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Temporal Structures in Positron Spectra and Charge-Sign Effects in Galactic Cosmic Rays.

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|October 28, 2023
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Cosmic positron fluxes measured by the Alpha Magnetic Spectrometer (AMS) show unique variations compared to electrons and protons over 11 years. Positrons are modulated more than protons, offering new insights into cosmic ray behavior.

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Area of Science:

  • Astrophysics
  • Particle Physics
  • Space Science

Background:

  • Cosmic rays, composed of charged particles, travel through space and are influenced by solar activity.
  • Understanding the behavior of different cosmic ray components, like positrons, electrons, and protons, is crucial for heliospheric physics.

Purpose of the Study:

  • To present precision measurements of cosmic positron fluxes over an 11-year solar cycle.
  • To compare the time variations of positron fluxes with those of electrons and protons.
  • To investigate the charge-sign and mass dependencies of cosmic rays in the heliosphere.

Main Methods:

  • Utilized 3.4×10^6 positron events collected by the Alpha Magnetic Spectrometer (AMS) on the International Space Station.
  • Analyzed daily cosmic positron fluxes in the rigidity range of 1.00 to 41.9 GV.
  • Compared positron flux variations with electron and proton flux data over an 11-year period.

Main Results:

  • Positron fluxes exhibit distinct time variations from electron fluxes on both short and long timescales.
  • A statistically significant hysteresis ( > 5σ) between electron and positron fluxes was observed below 8.5 GV.
  • Positron fluxes show similar time variations to proton fluxes but are modulated more significantly (< 7 GV).

Conclusions:

  • Daily positron flux measurements provide unique data for understanding cosmic ray modulation.
  • The observed differences in time variation and modulation between cosmic ray components highlight complex heliospheric processes.
  • Findings contribute to a deeper understanding of charge-sign and mass dependencies in cosmic ray propagation.