1. Calorimetry in space with PAMELA
Valter Bonvicini
INFN – Trieste
On behalf of the PAMELA Collaboration
OUTLINE:
Scientific goals of PAMELA
Overview of the PAMELA instrument
3. The Si-W imaging calorimeter: description and design details
4. Scientific results
5. Conclusions
Valter Bonvicini - CHEF2013, Paris, April 2013

2. The PAMELA Collaboration
Italy:
Bari
Florence
Frascati
Trieste
Naples
Rome
CNR, Florence
Moscow
St. Petersburg
Russia:
Germany:
Siegen
Sweden:
KTH, Stockholm
Valter Bonvicini - CHEF2013, Paris, April 2013

3. PAMELA scientific objectives PAMELA design performance
(A Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics)
PAMELA design performance
Study antiparticles in cosmic rays
Search for antimatter
Search for dark matter
Study cosmic-ray propagation
Study solar physics and solar modulation
Study the electron spectrum (local sources?)
energy range particles in 3 years
Antiprotons MeV GeV O(104)
Positrons MeV GeV O(105)
Electrons up to 500 GeV O(106)
Protons up to 700 GeV O(108)
Electrons+positrons up to 2 TeV (from calorimeter)
Light Nuclei up to 200 GeV/n He/Be/C: O(107/4/5)
AntiNuclei search sensitivity of 3x10-8 in He/He
Valter Bonvicini - CHEF2013, Paris, April 2013

4. Resurs-DK1 satellite + orbit
Resurs-DK1: multi-spectral imaging of earth’s surface.
PAMELA mounted inside a pressurized container.
Launch from Baikonur on June 15th, at 0800 UTC with a Soyuz-U rocket.
As of now, ~ 1013 triggers, > 30 TB of data downloaded. Lifetime extended till end of satellite operations.
Data transmitted to NTsOMZ, Moscow, via high-speed radio downlink, ~16 GB per day.
Quasi-polar (70.0°) and elliptical orbit (350 km km) – from 2010 circular orbit (70.0°, 600 km).
Traverses the South Atlantic Anomaly.
Crosses the outer (electron) Van Allen belt at south pole.
PAMELA
Resurs-DK1
Mass: 6.7 tonnes
Height: 7.4 m
Solar array area: 36 m2
350 km
70o
SAA
610 km
Valter Bonvicini - CHEF2013, Paris, April 2013

5. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
The PAMELA instrument
21.5 cm2sr
Time-of-flight
Trigger / Albedo rejection / Particle identification (up to 1 GeV/c) / dE/dx
3 double-layer scintillator paddles
Timing resolution:
(paddle)  110 ps
(ToF)  330 ps (MIPs)
Anticoincidence system
Rejection of events with particles
interacting with the apparatus
Plastic scintillator paddles
MIP efficiency > 99.9%
Si Tracker + magnet
Measures rigidity
5 Nd-B-Fe modules (0.43T)
6 planes of double-sided Si microstrip detectors
~3 µm resolution (bending view)
 MDR  1.2 TV
Mass: 470 kg
Power: ~ 360 W
Size: 130x70x70 cm3
Si-W Imaging Calorimeter
Shower-tail catcher (S4)
Plastic scintillator paddle, 1 cm thick
Main task: ND trigger
Neutron detector
36 3He counters
e/h discrimination at high energies
Valter Bonvicini - CHEF2013, Paris, April 2013

6. The PAMELA Imaging Calorimeter - 1
Main tasks:
lepton/hadron discrimination
e+/- energy measurement
Characteristics:
22 W plates (2.6 mm / 0.74 X0)
44 Si layers (X-Y), 380 µm thick
Total depth: 16.3 X0 / 0.6 lI
4224 channels
Self-triggering mode option
(> 300 GeV; GF~600 cm2 sr)
Mass: 110 kg
Power Consumption: 48 W
Design performance:
p,e+ selection efficiency ~ 90%
p rejection factor ~ 105
e rejection factor > 104
Energy resolution ~ 200 GeV
Valter Bonvicini - CHEF2013, Paris, April 2013

