status of the geant4 physics evaluation in atlas

Slide 1

Peter LochUniversity of Arizona

Tucson, Arizona 85721

Status of the GEANT4 Physics Evaluation in ATLASGeant4 WorkshopGeant4 Workshop

September 30, September 30, 20022002



Status of the Geant4 Physics Evaluation in Status of the Geant4 Physics Evaluation in ATLASATLAS

Status of the Geant4 Physics Evaluation in Status of the Geant4 Physics Evaluation in ATLASATLAS

With contributions from D. Barberis1, K. Kordas2, A. Kiryunin2, R. Mazini2, B. Osculati1, G. Parrour2, A. Rimoldi3, P. Strizenec2, V. Tsulaia4, M.J. Varanda4 et al.

1 – ATLAS Inner Detector/Pixels2 – ATLAS Liquid Argon Calorimeters3 – ATLAS Muon System4 – ATLAS Tile Calorimeter

Slide 2





Solenoid Forward Calorimeters (e)

Muon Detectors (μ)Electromagnetic Calorimeters (μ,e)

EndCap Toroid

Barrel Toroid Inner Detector (e,μ,π)Hadronic Calorimeters (e,μ,π) Shielding

EMB (LAr/Pb,Barrel)& EMEC (LAr/Pb,EndCap)

FCal (LAr/Cu/W)

HEC (LAr/Cu,EndCap) & TileCal (Scint/Fe,Barrel/Extended)

ATLAS: ATLAS: A Multi-Pur-A Multi-Pur-pose LHC pose LHC DetectorDetector

ATLAS: ATLAS: A Multi-Pur-A Multi-Pur-pose LHC pose LHC DetectorDetector

Slide 3





Strategies for G4 physics validation in ATLASStrategies for G4 physics validation in ATLAS

Muon energy loss and secondaries production in Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectorsthe ATLAS calorimeters and muon detectors

Electromagnetic shower simulations in calorimetersElectromagnetic shower simulations in calorimeters

Hadronic interactions in tracking devices and Hadronic interactions in tracking devices and calorimeterscalorimeters

ConclusionsConclusions

Strategies for G4 physics validation in ATLASStrategies for G4 physics validation in ATLAS

Muon energy loss and secondaries production in Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectorsthe ATLAS calorimeters and muon detectors

Electromagnetic shower simulations in calorimetersElectromagnetic shower simulations in calorimeters

Hadronic interactions in tracking devices and Hadronic interactions in tracking devices and calorimeterscalorimeters

ConclusionsConclusions

This Talk:This Talk:

Slide 4





Strategies for G4 Physics Validation in ATLAS

Strategies for G4 Physics Validation in ATLAS

Geant4 physics benchmarking: Geant4 physics benchmarking: compare features of interaction models with similar features in the old

Geant3.21 baseline (includes variables not accessible in the experiment); try to understand differences in applied models, like the effect of cuts

on simulation parameters in the different variable space (range cut vs energy threshold…);

Validation: Validation: use available experimental reference data from testbeams for various

sub-detectors and particle types to determine prediction power of models in Geant4 (and Geant3);

use different sensitivities of sub-detectors (energy loss, track multiplici-ties, shower shapes…) to estimate Geant4 performance;

tune Geant4 models (“physics lists”) and parameters (range cut) for optimal representation of the experimental detector signal with ALL relevant aspects;

Geant4 physics benchmarking: Geant4 physics benchmarking: compare features of interaction models with similar features in the old

Geant3.21 baseline (includes variables not accessible in the experiment); try to understand differences in applied models, like the effect of cuts

on simulation parameters in the different variable space (range cut vs energy threshold…);

Validation: Validation: use available experimental reference data from testbeams for various

sub-detectors and particle types to determine prediction power of models in Geant4 (and Geant3);

use different sensitivities of sub-detectors (energy loss, track multiplici-ties, shower shapes…) to estimate Geant4 performance;

tune Geant4 models (“physics lists”) and parameters (range cut) for optimal representation of the experimental detector signal with ALL relevant aspects;

