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XIII International Conference on Calorimetry in High Energy PhysicsPavia, Italy, May 2008
GEANT4 Physics Evaluation with Testbeam Data of
the ATLAS Hadronic End-Cap Calorimeter
A. Kiryunin, H. Oberlack, D. Salihagic, P. Schacht, P. Strizenec
“Simulation” session
May 29, 2008
Calor 2008 May 29, 2008
The validation of GEANT4 physics models is based on the detailedcomparison of experimental data from beam tests of modules of theATLAS hadronic end-cap calorimeter with GEANT4 predictions
• ATLAS hadronic end-cap calorimeter and its testbeam
• GEANT4: simulation framework, parameters and features
• Results of the validation
– 1 –
Calor 2008 May 29, 2008
ATLAS Hadronic End-Cap Calorimeter
• ATLAS hadronic end-cap calorimeter(HEC) — a liquid argon (LAr)
sampling calorimeter with parallelcopper absorber plates
• Pseudorapidity coverage:1.5 < |η| < 3.2
• Two wheels per end-cap: front andrear
• Total thickness:∼1.8 m, ∼103 X0, ∼10 λ
• Wheel outer diameter: ∼4 m
• Each wheel contains 32 identicalmodules
• Granularity ∆η × ∆ϕ:
– 0.1×2π/64 for |η| < 2.5– 0.2×2π/32 for |η| > 2.5
• Four longitudinal layers
– 2 –
Calor 2008 May 29, 2008
Beam tests of HEC modules
• Beam tests of HEC serial
modules in 2000-2001
• H6 beam line of the CERN SPS
• Secondary and tertiary beams:
– charged pions of 10-200 GeV
– electrons of 6-150 GeV– muons of 120, 150 and 180 GeV
• ∼20,000 triggers per run
• Set-up with three front and
three rear HEC modules
– 3 –
Calor 2008 May 29, 2008
GEANT4 based simulations of the HEC testbeam
• Stand-alone code for HEC testbeam simulations
• Detailed description:
– calorimeter modules (sensitive LAr, copper plates, electrodes)
– cryostat and LAr excluder
– beam elements (scintillator counters, MWPCs)
• Studies for validation of GEANT4 physics:– different hadronic physics lists
– influence of the Birks’ law
– time structure of hadronic showers
• GEANT4 simulations:
– version 9.0, released in June 2007
– range cut = 30 µm
– 4 –
Calor 2008 May 29, 2008
Hadronic physics lists
• QGSP
– based on theory-driven models
– quark-gluon-string model for
interactions
– pre-equilibrium decay model for the
fragmentation
• QGSP-BERT
– Bertini cascade model for
particle-nuclear interactions
below ∼10 GeV
• QGSP-BERT-HP
– high precision data-driven modeling
for low energy neutrons
Birks’ law
• Saturation of response in LAr for
particles with large dE/dx
• Parametrization:
∆E′= ∆E
A
1 + cρ
∆E∆x
A = 1
c = 0.0045 g/(MeV cm2)
ρ = 1.396 g/cm3
– 5 –
Calor 2008 May 29, 2008
Time structure of hadronic showers
100 GeV charged pions (Birks’ law ON)
T [ns]0 20 40 60 80 100
T [ns]0 20 40 60 80 100
dE
/ d
T
[MeV
/ns]
-110
1
10
210
310
Visible energy VS TimeVisible energy VS Time
QGSP
QGSP-BERT
QGSP-BERT-HP
T [ns]0 20 40 60 80 100
T [ns]0 20 40 60 80 100
Cu
mu
lati
ve f
ract
ion
C
0
0.2
0.4
0.6
0.8
1
Cumulative Fraction CCumulative Fraction C
T [ns]0 20 40 60 80 100
T [ns]0 20 40 60 80 100
1 -
C
-210
-110
1
1 minus C1 minus C
• QGSP-BERT predicts slower showers than QGSP and QGSP-BERT-HP
• Late energy depositions (after a few tens of nanoseconds) are at the percent level
– 6 –
Calor 2008 May 29, 2008
Measurement of calorimeter signals
• Convolution of time profiles and
shaping functions
• Resulting amplitude — measured at
the position of the maximum of the
shaping function TMAX
• 51 types of HEC channels:
different shaping functions
• For the HEC testbeam:
50 < TMAX < 70 ns
