Gamma-ray Large Area Space Telescope

1. Gamma-ray Large Area Space Telescope 15th INTERNATIONAL WORKSHOP ON VERTEX DETECTORS September 25 - 29, 2006Perugia,  Italy GLAST Silicon Tracker beam test results Stefano Germani INFN Perugia

2. Outline • GLAST: mission and science • The LAT instrument • The LAT Tracker • Beam test motivations • The LAT Calibration Unit • Beam test description • Preliminary results • Conclusions

3. The GLAST mission • High energy Gamma Ray observatory 2 instruments: • --Large Area Telescope (LAT) • --Gamma Ray Burst Monitor (GBM) • Observe γ ray sky (10 keV –300 GeV) All sky survay Pointed observations • Answer to important question in high energy astrophysics raised by results from EGRET • Lifetime 5 years (minimum) GBM: ~10 keV – 30 MeV LAT: ~20 MeV - >300 GeV • LAT assembly completed • Environmental tests completed • LAT is being integrated on • spacecraft • Tests will continue • (termal, vibrational …) • Launch end 2007

4. AGN spectrum GRB emission time structure LAT science and performances All sky survey with large field of vew (2.4 sr) Large energy range (20 MeV – 300 GeV) 30-100 GeV: unexplored energy window Small dead time ~ 25 μs

5. Tracker 4x4 Towers Array γ ACD (Aanti Coincidence Detector) : segmented plastic scintillator surrounding the 4x4 Traker Towers array Tracker: silicon microstrip 18 XY layers interleaved with W converters ~ 1.5 X0 e+ e- Calorimeter: 8 CsI(Tl) hodoscopic array layers ~ 8.5 X0 Thermal Blanket ACD Calorimeter DAQ Electronics The Large Area Telescope (LAT)

6. Space Environment Limitations and Requirements • Total mass budget: 3000 Kg • Total power budget 650 W • Tracker 160 W • Temperature Range +45  -15 °C • Vibrations at Launch • No consumables • Limited Data Flow (8-10 min contact/day @ 40 Mbps ) • Trigger rate: ~ 4 kHz • Downlink rate: ~ 370 Hz • Photon rate : few Hz

7. Tkr Tower Tray x xy plane x y y x x y y Tracker Design Overview • 16 tower modules 37  37cm2 active cross section/layer • 83m2 of Si 11500 SSD, ~ 1M channels strip pitch: 228 μm • 18 xy layers per tower • 19 “tray” structures • 12 with 3% X0 W on top • 4 with 18% X0 W on bottom • 3 with no converter foils • every tray is rotated by 90° wrt the previous one: W foils followed by x,y plane of detectors • 2mm gap between x and y oriented detectors • Trays stack and align at their corners • Electronics on sides of trays: • Minimize gap between towers

8. Tracker Readout Electronics  24 GLAST Tracker Fornt End (GTFE) chips mounted on Multi-Chip Module (MCM) on tray side  9 GLAST Tracker Readout Controllers (GTRC) per cable  Time Over Threshold (TOT) from layer-OR trigger signal Any single component (GTFE, GTRC, cable) can fail without affecting the other

9. MCM Kapton cables  4 layers flexible circuit each cable in the tower module is different  84-98 cm long Tracker Highlights 10368 Wafers Yeld ~ 99.5% Each Layer passed several Electrical Tests Each Tray passed thermal-cycle tests • Each Tower passed • vibrational tests • thermal vacuum tests MCM-SSD right-angle interconenction Difficult work but now the Tracker is complete and working well

10. Why Beamtest ? LAT performances have been studied with MC (GEANT4) and cosmic muons Need to verify MC with real data The whole energy, angle, position phase space will be available only in orbit Check basic quantities (energy deposit, hit multiplicities) Sample critical/typical points for detector performances and background rejection with particle Beam Check high level quantities (energy and direction reconstruction) Eventually tune MC

11. Photons: what to check ? γ Energy Spectrum Most of γwill have very low Energy Energy and Direction reconstruction performances scale with energy Check absolute values and scaling especially in the low energy region γ Angular Distribution wrt LAT axis Direction reconstruction performances scales with angle Most of γ will cross 2 Towers Check absolute values and scaling especially in the most probable region Check two towers effects Check passive material description

12. MMS Background: what to check ? Photons Protons Positrons Photons coming backword and hitting the CAL can mimic a track ACD can miss some p e+ can annihilate in MicroMeteorite Shild Protons hitting the CAL side can mimic a track Check efficiency Check hadron reactions Check efficiency Check efficiencies e+ γ γ

13. Flex Cable Check BackSplash High energy γ/electrons produce backsplash from calorimeter Can affect direction reconstruction Check hit multiplicity Tracker Towers readout by flex cables High multiplicity can saturate cables FIFO Max read hits (strips) / Cable = 128 Most backsplash hits in bottom layers Layer read from bottom to top (FIFO) Direction informations infirsts track hits Study optimal FIFO configurations (Max allowed hits/layer) and dead time

14. The Calibration Unit The LAT could not be tested on beam (environmental tests at NRL during beam time) anyway: To scan and test each single Tower for all configuartions is not feasible Most of of the events are contained in 2 towers The aim of the Beamtest is to check and eventually tune MC response Use Calibration Unit (2 complete Towers + 2 CAL) Calibration Unit allows to test all the geometry related configurations Impact position and angle 2 Towers crossing

