2. RCCN International Workshop sub-dominant oscillation effects in atmospheric neutrino experiments 9-11 December 2004, Kashiwa Japan Input data to the neutrino flux calculation : Primary cosmic ray fluxes at various solar activities Yoshiaki Shikaze (JAERI) for the BESS Collaboration (Balloon-borne Experiment with Superconducting Spectrometer) RCCN International Workshop sub-dominant oscillation effects in atmospheric neutrino experiments 9-11 December 2004, Kashiwa Japan Input data to the neutrino flux calculation : Primary cosmic ray fluxes at various solar activities Yoshiaki Shikaze (JAERI) for the BESS Collaboration (Balloon-borne Experiment with Superconducting Spectrometer) Balloo n To high altitude BESS spectrometer to be lunched Spectrometer Contents 1. Motivation 2. Spectrometer and Observations 3. Correction of Atmospheric Secondary Protons 4. Obtained Spectra at the Top of the Atmosphere 5. Solar modulation effects 6. Summary

3. Climax neutron monitor & Sunspot number Motivation : Solar activity Solar minimumSolar maximum

4. To understand the solar modulation, it is important to know time variation of low energy proton flux precisely. For the precise measurement by balloon experiment ( at 5g/cm 2 ), we must estimate the contamination of the atmospheric secondary protons, because as the energy decrease, secondary protons increase rapidly. Motivation : for low energy flux below 1GeV To understand the solar modulation, it is important to know time variation of low energy proton flux precisely. Solar Modulation Precise Low energy P flux Atmospheric secondary P Secondary-to-primary ratio of proton flux at air depth of 5g/cm 2 (Estimation results in Papini et al.)

5. To understand the solar modulation, it is important to know time variation of low energy proton flux precisely. For the precise measurement by balloon experiment ( at 5g/cm 2 ), we must estimate the contamination of the atmospheric secondary protons, because as the energy decrease, secondary protons increase rapidly. For the secondary estimation, we can measure the cosmic-ray data during ascending and descending periods and can use the data at different air depths for the tune of the secondary calculation (using transport equations; Papini et al.). Motivation : for low energy flux below 1GeV To understand the solar modulation, it is important to know time variation of low energy proton flux precisely. For the precise measurement by balloon experiment ( at 5g/cm 2 ), we must estimate the contamination of the atmospheric secondary protons, because as the energy decrease, secondary protons increase rapidly. Solar Modulation Atmospheric secondary P Precise Low energy P flux secondary P estimation BESS-99,2000 … ascent data (Cutoff Rigidity~0.4GV) BESS-2001 … descent data (Cutoff Rigidity~4.2GV). The observed data below the cutoff is pure atmospheric secondary protons. Ascent and descent data

6. Features 1. Large Acceptance of 0.3m 2 Sr 2. Compact and Simple Cylindrical Structure ⇒ High statistics & Small systematic error 3. Uniform magnetic field of 1T Proton selection β-band cut (after dE/dx-band cut) 4. PID by mass measurement Tracker (in B=1T) R = pc/Ze 50ps TOF counter dE/dx, β BESS Spectrometer Mass = ReZ(β -2 - 1) 1/2

7. Balloon Observations Flight Map of BESSSummary of BESS-2000 Pressure Altitude Live time~2.1h Live time~30.5h ( BESS-97~2000,2002 Cutoff Rigidity~ 0.4GV ) Ft.Sumner LynnLake ( BESS-2001 Cutoff Rigidity~ 4.2GV ) ~1000 km

8. Correction of Atmospheric Secondary Protons Secondary proton calculation (Papini et al.) based on transport equations AB C D E F 2 nd -p production processes A.Evaporation B.Recoil C.Slowing down D.Spallation E.Interaction loss F.Ionization energy loss loss processes Comparison of the calculation with observation 5.82g/cm 2 11.9g/cm 2 Primary Secondary (Papini et al.) Total (=primary +secondary ; Papini et al.) BESS-2001 Observed data ( Abe et al. ) Cutoff effect Primary Secondary (Secondary Only)

