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.