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Sergio Ricciarini ~ INFN Firenze on behalf of PAMELA collaboration Vertex 2006 15 th International Workshop on Vertex D

PAMELA Silicon Tracker experience and operation. Sergio Ricciarini ~ INFN Firenze on behalf of PAMELA collaboration Vertex 2006 15 th International Workshop on Vertex Detectors Perugia, 28 September 2006. Summary. Introduction. The PAMELA experiment.

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Sergio Ricciarini ~ INFN Firenze on behalf of PAMELA collaboration Vertex 2006 15 th International Workshop on Vertex D

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  1. PAMELA Silicon Tracker experience and operation Sergio Ricciarini ~ INFN Firenze on behalf of PAMELA collaboration Vertex 2006 15th International Workshop on Vertex Detectors Perugia, 28 September 2006

  2. Summary • Introduction. • The PAMELA experiment. • The magnetic spectrometer and silicon tracker. • Detectors and read-out electronics. • Tracker performances. • Preliminary analysis of a sample of data taken in flight. • Examples of events collected in flight by PAMELA. S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  3. ITALY: •INFN Florence and Physics Department of Florence University •Istitute of Applied Physics “Nello Carrara”, Florence • INFN Bari and Physics Department of Bari University • INFN and Physics Department of Rome "Tor Vergata" • INFN Naples and Physics Department of Naples University • INFN Trieste and Physics Department of Trieste University • INFN National Laboratories, Frascati GERMANY: Physics Department of Siegen University SWEDEN: Royal Institute of Technology, Stockholm RUSSIA: • Ioffe Physico-Technical Institute, St Petersburg • Cosmic Rays Laboratory, Moscow Engineering and Physics Institute, Moscow • Lab. of Solar and Cosmic Ray Physics, P.N. Lebedev Physical Institute, Moscow S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  4. PAMELA experiment operational launch (rest) Primary production  annihilation m() = 964 GeV (Ullio 1999) Al container filled with N2 at 1 atm 2 mm thick window • Main scientific objectives: • antiparticles in cosmic rays; • search for antimatter and dark matter; • cosmic-ray propagation; • solar modulation, solar physics. • Mission overview: • on-board Resurs-DK1 Russian satellite, launched from Bajkonur (Kazakhstan) 15 June 2006; • quasi-polar orbit 70° inclination, 350-600 km altitude; • long expected duration (> 3 years);  efficient rejection of atmospheric background (albedo);  high statistics, also at lower energies (geomagnetic effect). • Design goals for PAMELA performance: S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  5. PAMELA apparatus • Main requirements: high-sensitivity antiparticle identification, precise momentum measure. • Time-Of-Flight plastic scintillator strips + PMT:  trigger, albedo rejection;  mass identification up to E ~ 1 GeV;  charge identification from dE/dX. • Magnetic spectrometer with microstrip Si tracker:  charge sign and momentum from the curvature;  charge identification from dE/dX. • Electromagnetic calorimeter W/Si sampling; 16.3 X0, 0.6 λI:  discrimination e+ / p, e- / from shower topology;  direct E measurement for e-. max diameter: 102 cm height: 130 cm weight: 470 kg power: 355 W S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  6. Bmean = 0.43 T Bmax = 0.48 T Magnetic spectrometer • Permanent magnet (5 modules): • Nd-Fe-B alloy elements, residual magnetization 1.3 T; • Al frames, tower height 44.5 cm; • geometric factor 21.5 cm2· sr; • Bx ~ Bz < 0.1 By ; • 3-axis map: 70000 points, 5 mm pitch. l a d d e r ADC boards • Tracking system (6 planes, 8.9 cm apart): • 3 independent ladders per plane: • 2 Si microstrip sensors per ladder: • double sided, with double metallization on ohmic view; • integrated capacitive coupling; • FE electronics (VA1 chips) integrated on hybrid boards. VA1 chips hybrids Si sensors S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  7. Silicon detector ladder • Sensor dimensions: 70.0 mm x 53.3 mm x 300 μm. • Read-out: • 1024 read-out channels per ladder view; • strip/electrode coupling ~ 20 pF/cm; • channel capacitance to ground: < 10 pF junction view, < 20 pF ohmic view. • Bias: • VY -VX = + 80 V fed through guard ring surrounding the strips. • Bias resistor: • junction: punch-through, > 50 MΩ; • ohmic: polysilicon, > 10 MΩ. • Leakage current < 1 μA/sensor. S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  8. VA1 chip • Main features: • 1.2 µm CMOS ASIC (CERN - Ideas, Norway); • 6.2 mm · 4.5 mm chip area; 47 μm input pad pitch; • ± 2 V power rails; • 128 low-noise charge preamplifiers; • shaping time set to 1 μs; • ± 300 mV differential output range. • Operating point: • chosen for optimal compromise; • power consumption 1.0 mW/channel  total dissipation 37 W for 288 VA1 (36864 channels); • voltage gain 7.0 mV/fC  output saturation at ~ 10 MIP. S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  9. flight data physics run physics run calibration Tracking system electronics • General characteristics: • segmentation/redundancy of power and functional sections; • devices qualified for radiation hardness (TID, SEE); • compact mechanical