Speaker
Kenichi Sakai
(NASA/GSFC/CRESST/UMBC)
Description
The energy spectra of cosmic-ray protons and helium near solar minimum were precisely measured with BESS-Polar II (Balloon-borne Experiment with a Superconducting Spectrometer) during a long-duration flight over Antarctica in December 2007 and January 2008.The absolute fluxes and spectral shapes of primary protons and helium probe the origin and the propagation history of cosmic rays in the Galaxy. The spectra are also essential as inputs to calculate the spectrum of cosmic-ray antiprotons, which are secondary products of cosmic-ray interactions with the interstellar gas.To optimize the measurement of the magnetic rigidity of incident particles, obtained from the curvature of their trajectories in a solenoidal magnetic field of 0.8 Tesla, an improved calibration of the central JET-type drift chamber and two inner drift chambers was developed. We report absolute spectra of primary cosmic-ray protons to $\sim$ 160GeV and helium to $\sim$ 80 GeV/nucleon, and compare these to other current measurements. We also show the antiproton spectrum in the range 0.17 to 3.5 GeV and report the antiproton/proton ratio. The temporal variation of the antiproton/proton ratio, measured by BESS since 1993, covering solar minimum, solar maximum, and solar magnetic field reversal, provides a crucial test of charge-sign dependence of solar modulation.
| Registration number following "ICRC2015-I/" | 967 |
|---|---|
| Collaboration | -- not specified -- |
Author
Kenichi Sakai
(NASA/GSFC/CRESST/UMBC)