Slide 5





G4 Validation Strategies: Some Requirements…

G4 Validation Strategies: Some Requirements… Geometry description: Geometry description:

has to be as close as possible to the testbeam setup (active detectors

and relevant parts of the environment, like inactive materials in beams); identical in Geant3 and Geant4;

often common (simple) database used (muon detectors, calorimeters) to describe (testbeam) detectors in Geant3 and Geant4:

Environment in the experiment: Environment in the experiment: particles in simulations are generated following beam profiles (muon

detectors, calorimeters) and momentum spectra in testbeam (muon system);

features of electronic readout which can not be unfolded from experimental signal are modeled to best knowledge in simulation (incoherent and coherent electronic noise, digitization effect on signal…);

Geometry description: Geometry description: has to be as close as possible to the testbeam setup (active detectors

and relevant parts of the environment, like inactive materials in beams); identical in Geant3 and Geant4;

often common (simple) database used (muon detectors, calorimeters) to describe (testbeam) detectors in Geant3 and Geant4:

Environment in the experiment: Environment in the experiment: particles in simulations are generated following beam profiles (muon

detectors, calorimeters) and momentum spectra in testbeam (muon system);

features of electronic readout which can not be unfolded from experimental signal are modeled to best knowledge in simulation (incoherent and coherent electronic noise, digitization effect on signal…);

example: forward calorimeter uses actual machining and cabling database in simulations to describe electrode dimensions, locations and readout channel mapping;

example: forward calorimeter uses actual machining and cabling database in simulations to describe electrode dimensions, locations and readout channel mapping;

Slide 6





Geant4 Setups (1)Geant4 Setups (1) Muon Detector Testbeam Muon Detector Testbeam

Detector plasticCover (3mm thick) Silicon sensor (280 μm thick)

FE chip (150 μm thick)PCB (1 mm thick)

Hadronic Interaction in Silicon Pixel Detector Hadronic Interaction in Silicon Pixel Detector

Slide 7





Geant4 Setups (2)Geant4 Setups (2) Electromagnetic Barrel Accordion Calorimeter

Electromagnetic Barrel Accordion Calorimeter

10 GeV Electron Shower 10 GeV Electron Shower

Forward Calorimeter (FCal) Testbeam Setup

Forward Calorimeter (FCal) Testbeam Setup

FCal1 Module 0FCal1 Module 0

FCal2 Module 0FCal2 Module 0

ExcluderExcluder

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Muon Energy LossMuon Energy Loss

Reconstructed Energy [GeV]

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0

-3.5

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

Reconstructed Energy [GeV]Δ

events

/0.1

GeV

[%

]Fra

ctio

n e

vents

/0.1

GeV

10-4

10-3

10-2

10-1

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Eμ= 100 GeV, ημ ≈ 0.975

Electromagnetic Barrel Calorimeter EMB (Liquid Argon/Lead Accordion)

Electromagnetic Barrel Calorimeter EMB (Liquid Argon/Lead Accordion)

-100 1000 200 300 400 5000

600

100

200

300

400

500

700

800

Calorimeter Signal [nA]

Events

/10

nA

180 GeV μ

180 GeV μ

Hadronic EndCap Calorimeter (HEC) (Liquid Argon/Copper Parallel Plate)

Hadronic EndCap Calorimeter (HEC) (Liquid Argon/Copper Parallel Plate)

G4 simulations (+ electronic noise) describe testbeam signals well, also in Tile Calorimeter (iron/scintillator technology, TileCal);

some range cut dependence of G4 signal due to contribution from electromagnetic halo (δ-electrons);

G4 simulations (+ electronic noise) describe testbeam signals well, also in Tile Calorimeter (iron/scintillator technology, TileCal);

some range cut dependence of G4 signal due to contribution from electromagnetic halo (δ-electrons);

Slide 9





Secondaries Production by MuonsSecondaries Production by Muons

Muon Detector: Muon Detector: Muon Detector: Muon Detector:

extra hits produced in dedicated testbeam setup with Al and Fe targets (10, 20 and 30 cm deep), about ~37 cm from first chamber;

probability for extra hits measured in data at various muon energies (20-300 GeV);