• Measured signal — energy deposition
in a HEC channel integrated over a
few tens of nanoseconds
T [ns]0 200 400 600 800
T [ns]0 200 400 600 800
Sh
apin
g f
un
ctio
n
0
0.5
1
Shaping function for channel type 2Shaping function for channel type 2
• Two types of signal measurements are considered:
– after convolution with a shaping function– no time cut
– 7 –
Calor 2008 May 29, 2008
Simulation / Reconstruction / Analysis
• Simulated samples:– energy scans with negatively charged pions– energy scans with electrons
• 5000 events per beam particle type,
beam energy, physics list and Birks’
law switch
• Ratio of simulation times (for pions):– QGSP-BERT / QGSP = 1.7– QGSP-BERT-HP / QGSP = 4.9
• Energy reconstruction:– following experimental procedure– electromagnetic scale calibration
∗ defined by the sampling fraction∗ returns the total deposited energy for
electrons– cluster of the fix size (effective radius of
35-40 cm)
– Gaussian fit: E0 and σ– no electronic noise added to Monte Carlo
(MC) signals (spread of the noise wassubtracted from the resolution of the
experimental data)
• Analysed variables:– pion energy resolution σ/E0
– ratio e/π (ratio of energies in electronand pion clusters)
– fraction of energies in HEC longitudinallayers for charged pions
– 8 –
Calor 2008 May 29, 2008
Pion energy resolution
[GeV]BEAME0 50 100 150 200
[%
]0
/ E
σ
0
5
10
15
20
25 No time cutNo time cutQGSP-BERT-HP, Birks’ law ON
QGSP-BERT-HP, Birks’ law OFF
QGSP-BERT, Birks’ law ON
QGSP-BERT, Birks’ law OFF
QGSP, Birks’ law ON
QGSP, Birks’ law OFF
Exp
[GeV]BEAME0 50 100 150 200
[%
]0
/ E
σ0
5
10
15
20
25 After convolutionAfter convolution
Time cuts strongly influence the energy resolution
• QGSP-BERT: 10-30 % relative increase
• QGSP and QGSP-BERT-HP: relative increase by ∼5 %
– 9 –
Calor 2008 May 29, 2008
Pion energy resolution: Ratio to experiment
[GeV]BEAME0 50 100 150 200
[GeV]BEAME0 50 100 150 200
EX
P ) 0
/ E
σ /
( M
C ) 0
/ E
σ(
0.6
0.8
1
1.2
1.4
1.6No time cutNo time cut
QGSP-BERT-HP, Birks’ law ON
QGSP-BERT-HP, Birks’ law OFF
QGSP-BERT, Birks’ law ON
QGSP-BERT, Birks’ law OFF
QGSP, Birks’ law ON
QGSP, Birks’ law OFF
[GeV]BEAME0 50 100 150 200
[GeV]BEAME0 50 100 150 200
EX
P ) 0
/ E
σ /
( M
C ) 0
/ E
σ( 0.6
0.8
1
1.2
1.4
1.6After convolutionAfter convolution
QGSP describes well energy resolution below EBEAM ≃ 100 GeV.
– 10 –
Calor 2008 May 29, 2008
Pion energy resolution: Two-term parametrization
• σ/E0 = A/√
EBEAM ⊕ B
• Experimental values:
A = 69 ± 1 %√
GeV , B = 5.8± 0.1 %
• Simulation predictions:
Birks’ Physics After convolution
law list A[%√
GeV ] B [%]
QGSP 68.1 ± 0.8 6.2 ± 0.1OFF QGSP-BERT 57.1 ± 0.7 5.30 ± 0.09
QGSP-BERT-HP 60.2 ± 0.7 5.4 ± 0.1
QGSP 67.9 ± 0.8 6.9 ± 0.1ON QGSP-BERT 58.6 ± 0.7 5.83 ± 0.09
QGSP-BERT-HP 59.6 ± 0.7 6.13 ± 0.09
Birks’ law:• does not change the sampling term• increases the constant term
After convolution and with Birks’ lawswitched ON:• sampling term is described well by QGSP• constant term is predicted better by
QGSP-BERT and QGSP-BERT-HP
– 11 –
Calor 2008 May 29, 2008
Ratio e/π
[GeV]BEAME0 50 100 150
πe
/
1
1.1
1.2
1.3
1.4
1.5
1.6 No time cutNo time cutQGSP-BERT-HP, Birks’ law ON
QGSP-BERT-HP, Birks’ law OFF
QGSP-BERT, Birks’ law ON
QGSP-BERT, Birks’ law OFF
QGSP, Birks’ law ON
QGSP, Birks’ law OFF
Exp
[GeV]BEAME0 50 100 150
πe
/
1
1.1
1.2
1.3
1.4
1.5
1.6 After convolutionAfter convolution
Time cuts strongly influence e/π-ratio for QGSP-BERT: 4-8 % increase.
