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Rachid MaziniUniversite de Montreal
Peter LochUniversity of Arizona
Comparison of Experimental Electron
Signals with GEANT3 and GEANT4
Simulations for the ATLAS Forward
Calorimeter Prototype
• Overview of the Forward Calorimeter (FCal) in ATLAS
• FCal Module 0’s
• Monte Carlo set up with Geant4
• Results
• conclusions and Outlook
Rachid Mazini, UdM CALOR2000, October 12, 2000
ATLAS Calorimetry
ATLAS Calorimetry (Geant)
Calorimeters
Calorimeters
Calorimeters
Calorimeters
Hadronic Tile
EM Accordion
Forward LAr
Hadronic LAr End Cap
η ≅ 1.3
η ≅ 4.9
η ≅ 3.2
η ≅ 1.8
Hadronic Tile Calorimeter
Hadronic LAr EndCap Calorimeters
Forward LAr Calorimeters
Electromagnetic LAr Accordion Calorimeters
-6-4
-20
24
6
0
50
100
150
200
250
300
350
0
5
10
15
20
run 17 event 6
pseudo-rapidity η
azimuth φ [deg]
tran
sver
se e
nerg
y E
t [G
eV]
-6-4
-20
24
6
0
50
100
150
200
250
300
350
0
5
10
15
20
run 17 event 6
pseudo-rapidity η
azimuth φ [deg]
tran
sver
se e
nerg
y E
t [G
eV]
Rachid Mazini, UdM CALOR2000, October 12, 2000
ATLAS FCal
• one electromagnetic liquid argon/copper (FCal1)and two hadronic liquid argon/tungsten sections(FCal2/3) integrated into a common cryostat withthe electromagnetic endcap calorimeters;
• cylindrical section 45 cm deep with 90 cm diameter;
Depth[X0] Depth[λ] Weight[t]FCAL1 27.6 2.7 2.1FCAL2 91.2 3.7 3.9FCAL3 89.5 3.6 3.8
• thin gaps of liquid argon are required to avoid positivecharge build-up;
• Electrode Design:
– tube/rod electrodes assembly with cylindricalshell gap of 250/375/500 µm and tube spacing is7.5/8.18/9.0mm centre-to-centre in FCal1/2/3
– Tube material is copper, rods are copper inFCal1 and pure tungsten in FCal2/3. About12330/10320/8120 electrodes in FCal1/2/3
– liquid argon gap is maintained by peek fibre spac-ers
Rachid Mazini, UdM CALOR2000, October 12, 2000
ATLAS FCal
Hexagonal tube/rod pattern Tungsten ”slugs” in FCal2/3
• Two stage summing of electrodes (4/6/9 −→16/24/36) leads to “tiles” readout geometry;
• typical tile size is 0.2×0.2 in ∆η × ∆φ
Rachid Mazini, UdM CALOR2000, October 12, 2000
FCal Module 0
• prototypes for the electromagnetic (Fcal1) and onehadronic module (Fcal2);
• 1/4 ring modules at full depth sufficient for lateralelectromagnetic and hadronic shower containment;6.4 λ total hadronic depth −→ longitudinal accep-tance limitations at higher energies;
η = 3.7
50% lateral containment(pions, 100 GeV)
FCal1 Module 0(front)
80% containment
90% containment
r = 15 cm
# tiles: 192# channels: 256
bi−gain: 64
beam spot ~5 cm OFCal2 Module 0(back)
η = 3.7
r = 15 cm
# tiles: 128# channels: 160
bi−gain: 32
• Testbeam setup at CERN: H6(North area beam line;10-200 GeV/c pions, electrons and muons:)
Beam Particle Trigger(3 Scintillator Counters)
S1 S3
S2
Multi-Wire Proportional Chambers(1 x, 1 y plane each)
Veto System(Scintillator Veto Wall and Hole Veto)
Beamline(Particle Trigger, Position and Direction Measurement)
z
y
Concrete Beam Stop
Muon Counter(Scintillator)
Tail Catcher(Iron/Scintillator Calorimeter)
Low DensityArgon Excluder
Forward CalorimeterModules
1 2
Liquid ArgonCryostat
Test Area(Calorimeter Modules, Leakage Detectors, Particle Identification)
Rachid Mazini, UdM CALOR2000, October 12, 2000
FCal Module 0
• FCal modules in cryostat
Rachid Mazini, UdM CALOR2000, October 12, 2000
Monte Carlo Simulation
GEANT 3.21/11 and GEANT4.2.0R2 base simulationprogram;
Geometry Description
• Beam line: MWPC’s, S1/S2/S3 scintillators, Hole veto includ-ing Pb shielding, lead and iron walls in front of cryostat, Tail-Catcher, concrete beam stop, muon counter;
• Cryostat: wall structure with superinsulation and front/backliquid argon excluders;
• FCal1 and FCal2 modules:
– Dimensions of electrodes and modules measured (FCal1) orfrom drawings (FCal2);
– Electrode positioning (x, y) read from external file describ-ing the readout;
Particle generation:
• particle vertices in (x, y) and directions from reconstructed ex-perimental data; correlation between vertex and direction (beamfocusing) is automatically included; the same data files are usedfor both Geant3 and Geant4;
• particle momentum (20-200 GeV) smeared by an estimated0.5% beam momentum spread.