Geant4 can reproduce the distance of the extra hit to the muon track quite well;

extra hit probability can be reproduced between 3 – 10% for Fe, some larger discrepancies (35%) remain for Al (preliminary analysis);

subject is still under study (more news expected in mid-October);

extra hits produced in dedicated testbeam setup with Al and Fe targets (10, 20 and 30 cm deep), about ~37 cm from first chamber;

probability for extra hits measured in data at various muon energies (20-300 GeV);

Geant4 can reproduce the distance of the extra hit to the muon track quite well;

extra hit probability can be reproduced between 3 – 10% for Fe, some larger discrepancies (35%) remain for Al (preliminary analysis);

subject is still under study (more news expected in mid-October);

Slide 10





Geant4 Electron Response in ATLAS Calorimetry

Geant4 Electron Response in ATLAS Calorimetry

Overall signal characteristics:Overall signal characteristics:

Geant4 reproduces the average electron signal as function of the incident energy in all ATLAS calorimeters very well (testbeam setup or analysis induced non-line- arities typically within ±1%)…

…but average signal can be smaller than in G3 and data (1-3% for 20- 700 μm range cut in HEC);

signal fluctuations in EMB very well simulated;

electromagnetic FCal: high energy limit of resolution function ~5% in G4, ~ 4% in data and G3;

Overall signal characteristics:Overall signal characteristics:

Geant4 reproduces the average electron signal as function of the incident energy in all ATLAS calorimeters very well (testbeam setup or analysis induced non-line- arities typically within ±1%)…

…but average signal can be smaller than in G3 and data (1-3% for 20- 700 μm range cut in HEC);

signal fluctuations in EMB very well simulated;

electromagnetic FCal: high energy limit of resolution function ~5% in G4, ~ 4% in data and G3;

0 1 2 4 53

0

-2

-4

-6

2

0

-2

-4

-6

2

ΔE

rec M

C-D

ata

[%

]

noiseNoise Cut Level σ

GEANT4

GEANT4

GEANT3

GEANT3

stochastic term

%× GeV

9.2 9.40.3 0.40.2 0.5 9 9.6

data data

GEANT3GEANT3

GEANT4GEANT4

high energy limit %

TileCal: stochastic term 22%GeV1/2 G4/G3, 26%GeV1/2 data; high energy limit very comparable;

TileCal: stochastic term 22%GeV1/2 G4/G3, 26%GeV1/2 data; high energy limit very comparable;

FCal Electron ResponseFCal Electron Response

EMB Electron Energy Resolution

EMB Electron Energy Resolution

Slide 11





Geant4 Electron Signal Range Cut Dependence

Geant4 Electron Signal Range Cut Dependence maximum signal in HEC and FCal found at 20 μm – unexpected signal drop

for lower range cuts;

HEC and FCal have very different readout geometries (parallel plate, tubular gap) and sampling characteristics, but identical absorber (Cu) and active (LAr) materials;

effect under discussion with Geant4 team (M. Maire et al.), but no solution yet (??);

maximum signal in HEC and FCal found at 20 μm – unexpected signal drop for lower range cuts;

HEC and FCal have very different readout geometries (parallel plate, tubular gap) and sampling characteristics, but identical absorber (Cu) and active (LAr) materials;

effect under discussion with Geant4 team (M. Maire et al.), but no solution yet (??);

10-3 10-2 10-15

6

7

59

60

61

1.5

1.6

GEANT4 range cut [mm]

Sam

plin

g

Frac.

