Bartol Institute, University of Delaware
Observations of the Charge-Sign Dependence in Solar Modulation
Anti-correlation between cosmic ray fluxes and the level of solar activity (solar modulation) is caused by magnetic field fluctuations carried by the solar wind that scatter and/or decelerate Galactic cosmic rays. Cosmic ray electrons and nuclei respond differently to solar modulation, with the differences being clearly related to reversals of the solar magnetic field which occur every eleven years. If the heliospheric magnetic field has certain types of large scale order, the charge sign of cosmic ray particles can affect their propagation. Since electrons and nuclei have greatly different charge/mass ratios, the relation of velocity and magnetic rigidity (momentum/charge) is very different for these two particle species. Consequently a fully quantitative determination of the charge sign dependent component of solar modulation has yet to be made. Careful study of the behavior of the small flux of cosmic ray positrons relative to negative electrons (which have an identical relationship between velocity and rigidity) will allow a definitive separation of charge sign effects from those arising from velocity differences.