1. LSO Cal Geant4 Simulation
S. Germani
INFN Perugia
SuperB R&D Workshop
SLAC
15/02/08

2. Pourpose and Outline
Pourpose: Geant 4 simulation to prepare beamtest LSO crystals prototype for Fwd ECAL (2009)
Outline:
Intro
Leakage
Deposited Energy
Deposited Energy Fit
Dead Material and Modularity Effect
BaBar and CMS ECAL examples
Adding Projectivity
Dead Material variation
Upstream Matreial Effect
Slab
Dummy SVT and DCH
Difference between e- and  beam
Conclusions and Outlook
SLAC 15/02/08
LSO Cal G4 Simulation

3. Intro Study: First approch Geometry is a NxN LSO crystals matrix:
Crystals dimentions: 2x2x20 cm (17.54 X0)
No Dead Material
Particles Beam: e-
Energy: 50 (100 MeV)  5 (9)GeV
Direction: horizontal
Position: at the center of the matrix
Study:
Deposited energy
Leakage
SLAC 15/02/08
LSO Cal G4 Simulation

4. Deposited Energy and Leakage
Matrix 9x9
Fwd leak
Laterlal leak
Backsplash
Matrix 21x21
No Lateral Leak
SLAC 15/02/08
LSO Cal G4 Simulation

5. Edep Fit
Tested Asymmetrical Gauss function to fit the distribution of the Fraction of Deposited Energy (Edep/Ebeam):
P : most probable value (mpv)
P2*(P3-x) : running 
0.5 GeV
2.0 GeV
9.0 GeV
SLAC 15/02/08
LSO Cal G4 Simulation

6. Mean vs mvp and RMS vs 
As expected Mean and peak position (mpv) have different values but similar scaling with the energy
Chose running  value at E=Epeak as performance reference
Deposited energy RMS and (E=mpv) have different values but similar scaling with the energy
From now on use (mostly) mpv and (E=mpv) for performance evaluation
SLAC 15/02/08
LSO Cal G4 Simulation

7. Adding Dead Material and Modularity
BaBar like geometry
(B.Aubert et al. Nucl.Instrum.Meth.A479:1-116,2002) :
Each Crystal wrapped with
2 x 165 µm Tyvek
25 µm Al
13 µm Mylar
Each module wrapped with
300 µm Carbon-fiber
CMS like geometry
(CMS EDR IV ) :
Crystal inside Carbon Fiber matrix
Inner wall thickness µm
Outer wall thickness 200 µm
Crystal Carbon Fiber clearance µm
Module Gap µm
Mylar
C Fiber Al
Tyvek
Crystal
Crystal
Air
3x3 Module
3x3 Module
Carbon Fiber
Air
SLAC 15/02/08
LSO Cal G4 Simulation

8. Dead Material and Modularity effects
BaBar like
Dead material across modules not negligible
Module Size (3x3, 5x5) affect performances
CMS like
Xtal - Xtal C-Fiber thickness:
Inside Module : 400 µm
Across Module: 600 µm
Very small Module Size (3x3, 5x5) effect
CMS like dead material has smaller effect and module size dependency
LSO crystals should have sufficient mechanical strength (under ivestigatigation)
SLAC 15/02/08
LSO Cal G4 Simulation

9. Projectivity Module Matrix
In order to have more realistic dead/active material ratio implement Projective Geometry
Trapezioidal crystals
Projective Beam
Position fixed close to pointing distance
Direction with 2D opening angle
Matrix
SLAC 15/02/08
LSO Cal G4 Simulation

10. CMS like geometry with tyvek
Tyvek wrapping could improve light output (not simulated): what is the effect on CMS like geometry?
Tyvek thickness similar to BaBar
Effect is not negligible
SLAC 15/02/08
LSO Cal G4 Simulation

11. CMS like: C-fiber thickness
Change C-fiber thickness in CMS like geometry
Change both inner and outher wall thickness
As expected C-Fiber thickness affect performances
1 GeV:
0.82 %  1.07 % (0.25 %)
SLAC 15/02/08
LSO Cal G4 Simulation

