Transcript Document

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
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
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
PAMELA experiment
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Main scientific objectives:
• antiparticles in cosmic rays;
• cosmic-ray propagation;
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• search for antimatter and dark matter;
• 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).
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Design goals for PAMELA performance:
particle
operational
kin. energy range
antiproton
80 MeV - 190 GeV
(expected ~ 104/year)
positron
50 MeV - 270 GeV
(expected ~ 105/year)
electron
50 MeV - 400 GeV
proton
80 MeV - 700 GeV
e- + e+
up to 2 TeV
nuclei Z ≤ 6
100 MeV/n - 200 GeV/n
sensitivity in anti-He/He ratio
launch
(rest)
~ 10-7
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Primary
production
 annihilation
m() = 964 GeV
(Ullio 1999)
Al container
filled with N2 at 1 atm
2 mm thick window
PAMELA apparatus
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Main requirements: high-sensitivity antiparticle identification, precise momentum measure.
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Time-Of-Flight
plastic scintillator strips + PMT:
 trigger, albedo rejection;
 mass identification up to E ~ 1 GeV;
 charge identification from dE/dX.
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Magnetic spectrometer
with microstrip Si tracker:
 charge sign and momentum
from the curvature;
 charge identification from dE/dX.
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Electromagnetic calorimeter
W/Si sampling; 16.3 X0, 0.6 λI:
 discrimination e+ / p, e- / p
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
Magnetic spectrometer
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Permanent magnet (5 modules):
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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.
Bmean = 0.43 T
Bmax = 0.48 T
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ADC boards
ladder
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.
Si sensors VA1 chips
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
hybrids
Silicon detector ladder
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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.
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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
VA1 chip
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Main features:
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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
Tracking system electronics
General characteristics:
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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).
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ADC stage:
• 36 ADC sections, 1 ADC / ladder;
• ADC are operated in parallel at 0.5 Msps;
• event acquisition time 2.1 ms.
flight data
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DSP stage:
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calibration
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physics
run 1 DSP/view
physics(ADSP2187L);
run
12 DSP on
2 boards,
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
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
Temperatures in flight
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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
Noise in flight
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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.
X view (DSP 6)
Pedestal
Y view (DSP 3)
flight data
X view (DSP 6)
Noise
flight data
Y view (DSP 3)
flight data
N ~ 4 ADC counts
flight data
N ~ 9 ADC counts
yellow line = ground data average
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Cluster characteristics
one plane
flightdata
data--preliminary
preliminary
flight
flight
data - preliminary
allplanes
planes
all
one plane
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Cluster inclusion cuts: S > 7 N (seed), S > 4 N (neighbours).
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Signal/noise ratio
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Signal/noise ratio, calculated as Σ(S/N) over the cluster channels.
flight data - preliminary
plane 1
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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)
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
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Full charge discrimination capabilities studied
with beam-test data (GSI Darmstadt, 2006).
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events
Charge discrimination
beam–test data
Fragmentation of 12C projectiles on different targets
(Al, polyethylene).
Single-channel saturation at ~ 10 MIP affects BC discrimination.
flight data - preliminary
all planes
average cluster signal
Good H-He charge
discrimination capability.
He
H
magnetic rigidity R = |pc/Z|
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Spatial resolution
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Critically depends on the signal/noise ratio.
Resolution for junction (X, bending) view determines the momentum measurement.
Beam-test data - orthogonally incident MIP
sx = (2.77 ± 0.04) mm
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Best spatial resolution obtained with non-linear η
algorithm for normally incident MIP.
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Resolution measurement and sensor alignment done
at the last beam test of the flight model with protons
of known energies (CERN SPS, 2003).
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Whole-tracker alignment checked with cosmic rays
collected at ground level during final qualification
tests (INFN Rome “Tor Vergata” laboratories, 2005).
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In flight: alignment parameters will be checked with
high-energy electrons after collecting a sufficient
statistical sample (at least 3 months of data taking).
sy = (13.1 ± 0.2) mm
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Momentum resolution
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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.
mult. scatt.
spat. resol. X
magnetic rigidity R = |pc/Z|
magnetic deflection η = 1/R = |Z/pc|
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
MDR ~ 1 TV
Flight data:
10 GV
electron
with electr. shower
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Flight data:
1.56 GV
positron
with electr. shower
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Flight data:
36 GV
proton
with hadronic shower
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Flight data:
18 GV
antiproton
without shower
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
Flight data:
9.7 GV
He nucleus
without shower
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
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.
S. Ricciarini – PAMELA Silicon Tracker – Vertex 2006, Perugia 28 September 2006
trigger rate