7. The PAMELA Imaging Calorimeter - 2
44 Si detector views (22X and 22Y)
8x8 cm2 detectors arranged in a
3x3 matrix
32 strips/detector, 2.4 mm pitch
Strips of detectors in the same row
(column) are bonded together
(ladder)  24 cm long strips
Each ladder (32 channels) is read
out by 2 CR1.4P front-end chips
 6 front-end chips/view
In total:
396 silicon detectors
264 CR1.4P chips
4224 channels
Valter Bonvicini - CHEF2013, Paris, April 2013

8. The PAMELA Imaging Calorimeter - 3
Front-end  CR1.4P ASIC (full custom design)
Design characteristics:
- 16 channels/chip
- channel structure: CSA, shaper, T/H, out. mux.
- input-selectable calibration circuit
- integrated self-trigger circuit
- shaping time = 1 µs
- sensitivity = 5 mV/MIP
- wide dynamic range: 7.1 pC = 1400 MIP (1 MIP =
4.9 fC)
- ENC ≈ 2700 e- rms + 5 e- /pF
ADC:
bit ADC/view  44 ADCs (AD977A)
- total calorimeter proc. time ~ 700 µs
Readout:
- Calorimeter divided into 4 sections:
Odd_X, Odd_Y, Even_X, Even_Y
- 1 DSP/section (ADSP2187)  4 DSPs
on-line calibration
data compression
- 1 FPGA/section (A54SX72)  4 FPGAs
Architecture of one channel of the CR1.4P
1-MIP signal distribution
(S/N ~ 10)
Valter Bonvicini - CHEF2013, Paris, April 2013

9. interacting antiproton (flight data)
84 GeV/c
interacting antiproton (flight data)
Valter Bonvicini - CHEF2013, Paris, April 2013

10. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
92 GeV/c positron
(flight data)
Valter Bonvicini - CHEF2013, Paris, April 2013

11. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
Flight data: 36 GeV/c
interacting proton
Valter Bonvicini - CHEF2013, Paris, April 2013

12. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
Flight data:
32.3 GeV/c positron
Valter Bonvicini - CHEF2013, Paris, April 2013

13. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
Antiproton results
Simon et al. (ApJ 499 (1998) 250)
Ptuskin et al. (ApJ 642 (2006) 902)
Donato et al. (PRL 102 (2009) )
O. Adriani et al., PRL 102, (2009);
O. Adriani et al., PRL 105, (2010)
Valter Bonvicini - CHEF2013, Paris, April 2013

14. Positron selection with the calorimeter - 1
Rigidity: GV e-
Events
p (non-int)
p (int)
Events (x 103)
p (non-int) e+
p (int)
Fraction of charge released along the calorimeter track (left, hit, right)
Valter Bonvicini - CHEF2013, Paris, April 2013

15. Positron selection with the calorimeter - 2
Rigidity: GV e-
Events e+
Events p
Fraction of charge released along the calorimeter track (left, hit, right) +
Energy-momentum match
Valter Bonvicini - CHEF2013, Paris, April 2013

16. Positron selection with the calorimeter - 3
Rigidity: GV e-
Events
Events e+ p
Energy-momentum match
Starting point of shower
Longitudinal profile
Fraction of charge released along the calorimeter track (left, hit, right) +
Valter Bonvicini - CHEF2013, Paris, April 2013

17. Positron-to-electron fraction - 1
O. Adriani et al., Nature 458
(2009)
O. Adriani et al, Astropart.
Phys. 34 (2010) 1-11.
Moskalenko and Strong,
Astrophys. J.493, (1998)
Valter Bonvicini - CHEF2013, Paris, April 2013