12. Dead Material and Modularity Conclusions
If LSO crystals have the needed mechanichal strength CMS like dead material has smaller effect on performances
Selecting CMS like configuration modularity has small impact on performances
Adding reflective/diffusive material (like Tyvek) or changing C-fiber thickness (few 100s m) in CMS like configuration has not negligible effect on performances
SLAC 15/02/08
LSO Cal G4 Simulation

13. Upsteram Material Effect: geometry
Xtals:
2.50 x 2.50 cm Front
2.88 x 2.88 cm Back
Pointing distance ~ 1.5 m
Matrix:
3x3 Xtals module
CMS like
BaBar like
7x7 module matrix
Upstream material
2 configurations with several thickness
Slab close to Matrix
Variable thickness C-Fiber
Dummy Detectors
SVT:
5 x 300 m Si layers
DCH:
variable thickness
Ar C-Fiber layers
Slab
Dummy
SVT
Dummy
DCH
SLAC 15/02/08
LSO Cal G4 Simulation

14. Deposited Energy e-,  Peak shifted (ionization loss) 1 GeV e-
Electrons and photons show very different behavior
No Peak shift
1 GeV 
Distribution shoulder (upstream interacting  2nd component)
SLAC 15/02/08
LSO Cal G4 Simulation

15. Edep vs Ebeam: e- beam on C-Fiber Slab
rms
Upstream material effect dominant at low energies
Internal dead material effect dominant at high energies
Transition region between 300 and 400 MeV (highlighted)
SLAC 15/02/08
LSO Cal G4 Simulation

16. Edep vs X0: e- on Slab
Material in front of BaBar ECAL ranges between 0.3 and 0.6 X0 (highligthed)
CMS and BaBar like peak position shaw similar behavior
BaBar like  more low Energies and large upstream material X0
Effect not negligible in X0
SLAC 15/02/08
LSO Cal G4 Simulation

17. Edep vs X0: e- on Slab and SVT+DCH
CMS like geometry
SVT+DCH have larger effect on both peak position and 
Larger distance from crystal matrix: secondaries loss
SLAC 15/02/08
LSO Cal G4 Simulation

18. Edep vs X0: e- and  beam on SVT+DCH
effect of 2nd  component
e- ionization loss
small effect on main  distr
Peak position
e- show ionization loss effect
Almost constant for  E
Small effect on main  distribution
Asymmetry (Epeak-Emean)
Photons converting in upstream material affect  distribution asymmetry
SLAC 15/02/08
LSO Cal G4 Simulation

19. Edep vs Ebeam: beam material comparison
Peak position
Not affected for 
Big effect on low Energy e-
All effects negligible at High Energy E
Small effect on main  distribution
Big effect on low E e-
Smaller effect on High Energy e- wrt 
Transition region between 400 MeV and 1 GeV (highligthed)
Beam
SLAC 15/02/08
LSO Cal G4 Simulation

20. Edep vs Ebeam:  beam on SVT+DCH
Since  distrubution main component is not affected main effect on resolution is dominated by internal dead material
SLAC 15/02/08
LSO Cal G4 Simulation

21. Edep vs X0: on SVT+DCH
The effect on the  is small even with large upstream material tickness
The effect on the distribution asymmetry (Epeak-Emean) is quite big with large upstream material
SLAC 15/02/08
LSO Cal G4 Simulation

22. Upstream Material Conclusions
e- and  are affected in different ways
e- have a transition with energy from upstream material dominated to internal material dominated resolution
 have a two components behavior
the main component remains internal material dominated
the 2nd component becomes important only for large upstream material thickness (> X0 depending on energy)
The SVT+DCH geometry seems to have bigger effect wrt the Slab one
Distance effect
SLAC 15/02/08
LSO Cal G4 Simulation

23. The work is proceeding adding geometrical details in several steps:
Summary and Outlook
The work is proceeding adding geometrical details in several steps:
Dead Material
Projectivity
Effect of upstream material
Next step will be define a geometry which is a subset (module) of a realistic Fwd ECAL geometry:
Matrix  Rings subsets
SLAC 15/02/08
LSO Cal G4 Simulation