[%

]E

dep [

GeV

] σ

/E [

%]

10-2 10-1 1 10

4.1

4.2

4.3

1.9

2

2.1

GEANT4 range cut [mm]

σ/E

[%

]E

vis [G

eV

]

FCal 60 GeV ElectronsFCal 60 GeV Electrons HEC 100 GeV ElectronsHEC 100 GeV Electrons

20 μm 20 μm

Geant3 Geant3

Slide 12





Electron Shower Shapes & Composition (1)


Shower shape analysis:Shower shape analysis:

Geant4 electromagnetic showers in the EMB are more compact longitudinally than in G3: about 3-13% less signal in the first 4.3X0, but 1.5-2.5% more signal in the following 16X0, and 5-15% less signal (large fluctuations) in the final 2X0 for 20-245 GeV electrons;

Geant4 electron shower in TileCal starts earlier and is slightly narrower than in G3:

Shower shape analysis:Shower shape analysis:

Geant4 electromagnetic showers in the EMB are more compact longitudinally than in G3: about 3-13% less signal in the first 4.3X0, but 1.5-2.5% more signal in the following 16X0, and 5-15% less signal (large fluctuations) in the final 2X0 for 20-245 GeV electrons;

Geant4 electron shower in TileCal starts earlier and is slightly narrower than in G3:

0 1 2 3-1-2-30

0.1

0.2

0.3

0.4

0.5

0.6

dE/E

per

RM

Distance from shower axis [RM = 2.11cm]0 2.5 5 7.5 10 12.5 15 17.5 200

0.02

0.04

0.06

0.08

0.1

0.12

Shower depth [X0 = 2.25cm]

dE/E

per

X0 TileCal 100 GeV ElectronsTileCal 100 GeV Electrons TileCal 100 GeV ElectronsTileCal 100 GeV Electrons

Slide 13







Shower composition:Shower composition:

cell signal significance spectrum is the distribution of the signal-to-noise ratio in all individual channels for all electrons of a given impact energy;

to measure this spectrum for simulations requires modeling of noise in each channel in all simulated events (here: overlay experimental “empty” noise events on top of Geant4 events)

spectrum shows higher end point for data than for Geant4 and Geant3, indicating that larger (more significant) cell signals occur more often in the experiment -> denser showers on average;

Shower composition:Shower composition:

cell signal significance spectrum is the distribution of the signal-to-noise ratio in all individual channels for all electrons of a given impact energy;

to measure this spectrum for simulations requires modeling of noise in each channel in all simulated events (here: overlay experimental “empty” noise events on top of Geant4 events)

spectrum shows higher end point for data than for Geant4 and Geant3, indicating that larger (more significant) cell signals occur more often in the experiment -> denser showers on average;

10-1

10-4

10-3

10-2

10-5

10-6R

el. e

ntr

ies electronic

noiseelectronic

noise

shower signalsshower signals

0 50 100 150 200 250 300

noiseCell Signal Signifi cance Γ σ

FCal 60 GeV Electrons

excess in experimentexcess in

experiment

Slide 14





Individual Hadronic InteractionsIndividual Hadronic Interactions

Inelastic interaction properties:Inelastic interaction properties:

energy from nuclear break-up in the course of a hadronic inelastic interactions causes large signals in the silicon pixel detector in ATLAS, if a pixel (small, 50 μm x 400 μm), is directly hit;

this gives access to tests of single hadronic interaction modeling, especially concerning the nuclear part;

testbeam setup of pixel detectors supports the study of these interactions;

presently two models in Geant4 studied: the parametric “GHEISHA”-type model (PM) and the quark-gluon string model (QGS, H.P. Wellisch);

Inelastic interaction properties:Inelastic interaction properties:

energy from nuclear break-up in the course of a hadronic inelastic interactions causes large signals in the silicon pixel detector in ATLAS, if a pixel (small, 50 μm x 400 μm), is directly hit;

this gives access to tests of single hadronic interaction modeling, especially concerning the nuclear part;

testbeam setup of pixel detectors supports the study of these interactions;

presently two models in Geant4 studied: the parametric “GHEISHA”-type model (PM) and the quark-gluon string model (QGS, H.P. Wellisch);

Special interaction trigger

~3000 sensitive pixels

Slide 15





Individual Hadronic Interactions: Energy Release

Individual Hadronic Interactions: Energy Release

Interaction cluster:Interaction cluster:

differences in shape and average (~5% too small for PM, ~7% too small for QGS) of released energy distribution for 180 GeV pions in interaction clusters;

fraction of maximum single pixel release and total cluster energy release not very well reproduced by PM (shape, average ~26% too small);