For QGSP and QGSP-BERT-HP increase is smaller: 1-2 %.
Ratio e/π is 2-3 % larger, when Birks’ law is switched ON for all physics lists.
– 12 –
Calor 2008 May 29, 2008
e/π: Ratio to experiment
[GeV]BEAME0 50 100 150
[GeV]BEAME0 50 100 150
EX
P )π
/ (
e /
MC
)π(
e /
0.8
0.9
1
1.1
1.2
1.3 No time cutNo time cutQGSP-BERT-HP, Birks’ law ON
QGSP-BERT-HP, Birks’ law OFF
QGSP-BERT, Birks’ law ON
QGSP-BERT, Birks’ law OFF
QGSP, Birks’ law ON
QGSP, Birks’ law OFF
[GeV]BEAME0 50 100 150
[GeV]BEAME0 50 100 150
EX
P )π
/ (
e /
MC
)π(
e /
0.8
0.9
1
1.1
1.2
1.3 After convolutionAfter convolution
After applying time cuts and with Birks’ law switched ON: all three physics lists describe e/π ratio well.
– 13 –
Calor 2008 May 29, 2008
Fraction of energy in HEC longitudinal layers
After convolution, Birks’ law ON
0 50 100 150 200
SU
M>
/ EL
AY
ER
F =
<E
0.1
0.2
0.3
0.4
0.5
0.6 Layer 1Layer 1
QGSP
QGSP-BERT
QGSP-BERT-HP
Exp
0 50 100 150 200
0.4
0.45
0.5
0.55
0.6 Layer 2Layer 2
0 50 100 150 200
0
0.05
0.1
0.15
0.2
0.25 Layer 3Layer 3
[GeV]BEAME0 50 100 150 200
0
0.02
0.04
0.06
Layer 4Layer 4
Four HEC longitudinal layers: 8/16/8/8 LAr gaps, 1.5/2.9/3.0/2.8 λ
F =< ELAY ER > /ESUM , where ESUM = Σ < ELAY ER >
– 14 –
Calor 2008 May 29, 2008
Fraction of energy in HEC longitudinal layers: Ratio to experiment
After convolution, Birks’ law ON
0 50 100 150 2000 50 100 150 200
EX
P /
F M
CF
0.7
0.8
0.9
1
1.1
1.2
1.3 Layer 1Layer 1
0 50 100 150 2000 50 100 150 200
0.7
0.8
0.9
1
1.1
1.2
1.3 Layer 2Layer 2
0 50 100 150 2000 50 100 150 200
0.8
1
1.2
1.4
1.6
1.8
2 Layer 3Layer 3
[GeV]BEAME0 50 100 150 200
[GeV]BEAME0 50 100 150 200
0
1
2
3
4 Layer 4Layer 4
QGSP
QGSP-BERT
QGSP-BERT-HP
• Fraction of energy in the second (main) layer is described within a few percent by all physics lists
• QGSP: hadronic showers start earlier and are more compact
• QGSP-BERT and QGSP-BERT-HP: good description of shower profiles (except lowest beam energy)
• Only small differences between “No time cut” and “After convolution” measurements
• No dependence on Birks’ law switch
– 15 –
Calor 2008 May 29, 2008
Conclusions
GEANT4 based simulations of the HEC testbeam were caried out with different physics lists, namely:
QGSP, QGSP-BERT and QGSP-BERT-HP. Influence of the Birks’ law and time cuts on the calorimeterperformance parameters was investigated. Comparison with experimental results, obtained during beam
tests of HEC modules, was done.
• Usage of the Birks’ law increases the e/π-ratio and the constant term of the energy resolution forcharged pions
• QGSP-BERT physics list predicts much slower hadronic showers than QGSP and QGSP-BERT-HP
• Applying of time cuts (following the experimental procedure of signal measurements in calorimetercells) has influence on the energy resolution and response for charged pions
• After applying time cuts and with Birks’ law switched ON: the better description of studied experi-mental parameters, in total, is given by QGSP-BERT and QGSP-BERT-HP
– good description of longitudinal profiles of hadronic showers
– agreement in the e/π-ratio– rather close predictions of the resolution at high beam energies (i.e. of the constant term)
• Questions addressed to GEANT4 experts:
– better description of the sampling term of the energy resolution for charged pions for BERT-basedphysics lists
– decrease of the simulation time for QGSP-BERT-HP or/and improvement of the neutron physics inQGSP-BERT
– 16 –