1. Effects of atmospheric electric field on muon intensity observed in GRAPES-3 experiment
B. Hariharan
Tata Institute of Fundamental Research, India
CRI274 / PoS(ICRC2017)481

2. Outline GRAPES-3 tracking muon telescope Electric field measurements
Thunderstorm event on 30 Sep 2015
Monte Carlo simulations
Summary
Future outlook

3. GRAPES-3 tracking muon telescope
Located at Ooty, India.
11.4°N, 76.7°E, 2200 m m.s.l..
PRC as a basic element.
Dimension 600 X 10 X 10 cm3.
Wall thickness of 2.3 mm.
Totally 3712 PRCs.
16 muon telescopes (each 35 m2).
Total area covered is 560 m2.
Total coverage of 2.3 sr.
2.4 m (~550 g.cm-2) thick concrete blocks are used as absorber.
Threshold of muon is sec(θ) GeV

4. Each telescope with 4 layers.
Alternative layers arranged orthogonally.
Reconstructs muon tracks in 225 directions with an accuracy of 4°.
13 X 13 = 169 effective directions.
Possibility of different configuration.
Records 4X109 muons daily with statistical error of ~0.002%.
Muon rate is successfully corrected for detector efficiency variation (PoS(ICRC2017)357).

5. Electric field measurements
Boltek EFM-100.
Installed at 4 locations.
GRAPES-3
GRAPES-2
GOOD SHEPHERD
GOOD LYNTON
Records every 50 ms.
Omni-directional measurements.

6. Thunderstorm event on 30 Sep 2015
5/9 Directions
> 0.5% decrease

7. Time evolution 1/2

8. Time evolution 2/2

9. Data selection
Total regions = 61/169

10. Fast Fourier Transform analysis
Slow and ultra fast variations were removed (∆f = cpd).
-1.2% (9 σ)
Filtered
Expanded view

11. Monte Carlo simulations
CORSIKA v74001 is used with SIBYLL-FLUKA.
7.4 X 1010 proton showers.
Energy range from 10 GeV to 10 TeV.
Angular range of 0° ≤ θ ≤ 60° and 0° ≤ ɸ ≤ 360°.
ECUTS:
Hadron: 50 MeV
Muon: 10 MeV
Electron: 1 GeV
Gamma: 1 GeV
Modified EFIELD is used (PoS(ICRC2017)305).
At the altitude of 8-10 km above m.s.l..
60 steps of electric field ranges from -15 to 15 kV.cm-1.
One set without electric field for background.

12. Results
Muon variation of -1% ≈ Electric potential of 1 GV

13. V.V. Alexeenko et al., 1987ICRC....4..272Am
V.V. Alexeenko et al., 1987ICRC A

14. From experimental dataG3 GS G2 GL
Baksan
V.V. Alexeenko et al.,
Physics Letters A 301 (2002) 299–306
GRAPES-3

15. Summary
Muon intensity always decreases irrespective of polarity of the applied field.
There is a small increase in muon flux at small negative field.
Quadratic dependence is seen both in simulation and observation.
Electric potential of order Giga Volt is required to get change in GRAPES-3 muon flux

16. Future outlook Probing more events.
Simulation for different electric field profiles.
Simulation for different muon threshold.
Directional dependence.
GRAPES-3 as voltmeter.

17. Thank you !!!

19. Combined from all direction

20. Time evolution

21. 1.25
Muon variation of -1% ≈ Electric potential of 1 GV