25 deg; 5 pe / MeV
• σ(E) ≈ 3%; σ(x,y) ≈ 4 mm; σ(t) ≈ 1 ns; at 1GeV
• - 0.12 < η < 0.12; Δφ = 100 deg; at R = 460 cm
• L0 trigger available at < 900 ns
• Module tested, calibrated in test beam; 1 or 2 modules to be installed in 04/08
• 3rd module during 2008; • Ultimately 5 modules with 18 000 crystals
expected by 2010
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ElectroMagnetic Calorimeter: EMCAL
• Pb-Scintillator em calorimeter for• Jet physics in conjunction with
tracking and PID• Approximately opposite to PHOS• -0.7 <η < 0.7; Δφ = 107 deg• EM resolution σ(E) < 0.1/√E• 13 000 projective towers in ‘Shashlik’
geometry with APD R/O• L0 trigger in < 900 ns for high-pT jets,
photons, electrons
Status: project approved in Dec 2007 2 of 12 supermodules early 2009
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Partial view of Muon chambers
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TOF Standalone PID (80 ps res. as in the PPR)
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