1. Progress report of the GLAST ACD Beam Test at CERN (Backsplash study) simulation and analysis Tsunefumi Mizuno, Hirofumi Mizushima (Hiroshima Univ.) and Tuneyoshi Kamae (SLAC) October 1 st, 2002 Detector Geometry/ACD tile numbering: pp.2-3 350GeVProton Calibration and simulation: pp.4-6 Real Data for 200GeV/50GeV e-:pp.7-11 Comparison between data and simulation: pp.12-15 Effect of the gap: pp.16-18 Summary: p.19

2. Detector Geometry Veto Scint 20cm x 20cm x 1 cm with a hole (1cm diameter) Trigger Scint 1cm x 1cm x 1cm Absorber (Pb) 20cm x 20cm x 1 cm with a hole (1cm diameter) ACD 54cm x 24cm x 1cm Calorimeter Absorber 20cm x 20cm thickness and material is adjustable Calorimeter Gap 20cm x 20cm thickness and material is adjustable 45cm Note: So far, we have been using G4 simulation program developed before the Beam Test. Detector Geometry (shown above) is not the same as, but similar to, that of experiment. 47cm 1cm 53cm Beam

3. Nomenclature of ACD tile numbering There were 8 ACD tiles in the Beam Test. Here, the leftmost tile seen from Calorimeter is called “1 st ” and the rightmost one is called “8th”. Calorimeter ACD tiles Beam “1 st ” tile “8 th ” tile

4. Proton (350GeV) Calibration (1) “1 st” tile (run09) Peak~1220 Pedestal~149 “2 nd ” tile (run07) Peak~690 Pedestal~147 “3 rd ” tile (run06) Peak~1180 Pedestal~146 “4 th ” tile (run05) Peak~1150 Pedestal~144

5. Proton (350GeV) Calibration (2) “5 th ” tile (run04) Peak~1090 Pedestal~164 “6 th ” tile (run03) Peak~1630 Pedestal~153 “7 th ” tile (run02) Peak~730 Pedestal~158 “8 th ” tile (run01) Peak~1250 Pedestal~141

6. Energy deposition of 350 GeV Proton We assume that the peak position for 350 GeV proton corresponds to 1.7 MeV. G4 Simulation with 350 GeV Proton

7. Real data for 200 GeV e- (1) data: run45 (2inch Pb without gap) background: run11 “1 st” tile “2 nd ” tile “3 rd ” tile “4 th ” tile data background

8. Real data for 200 GeV e- (2) “5 th” tile “6 th ” tile “7 th ” tile data background data: run45 (2inch Pb without gap) background: run11 Note: In this report, we just subtract background run histogram (blue) from backsplash run one (black).

9. Real data for 200 GeV e- (3) Calorimeter ACD tiles Beam “1 st ” tile “8 th ” tile backsplash level differs by a factor of ~2 between tiles data: run45 (2inch Pb without gap) background: run11

10. Real data for 50 GeV e- (1) data: run47 (2inch Pb without gap) background: run11 “1 st” tile “2 nd ” tile “3 rd ” tile “4 th ” tile data background

11. Real data for 50 GeV e- (2) “5 th” tile “6 th ” tile “7 th ” tile data background data: run47 (2inch Pb without gap) background: run11 Note: In this report, we just subtract background run (blue histogram) from backsplash run (black histogram).

12. Comparison between data and simulation: 200 GeV e- (1) “1 st ” tile simulation data “2 nd ” tile “3 rd ” tile “4 th ” tile Note1: Statistical errors for simulation are similar to those of real data, but we do not show them for clarity. Note2: In blue histograms (simulation), we do not take scintillator response into account.

13. Comparison between data and simulaiton: 200 GeV e- (2) “5 th ” tile simulation data “6 th ” tile “7 th ” tile Simulation well predicts backsplash data for 200 GeV e-.

14. Comparison between data and simulation: 50 GeV e- (1) “1 st ” tile simulation data “2 nd ” tile “3 rd ” tile “4 th ” tile Note1: Statistical errors for simulation are similar to those of real data, but we do not show them for clarity. Note2: In blue histograms (simulation), we do not take scintillator response into account.

15. Comparison between data and simulaiton: 200 GeV e- (2) “5 th ” tile simulation data “6 th ” tile “7 th ” tile Simulation well predicts backsplash data for 50 GeV e-. To solve remaining difference, we may need to improve background subtraction and take response of scintillators into account.

16. Effect of the gap (1) Calorimeter without gap (1inch Pb)x4 ACD tiles Beam(50GeV/200GeV e-) Calorimeter with gap (1inch Pb and air gap)x4 ACD tiles Beam (50GeV/200GeV e-) Calorimeter with gap was used for some data and this might affect the backsplash as illustrated below. To estimate this effect, we run simulation. Excess in backsplash

17. Effect of the gap (2): 200GeV e- “1 st ” tile “4 th ” tile “7 th ” tile with gap without gap Gap might affect the backsplash of the “1 st ” (outermost) tile by a factor of 2 for 200GeV e-. The effect could be negligible for the inner tiles.

18. Effect of the gap (3): 50GeV e- “1 st ” tile “4 th ” tile “7 th ” tile with gap without gap Gap might affect the backsplash of the “1 st ” (outermost) tile by a factor of 1-2 for 50GeV e-. The effect could be negligible for the inner tiles.

19. Summary We analyzed 50GeV and 200GeV e- data (2inch Pb without gap) and compared them with simulation predictions. The simulation reproduces the data well. The effect of the gap of calorimeter might be up to by a factor of 2 for the outermost tile, but could be negligible for inner ones. We will update simulator geometry. We may need to improve background subtraction and take scintillator response into account. We will analyze/simulate data with calorimeter gap.