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 !