1. Geant4 Simulation of the Pierre Auger Fluorescence Detector
Pedro Assis1, Patrícia Gonçalves1, Libor Nozka2,
Mário Pimenta1, Bernardo Tomé1
1- Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Lisboa, Portugal
2 - Institute of Physics of the Academy of Sciences of the Czech Republic, Praha, Czech Republic
11th Geant4 Collaboration Workshop and Users Conference
9-14 October 2006
LIP - Lisboa & IST - Lisboa

2. Ultra High Energy Cosmic Rays (UHECR)
Charged Cosmic Rays Spectrum
Many questions:
Sources ? Acceleration mechanisms ?
GZK cutoff ?
Same physics laws ?
A ver:
Interesse de UHECR
Interesse de Auger ; Futuro de Auger.
EGRET (Energetic Gamma Ray Experiment Telescope) all sky map: Vela, Geminga & Crab pulsars ; AGN 3C279
~300 the GeV scale, only a the TeV;
Ver INTEGRAL
Arranjar plot de interaction length dos gammas que va ate 10^20 eV
E > 1020 eV !

3. UHECR detection Extensive Air Showers (EAS) Light detection from space
Fluorescence from air N2 molecules
isotropic emission along the shower
Cherenkov light
collimated with the shower
Fluorescence: 4-5 photons/m per ionizing particle.
Direct detection of shower particles
Scintillators, Cherenkov radiators (e.g. water),...

4. The Southern Pierre Auger Observatory
A giant hybrid detector in Argentina
FOV = 30o x 30o
telescope building
“Los Leones”
LIDAR station
communication tower
Cherenkov water tank
Surface Array
1600 detector stations;
1.5 Km spacing;
3000 Km2 .
Representar o FOV em azimuth de um telescópio.
Fluorescence Detectors
4 housings;
6 telescopes in each;
Malargue, Argentina

5. Schmidt optics

6. Corrector ring
Ring shaped lens to increase the telescope aperture (~2x);
No significant degradation of optics performance.
Toroidal profile

7. Corrector ring in Geant4
- G4Polycone;
- Discretization of ring profile:
Equidistant slices along Z ; Ri vs Zi from ring profile equation. R1 R2 RN Z1 Z2 ZN
...
N - to be optimized...

8. Corrector ring in Geant4

9. Mirror 3.5 x 3.5 m2 spherical mirror; 3.4 m curvature radius;
Made of square or hexagonal mirror segments (MS) with spherical curvature;
Hexagonal MS mirror implemented in the simulation.
4 different MS shapes to fit the mirror curvature:
Each mirror is made of 60 mirror segments.

10. Mirror segments (MS) in Geant4
Union of G4Trd solids ;
Intersection of resulting boolean solid with a G4Sphere.
(Rmin = Radius of curvature; Rmax = Rmin + thickness)
The four MS types are described in the simulation.
MS parameters (curvature, reflectivity, distance to camera) are read for each fluorescence telescope ;
Access to a mirror segment DB is also possible.

11. Assembled mirror

12. Camera Camera frame Spherical focal surface; Hexagonal PMT´s;
Reflecting light guides (“Mercedes”) to maximize
light collection.
6 “Mercedes” light collectors

13. Mercedes light collectors in Geant4
Union of 3 G4Polyhedra solids

14. Assembled camera
PMTs described as hexagonal volumes (shown in red) and defined as sensitive volumes.

15. Assembled telescope

18. Seeing light...

21. Some very preliminary results

22. Mirror “X-ray” Uniform illumination of the mirror (q=0o) ;
Photon positions detected behind the mirror.

23. Camera “X-ray” Uniform illumination of the camera (q=0o);
Average photon distribution over the PMT surface:
Effect of non-uniformities of photocathodes can be introduced in the simulation.

24. PSF vs theta – an example
10 mm
q=0o
q=5o
q=10o
q=15o

25. Direction Scans
Th=0º; Phi=0º

26. Direction Scans
Th=15º; Phi=0º

27. Direction Scans
Th=30º; Phi=0º

28. Position Scans Spots at Phi=0º; 90º; 180º; 270º Photons direction:
Th=0º; Phi=0º

29. Position Scans Spots at Phi=0º; 90º; 180º; 270º Photons direction:
Th=0º; Phi=0º

30. Position Scans Spots at Phi=0º; 90º; 180º; 270º Photons direction:
Th=15º; Phi=0º

31. Position Scans
Spots at
Phi=0º; 90º; 180º; 270º
Photons direction:
Th=0º; Phi=0º

32. A SHOWER… 1000 Photons

33. A SHOWER… 100 Photons

34. A SHOWER… 100 Photons

35. A SHOWER… 100 Photons

36. A SHOWER… Photons

37. Summary
A full Geant4-based simulation of the Auger fluorescence detectors was developed;
Integration in the Auger simulation chain is being carried;
Detailed comparisons with the ray-tracing software will be performed.

38. Optics of Auger Fluorescence Detectors
Schmidt optics telescope.
Mirror:
f/1 spherical mirror ;
3.5 m x 3.5 m;
PSF = 0.5o.
Camera:
440 hexagonal pixels/PMT´s;
1.5o x 1.5o pixel FOV;
Spherical focal surface.
Diaphragm centered on the center of curvature of the mirror:
- Ver que simulacoes do FD existem;
- Ver a calibração do sistema óptico.
Full Geant4 simulation will be implemented at LIP.
Other LIP activities:
Reconstruction and analysis of the Fluorescence Detectors data;
Calibration at CERN testbeam facilities of a water tank using horizontal muons.