9. Tune recoil generation function to agree with the observed proton data. Correction of Atmospheric Secondary Protons Secondary proton calculation (Papini et al.) based on transport equations modified [BESS-2001 at Ft. Sumner (cutoff rigidity~4.2GV)] Comparison of the calculation with observation 5.82g/cm 2 11.9g/cm 2 Primary Secondary (Papini et al.) Total (=primary +secondary ; Papini et al.) Cutoff effect BESS-2001 Observed data ( Abe et al. ) AB C D E F 2 nd -p production processes loss processes A.Evaporation B.Recoil C.Slowing down D.Spallation E.Interaction loss F.Ionization energy loss Comparison of the calculation with observation 5.82g/cm 2 11.9g/cm 2 Primary Total (=primary +secondary; Papini et al.) BESS-2001 Observed data ( Abe et al. ) Cutoff effect Secondary (Papini et al.) Total (This work) Secondary (This work)

10. Tune recoil generation function to agree with the observed proton data. Correction of Atmospheric Secondary Protons Secondary proton calculation (Papini et al.) based on transport equations modified [BESS-2001 at Ft. Sumner (cutoff rigidity~4.2GV)] Comparison of the calculation with observation 5.82g/cm 2 11.9g/cm 2 Primary Total (=primary +secondary; Papini et al.) BESS-2001 Observed data ( Abe et al. ) Cutoff effect Total (This work) Secondary (Papini et al.) Secondary (This work) Recoil proton generation function Our detectable energy range Papini et al. This work

11. Correction of Atmospheric Secondary Protons Growth curve (Air depth dependence) of proton flux at Lynn Lake [Cutoff R~0.4GV] Estimation as Primary + Secondary This work Papini et al. Observed proton data (BESS-2000 ascent data at Lynn Lake) Kinetic Energy region: 0.29-0.34(GeV) This work Papini et al. Observed proton data (BESS-2000 ascent data at Lynn Lake) Kinetic Energy region: 0.63-0.73(GeV) Start from floating level

12. Proton and Helium Spectra at the Top of the Atmosphere from 1997 to 2002

13. Kinetic Energy per Nucleon

14. Proton and Helium Spectra at the Top of the Atmosphere from 1997 to 2002 Kinetic Energy per Nucleon

15. Proton and Helium Spectra at the Top of the Atmosphere from 1997 to 2002 Proton flux

16. Proton and Helium Spectra at the Top of the Atmosphere from 1997 to 2002 (He flux) x 1/10

17. Solar modulation effects on our obtained data Force Field Approximation (1 parameter; Modulation parameter φ) I(E k,r 1AU ) = I(E k +φ,r b ) x (E k +m) 2 – m 2 (E k +φ+m) 2 - m 2 I(r) / p(r) 2 = I(r b ) / p(r b ) 2, E(r) = E(r b ) - φ I(r) / p(r) 2 = I(r b ) / p(r b ) 2, E(r) = E(r b ) - φ (ref. Φ~500MV for BESS-97 in Myers et al. ) BESS-97 proton Interstellar Proton Flux = Aβ R P1P1 -P 2 demodulate Φ~500MV

18. Solar modulation effects on our obtained data fitting for Φ obtained by fitting (ref. Φ~500MV for BESS-97 in Myers et al. ) Force Field Approximation (1 parameter; Modulation parameter φ) I(E k,r 1AU ) = I(E k +φ,r b ) x (E k +m) 2 – m 2 (E k +φ+m) 2 - m 2 Interstellar Proton Flux = Aβ R P1P1 -P 2

19. Summary To understand the solar modulation, it is important to know time variation of low energy proton flux precisely. Low energy proton and helium spectra at a different solar activities during a period of solar minimum, 1997, through post-maximum, 2002 have been measured by BESS. Their spectra at TOA were obtained by using the calculation of atmospheric protons revised to agree with the observed protons at different air depths. The obtained spectra were consistent with other experimental data of cosmic-ray measurements. From the check of the solar modulation effects, Interstellar Proton spectrum was obtained by assuming a) Force Field Approximation, b) φ=500MV for BESS-97 and c) simple spectrum formula with 3 parameters.

20. Thank you !