1. R 3 B Gamma Calorimeter Agenda. ● Introduction ● Short presentation on the first simulations@USCsimulations@USC ● Task definition for R&D period (2005-2006) ● Simulations (USC, Madrid, Krakow) ● Crystal-readout tests (EXL, USC, Madrid) ● High-energy gamma tests. Accelerator tests (all) ● Electronics (Krakow) ● Geometry/structure design (Madrid, USC, UPC) ● Organization in working subgroups?? ● Synergy with other collaborations. Task sharing. Communications ● Idea collections (1 st March) / Next meeting?

2. Gamma calorimeter for R3B: a first simulation INDEX ● The kinematics ● Initial simulation ● The physical requirements ● Outlook Héctor Alvarez Pol for the R3B collaboration GENP - Univ. Santiago de Compostela 11 February 2005

3. Kinematical constrains Due to the boost, gammas are basically emitted in the forward direction. A large open zone in the backwards region reduces dramatically the crystal bulk needed. E CM = 10 MeV Gammas are emitted with energies up to E lab = 3.2 E CM ( = 0.82) --> To correct for the Lorentz boost it is mandatory a high granularity. --> A huge crystal length is required for full energy absorption ( = 0.82)

4. Calorimeter main requirements

5. Starting the simulation: main features ● A GEANT 4 simulation ● Simple geometry: G4Sphere (inner, outer radius, initial and delta and ). ● A large set of materials is included both for the crystal and the environments; for the crystals: LaBr 3, CsI, NaI, PWO, BGO...; for the environment: air, vacuum... ● Full physics (em, hadronic) packages included. ● Messenger commands for user control under G4UIRoot (online). ● ROOT libraries included for fully integrated analysis interface. ● Partially documented (code is documented in the C++ style, that is, readable ;-) Present studies include absorption length for different materials, Moliere radius and energy loss spectra, single interaction probability on the first crystal layer, geometry optimization...

6. From energy resolution and total absorption... Very good angle resolution for instance, for ∆ E CM /E CM < 2% ∆Ө < 0.017 rad (1 degree) [worst case] Very large crystal length in order to be able to absorb with reasonable efficiency (>80%) the full energy of the most energetic events

7. Two possible configurations under investigation 1 - Single -highly segmented- crystal layer - long and thin crystals - LaBr 3 ? 2 - Double crystal layer - inner layer (green) with large granularity (LaBr 3 ?) - outer layer with low granularity and high energy resolution (cooled NaI ?)

8. Summary and outlook ● First GEANT 4 simulation ● First conclusions on geometry in Tech. Report ● Software available, users and developers are welcome

10. User interface / macros for batch ● Commands allow the control of the program from user interface or macros. ● Commands can be added easily in Messenger classes (requires code recompilation). ● OpenGL/(Dawn)/... viewers for graphical output. ● A ROOT file is created for the storage of TTree / TH1D / TH2D... ● Online histograms are available while running an interactive session.

11. An example macro – Commands for output verbosity – Commands for geometry control – Commands for primaries control –...

12. Note: about the kinematics... Lorentz transformation (P || is the component of P parallel to v): E' = E + P || = E + Pcos ( remember, for gammas, E = P ) For an isotropic angular emission the distribution in cos is flat! Then, for protons at T=700MeV ( =0.8197507, =1.74605 ) : E' = 1.74605 E + 1.43132571 E cos In the limit: cos = 1 → E'=3.1774 E cos = -1 → E'=0.3147 E and the energy distribution is also flat! See, for instance, Simply Kinematics from G.I. Kopilov, p.124-128 Gammas of 10 MeV

13. Crystal selection: full absorption results ● Full sphere (4) with gamma emission from the center (no boost, 4 - iso). Inner radius is always 0. ● Results were obtained modifying the sphere outer radius and the energy of the emitted gamma. We represent the percentage of gammas with full energy deposited on the crystal, as a function of the crystal sphere radius and the gamma energy

14. Why the absorption drops at high energies? ● Number of interactions (Photo, Compton or Pair Conversion) in a 500 mm thick crystal ball (250 < r < 750) ● Conversion dominates for larger energies; conversion photons can escape from the crystal bulk.

15. Why the absorption drops at high energies? (2) Sphere params: ● inner radius: 0cm ● outer radius: 20cm ● gamma energy: 30 MeV Efficiency 65% 1.2% lost below 1% of gamma energy 4.5% lost below 511 keV peak 0.7% lost in 511 keV photons 9.9% lost below 3% of gamma energy

16. Why the absorption drops at high energies? (3) Sphere params: ● inner radius: 0cm ● outer radius: 20cm ● gamma energy: 10 MeV Efficiency 86.5% 0.6% lost below 3% of gamma energy 2.3% lost below 511 keV peak 0.5% lost in 511 keV photons 5.2% lost below 10% of gamma energy

17. Selecting the backwards opening angle ● Due to the boost, gammas are basically emitted in the forward direction. A large open zone in the backwards region reduces dramatically the crystal bulk needed. ● To check the effect on the efficiency, a set of simulations with different opening angles (“angle” in next slide) was made. ● Two different sets of gammas of 5 and 10 MeV are boosted as primary source.

18. Selecting the backwards opening angle

19. Appendix: some calculations... Proton mass: m = 938.27203 MeV and kinetic energy T = 700 MeV Using T = E - m → T + m = m / √ (1-v 2 ) Then: v 2 = 1 – m 2 / (T + m) 2

20. Is the energy deposited on one crystal?

21. Spectra of energy outside the incidence crystal