18. Positron-to-electron fraction - 2
Valter Bonvicini - CHEF2013, Paris, April 2013

19. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
Summary
PAMELA has been in orbit and studying cosmic rays for ~ 7 years. ~ 1013 triggers
and > 30 TB of data have been downlinked.
The Imaging Calorimeter has been performing nominally throughout this period:
basic performance (noise, signal, baseline...) are nominal and stable;
science performance (energy resolution, particle id., etc.) are consistent with
design specifications;
no degradations/failures/functionality loss observed so far;
the calorimeter proved to be a key instrument to achieve the scientific
results of PAMELA.
Antiproton-to-proton flux ratio and antiproton energy spectrum (~100 MeV GeV)
show no significant deviations from secondary production expectations.
High energy positron fraction (>10 GeV) increases significantly (and unexpectedly!)
with energy (recent confirmation by AMS). Primary source?
The proton and helium nuclei spectra have been measured up to 1.2 TV. The
observations challenge the current paradigm of cosmic ray acceleration and
propagation.
Waiting for other AMS results to compare contemporary measurements.
Valter Bonvicini - CHEF2013, Paris, April 2013

20. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
~ Spare slides ~
Valter Bonvicini - CHEF2013, Paris, April 2013

21. Orbital environment and in-flight operation
Particle rate:
max. at the poles (cutoff <100 MV)
min. at the equator (cutoff ~15 GV)
Calorimeter operation:
Calibration performed every 95 min. (at
the ascending node)
Data acquisition:
- special run after calibration (“full mode”)
 ~ 10 kByte/ev.
- normal physics runs (“compressed
mode”)  ~ 1 kByte/ev.
Slow control:
Temperatures
Detector leakage currents
Calibration & supply voltages
~ 25 Hz
ascending node
Valter Bonvicini - CHEF2013, Paris, April 2013

22. Calorimeter in-flight performance - 2
~24.3
~24.0
GROUND (muons)
FLIGHT (relativistic particles)
Valter Bonvicini - CHEF2013, Paris, April 2013

23. Calorimeter in-flight performance - 1
January 2008
July 2006
Valter Bonvicini - CHEF2013, Paris, April 2013

24. Calorimeter in-flight performance - 2
January 2008
July 2006
Valter Bonvicini - CHEF2013, Paris, April 2013

25. H and He absolute fluxes @ high energy
2.85
2.67
232 GV
Spectral index
2.77
2.48
243 GV
O. Adriani et al., Science 332 (2011) 69
Deviations from single power law (SPL):
Spectra gradually soften in the range 30÷230GV
Spectral hardening @ R~235GV ~0.2÷0.3
SPL is rejected at 98% CL
Origin of the structures?
- At the sources: multi-populations, etc.?
- Propagation effects? (e.g. P. Blasi et al., Phys.Rev.Lett. 109 (2012) H He
Valter Bonvicini - CHEF2013, Paris, April 2013

26. interacting anti-proton
Flight data: 11.6 GeV/c
interacting anti-proton
Valter Bonvicini - CHEF2013, Paris, April 2013

27. non-interacting anti-proton
Flight data: 18 GeV/c
non-interacting anti-proton
Valter Bonvicini - CHEF2013, Paris, April 2013

28. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
Flight data: 14.7 GV
Interacting nucleus
(Z = 8)‏
Valter Bonvicini - CHEF2013, Paris, April 2013

29. calorimeter self-trigger (m.p. electron)
Valter Bonvicini - CHEF2013, Paris, April 2013

30. Valter Bonvicini - CHEF2013, Paris, 22-25 April 2013
13 GV
Interacting He
Valter Bonvicini - CHEF2013, Paris, April 2013

31. CALO SELF TRIGGER EVENT: 167103 MIP RELEASED
279 MIP in S4
26 Neutrons in ND
Valter Bonvicini - CHEF2013, Paris, April 2013

32. Charge identification with the Calorimeter
Truncated mean of multiple dE/dx measurements in different silicon planes
Valter Bonvicini - CHEF2013, Paris, April 2013

33. Energy-momentum match
Preliminary e- e+
‘Electron’
‘Hadron’
p, d p
Valter Bonvicini - CHEF2013, Paris, April 2013