QGS does better job on average (identical to data) for this variable, but still shape not completely reproduced yet (energy sharing between pixels in cluster);

Interaction cluster:Interaction cluster:

differences in shape and average (~5% too small for PM, ~7% too small for QGS) of released energy distribution for 180 GeV pions in interaction clusters;

fraction of maximum single pixel release and total cluster energy release not very well reproduced by PM (shape, average ~26% too small);

QGS does better job on average (identical to data) for this variable, but still shape not completely reproduced yet (energy sharing between pixels in cluster);

PM QGS Experiment

PM QGS Experiment

log(energy equivalent # of electrons)

Slide 16





More on Individual Hadronic InteractionsMore on Individual Hadronic Interactions

Spread of energy:Spread of energy:

other variables tested with pixel detector: cluster width, longest distance between hit pixel and cluster barycenter -> no clear preference for one of the chosen models at this time (most problems with shapes of distributions);

Charged track multiplicity:Charged track multiplicity:

average charged track multiplicity in in-elastic hadronic interaction described wellwith both models (within 2-3%), with aslight preference for PM;

Spread of energy:Spread of energy:

other variables tested with pixel detector: cluster width, longest distance between hit pixel and cluster barycenter -> no clear preference for one of the chosen models at this time (most problems with shapes of distributions);

Charged track multiplicity:Charged track multiplicity:

average charged track multiplicity in in-elastic hadronic interaction described wellwith both models (within 2-3%), with aslight preference for PM;

PM QGS Experiment

Slide 17





Geant4 Hadronic Signals in ATLAS Calorimeters

Geant4 Hadronic Signals in ATLAS Calorimeters

Calorimeter pion response:Calorimeter pion response:

after discovery of “mix-and-match” problem (transition from low energy to high energy char-ged pion models) in the deposited energy from energy loss of charged particles in pion showers in the HEC (G4 4.0, early 2002): fixes suggested by H.P. Wellisch (LHEP, new energy thresholds in model transition + code changes) and QGS model tested;

e/π signal ration in HEC and TileCal still not well reproduced by Geant4 QGS or LHEP - but better than with GCalor in Geant3.21;

energy dependence in HEC in QGS smoother, “discontinuities” between ~20 GeV and ~80 GeV gone;

Calorimeter pion response:Calorimeter pion response:

after discovery of “mix-and-match” problem (transition from low energy to high energy char-ged pion models) in the deposited energy from energy loss of charged particles in pion showers in the HEC (G4 4.0, early 2002): fixes suggested by H.P. Wellisch (LHEP, new energy thresholds in model transition + code changes) and QGS model tested;

e/π signal ration in HEC and TileCal still not well reproduced by Geant4 QGS or LHEP - but better than with GCalor in Geant3.21;

energy dependence in HEC in QGS smoother, “discontinuities” between ~20 GeV and ~80 GeV gone;

HEC Pions

QGS

LHEP

e/π

sig

nal ra

tio

e/π

sig

nal ra

tio

Pion energy [GeV]

Slide 18





Geant4 Hadronic Signal Characteristics (1)Geant4 Hadronic Signal Characteristics (1)

Pion energy resolution:Pion energy resolution:

good description of experimental pion energy resolution by QGS in TileCal; LHEP cannot describe stochastic term, but fits correct high energy limit;

larger discrepancies in HEC: stochastic term significantly too large for QGS and LHEP, but reasonable description of high energy behaviour by QGS;

Pion energy resolution:Pion energy resolution:

good description of experimental pion energy resolution by QGS in TileCal; LHEP cannot describe stochastic term, but fits correct high energy limit;

larger discrepancies in HEC: stochastic term significantly too large for QGS and LHEP, but reasonable description of high energy behaviour by QGS;

