1. Cosmic-Ray Lithium and Beryllium Isotopes in the PAMELA-Experiment
Wolfgang Menn
University of Siegen
On behalf of the PAMELA collaboration
ICRC Busan – 13th July 2017

2. A wide Range of Measurements:
PAMELA
Payload for Antimatter Matter Exploration and Light Nuclei Astrophysics
A wide Range of Measurements:
Search for Antimatter ( p, He, e+ ) and Dark Matter
Study of Cosmic Ray Propagation: p, He, e-, B, C
Solar Particles
Solar Modulation
Interactions between energetic Particles and the Earth Magnetic Field
We published results in all these fields:
Highlight talk by M. Boezio

3. PAMELA and its Measured Quantities
GF: 21.5 cm2 sr Mass: 470 kg
Size: 130x70x70 cm3
Power Budget: 360W
Velocity (β)
(Multiple dEdx)

4. Isotope Measurements with the Velocity versus Rigidity Technique
Rigidity from spectrometer
Beta from ToF, dEdx, …
Mass Resolution: { {
β-Measurement Spectrometer

5. PAMELA Instrument: Spectrometer
microstrip Si tracking system + permanent magnet
Measures Rigidity R: R=p / Z∙e
6 layers of silicon microstrip detectors
3 µm resolution in bending view
magnetic field ~ 0.45 T
→ MDR ~ 1 TV

6. PAMELA Spectrometer 6 layers @ 3 µm, 0.45 T → MDR ~1000 GV
(dR/R)mult ~ (x/X0)/(beta · B·dL)
Silicon Tracker doesn`t need support structure → minimal multiple scattering
~3.5 %

7. PAMELA Instrument: Time-of-Flight
Time-Of-Flight (TOF):
plastic scintillators + PMT
time resolution:
~ 300 ps for Z = 1
~ 100 ps for Z = 2
~ 85 ps for Z = 3
~ 80 ps for Z = 4

8. Charge Selection ToF: Charge (after conversion Trk: dEdx vs. 1/beta
from dEdx) vs. beta
Trk: dEdx vs. 1/beta

9. Velocity (ToF) versus Rigidity Technique

10. Mass Resolution for Flight Data Helium
0.29 amu

11. Mass Resolution for Flight Data Helium
PAMELA Tof + Spectrometer
Mass Resolution for 4He
4He

12. Isotope Measurements with the Velocity versus Rigidity Technique
Rigidity from spectrometer
Beta from ToF, Cherenkov, dEdx…
Mass Resolution: { {
β-Measurement Spectrometer
Multiple dE/dX
measurement

13. PAMELA Instrument: Calorimeter
Electromagnetic W/Si calorimeter
44 Si layers (X/Y) +22 W planes
380 µm silicon strips, 4224 channels
16.3 X0, 0.6 λI
Dynamic range ~1100 mip

14. Calorimeter: Truncated Mean Method
Only usuable for non-interacting events
Energy loss in each silicon layer of the calorimeter:
Cut away highest 50%
Use the lower 50% (black points) to calculate a mean dEdx

15. Multiple dE/dx versus Rigidity Technique

16. Mass Resolution for 4He

17. Mass Resolution for 4He
More sophisticated method to analyze the calorimeter data
NOT used for the analysis presented in this work!

18. Published: Hydrogen & Helium Isotope Fluxes and Ratio
using ToF & Calorimeter (2006 & 2007 Data)
Measurements of Cosmic-Ray Hydrogen and Helium Isotopes with the PAMELA experiment
ApJ 818, 1, 68 (2016) 

19. Mass Resolution for Lithium and Beryllium

20. Mass Resolution: Examples
Input: 7Li / 6Li = 1.0

21. Getting Isotope Counts
Compare flight data distributions with „model“ distributions
(using Likelihood-Software like TFractionFitter, RooFit…)
Model: GEANT4- Simulation of the PAMELA-Experiment
Calorimeter: Create simulated dEdx distributions
ToF: Create simulated 1/β distributions
TFractionFitter:
Black Points: Data Red: 6Li Blue: 7Li Grey: 6Li + 7Li
→ Number of 6Li and 7Li in the histogram

22. GEANT4 simulation of PAMELA is good, but not 100% perfect...
How does a non-perfect model affect the result?

23. Effect of a “Wrong” Model Distribution
Input: 7Li / 6Li = 1.0
Δm Flight= 0.45 amu
Quite small effect on the ratio using a wrong „width“

24. Effect of a “Wrong” Model Distribution
Input: 7Li / 6Li = 1.0
Δm Flight = Δm Simulation = 0.45 amu
Both Simulated Distributions have a „shift“
Big effect on the ratio!

25. Deriving the “Shift” Using Flight Data: Beryllium
Example: Shift of the simulated calorimeter distribution:
Use ToF to select 7Be both for flight data and simulation
Compare calorimeter distributions
Flight Data Simulated 7Be (+ 9Be for contamination)
7Be + 9Be Be
ToF
Calorimeter
7Be sel.
7Be sel.

26. Deriving the “Shift” Using Flight Data: Beryllium
Shift of the simulated calorimeter distribution for 7Be
Simplification: Shift function is used for simulation of 7Be, 9Be, 10Be

27. Deriving the “Shift” Using Flight Data: Lithium
Example: Shift of the simulated calorimeter distribution:
Use ToF to select 6Li and 7Li both for flight data and simulation
Compare calorimeter distributions
Flight Data Simulated 6Li + 7Li
7Li sel.
ToF
Calorimeter
7Li sel.
6Li sel.
6Li sel.

28. Deriving the “Shift” Using Flight Data: Lithium
Shift of the simulated calorimeter distribution for 6Li and 7Li
Simplification: Shift function is used for simulation of 6Li and 7Li

29. Deriving Isotopic Fluxes and Ratios
Raw counts: Get raw isotope counts using Likelihood method
(Simulated distributions are shifted, systematic error of the shift functions is propagated into systematic error of the raw counts)
Efficiencies: From simulations, checked with flight data using redundant detectors
Livetime
Interaction losses
Geometry Factor …
Propagate systematic errors!
So far no isotopic fluxes, only ratios
Work in Progress!

30. Preliminary Results
7Li / 6Li
7Be / (9Be + 10Be)

31. Summary
Momentum resolution of PAMELA spectrometer ca. 3.5 %
H and He with Tof & Calorimeter: Analysis ( 0.1 GeV/n – 1.3 GeV/n) published
Li and Be with ToF & Calorimeter: Results show that PAMELA will be able to provide new data for Lithium and Beryllium isotopes up to ~ 1.2 GeV/n.
Thank You !