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High-energy Electron Spectrum From PPB-BETS Experiment In Antarctica
Kenji Yoshida1, Shoji Torii2 on behalf of the PPB-BETS
collaboration
1Shibaura Institute of Technology, Japan
2Waseda University, Japan
HEAD 2010 2 March 3, 2010
Side view of the detector
9 r.l
.
Trajectory of PPB-BETS
PPB-BETS Observations in Antarctica
Observation:• 13 days in Jan. 2004• Altitude: ~35km
PPB-BETS : Imaging calorimeter• Event selection• Energy measurements• Direction measurements
HEAD 2010 3
Electron Selection- Proton Rejection -
Proton rejection by using the lateral spread of the cascade shower
R.E. parameter = Ratio of energy deposition within 5mm from the shower axis to the total
March 3, 2010
Observed Events100GeV Electrons
250GeV Protons
R.E. distributions
Electron Candidate
Proton Candidate
HEAD 2010 4
Electron Selection- Gamma-ray Rejection -
Fiber signals along the shower axis at top layer => Separation between electrons and gamma rays
March 3, 2010
Electron Candidate
Gamma-ray Candidate
e gamma
Distributions of the nearest hit fiber positions from the shower axis
HEAD 2010 5
Determination of Electron Energy
March 3, 2010
The number of shower particles at shower maximum => Electron energy
HEAD 2010 6
Electron Energy Spectrum- BETS+PPB-BETS -
March 3, 2010
A power-law spectrum : Acceptable at the 95% C.L.
cn2 = 1.605 (d.o.f.=11)
HEAD 2010 7
Search for Anisotropies of Cosmic-ray Electrons
above 100GeV
March 3, 2010
=> No significant anisotropies within statistical errors
Ratio of the observed arrival distribution (>100GeV) to isotropic distribution along the Galactic longitude
HEAD 2010 8
SummaryBETS + PPB-BETS cosmic-ray electron spectrum from 10GeV to 800GeV: => A power-law spectrum E-3.05
Search for cosmic-ray electron anisotropies above 100GeV by PPB-BETS: => Isotropic distribution within statistical
errorsFor detection of nearby source signatures=> Electron observation up to 10 TeV by
CALETMarch 3, 2010
HEAD 2010 9
Backup
March 3, 2010
30th ICRC (Merida) 10 4 July 2007
Effective Geometrical Factor (SW)
Simulation under the same condition of the observations and analysis
30th ICRC (Merida) 11 4 July 2007
Derivation of Cosmic-Ray Electron Energy Spectrum
◆ Ne: The Number of electron candidates◆ CRE: Correction factor of proton contamination in the R.E. cut
with energy dependence (~0.68)◆ Ceg: Correction factor of gamma-ray contamination (~0.84)◆ Cenh: Correction of enhancement of flux due to
the energy resolution (0.97)◆ C2nd: Correction of secondary electrons in the atmosphere
(1.3x10-5 (m-2s-1sr-1GeV-1) @100GeV)◆ Catm: Correction of energy loss of primary electrons
in the overlying atmosphere (1.37)
30th ICRC (Merida) 12 4 July 2007
Uncertainty of Determination of Arrival Directions
Angular resolution with scintillating fibers of PPB-BETS detector:
~0.5 deg
Differences between Geomagnetic Aspect Sensorand Sun Aspect Sensor:
~5 deg
HEAD 2010 13
Atmospheric Gamma-ray Spectrum
March 3, 2010
=> Consistent with ECC
HEAD 2010 14
Proton Rejection Power
March 3, 2010
Reduction of proton background:
Total Rejection Power of Protons: ~20 x 10 x 20 = 4x 103
On-board Trigger by the 1st and 2nd levels: ~ 95 %
Selection of Contained Events in Detector: ~ 90 %Lateral spread of cascade shower: ~95 %
30th ICRC (Merida) 15 4 July 2007
Basic Parameters of PPB-BETS
Instrument Weight ~200 kg
Total Weight (including ballast)
~480 kg
Power Consumption 70 WData Transfer Rate (Iridium Phone)
2.4 kbps
(Down Link to the Station) 64 kbpsEnergy Range 10~1000 GeVGeometrical Factor (SW) 500 ~ 600 cm2srEnergy Resolution 10~25 %Angular Resolution 0.35 ~ 0.60
deg.