GEANT Simulation of the AGILE Gamma-Ray Imaging Detector (GRID) EFFECTIVE AREA AND BACKGROUND REJECTION

1
GEANT Simulation of the AGILE Gamma-Ray Imaging
Detector (GRID) EFFECTIVE AREA AND BACKGROUND
REJECTION

• Veronica Cocco (University and INFN, Roma Tor
  Vergata)
• Paolo Lipari (University and INFN, Roma La
  Sapienza)
• Francesco Longo (University and INFN, Ferrara)
• Marco Tavani (IFC-CNR, Milano)
• Contributions from
• G.Fedel, A.Pellizzoni

2
OUTLINE

• Montecarlo simulations with GEANT 3.21
• Studies on the Expected Background
• Optimization of the Trigger Strategies
• Calculation of

• Effective area
• Background rejection

3
AGILE

• GRID
• SuperAGILE
• Mini-Calorimeter
• 30MeV 50 GeV
• 10 40 keV
• Impulsive events
• Low deadtime

4
AGILE
5
DETECTOR DESCRIPTION
60 cm

• Top Anticoincidence
• Lateral Anticoincidences
• SuperAGILE
• Silicon Tracker
• Mini-Calorimeter
• Mechanical structure
• (not shown in the figure)

15 cm
22 cm
5 cm
40 cm
6
SuperAGILE

• Silicon detectors, Electronics, Tungsten ring,
  honeycomb
• Collimators and coded mask

7
TRACKER

• Silicon detectors, tungsten converter layers
  (0.07 X0 each), front-end electronics, honeycomb
  tray structure
• Capacitive coupling
• Strip floating
• Cluster identification

8
Fit with Experimental Data
Test-beam data collected at CERN (May 2000), PS -
T11 beam (?- and e-), pmax 3.6 GeV/c, AGILE
tracker prototype
Fedel et al. (2000)
9
Capacitive coupling
10
Event Generation

• Particle/Albedo-photon Background
• Astrophysical point sources
• Particle/photon tracks originating on a spherical
  surface
• Montecarlo methods for the generation of the
  distribution functions

AGILE Payload
AGILE Satellite
11
Event Generation
Simulation of an isotropic flux
Gamma-rays coming from a fixed direction
12
Expected particle/albedo-photon background for an
Equatorial Orbit

• Particle flux from SAS-2 and BeppoSAX data (0.3
  cm-2 s-1 for Ekin ? 1 MeV )
• 3 main components e, e-, p
• Spectral data from AMS and Marya
• Assumptions
• 1) isotropic distribution for e, e-, and
  low energy protons
• 2) sky-incidence for high energy p (Ekin ? 7
  GeV )
• Albedo photons from the Earth (from SAS-2 data)
• Thompson et al. 1981

13
Expected particle/albedo-photon background for an
Equatorial Orbit

• Albedo photons from the Earth (from SAS-2 data)
• Thompson et al. 1981

14
Trigger Levels

• Level-1
• Level-2

• Hardware Implementation
• Information from Silicon Tracker and AC panels
• Track topology at the chip level
• Software Implementation
• Analog Information on the released charge in the
  Si-microstrips
• Track topology at the cluster level
• 3D-reconstruction to reject albedo photons

15
Simulated events
Gamma-ray (50 MeV, ? 0?)
Gamma-ray (1 GeV, ? 0?)
Electron ( p 0.04 GeV/c, ? 120?)
Proton ( p 1. GeV/c, ? 120?)
16
Charge deposited in the Tracker Si-microstrips
for a typical gamma-ray event
Optimal spatial resolution 40 ?m for a broad
range of incidence angles (0?-50?)
50 MeV gamma-ray, ? 50?
17
SUMMARY OF ON-BOARD BACKGROUND REJECTION

• Expected total rate of particle/albedo-photon
• entering into the Tracker volume 2-3
  KHz
• Level-1Trigger cut ?100
  Hz
• Level-2 processing cut 20-30
  Hz
• On-board Background Rejection
  10-2

18
AGILE-GRID Effective Area
19
Conclusions

• Use of best available background data
• Detailed model of all AGILE subsystems
• MC crucial to optimize on-board data processing