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Explore the measurements of antimatter, dark matter, and cosmic ray propagation using the PAMELA payload. Study interactions between energetic particles and the Earth's magnetic field.
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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
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
PAMELA and its Measured Quantities GF: 21.5 cm2 sr Mass: 470 kg Size: 130x70x70 cm3 Power Budget: 360W Velocity (β) (Multiple dEdx)
Isotope Measurements with the Velocity versus Rigidity Technique • Velocity versus Rigidity Technique: • Rigidity from spectrometer • Beta from ToF, dEdx, … • Mass Resolution: { { β-Measurement Spectrometer
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
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 %
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
Charge Selection ToF: Charge (after conversion from dEdx) vs. beta Trk: dEdx vs. 1/beta
Mass Resolution for Flight Data Helium PAMELA Tof + Spectrometer Mass Resolution for 4He 4He
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
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
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
Mass Resolution for 4He More sophisticated method to analyze the calorimeter data NOT used for the analysis presented in this work!
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)
Mass Resolution: Examples Input: 7Li / 6Li = 1.0
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
GEANT4 simulation of PAMELA is good, but not 100% perfect... How does a non-perfect model affect the result?
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“
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!
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.
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
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.
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
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!
Preliminary Results 7Be / (9Be + 10Be) 7Li / 6Li
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 !