15. The Calibration Unit ~ 820 mm ~ 1500 mm tower 2 tower 1 bay 0 tower 3

16. Where ? CERN Need wide energy range (50 MeV – 300 GeV) Need several particle types ( γe± protons) H4 line – extracted from SPS e-, p, π 10 – 280 GeV Beam time: 4–15/9 T9 line – extracted from PS e±, p, π 0.5 – 10 GeV Beam time: 24/7 – 22/8

17. Analysis Status Beamtest is finished 10 days ago data analysis started but ALL PLOTS shown in the following slides are PRELIMINARY

18. S4 Photons (Magnet ON) and Charged Particles (Magnet OFF) SSDs Dump Magnet C2 Sh S2 SSDs C1 GLAST CU S1 S0 S4 SSDs Dump Positrons Magnet C2 Sh S2 SSDs C1 S1 S0 GLAST CU Setup at T9 (CERN - PS)

19. Setup at T9 Picture CU SSDs Magnet Scintillators Dump

20. PRELIMINARY T9 data - Photons Tagged γ Fixed tagger position use different beam energies (and Magnet B) to cover the needed energy spectrum Use tagger to measure photon direction and energy Small momentum range and limited rate Ebeam: 0.5, 1 1.5 2.5GeV Full bremsstrahlung No momentum or rate limitations Assume gamma direction from beam For both cases measurements at several angles (0, 30, 50 deg)

21. Tagged Photons Photon Energy measured by Tagger • e- beam energy: • 0.5 GeV • 1 GeV • 1.5 GeV • 2.5 GeV PRELIMINARY Electron Energy measured by Tagger+CU PRELIMINARY Full range covered: 50 MeV  1.4 GeV

22. First look at Beam Data vs MC I Conversion Point PRELIMINARY Full bremsstrahlung Beam Data MC

23. First look at Beam Data vs MC II Full bremsstrahlungBeam Data MC Direction Error CAL Energy vs Layer PRELIMINARY PRELIMINARY

24. Event Display γ

25. CU CU T9 data – charged particles Protons: E = 10, 6 GeV Small angles on MMS Angle 30, 60, 90 deg Electrons: All the γconfigurations for comparison Several other positions energies and angles Positrons: Only a small angle on MMS

26. Setup at H4 (CERN – SPS) C2 S2 C1 GLAST CU S1 Cherenkov upstream GOLIATH CU BEAM Scintillators

27. H4 data Electrons: E 10  280 GeV (10, 20, 50, 100, 200, 280 GeV) Angle 0  90 deg (0, 10, 20, 30, 45, 60 90 deg) Several impact points Several FIFO configurations Number of Hits in thick W converter layers PRELIMINARY Number of reconstructed tracks Protons: E 10  150 GeV (10, 20, 100, 150 GeV) Angle 0  90 deg (0, 30, 45, 60, 90 deg) PRELIMINARY

28. First look at Beam Data vs MC Number of Tracker Hits 20 GeV electrons Beam Data MC PRELIMINARY

29. Conclusions • Program completed both at T9 and H4 • We have a lot of data • CU configurations • Energies • Particles • Data analysis is started • Tagger performances • Beam systematics • Hit multiplicity • FIFO configurations • Direction reconstruction • Efficiency • Background • … under study • First look analysis show reasonable agreement with MC • Heavy Ions test beam scheduled for November at GSI

30. Backup Slides

31. ASI Italian contribution to the Tracker INFN/ASI responsabilities for the LAT-TKR construction Tracker Tower built and tested in Italy

32. Requirement - Present Value LAT Science Requiremnts Large Energy Range: 20 MeV -300 GeV Large Effective Area: > 8000 cm2 10000 cm2 (at 10 GeV) Wide Field of View: > 2 sr 2.4 sr Dead Time: < 100 μs/event 25 μs/event Energy Resolution : < 10 % 9 % (at 100 MeV) Point Source Sensitivity: < 6x10-9 cm-2s-1 3x10-9 cm-2s-1 (>100 MeV) (on axis 100 MeV - 10 GeV) Angular Resolution – 68%: < 0.15°0.086°(thin) (on axis E>10 GeV) 0.115°(total) Spectral coverage and ground based observations overlap Bright sources variability and GRBs monitor Transient sources emission time structures Spectral studies Good Source localization and minimize sources confusion

33. EGRET – LAT properties

34. LAT Performances

35. TLM:Ku-band SA @ 40 Mbps S-band SA @ 1,2,4,8 kbps MA@ 1 kbps CMD: S-band SA @ 4 kbps MA @ 0.25 kbps GLAST GPS GPS Timing & Position Data TDRS TLM: S-band @ 2.5 Mbps CMD: S-band @ 2 kbps White Sands Complex/GFEP Ground Stations USN: Hawaii;Australia Data Downlink and Commands

36. Tracker Features • Conversion Efficiency > 58% • Aspect (H/W) ratio < 0.45 (wide field of view) • Active area > 19,000 cm2 (Fraction > 88%) • 6-in-a-row tracker trigger • Efficiency > 90% • Single layer trigger rate < 50 kHz • Average Noise occupancy < 5x10-5 • Hit efficiency > 98%

37. Layer assembly

38. Silicon Sensor Devices Specifications Hamamatsu Photonics