CUTS:10 KeV (Geant3) and 0.5, 1, and 2mm range cut (Geant4):
G3 G4(0.5mm) G4(1mm) G4(2mm)ELAr(KeV); γ 10 4.4 6.18 8.67ECu(KeV); γ 10 17.1 24.6 35.7CPU (s/GeV) 3.8 0.75 0.68 0.61
Rachid Mazini, UdM CALOR2000, October 12, 2000
Test Beam set up in Geant4
Geant4 set up:
Rachid Mazini, UdM CALOR2000, October 12, 2000
FCal Modules in Geant4
FCal1 FCal2
Reconstruction of Monte Carlo Data
• visible energy in individual electrodes collected intotiles using the experimental cabling/readout descrip-tion database;
• experimental noise from randomly triggered “empty”events is added cell by cell, using the experimentaland Monte Carlo electron calibration constants cexp
(in GeV/ADC) and cMC (inverse sampling fraction):
Erec = cMCEvis + cexpA (GeV )
in any given tile; A is the noise signal in ADC counts.
• cexp and cMC are both calculated from the average60 GeV signal.
Sampling fraction:
G3(10KeV) G4(0.5mm) G4(1mm) G4(2mm)
c−1MC(%) 1.44 1.42 1.41 1.36
Rachid Mazini, UdM CALOR2000, October 12, 2000
Results
40 GeV Electron Signal Distributions
0
0.01
0.02
0.03
0.04
0.05
0.06
-20 0 20 40 60 80Reconstructed Energy [GeV]
rela
tive
entr
ies/
1 G
eV
Experiment
G3 + Noise
Reconstructed Energy [GeV]
Experiment
G4(0.5mm) + Noise
0 20 40 60 80
Rachid Mazini, UdM CALOR2000, October 12, 2000
Results
200 GeV Electron Signal Distributions
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
50 100 150 200 250 300Reconstructed Energy [GeV]
rela
tive
entr
ies/
4 G
eV ExperimentG3 + Noise
Reconstructed Energy [GeV]
ExperimentG4(0.5mm) + Noise
100 150 200 250 300
Rachid Mazini, UdM CALOR2000, October 12, 2000
Results
FCal1 Electron Energy Resolution
Beam Energy [GeV]
Rel
ativ
e E
nerg
y R
esol
utio
n σ/
E [%
]
Erec G3 + noise
Erec G4(0.5mm) + noise
Erec Experiment
0
5
10
15
20
25
30
35
40
45
0 25 50 75 100 125 150 175 200 225
Exp. G3(10KeV) G4(0.5mm) G4(1mm) G4(2mm)
A 39.2±10.9 38.4±9.1 30.5±13.1 30.8±14.8 45.9±29.9
B 7.87±0.21 7.64±0.17 7.54±0.16 7.73±0.17 7.55±0.62
c 4.1±0.5 4.5±0.4 5.2±0.6 5.6±0.3 4.9±1.3
A[%GeV−1/2], B[GeV] and C[%] are the fitted resolution parameters
Rachid Mazini, UdM CALOR2000, October 12, 2000
Results
FCal1 Electron Signal Linearty
-3
-2
-1
0
1
2
3
4
-4
-3
-2
-1
0
1
2
3
4
0 25 50 75 100 125 150 175 200 225
Geant3
Geant4 (1.0 mm range cut)
Rel
ativ
e D
iffe
renc
e M
C-D
ata
[%]
Beam Energy [GeV]
Rachid Mazini, UdM CALOR2000, October 12, 2000
Geant4 Simulation
FCal1 Electron Energy Resolution for
Various Noise Cuts
0
5
10
15
20
25
30
35
40
45
0
5
10
15
20
25
30
35
40
0 25 50 75 100 125 150 175 200 225
no noise cut
1σ noise cut
2σ noise cut
3σ noise cut
no noise cut
1σ noise cut
2σ noise cut
3σ noise cut
Geant3
Geant4 (0.5 mm range cut)
Rel
ativ
e E
nerg
y R
esol
utio
n σ/
E [%
]
Beam Energy [GeV]
Rachid Mazini, UdM CALOR2000, October 12, 2000
Results
Detailed Look at Signal Composition
Cell Signal Significance [σnoise]
Rel
. Ent
ries
10-6
10-5
10-4
10-3
10-2
10-1
0 50 100 150 200 250 300
More highly significant signals in experiment than in both
Geant3 and Geant4!
Rachid Mazini, UdM CALOR2000, October 12, 2000
Conclusion
Conclusion and Outlook
• comparison of Geant3 and Geant4 for FCAL1 Module0 shows a good agreement for both signal and energyresolution;
• adding noise to simulated data at cell level producesa rather good agreement between data and MonteCarlo for global; energy sums and resolution, at thelevel of (few) percent;
• Geant4 compares well to the experimental data. How-ever, more statistics is going to be produced for moredetailed comparisons of shower development and sig-nal fluctuations
Rachid Mazini, UdM CALOR2000, October 12, 2000