1. Numerical Studies of Neutrino Radiation in Solar Flares Ryuji Takeishi Terasawa lab. M2 Institute for Cosmic Ray Research The University of Tokyo 1

2. Overview Introduction Methods Results Discussion Conclusions 2

3. flare An explosion on the solar surface ・ releases 10 28~32 erg in 10 1-3 sec ・ accelerates particles (proton: ~10GeV,electron: ~10MeV) Solar Flare 3 p ν ・ γ(line) ・ｎ e Radio ・Ｘ・ γ Observing secondary particles can reveal flare acceleration mechanism

4. Solar Flare Region ~70 万 km ~500km 2000km Core Radiative envelope Convective envelope Photosphere Chromosphere Corona Magnetic reconnection → Solar flare νradiation Proton reaction 4

5. Current detecter : No detection Next detector : Calculation required Solar Flare Neutrino Observation 5 Calculate neutrino event number in HK by simulating proton reaction in solar flare Super-Kamiokande (SK) Hyper-Kamiokande (HK)

6. Neutrino Generation Processes 6 Proton acceleration （ up to ~10GeV ） Proton reaction in solar atmosphere p + N → p + N´+ kπ + + kπ － + rπ 0 p + N → n + N´+ (k+1)π + + kπ － + rπ 0 πdecay π ± → μ ± + ν μ (ν μ ), π 0 → 2γ, μ ± → e ± + ν e (ν e ) + ν μ (ν μ ) N: nuclei k, r : multiplicity H,He gas pp π π π+π+ νμνμ μ+μ+ e+e+ νeνe νμνμ

7. Methods 1 7 Use Geant4 toolkit Set boxes stacked in the vertical direction as a modeled solar atmosphere p p Theoretical model （ Gingerich et al. 1971 ） Simulation model

8. Methods 2 2 initial proton spectra Model A E max =10GeV N p ∝ E -3 N p (>500MeV) = 10 29 100GeV500MeV ∝ E -1 E NpNp 10GeV500MeV ∝ E -3 E NpNp Powerd spectrum, E min =500MeV, E p = 10 26 erg Model B E max =100GeV N p ∝ E -1 N p (>500MeV) = 5.1×10 27 8

9. Methods 3 Magnetic mirror effect should broaden proton pitch angle ↓ proton injection angles distribute homogeneously over 2πSr 9 A:magnetic mirror ratio (A~10 -2~-1 ) N p = 10 29 → N p = 10 29 ×A p ν

10. Results 1 νfluence Φ on the Earth’s orbit from a solar flare behind the Sun ν e,ν μ Φ= 19.7 / cm 2 Energy fluence = 2.1 GeV/cm 2 = 107MeV ν e,ν μ Φ= 12.1 / cm 2 Energy fluence = 4.8 GeV/cm 2 = 400MeV Model A E max =10GeV, N p ∝ E -3, N p =10 29 A Model B E max =100GeV, N p ∝ E -1, N p = 5.1×10 27 A ν e, ν μ 10

11. SK での検出に必要なフラックス SK で 1event 検出するには Φ ν × σ νp ×N pSK =1 σ νp ~10 -38 cm 2 (E/GeV) → =100MeV とすると σ νp ~10 - 39 cm 2 SK 水 22.5kton → N pSK =10 34 よって Φ ν = 10 5 cm -2 が 1event に必要 HK では N pSK が 20 倍 Φ ν = 5×10 3 cm -2 が 1event に必要 解析時には ν の エネルギーに応じた 断面積を掛ける Event number in HK (Fargion et al. 2004) N ev = Σ σ ν (E ν ) N HK i = e, μ i ii i νfluence from simulation results νcross section Reaction particle number In HK 11

12. Results 2 Event number in HK from a solar flare behind the Sun 12 Model A E max =10GeV, N p ∝ E -3, N p =10 29 A ν e – p ν e – n ν e - e ν μ - e ν μ – p ν μ – n ν e - e total ν e – p (bound) ν μ - p (bound) ν e – p ν e – n ν e - e ν μ - e ν μ – p ν μ – n ν e - e total ν e – p (bound) ν μ - p (bound) Model B E max =100GeV, N p ∝ E -1, N p = 5.1×10 27 A Nev = 9.9×10 -4 A Nev = 2.6×10 -3 A

13. Results 3 Event number in HK from different solar flare positions 13 ν θ Earth Sun behind the Sun in front of the Sun Nev = 10 -5 A ~ 10 -3 A << 1 preliminary

14. Discussion 1 Neutrino event number from one solar flare is less than 10 -5 ~ 10 -3, so detection in HK is difficult Solar flare neutrino detection requires ~10 3 times sensitivity, so it will not become noise of other signal 14

15. Crosby et al.(1992) Discussion 2 Estimate event frequency from solar flare frequency Model A ( E max =10GeV, N p ∝ E -3, N p =10 29 A ) 8.3A×10 -3 / year → 120 / A year/1event Model B ( E max =100GeV, N p ∝ E -1, N p = 5.1×10 27 A ) 1.9A×10 -2 / year → 52 / A year/1event ( Consider only solar cycle maximum and flare behind the Sun ) 15

16. Conclusion Solar flareνevent number is < 10 -3 Detection in HK needs >100 year Solar flareνwill not become noises of otherνsignals 16