measurements of cosmic-ray helium, lithium and beryllium isotopes with the pamela- experiment...
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Measurements of Cosmic-Ray Measurements of Cosmic-Ray Helium, Lithium and Beryllium Helium, Lithium and Beryllium
Isotopes with the PAMELA-Isotopes with the PAMELA-ExperimentExperiment
Wolfgang Menn
University of Siegen
On behalf of the PAMELA collaboration
ICRC 2011 Beijing - 15 August 2011
PAMELAPAMELA
• Search for AntimatterSearch for Antimatter
• Search for Dark MatterSearch for Dark Matter
• Study of Cosmic Ray Propagation (e. g. Study of Cosmic Ray Propagation (e. g. IsotopesIsotopes))
• Study Solar PhysicsStudy Solar Physics
• Study Solar ModulationStudy Solar Modulation
• Measurements in the Earth Magnetic EnvironmentMeasurements in the Earth Magnetic Environment
PPayload for ayload for AAntimatter ntimatter MMatter atter EExploration and xploration and LLight Nucleiight Nuclei AAstrophysicsstrophysics
Isotope Measurements with theIsotope Measurements with the Velocity versus Rigidity TechniqueVelocity versus Rigidity Technique
Velocity versus Rigidity Technique:
•Rigidity from magnetic spectrometer•Beta from ToF, Cherenkov, dEdx…
Mass Resolution:
β-Measurement Spectrometer
Isotope Experiments (ISOMAX etc.): 3σ < Δmmass resolution ~ 0.3 amu
Spectrometer:Measures Rigidity R: R=p / Z∙e
Permanent magnet:•magnetic field ~ 0.45 T
Si-microstrip tracking system: •6 layers of silicon microstrip detectors•3 µm resolution in bending view → MDR ~ 1 TV
PAMELA Instrument: SpectrometerPAMELA Instrument: Spectrometer
45 cm
PAMELA SpectrometerPAMELA Spectrometer
• 6 layers @ 3 µm, 0.45 T , 0.45 m height→ MDR ~1000 GV
CERN Beam Test
Proton Data
•(dR/R)mult ~ (x/X0)/(beta · B·dL)•Silicon Tracker doesn`t need support structure → minimal multiple scattering
~3.5 %
IsotopeMeasurements
Time-Of-Flight (TOF): plastic scintillators + PMTtime resolution ~300 ps for Z=1, ~100ps for Z ≥ 2
PAMELA Instrument: Time-of-FlightPAMELA Instrument: Time-of-Flight
78 cm
Velocity versus Rigidity TechniqueVelocity versus Rigidity Technique
4He
PAMELA Tof + SpectrometerExpected Mass Resolution for 4He
125 400 800 1200 Ekin (MeV/nuc)
PAMELA:Helium Isotopes with ToFPAMELA:Helium Isotopes with ToF
He4
He3
He3
He4
PAMELA:Helium Isotopes with ToFPAMELA:Helium Isotopes with ToF
Data
125 400 800 1200 Ekin (MeV/nuc)
Measurements of Helium IsotopesMeasurements of Helium Isotopes
PAMELA ToFpreliminary
OG1.1 842: „Measurement of Deuterium and 3He component in cosmic rays with Pamela experiment“
Electromagnetic W/Si calorimeter44 Si layers (X/Y) +22 W planes380 µm thick silicon strips, 4224 channels16.3 X0, 0.6 λI
Dynamic range ~1100 mip
PAMELA Instrument: CalorimeterPAMELA Instrument: Calorimeter
PAMELA CalorimeterPAMELA Calorimeter
Select non-interacting eventsFor example: 2.98 GV Lithium
Energy loss in each silicon layer of the calorimeter:
non-interacting events: ~ 70-80% loss in statistics
Expected energy-loss calculated with Bethe-Bloch equation
Cut away highest 50%
Use the lower 50% (black points) to calculate a mean dEdx
““Truncated Mean” MethodTruncated Mean” Method
Helium
He4
He3
Spectrometer + ToF Spectrometer + Calorimeter dEdx
ComparisonComparison
He4
He3
He3
He4
Chi² - MethodChi² - Method
Example:Helium 3.0 GV:Bethe-Bloch calculationCompare data points with theoretical prediction
Best Chi² wins!
Plot Chi² vs. Mass
Chi² - MethodChi² - Method
No good minimum for Chi²
He4
He3
Comparison ToF & Calorimeter (Chi²-Method)Comparison ToF & Calorimeter (Chi²-Method)
Helium 2.5 – 2.7 GV
ToF: 0.42 amu Calorimeter (Chi²): 0.25 amu
Mass resolution with “Bethe-Bloch-Chi²” MethodMass resolution with “Bethe-Bloch-Chi²” MethodHeliumHelium
ToF
Calorimeter(Chi²-Method)
Different methods still under test, work in progress…
125 400 800 1200 Ekin (MeV/nuc)
Measurements of Helium IsotopesMeasurements of Helium Isotopes
PAMELA ToFpreliminary
PAMELA Calorimeter
OG1.1 842: „Measurement of Deuterium and 3He component in cosmic rays with Pamela experiment“
““Truncated Mean” Method: LithiumTruncated Mean” Method: Lithium
““Truncated Mean” Method: LithiumTruncated Mean” Method: LithiumGEANT4 simulation of Calorimeter: IOFFE Institute St. Petersburg
E.A. Bogomolov, G.I. Vasilyev, S.Yu. Krut’kov
Example: Li 2.9 – 3.1 GV
““Truncated Mean” Method: LithiumTruncated Mean” Method: Lithium
3.3 – 3.5 GV
Measurements of Lithium IsotopesMeasurements of Lithium Isotopes
preliminary
““Truncated Mean” Method: BerylliumTruncated Mean” Method: Beryllium
2.9 – 3.1 GV
““Truncated Mean” Method: BerylliumTruncated Mean” Method: Beryllium
3.3 – 3.5 GV
““Truncated Mean” Method: BerylliumTruncated Mean” Method: Beryllium
““Truncated Mean” Method: BerylliumTruncated Mean” Method: Beryllium
GEANT4 simulation for Beryllium shows room for improvement:Do NOT use all layers?
Measurements of Beryllium IsotopesMeasurements of Beryllium Isotopes
PAMELApre-preliminary
preliminary
preliminary
SummarySummary
•Momentum resolution of PAMELA spectrometer ca. 3.5 %•ToF analysis underway, shows expected mass resolution•Analysis using multiple dEdx with calorimeter in progress•Helium results show improved mass resolution compared to ToF•GEANT4 simulation is used for comparison with data•First results show that PAMELA will be able to provide new data for Lithium and Beryllium isotopes up to ~ 1 – 1.5 GeV/n
Work in Progress ….
Thank You !