Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 1Slide 1

Andrea Dell’AcquaCERN EP/SFT

dellacqu@mail.cern.ch

Andrea Dell’AcquaCERN EP/SFT

dellacqu@mail.cern.ch

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

On behalf of the ATLAS Geant4 Validation Team

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 2Slide 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

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 3Slide 3

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

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

Electromagnetic processes in tracking detectors Electromagnetic processes in tracking detectors and shower simulations in calorimetersand 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 the Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectorsATLAS calorimeters and muon detectors

Electromagnetic processes in tracking detectors Electromagnetic processes in tracking detectors and shower simulations in calorimetersand shower simulations in calorimeters

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

ConclusionsConclusions

This Talk:This Talk:

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 4Slide 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 references 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 respects;

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 references 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 respects;

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 5Slide 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…);

Work as much as possible in a common simulation Work as much as possible in a common simulation framework framework

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…);

Work as much as possible in a common simulation Work as much as possible in a common simulation framework framework

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 6Slide 6

Geant4 Setups (1)Geant4 Setups (1) Muon Detector TestbeamMuon 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 DetectorHadronic Interaction in Silicon Pixel Detector

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 7Slide 7

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

10 GeV Electron Shower10 GeV Electron Shower

Forward Calorimeter (FCal) Testbeam Setup

Forward Calorimeter (FCal) Testbeam Setup

FCal1 Module 0FCal1 Module 0

FCal2 Module 0FCal2 Module 0

ExcluderExcluder

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 8Slide 8

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);

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 9Slide 9

Secondaries Production by MuonsSecondaries Production by MuonsMuon 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 or between the chambers;

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

• 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;

agreement at the

level of <1%

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 10Slide 10

Silicon Detectors – ionisation and PAI model

Standard ionisation model compared to PAI model for 100 GeV pions crossing a Pixel detector module (280 m thick silicon):

• distribution around peak identical

• PAI model does not link properly to -ray production

• more important is the correct spatial distribution of ionisation energy loss: range cut should match detector resolution (<10 m for Pixels)

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 11Slide 11

Deposited energy (keV)

20 GeV electrons

20 GeV pions

300 GeV muons

Transition Radiation Tracker• Very good agreement with data (and G3) for pions and

muons • Several models tried for describing transition radiation

with moderate success Currently “on-hold” in favour of a home-grown TR model as

the G4 one turns out to be too demanding in terms of geometry and tracking

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 12Slide 12

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-linearities 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 reso- lution 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-linearities 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 reso- lution function ~5% in G4, ~ 4% in data and G3;

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 41.%GeV1/2 G4, 38.6%GeV1/2 data; high energy limit very comparable;

TileCal: stochastic term 41.%GeV1/2 G4, 38.6%GeV1/2 data; high energy limit very comparable;

TileCal Electron Energy ResolutionTileCal Electron Energy Resolution

EMB Electron Energy Resolution

EMB Electron Energy Resolution

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 13Slide 13

Electron Shower Shapes & Composition (1)

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 20

0

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

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 14Slide 14

Geant4 Hadronic Signals in ATLAS Calorimeters

Geant4 Hadronic Signals in ATLAS CalorimetersCalorimeter pion response:Calorimeter pion response:

Rather difficult start, with inadequate models (“GHEISHA++”) and “mix-and-match” problems (transition from low energy to high energy charged pion models) fixes suggested by H.P. Wellisch (LHEP, new energy thresholds in model transition + code changes) and new models (QGS) improved the situation dramatically

Calorimeter pion response:Calorimeter pion response:Rather difficult start, with inadequate models (“GHEISHA++”) and “mix-and-match” problems (transition from low energy to high energy charged pion models) fixes suggested by H.P. Wellisch (LHEP, new energy thresholds in model transition + code changes) and new models (QGS) improved the situation dramatically

Quantitative agreements between data and G4 for most of the observables, with QGS models which seem to provide the better answer

finally going in the right direction!

Still a few problems and open questions, that will require further investigation (in particular shower shape and pion energy deposition)

TileCalPion non-linearity

HEC Pions

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 15Slide 15

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;

All recent simulations show definite improvements as far as QGSP is concerned (and wrt Geant3)

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;

All recent simulations show definite improvements as far as QGSP is concerned (and wrt Geant3)

HEC Pion Energy Resolution

TileCal Pion Energy Resolution

stoch. constData 68.89 5.82

QGSP 70.26 6.00

G3 64.44 4.70

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 16Slide 16

Pion longitudinal shower Pion longitudinal shower profiles:profiles:

measured by energy sharing in four depth segments of HEC; all available Geant4 models studied;

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

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 Pion longitudinal shower profiles:profiles:

measured by energy sharing in four depth segments of HEC; all available Geant4 models studied;

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

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)

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 17Slide 17

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

remaining discrepancies, especially for hadrons, are remaining discrepancies, especially for hadrons, are addressed and progress is continuous and measurable;addressed and progress is continuous and measurable;

ATLAS can has a huge amount of the right testbeam data for ATLAS can has a huge amount of the right 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 is definitely becoming a mature and useful product Geant4 is definitely becoming a mature and useful product for larga scale detector response simulation!for larga scale detector response simulation!

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

remaining discrepancies, especially for hadrons, are remaining discrepancies, especially for hadrons, are addressed and progress is continuous and measurable;addressed and progress is continuous and measurable;

ATLAS can has a huge amount of the right testbeam data for ATLAS can has a huge amount of the right 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 is definitely becoming a mature and useful product Geant4 is definitely becoming a mature and useful product for larga scale detector response simulation!for larga scale detector response simulation!

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 18Slide 18

Geant4 Electron Signal Range Cut Dependence

Geant4 Electron Signal Range Cut Dependencemaximum 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 10-1

5

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

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 19Slide 19

Electron Shower Shapes & Composition (2)

Electron Shower Shapes & Composition (2)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 simu- lations 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 simu- lations 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

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 20Slide 20

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

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 21Slide 21

Individual Hadronic Interactions: Energy Release

Individual Hadronic Interactions: Energy ReleaseInteraction 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)

Andrea Dell’Acqua

CERN EP/SFT

Andrea Dell’Acqua

CERN EP/SFT

Status of the GEANT4 Physics Evaluation in ATLAS Slide 22Slide 22

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 well with both models (within 2-3%), with a slight 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 well with both models (within 2-3%), with a slight preference for PM;

PM QGS Experiment