Cosmic-Ray Lithium and Beryllium Isotopes in the PAMELA-Experiment Wolfgang Menn

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

2. PAMELA Payload for Antimatter Matter Exploration and Light NucleiAstrophysics • 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 • Velocity versus Rigidity Technique: • Rigidity from spectrometer • Beta from ToF, dEdx, … • Mass Resolution: { { β-Measurement Spectrometer

5. PAMELA Instrument: Spectrometer • 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 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 • 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 7Be / (9Be + 10Be) 7Li / 6Li

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 !