Physics Validation of the Simulation Packages in a LHC-wide effort

1. CHEP’04, Interlaken, 27th September 2004 Physics Validation of the Simulation Packages in a LHC-wide effort Alberto Ribon CERN PH/SFT on behalf of the LCG Simulation Physics Validation group Track 2 “Event Processing” #493

2. Geant4 Project FLUKA Project Experiment Validation MC4LHC Simulation Project Leader G.Cosmo Subprojects Framework A. Dell’Acqua Geant4 J.Apostolakis FLUKA Integration A.Ferrari Physics Validation F.Gianotti Shower Param Generator Services P.Bartalini WP WP WP WP WP WP Work packages WP WP WP WP WP WP WP WP WP

3. LCG physics validation project goals: • compare Geant4, Fluka with the LHC test-beam data • test coherence of results across experiments and sub-detector technologies • study simple benchmarks relevant to LHC • “certify” that simulation packages and framework are ok for LHC physics • weaknesses and strengths of the packages More details: http://lcgapp.cern.ch/project/simu/validation/

4. Physics Validation • First cycle of electromagnetic physics validation completed at thepercent level. We will focus here only on the (most difficult!) hadronic physics validation. • As for the choice of the Geant4 Physics List, the validation should be targeted to each considered application domain: e.g. for high-energy physics one should consider different observables than, for instance, medical physics, or space science. • The criteria to consider a simulation “good” or “bad” should be based on the particular application: e.g., for LHC experiments, the main requirement is that the dominant systematic uncertainties for all physics analyses should not be due to the imperfect simulation.

5. LHC physics simulation Validation project Does this meet LHC physics requirements (e.g. for compositeness) ? Check with (fast ?) simulations that this is good enough Suppose that e.g. for e/ :  (G4-test-beam data)~10% If not : Needs input/help from the experiment physics groups

6. Validation setups Type • Two main types of test-beam setups: • 1. Calorimeters: the typical test-beams (made mainly for detector purposes). • The observables are the convolution of many effects and interactions. In other words, one gets amacroscopictest. • 2.Simple benchmarks: typical thin-target setups with simple geometry (made, very often, for validation purposes). • It is possible to test atmicroscopiclevel asingle interaction or effect. • These two kinds of setup provide complementary information!

7. Double-differential neutron production (p,xn) Proton beam energies:113, 256, 597, 800 MeV Neutron detectors (TOF, scintillators) at 5 angles. Study of theneutron production spectrum (kinetic energy) at fixed angles.

8. benchmark studies

9. benchmark studies G4: QGSP_BERT • ratio simulated / experimental data • for data shown on previous slide • error bars include errors from • experimental data (stat+syst) and from • simulation (stat) • - dominated by experimental syst. errors • typical agreement at level of 1 σ to 2σ FLUKA G4: QGSP_BIC

10. Pion absorption – experiments • K. Nakai at al., PRL 44, 1446 (1980) • D. Ashery et al, PR C23, 2173 (1991) • Nakai – look for gammas emitted after pion absorption • Ashery – look for transmitted (not absorbed) pions pi +/- pi+/- beams of energies between 23 – 315 MeV beam monitoring counters thin target (Al, Cu, Au) detectors

11. Total inelastic cross section

12. Absorption Xsection for pi+ • both G4 and Fluka show reasonable agreement • in some cases Fluka seems to be a bit better • difficult to make more conclusions because of big uncertainties in the experimental data

13. Absorption Xsection for pi- • same remarks as for pi+ • for heavy material (Au) the shape of the QGSP_BERT quite different • G4: best agreement for ‘medium-weight’ materials

14. Hadronic interactions in ATLAS pixel test-beam 180 GeV/c nominal + beam Geant4 Geometry. Use the same Geometry also with Fluka, using FLUGG (interface between the Transportation and Physics of Fluka and Geant4 Navigation of the Geometry).

15. Number of reconstructed tracks

16. Pseudorapidity distribution

17. Ratio max Eloss / total Eloss QGSP is in excellent agreement with data.

18. QGSP produces too narrow clusters. FLUKA, LHEP and QGSC are in good agreement with data. Cluster size In conclusion, FLUKA, Geant4 are in reasonable good agreement with the data, but some observables can be improved.

19. LHC hadronic calorimeter test-beams : • ATLAS: • HEC: copper + LAr HEC1 + HEC2, 4 longitudinal compartments 6-150 GeV for electrons; 10-200 GeV for charged pions; 120, 150, 180 GeV for muons. • Tilecal : iron + scintillator tile 2 extended barrel + 1 barrel + barrel 0 modules 20-180 GeV electrons and charged pions; 1, 2, 3, 5, 9 GeV charged pions. • CMS: • combinedECAL + HCAL : ECAL : prototype of 7 x 7 PbWO4 crystals HCAL : copper + scintillator tile each tile is read out independently Max magnetic field of 3 T 10-300 GeV muons, electrons, and hadrons.

20. ATLAS HEC test beam setup

21. ATLAS Tilecal test beam setup extended barrel module extended barrel module η=0.65 η=0.25 0.25 0.65

22. CMS HCAL & ECAL test beam setup 1 7 17 Crystal 25 h 8 7 6 5 4 3 2 1 f

23. energy resolution of pions

24. e/π ratio

25. ATLAS HEC: leakage

26. ATLAS HEC: energy deposition There are 4 longitudinal segments: 2 in HEC1 and 2 in HEC2. F is the fraction of the total energy deposition in each layer.

27. ATLAS Tile: πshower profile barrel / Etot EB EB barrel M0 EB + M0 / Etot 

28. CMS longitudinal shower profile in HCAL for 100 GeV pions

29. Conclusions • Geant4 electromagnetic physics has been already validated at percent level. In the next future, we will try to push it at the permil level. • First round of hadronic physics validation has been completed, with good results. For the observables we have checked in the case of the simple benchmarks (pixels, neutron double differential, pion absorption) there is a reasonable agreement between data and both Geant4 and Fluka, more or less at the same level. For the calorimeter test-beams, Geant4 describes well the pion energy resolution, σ/E, and the ratio e/. The shape of hadronic showers still needs further improvements. • Geant4 studies of radiation background in the LHC caverns are in progress, and they will be soon compared with Fluka.