QGS

G

p

G3

ex

4σ = 75.79±1.10 % GeV 5.53±0

σ = 64.44±1.03 % GeV 4.70±0.16 %E

σ = 68.89±1.46 % GeV 5.82±0.14 %E

.17 %E

HEC Pion Energy Resolution

TileCal Pion Energy Resolution

Pion energy [GeV]

rela

tive e

nerg

y r

eso

luti

on

[%

]

Exp

GCalor

Slide 19





Pion longitudinal shower profiles:Pion longitudinal shower profiles:

measured by energy sharing in four depth segments of HEC; both Geant4 models (LHEP and QGS) studied;

rather poor description of experimental energy sharing by QGS; pion showers start too early;

LHEP describes longitudinal energy sharing in the experiment quite well for pions in the the studied energy range 20-200 GeV (at the same level as GCalor in Geant3.21);

Pion longitudinal shower profiles:Pion longitudinal shower profiles:

measured by energy sharing in four depth segments of HEC; both Geant4 models (LHEP and QGS) studied;

rather poor description of experimental energy sharing by QGS; pion showers start too early;

LHEP describes longitudinal energy sharing in the experiment quite well for pions in the the studied energy range 20-200 GeV (at the same level as GCalor in Geant3.21);

Geant4 Hadronic Signal Characteristics (2)Geant4 Hadronic Signal Characteristics (2)

Slide 20





Conclusions (1):Conclusions (1):

Geant4 can simulate relevant features of muon, electron and Geant4 can simulate relevant features of muon, electron and pion signals in various ATLAS detectors, often better than pion signals in various ATLAS detectors, often better than Geant3;Geant3;

remaining discrepancies, especially for hadrons, are remaining discrepancies, especially for hadrons, are addressed and progress can be expected in the near future;addressed and progress can be expected in the near future;

ATLAS has a huge amount of appropriate testbeam data for ATLAS has a huge amount of appropriate testbeam data for the calorimeters, inner detector modules, and the muon the calorimeters, inner detector modules, and the muon detectors to evaluate the Geant4 physics models in detail;detectors to evaluate the Geant4 physics models in detail;

feedback loops to Geant4 team are for most systems feedback loops to Geant4 team are for most systems established since quite some time; communication is not a established since quite some time; communication is not a problem;problem;

Geant4 can simulate relevant features of muon, electron and Geant4 can simulate relevant features of muon, electron and pion signals in various ATLAS detectors, often better than pion signals in various ATLAS detectors, often better than Geant3;Geant3;

remaining discrepancies, especially for hadrons, are remaining discrepancies, especially for hadrons, are addressed and progress can be expected in the near future;addressed and progress can be expected in the near future;

ATLAS has a huge amount of appropriate testbeam data for ATLAS has a huge amount of appropriate testbeam data for the calorimeters, inner detector modules, and the muon the calorimeters, inner detector modules, and the muon detectors to evaluate the Geant4 physics models in detail;detectors to evaluate the Geant4 physics models in detail;

feedback loops to Geant4 team are for most systems feedback loops to Geant4 team are for most systems established since quite some time; communication is not a established since quite some time; communication is not a problem;problem;

Slide 21





lack of man power in all ATLAS systems makes it hard to lack of man power in all ATLAS systems makes it hard to follow up on Geant4 progress; hard to catch up with G4 follow up on Geant4 progress; hard to catch up with G4 evolution! Need to look into more automated benchmark tests ??evolution! Need to look into more automated benchmark tests ??

Geant4 is definitively a mature and useful product for large Geant4 is definitively a mature and useful product for large scale detector response simulations!scale detector response simulations!

lack of man power in all ATLAS systems makes it hard to lack of man power in all ATLAS systems makes it hard to follow up on Geant4 progress; hard to catch up with G4 follow up on Geant4 progress; hard to catch up with G4 evolution! Need to look into more automated benchmark tests ??evolution! Need to look into more automated benchmark tests ??

Geant4 is definitively a mature and useful product for large Geant4 is definitively a mature and useful product for large scale detector response simulations!scale detector response simulations!

Conclusions (2):Conclusions (2):

status of the geant4 physics evaluation in atlas

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