Geant4 simulations for the calorimeter prototypes D. Di Julio, J. Cederkäll, P. Golubev, B. Jakobsson Lund University, Lund, Sweden

Outline Simulation overview –Geometry –Physics list Benchmark simulations Response to gammas and protons Light collection Future work

Geometry Material: CsI Separation distance: 0.4 mm, vacuum 15 crystals 10x mm 15x42 10x10

Physics list For gamma: –Low energy package – Photoelectric and conversion, Rayleigh, Compton Scattering For e - and e + : –Low energy package for e - –Multiple scattering, ionization, Bremsstrahlung, and annihilation (for e + ) For protons –QGSP physics list

Preliminary simulations Compare with previous calculations Performed by Thomas Zerguerras 20 MeV gamma Large single block: 110x110x200mm 3 5x5 array of crystals, 22x22x200mm mm between crystals, space filled with kapton

500 keV gamma Large fraction of full energy events in center crystal ~60% of events lie in full energy peak in center crystal Some energy deposition in surrounding crystals

500 keV gamma Sum spectrum for entire block, ~91% of the events lie in the full energy peak On average, 1 crystal out of 15 is fired per incident gamma, 6 max width at half max ~ 1 crystal

15 MeV gamma Energy deposited in more crystals Number of full energy events decreases No significant full energy peak in center crystal

15 MeV gamma Sum spectrum for entire block, full energy peak appears, ~13% of the events lie in the full energy peak ~3 crystals out of 15 fire per incident Gamma,11 at most, width increases ~3 crystals

28 MeV gamma Large spread of energy deposition Very few fully contained events, no full energy peak in center crystal

28 MeV gamma Full energy peak can be seen, only about ~2.5% of events lie in full energy peak 4.5 crystals out of 15 fire on average, 12 at most, width ~4 crystals

50 MeV protons Energy deposited mostly in center crystal, little to no energy spread

180 MeV protons Large full energy peak in central crystal Some energy deposition in nearby crystals

180 MeV protons Sum spectrum for entire block, full energy peak appears, ~80% of the events lie in the full energy peak 1.5 crystals out of 15 fire on average, 11 at most, width ~1 crystals

Light Collection Preliminary simulations to investigate light collection Input: –Photon emission spectrum, light yield, fast and slow time components –Need absorption length for tracking –G4LogicalBorderSurface with reflection properties of VM2000 was used for the simulations D. Motta et al. NIM A 547 (2005) 368. J.D. Valentine et al. NIM A 325 (1993) 147.

Future Work Addition of reflector between crystals 2 nd prototype geometry Light collection in single crystals Threshold effects