Physics validation meeting W. Pokorski / CERN

1. Physics validation meeting W. Pokorski / CERN Simulation Application for the LHCb Experiment

2. Physics validation • comparison to the test-beam data • validation of Rayleigh scattering, Cherenkov radiation, photoelectric effect, energy loss in the Silicon for RICH detectors • studies of different hadronic physics models in hadronic calorimeter simulations • comparison to the Geant 3 simulation • occupancies, momentum distributions, time of flight, energy deposition distributions, etc 11

3. RICH detectors in LHCb • To identify charged particles in the momentum range 1-150 GeV/c. • Two detectors: RICH1, RICH2. Momentum range RICH1: Aerogel 210 GeV/c C4F10< 70 GeV/c RICH2: CF4 <150 GeV/c. • Photo Detectors: Baseline solution- HybridPhotodiodes (HPD). • RICH test beam presented: To test the performance of the • Aerogel radiator. S. Easo

4. Test beam Set-up at CERN S. Easo Beam from CERN-PS:πˉandp/πin the range 6 – 10GeV/c (Δp/p = 1%)

5. Simulation of the Testbeam Setup. Mirror Rad. of Curvature=1185 mm. Four Pad Hpds are used. Hpd Mirror Vessel Filter S. Easo Aerogel

6. A Typical event in the Testbeam Red lines: Charged particle Green lines : Photons. Transmission in Aerogel, Cherenkov radiation, Rayleigh scattering, etc, simulated properly S. Easo

7. Cherenkov Angle reconstruction • Results per single photoelectron in (mrad): Aerogel from Novosibirsk Data MC resolution Without Misalignment MC Data MC Components ofσθ in mrad for the case with filter. Pixel size : 1.3 Chromatic: 2.5 Emission Pt: 1.1 Beam divergence: 0.7 Misalignment: ~ 2.2 (not included in σθ MC )

8. Photoelectric Effect at the HPD • Standard Geant4 processes not applicable in this case • (tabularized quantum efficiency data available from the manufacturer) • A Special class created to generate the photoelectrons, • which is derived from a GEANT4 base class. • This process uses the quantum efficiency data • and the results of Fountain focussing tests. • Electron Energy: High Voltage applied. • Direction: From Fountain focussing. • The quantum efficiency data includes the loss of photons by • reflection at the Hpd quartz window surface. S. Easo

9. Hit Creation in the Si Detector • Implemented using a special process class since the standard • Geant4 procedure too complex for this purpose • the only important point: photoelectrons loose all their energy in the Si • The backscattering causes a loss of efficiency in creating hits • Parameterized efficiency = 1.0 - B* N/S • where N = threshold cut in terms of width of the pedestal = 4 • S= Signal to noise ratio=10 • B= backscattering probability=0.18. S. Easo

10. RICH1 with SingleParticleGun RICH1 Event Pion with 7 GeV/c. Cherenkov Photons In Aerogel and C4F10. Rayleigh scattering Switched off for Illustration. S. Easo

11. RICH Simulation Plans. S.Easo, RAL, 14-04-2003 • At least one test beam expected in October 2003 with • gas radiators and new versions of the Photodetectors. • Another testbeam with new versions of Aerogel also possible • in October. • All these will be simulated using GEANT4. • In addition, we are expecting the LHCb-RICH simulation • within the GAUSS framework to be in production • by the end of 2003.

12. HCAL Test beam • HCAL is a sampling device made out of steel as absorber and • scintillating tiles are active material. • The scintillating tiles run parallel to the beam axis. • It will provide data for the LHCb hadron trigger. • Testbeam studies of the response to particles incident at • various angles is studied • comparison to simulation I. Belyaev + A. Berdiouguine et al.

13. Energy Response in HCAL Response to 50 GeV/c Pions Histogram : Real Data Dots: Simulation • Testbeam (1) Data , GEANT3 • (MICAP +FLUKA). • HCAL TDR. • Testbeam (2) Data, GEANT4. I. Belyaev + A. Berdiouguine et al.

14. Data and G3 Energy Resolution of HCAL • Testbeam Data, GEANT3 • GEANT3 with GEISHA, FLUKA,MICAP • Testbeam Data , GEANT4 • G4+GEISHA agrees with G3+GEISHA. • Need help to understand and use • G4 with QGS+CHIPS • Data • G4 (QGS+CHIPS) G4(GEISHA) Data and G4 I. Belyaev + A. Berdiouguine et al. 10

15. Calorimeters test-beam • ALL LHCb calorimeters Spd/Prs/Ecal/HCal will have test beam periods this summer between the middle of June and end of August • very detailed and realistic Xml description of all our complex modules calorimeters in Gauss (the LHCb simulation application) - no plans to perform a stand alone G4 simulation for our calorimeters • if needed, addition (simplified) geometry will be implemented to be used within Gauss • full simulation of test beam setups will be performed with Geant4 (Gauss) and the data will compared I. Belyaev

16. Vertex Locator physics validation (1/2) Geant3 Geant4 Geant3 Geant4 Energy deposition in the silicon (eV) Number of hits per event 12

17. Vertex Locator physics validation (2/2) Geant3 Geant4 Geant3 Geant4 Time of Flight (ns) Particle energy (GeV) 13

18. Outer Tracker physics validation (1/2) Geant3 Geant4 Number of hits per event XY distribution 14

19. Outer Tracker physics validation (2/2) Geant3 Geant4 Momentum distribution (GeV) Time Of Flight (ns) 15

20. Summary • LHCb puts no further effort on developing G3 based application, all of it has been moved to G4 based one • we can run GEANT4 simulation with all the subdetectors included (complete LHCb detector geometry), realistic Pythia events and Geant4 proposed physics list • we are testing/validating subdetector specific code and physics processes • we are planning large test productions starting from the summer • definite move from the old Geant3 simulation to the new Geant4 based one, early next year • conclusion: we are serious about Geant4 and we are very interested in the physics validation 16