1. Measurements of Cosmic-Ray Lithium and Beryllium Isotopes
with the PAMELA-Experiment
Wolfgang Menn
University of Siegen
On behalf of the PAMELA collaboration
ECRS Torino – 5th September 2016

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

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

9. Velocity (ToF) versus Rigidity Technique for H and He

10. Mass Resolution for Flight Data Helium

11. Velocity versus Rigidity Technique
PAMELA Tof + Spectrometer
Expected Mass Resolution for 4He
4He

12. Latest Reduction of Flight Data
2006 – 2014
Modified „Nuclei“ tracking algorithm
Cleaning of tracker event from MIP and He-hits
Removing multiple-seed clusters
Applying position-finding digital algorithm for saturated clusters
ToF with improved time-walk correction for Z>2
Work in Progress
Create simulated data for modified „Nuclei“ tracking algorithm

13. Velocity (ToF) versus Rigidity Technique

14. 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

15. 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

16. 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

17. Selection Method Discarded ! What is a „non interacting“ event?
Strict Selection: All events with interactions are discarded
Modified selection: Use information of the „clean“ part in the calorimeter, neglect the lower part
Discarded !

18. Multiple dE/dx versus Rigidity Technique

19. Mass Resolution with Calorimeter “Truncated Mean”
4He

20. Published: Hydrogen & Helium Isotope Fluxes and Ratio
using ToF & Calorimeter (2006 & 2007 Data): ApJ A (2016)

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

22. Calorimeter “Truncated Mean” Method: Lithium
2006 – 2014 Data
GEANT4 simulation
TFractionFitter
6Li Li

23. ToF: Lithium
2006 – 2014 Data
GEANT4 simulation
TFractionFitter

24. Mass Resolution For Lithium

25. Calorimeter “Truncated Mean” Method: Beryllium
2006 – 2014 Data
GEANT4 simulation
TFractionFitter

26. ToF: Beryllium
2006 – 2014 Data
GEANT4 simulation
TFractionFitter

27. Mass Resolution For Beryllium

28. Deriving Isotopic Fluxes and Ratios
Efficiencies
Livetime
Interaction losses
Geometry Factor …
So far no isotopic fluxes, only ratios
Work in Progress!

29. Getting the Efficiency in the Calorimeter
GEANT4- Simulation of the PAMELA-Experiment
Derive Efficiency for specific set of selection cuts
Check with flight data:
Use redundant detectors to select flight data 6Li and 7Li
Derive Efficiency in the same way as for simulated data
ToF–β vs. R ToF-dEdx vs. R Trk-dEdx vs. R

30. Measurements of Lithium Isotopes

31. Measurements of Beryllium Isotopes
7Be / (9Be + 10Be)

32. Work in Progress: Derive Systematic Error
An offset in the simulated distributions will change the ratio of the isotope counts
Hydrogen and and Helium: Dominant peak (1H, 4He) and high statistics: Simulated distribution can be checked quite easily
Lithium: 7Li / 6Li ~ 1, low statistics, mass resolution > 0.4 amu
? ?
Backup slide: ISOMAX balloon experiment 1998

33. Checking the Simulated Calorimeter Distribution
with Flight Data
Use redundant detectors to select flight data 6Li and 7Li
Use ToF vs. Rigidity: How does this selection affect the distribution of the calorimeter truncated mean? Are the distributions fully independent?
Check with simulated data…

34. Checking the Simulated Calorimeter Distribution
with Flight Data
Apply selection cuts β vs. R and see how they affect calorimeter truncated mean

35. Checking the Simulated Calorimeter Distribution
Full set simulated data 6Li Li
Simulated data
β-R selected: Li
7Li

36. Checking the Simulated Calorimeter Distribution
Comparing mean value of full set of simulated data vs β-R selected
6Li Li
Blue: full set
Red: β-R selected
Difference

37. Checking the Simulated Calorimeter Distribution
Finally: Comparing mean value of full set of simulated data vs β-R selected flight data
6Li Li
Blue: full set simulated data
Red: β-R selected
flight data
Difference
Good match to the expectations !
Use the method to fine-tune and check the simulated distributions

38. Summary
Momentum resolution of PAMELA spectrometer ca. 3.5 %
Published: H and He with Tof & Calorimeter: Analysis ( 0.1 GeV/n – 1.3 GeV/n)
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 !

39. Backup Slides

40. Work in Progress: Derive Systematic Error
Just for comparison: ISOMAX balloon experiment 1998:
ISOMAX was especially designed to measure 10Be/9Be ratio

41. BESS
MDR = 200 GV
B = 0.5 T
L = 1 m

42. ISOMAX Mass Resolution For Beryllium

43. Comparison ToF & Calorimeter
2.5 – 2.7 GV
ToF
Calorimeter:
Truncated mean
Chi² B.-B.

44. ISOMAX Mass Resolution

45. AMS-01 R=5.56 GV MDReff=32 GV each track layer = 0.65 % X0
(PAMELA %)
Expected He4
mass resolution:
0.4 2GV
Data looks worse!
R=5.56 GV MDReff=32 GV

46. Definition of “non interacting”
qtot= Total energy loss in each layer
qtrack: Energy loss in the three strips closest to the track
Perfect event: qtrack/qtot = 1
Old selection (until ICRC 2013): Integral qtrack/qtot > 0.9

47. 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
CERN Beam Test
Proton Data
~3.5 %

48. Calorimeter “Truncated Mean” Method: Lithium
2006 – 2008 Data
ICRC 2013
GEANT4 simulation
TFractionFitter
7Li
6Li
6Li Li

49. ISOMAX Mass Resolution

50. Measurements of Beryllium Isotopes (2)
Difficult: Separate 9Be and 10Be…
Large systematic error…
Probably we need to use „Chi²-Method“ (or TMVA etc.) to get a better mass resolution…

51. Alternative Analysis: Make Use of Particle’s Slowdown
Move the calculated Bethe-Bloch-Curve for a given Mass through the measured Data and calculate a Chi² value
The best Chi² wins!

52. Mass resolution with “Bethe-Bloch-Chi²” Method 4He
Different methods still under test, work in progress…