1. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 1 Peter Loch University of Arizona Tucson, Arizona 85721 Peter Loch University of Arizona Peter Loch University of Arizona Status of the Geant4 Physics Evaluation in ATLAS With contributions from D. Barberis 1, K. Kordas 2, A. Kiryunin 2, R. Mazini 2, B. Osculati 1, G. Parrour 2, A. Rimoldi 3, P. Strizenec 2, V. Tsulaia 4, M.J. Varanda 4 et al. 1 – ATLAS Inner Detector/Pixels 2 – ATLAS Liquid Argon Calorimeters 3 – ATLAS Muon System 4 – ATLAS Tile Calorimeter

2. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 2 Peter Loch University of Arizona Tucson, Arizona 85721 Solenoid Forward Calorimeters (e) Muon Detectors (μ)Electromagnetic Calorimeters (μ,e) EndCap Toroid Barrel ToroidInner 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- pose LHC Detector ATLAS: ATLAS: A Multi-Pur- pose LHC Detector

3. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 3 Peter Loch University of Arizona Tucson, Arizona 85721 Strategies for G4 physics validation in ATLAS Strategies for G4 physics validation in ATLAS Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectors Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectors Electromagnetic shower simulations in calorimeters Electromagnetic shower simulations in calorimeters Hadronic interactions in tracking devices and calorimeters Hadronic interactions in tracking devices and calorimeters Conclusions Conclusions Strategies for G4 physics validation in ATLAS Strategies for G4 physics validation in ATLAS Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectors Muon energy loss and secondaries production in the ATLAS calorimeters and muon detectors Electromagnetic shower simulations in calorimeters Electromagnetic shower simulations in calorimeters Hadronic interactions in tracking devices and calorimeters Hadronic interactions in tracking devices and calorimeters Conclusions Conclusions This Talk:

4. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 4 Peter Loch University of Arizona Tucson, Arizona 85721 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;

5. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 5 Peter Loch University of Arizona Tucson, Arizona 85721 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;

6. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 6 Peter Loch University of Arizona Tucson, Arizona 85721 Geant4 Setups (1) Muon Detector Testbeam Detector plastic Cover (3mm thick) Silicon sensor (280 μm thick) FE chip (150 μm thick) PCB (1 mm thick) Hadronic Interaction in Silicon Pixel Detector

7. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 7 Peter Loch University of Arizona Tucson, Arizona 85721 Geant4 Setups (2) Electromagnetic Barrel Accordion Calorimeter 10 GeV Electron Shower Forward Calorimeter (FCal) Testbeam Setup Forward Calorimeter (FCal) Testbeam Setup FCal1 Module 0 FCal2 Module 0 Excluder

8. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 8 Peter Loch University of Arizona Tucson, Arizona 85721 Muon Energy Loss Reconstructed Energy [GeV] 0.10.20.30.40.50.60.70.80.91 0 -3.5 -3.0 -2.5 -2.0 -1.5 -0.5 Reconstructed Energy [GeV] Δ events/0.1 GeV [%] Fraction events/0.1 GeV 10 -4 10 -3 10 -2 10 -1 0.10.20.30.40.50.60.70.80.91 E μ = 100 GeV, η μ ≈ 0.975 Electromagnetic Barrel Calorimeter EMB (Liquid Argon/Lead Accordion) Electromagnetic Barrel Calorimeter EMB (Liquid Argon/Lead Accordion) -1001000200300 400 500 0 600 100 200 300 400 500 700 800 Calorimeter Signal [nA] Events/10 nA 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);

9. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 9 Peter Loch University of Arizona Tucson, Arizona 85721 Secondaries Production by Muons 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);

10. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 10 Peter Loch University of Arizona Tucson, Arizona 85721 Geant4 Electron Response in ATLAS Calorimetry Overall signal characteristics: Overall signal characteristics: Geant4 reproduces the average electron signal as func- tion 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 reso- lution function ~5% in G4, ~ 4% in data and G3; Overall signal characteristics: Overall signal characteristics: Geant4 reproduces the average electron signal as func- tion 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 reso- lution function ~5% in G4, ~ 4% in data and G3; 012453 0 -2 -4 -6 2 0 -2 -4 -6 2 ΔE rec MC-Data [%] GEANT4 GEANT3 9.29.40.30.40.20.599.6 data GEANT3 GEANT4 TileCal: stochastic term 22%GeV 1/2 G4/G3, 26%GeV 1/2 data; high energy limit very comparable; TileCal: stochastic term 22%GeV 1/2 G4/G3, 26%GeV 1/2 data; high energy limit very comparable; FCal Electron Response EMB Electron Energy Resolution

11. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 11 Peter Loch University of Arizona Tucson, Arizona 85721 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 -1 5 6 7 59 60 61 1.5 1.6 GEANT4 range cut [mm] Sampling Frac. [%] E dep [GeV] σ/E [%] 10 -2 10 -1 110 4.1 4.2 4.3 1.9 2 2.1 GEANT4 range cut [mm] σ/E [%] E vis [GeV] FCal 60 GeV Electrons HEC 100 GeV Electrons 20 μm Geant3

12. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 12 Peter Loch University of Arizona Tucson, Arizona 85721 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 4.3X 0, but 1.5-2.5% more signal in the following 16X 0, and 5-15% less signal (large fluctuations) in the final 2X 0 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 4.3X 0, but 1.5-2.5% more signal in the following 16X 0, and 5-15% less signal (large fluctuations) in the final 2X 0 for 20-245 GeV electrons; Geant4 electron shower in TileCal starts earlier and is slightly narrower than in G3: 0123-2-3 0 0.1 0.2 0.3 0.4 0.5 0.6 dE/E per R M Distance from shower axis [R M = 2.11cm] 02.557.51012.51517.520 0 0.02 0.04 0.06 0.08 0.1 0.12 Shower depth [X 0 = 2.25cm] dE/E per X 0 TileCal 100 GeV Electrons

13. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 13 Peter Loch University of Arizona Tucson, Arizona 85721 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 -6 Rel. entries electronic noise electronic noise shower signals 050100150200250300 FCal 60 GeV Electrons excess in experiment

14. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 14 Peter Loch University of Arizona Tucson, Arizona 85721 Individual 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

15. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 15 Peter Loch University of Arizona Tucson, Arizona 85721 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); PMQGSExperiment PMQGSExperiment log(energy equivalent # of electrons)

16. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 16 Peter Loch University of Arizona Tucson, Arizona 85721 More 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; PMQGSExperiment

17. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 17 Peter Loch University of Arizona Tucson, Arizona 85721 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 signal ratio Pion energy [GeV]

18. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 18 Peter Loch University of Arizona Tucson, Arizona 85721 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 HEC Pion Energy Resolution TileCal Pion Energy Resolution Pion energy [GeV] relative energy resolution [%] Exp GCalor

19. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 19 Peter Loch University of Arizona Tucson, Arizona 85721 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)

20. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 20 Peter Loch University of Arizona Tucson, Arizona 85721 Conclusions (1): Geant4 can simulate relevant features of muon, electron and pion signals in various ATLAS detectors, often better than Geant3; Geant4 can simulate relevant features of muon, electron and pion signals in various ATLAS detectors, often better than Geant3; remaining discrepancies, especially for hadrons, are addressed and progress can be expected in the near future; remaining discrepancies, especially for hadrons, are addressed and progress can be expected in the near future; ATLAS has a huge amount of appropriate testbeam data for the calorimeters, inner detector modules, and the muon detectors to evaluate the Geant4 physics models in detail; ATLAS has a huge amount of appropriate testbeam data for the calorimeters, inner detector modules, and the muon detectors to evaluate the Geant4 physics models in detail; feedback loops to Geant4 team are for most systems established since quite some time; communication is not a problem; feedback loops to Geant4 team are for most systems established since quite some time; communication is not a problem; Geant4 can simulate relevant features of muon, electron and pion signals in various ATLAS detectors, often better than Geant3; Geant4 can simulate relevant features of muon, electron and pion signals in various ATLAS detectors, often better than Geant3; remaining discrepancies, especially for hadrons, are addressed and progress can be expected in the near future; remaining discrepancies, especially for hadrons, are addressed and progress can be expected in the near future; ATLAS has a huge amount of appropriate testbeam data for the calorimeters, inner detector modules, and the muon detectors to evaluate the Geant4 physics models in detail; ATLAS has a huge amount of appropriate testbeam data for the calorimeters, inner detector modules, and the muon detectors to evaluate the Geant4 physics models in detail; feedback loops to Geant4 team are for most systems established since quite some time; communication is not a problem; feedback loops to Geant4 team are for most systems established since quite some time; communication is not a problem;

21. Status of the GEANT4 Physics Evaluation in ATLAS Geant4 Workshop September 30, 2002 Slide 21 Peter Loch University of Arizona Tucson, Arizona 85721 lack of man power in all ATLAS systems makes it hard to follow up on Geant4 progress; hard to catch up with G4 evolution! Need to look into more automated benchmark tests ?? lack of man power in all ATLAS systems makes it hard to follow up on Geant4 progress; hard to catch up with G4 evolution! Need to look into more automated benchmark tests ?? Geant4 is definitively a mature and useful product for large scale detector response simulations! Geant4 is definitively a mature and useful product for large scale detector response simulations! lack of man power in all ATLAS systems makes it hard to follow up on Geant4 progress; hard to catch up with G4 evolution! Need to look into more automated benchmark tests ?? lack of man power in all ATLAS systems makes it hard to follow up on Geant4 progress; hard to catch up with G4 evolution! Need to look into more automated benchmark tests ?? Geant4 is definitively a mature and useful product for large scale detector response simulations! Geant4 is definitively a mature and useful product for large scale detector response simulations! Conclusions (2):