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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. - PowerPoint PPT Presentation
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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
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
Spectrometer
Balloon
To high altitude
BESS spectrometer to be lunched
(Balloon-borne Experiment with Superconducting Magnet Spectrometer)
Motivation of the Observation
Climax Neutron monitor & sunspot number
97 98 99 00Solar minimum Solar maximum
Half cycle of the solar modulation
Year
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/cm2 consist 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).
The observed data below the cutoff is pure atmospheric secondary protons.
Solar Modulation
Atmospheric secondary protons
Observation
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
Proton selection
β-band cut
4. PID by mass measurement
Mass = ReZ(β-2 - 1)1/2
Tracker (in B=1T) R = pc/Ze
50ps TOF counter dE/dx, β
BESS Spectrometer and Balloon Observations
Fight Trajectory (1993-2000)
Map of Northern Canada
Lynn LakePeace River Ft Mcmurray
Flight to ~1000km west
(Cutoff Rigidity ~0.4GV)
120W 100W
54N
60N
Summary of BESS-2000
Pressure
Altitude
Live time~2.1h
Live time~30.5h
Correction of Atmospheric Secondary Protons
Papini et al. based on transport equations
Use dpmjet3 for proton energy after interaction
Re-tune generation function of recoil protons from air nuclei
modified
Comparison of the re-tuned calculation with observed proton data at different air depths
5.82g/cm2
11.9g/cm2
17.6g/cm2
Recoil proton generation function
Our detectable range
Papini et al.
re-tuned
tuned (Asaoka et al.)
Correction of Atmospheric Secondary ProtonsGrowth curve of proton flux below the kinetic energy of 1GeV
Blue line… recoil tune in Asaoka et el.
Light blue line… recoil re-tuneRed circles…observed proton data
Proton and Helium Spectra at the Top of the Atmosphere from 1997 to 2000
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.
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 ]
The data in 2000 is difficult to fit by Force Field approximation up to low energy.
Fitting line for 2000 is lower than data.
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.
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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