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Contents 1. Motivation of the Observation

To high altitude. The 28th ICRC (ICRC2003, Tsukuba, Japan) Oral session on Solar&Heliospheric Phenomena (SH3.4; Long-term variations) Solar modulation effect on the cosmic-ray proton spectra measured by BESS Yoshiaki Shikaze (Kobe University) for the BESS Collaboration. Balloon.

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Contents 1. Motivation of the Observation

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  1. To high altitude The 28th ICRC (ICRC2003, Tsukuba, Japan)Oral session on Solar&Heliospheric Phenomena (SH3.4; Long-term variations)Solar modulation effect on the cosmic-ray proton spectra measured by BESSYoshiaki Shikaze (Kobe University)for the BESS Collaboration Balloon BESS spectrometer to be lunched (Balloon-borne Experiment with Superconducting Magnet Spectrometer) Contents 1. Motivation of the Observation 2. BESS Spectrometer and Balloon Observations 3. Correction of Atmospheric Secondary Protons 4. Proton and Helium Spectra at the Top of Atmosphere from 1997 to 2000 5. Solar modulation effects on our obtained data 6. Summary Spectrometer

  2. Motivation of the Observation Climax Neutron monitor & sunspot number 97 98 99 00 Year Solar minimum Solar maximum Half cycle of the solar modulation

  3. Motivation of the Observation For low energy protons, the solar modulation effect is large. To understand the solar modulation, it is important to know time variation of low energy proton flux precisely. Our proton data measured at air depth of 5g/cm2consist of primary and secondary components. As the energy decrease, secondary protons increase. Increase of the secondary fraction in observed protons Difficulty in correction of atmospheric secondary protons at low energy region. For tune of the calculation using transport equations on the correction of atmospheric secondary protons, we have measured proton data during ascent (cutoff Rigidity~0.4GV) and descent (cutoff Rigidity~4.2GV). Solar Modulation Atmospheric secondary protons Observation The observed data below the cutoff is pure atmospheric secondary protons.

  4. 4. PID by mass measurement Mass = ReZ(β-2 - 1)1/2 50ps TOF counter dE/dx, β Tracker (in B=1T) R = pc/Ze Proton selection β-band cut BESS Spectrometer and Balloon Observations Features 1. Large Acceptance of 0.3m2Sr 2. Compact and Simple cylindrical structure 1, 2 ⇒ High statistics & low systematic error 3. Uniform magnetic field of 1T

  5. Summary of BESS-2000 Pressure Live time~2.1h Live time~30.5h Altitude BESS Spectrometer and Balloon Observations Map of Northern Canada FightTrajectory (1993-2000) 60N Lynn Lake Peace River Ft Mcmurray (Cutoff Rigidity ~0.4GV) 54N Flight to ~1000km west 120W 100W

  6. Recoil proton generation function Comparison of the re-tuned calculation with observed proton data at different air depths Papini et al. Our detectable range 5.82g/cm2 re-tuned 11.9g/cm2 tuned (Asaoka et al.) 17.6g/cm2 Correction of Atmospheric Secondary Protons Use dpmjet3 for proton energy after interaction Re-tune generation function of recoil protons from air nuclei modified Papini et al. based on transport equations

  7. Correction of Atmospheric Secondary Protons Growth curve of proton flux below the kinetic energy of 1GeV Red circles…observed proton data Blue line… recoil tune in Asaoka et el. Light blue line… recoil re-tune

  8. Proton and Helium Spectra at the Top of the Atmosphere from 1997 to 2000

  9. Solar modulation effects on our obtained data Helium to Proton ratio Correlation of proton flux with Climax data Correlation at about 10GeV Modulation of proton and helium in the same year is ruled by rigidity.

  10. Solar modulation effects on our obtained data Force Field Approximation Interstellar proton flux is assumed by the simple function with 3 parameters. Results of modulation parameter φ and χ2 Fitting range (GeV/n) : [ x, 20 ] Fitting line for 2000 is lower than data. The data in 2000 is difficult to fit by Force Field approximation up to low energy.

  11. Summary • Low energy proton and helium spectra from solar minimum to maximum were obtained. • by using the calculation of atmospheric protons revised to agree with the observed secondary protons. • From our spectra obtained precisely to low energy region in which cosmic rays are very sensitive to and largely affected by the solar modulation, the following modulation effects were observed. 1) 2) 3) The result on the He/p ratio indicates that solar modulation is mainly ruled by rigidity. Proton flux at about 10GeV/n had good correlation with the Climax neutron intensity. The fitting result of our proton spectra by the Force Field approximation indicates the difficulty to describe precisely the large modulation effect at the solar maximum in 2000.

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