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Validation of GEANT4 by the CMS Experiment

Validation of GEANT4 by the CMS Experiment. Pedro Arce (CIEMAT/CERN) On behalf of the CMS Simulation Group GEANT4 Workshop ’03, TRIUMF, 2nd August 2003. Index. Status of CMS GEANT4 simulation (OSCAR) Silicon tracker studies EM calorimeter studies Muon physics studies

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Validation of GEANT4 by the CMS Experiment

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  1. Validation of GEANT4 by the CMS Experiment Pedro Arce(CIEMAT/CERN) On behalf of the CMS Simulation Group GEANT4 Workshop ’03, TRIUMF, 2nd August 2003 GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  2. Index • Status of CMS GEANT4 simulation (OSCAR) • Silicon tracker studies • EM calorimeter studies • Muon physics studies • Hadronic calorimeter studies • Conclusions GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  3. OSCAR status • OSCAR (Object Oriented Simulation for Cms Analysis and Reconstruction) is (almost) ready to substitute GEANT3-based simulation in the official CMS production • Extensive physics checking has been carried to test GEANT4 physics vs. GEANT3 and vs. TestBeam data where available • 1.2 M single particle events + 300 k full events have been produced • CMS DC04 challenge (50 M events) have started this summer with GEANT3 simulation, we hope to make a major part of this production with GEANT4 GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  4. OSCAR status (II) • CPU is acceptable: 1.5 - 2 X GEANT3 • Memory is acceptable: 220 Mb OSCAR vs. 100 Mb GEANT3 simulation • Crashing rate is acceptable: 1 / 20000 events • Becoming smaller at each GEANT4 release • Still some problems in tracking and hadronic physics GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  5. Sliced view of CMS barrel detectors View of CMS muon system View of CMS pixel detector GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  6. dE/dx in Silicon Detector • dE/dx has been studied for: • Particle Types: Muon, Pion, Kaon and Electron • Momenta:2, 3, 4, 5 and 10 GeV • It is compared with: • GEANT3 • ALEPH data • PHOBOS data OSCAR (GEANT4) CMSIM (GEANT3) GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  7. dE/dx in Silicon Detector (II) RELATIVISTIC RISE • We do not have that much data available ;) • PHOBOS: relativistic rise for pions between 0.5 – 8 GeV is 4% (with pads!) • ALEPH: relativistic rise for pions between 1 – 18 GeV is 7% (but only 2 layers!) • We lack any data about electrons • GEANT4/GEANT3 with the proposed settings: we “measure” a 4% rise between 1 and 10 GeV. GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  8. Resolutions in Silicon Detector  PT = 10 GeV Pt resolution: Lower resolution probably due to smaller spread from multiple scattering (~< 10 %)  PT = 100 GeV GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  9. EM calorimeter • SETUP: • CMS electromagnetic calorimeter: lead tungstate crystals pointing to interaction point • Photon of E = 30 GeV enters front face of crystal • No magnetic field • What was compared: • E in hottest crystal, in 3x3, in 5x5 matrix • E total • dNhits/dt, for 1 ns time slices • GEANT3.21 vs. GEANT4.5.1 GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  10. GEANT4 electromagnetic shower looks thinner than GEANT3 • Test beam data seems to agree with GEANT4 (more detailed) EM calorimeter Shower shape: From GEANT4 gallery: Electron 5 Gev in PbWO4 GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  11. GEANT3 GEANT3 GEANT4 GEANT4 Energy resolution in EM calorimeter GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  12. Muon Physics Single block of iron • To concentrate on physics differences • Similar results for other materials Single muons of 10, 100, 1000 GeV • Energy loss • Delta rays • Bremsstrahlung • Pair production • Muon nuclear interaction (negligible) • Multiple scattering Dependency with production cuts (plots shown with 0.1 mm) Check new ´integral´ processes in GEANT4(GEANT4.5.0.ref02) • No difference found GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  13. Total Energy Lost 10 GeV 100 GeV 1000 GeV GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  14. Bremsstrahlung 10 GeV 100 GeV 1000 GeV GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  15. Pair Production 10 GeV 100 GeV 1000 GeV GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  16. Multiple scattering 10 GeV 100 GeV 1000 GeV GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  17. Multiple scattering 50 GeV  GEANT3.21 vs GEANT4.5.2.ref01 GEANT3 GEANT4.5.2.ref01 LEP I Z events in L3 detector (45 GeV) GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  18. Muon Physics PT Resolution: GEANT3 GEANT4 GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  19. EM calor. + Hadr. calor. testbeam • 2002 Testbeam Set-up for CMS HCAL • A module of copper absorber plates with scintillator tile sampling • 28 scintillator plates with absorber of varying thickness in between (only 3 samplings) • A prototype lead tungstate crystal electromagnetic calorimeter • Energies: 225 GeV  (for calibration), 10-300 GeV , 10-300 GeV e- • Magnetic Field: 0, 0.75, 1.5, 3 tesla (direction parallel to the face of the scintillator) • Configuration: Only HCAL or ECAL + HCAL • 5000 events were taken for each set-up • Response of the Calorimeter was studied as a function of: • Magnetic field: effect on scintillator • Absorber thickness: optimisation of resolution versus containment • Absorber depth: energy containment • Electromagnetic Calorimeter contribution: e/ effects • GEANT4.4.1 (physics list 1.8) GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  20. Resolution and Energy Response • All known contributions to ECal and HB resolutions added • Ecal resolution “matched” to data measured e- resolution Resolutions: M.C. & data agree very well Source of discrepancy could be e/h (e.m. & nuclear x-sec), punch through (shower length) ? GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  21. Hadr. calor. GEANT4 vs GEANT3 - 50 GeV: • Energy deposited in each layer of Hadr. Calor. shows good agreement GEANT3-GEANT4 GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  22. Hadr. calor. GEANT4 vs GEANT3 - 20, 30, 50, 100, 300 GeV: • Energy deposited in EM Calor., Hadr. Calor. and outer layers of Hadr. Calor. is different • GEANT4 shower is shorter • Test beam data seems to agree better with GEANT3, new data being analysed now Outer layers Hadr. Calor. Hadr. Calor. EM Calor. GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

  23. Summary • CMS GEANT4-based simulation is almost ready to substitute GEANT3 one • Big effort has been made during recent months to compare GEANT4 with GEANT3 and with Test Beam data where available • Small differences observed sometimes • Precision of test beam data can hardly favour GEANT3 or GEANT4 in most cases • All physics groups agree in switching to GEANT4 as official CMS simulation tool GEANT4 Validation by CMSPedro Arce(CIEMAT/CERN)

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