assembly; • limited total power consumption (63 W); • limited data bandwidth occupation (~ 10 Gbyte/day available). ADC stage: • 36 ADC sections, 1 ADC / ladder; • ADC are operated in parallel at 0.5 Msps; • event acquisition time 2.1 ms. DSP stage: • 12 DSP on 2 boards, 1 DSP/view (ADSP2187L); • control logics on FPGA chips (A54SX); • typical data compression factor 15  ~ 4 kbyte/event; • typical compression time 1.1 ms. S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  10. Tracker performances • Preliminary analysis of a sample of data taken in ~12 hours of flight. • Data show that the tracking system is working nominally as expected. • Thermal environment. • Noise performances. • Cluster multiplicity and total signal. • Signal correlation between X and Y views. • Signal/noise. • Charge discrimination capabilities. • Spatial resolution. • Momentum resolution. S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  11. Temperatures in flight • After power-up temperature remains stable: • < 1º C variations along orbit; • < 10º C difference between PAMELA off and on. • Heat from VA1 on hybrids radiated to the magnetic tower: • black IR absorbing painting on the walls; • heat released from magnetic tower to cooling loop (liquid iso-octane). At power-up: 21º C (5000 s ~ 0.9 orbits) 8 days after power-up: 28º C (10000 s ~ 1.8 orbits) S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  12. Noise in flight Noise performance is nominal, as can be seen for a typical calibration taken in flight. Y (ohmic) view has worse performance because of double metallization. Pedestal X view (DSP 6) Y view (DSP 3) flight data flight data Noise X view (DSP 6) Y view (DSP 3) flight data flight data N ~ 4 ADC counts N ~ 9 ADC counts yellow line = ground data average S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  13. Cluster characteristics flight data - preliminary flight data - preliminary flight data - preliminary one plane all planes all planes one plane Cluster inclusion cuts: S > 7 N (seed), S > 4 N (neighbours). S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  14. Signal/noise ratio Signal/noise ratio, calculated as Σ(S/N) over the cluster channels. This sample contains also non-MIP cosmic rays (He etc.). Typical average signal/noise measured at beam-test for orthogonally incident MIP: 56 (X view)26 (Y view) flight data - preliminary plane 1 S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  15. Charge discrimination flight data - preliminary He all planes beam–test data H Good H-He charge discrimination capability. magnetic rigidity R = |pc/Z| • Full charge discrimination capabilities studied with beam-test data (GSI Darmstadt, 2006). • Fragmentation of 12C projectiles on different targets (Al, polyethylene). • Single-channel saturation at ~ 10 MIP affects B-C discrimination. events average cluster signal S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  16. Spatial resolution sx = (2.77 ± 0.04) mm sy = (13.1 ± 0.2) mm Critically depends on the signal/noise ratio. Resolution for junction (X, bending) view determines the momentum measurement. Beam-test data - orthogonally incident MIP Best spatial resolution obtained with non-linear η algorithm for normally incident MIP. Resolution measurement and sensor alignment done at the last beam test of the flight model with protons of known energies (CERN SPS, 2003). Whole-tracker alignment checked with cosmic rays collected at ground level during final qualification tests (INFN Rome “Tor Vergata” laboratories, 2005). In flight: alignment parameters will be checked with high-energy electrons after collecting a sufficient statistical sample (at least 3 months of data taking). S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  17. Momentum resolution mult. scatt. spat. resol. X MDR ~ 1 TV Measured at beam test with protons of known momentum (CERN SPS, 2003). In flight cross-check with E measured by calorimeter for high-energy electrons. magnetic rigidity R = |pc/Z| magnetic deflection η = 1/R = |Z/pc| S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  18. Flight data: 10 GV electron with electr. shower S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  19. Flight data: 1.56 GV positron with electr. shower S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  20. Flight data: 36 GV proton with hadronic shower S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  21. Flight data: 18 GV antiproton without shower S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  22. Flight data: 9.7 GV He nucleus without shower S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

  23. Conclusions • PAMELA is taking data since 11 July 2006. • Up to now >900 Gbyte of data downlinked to ground. • Acquired ~ 90 · 106 events. • Apparatus operating also within radiation belts (SAA). • Magnetic spectrometer on-flight performances are nominal. • Data processing and analysis tools have been developed and used; they are now being finalized. • Next step: systematic data analysis. • Precise determination of detector characteristics. • Application to physics research items. trigger rate S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006

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