Cosmic-ray electrons and positrons are a unique probe of the propagation ofcosmic rays as well as of the nature and distribution of particle sources inour Galaxy. Recent measurements of these particles are challenging our basicunderstanding of the mechanisms of production, acceleration and propagation ofcosmic rays. Particularly striking are the differences between the low energyresults collected by the space-borne PAMELA and AMS-02 experiments and oldermeasurements pointing to sign-charge dependence of the solar modulation ofcosmic-ray spectra. The PAMELA experiment has been measuring the time variationof the positron and electron intensity at Earth from July 2006 to December 2015covering the period for the minimum of solar cycle 23 (2006-2009) till themiddle of the maximum of solar cycle 24, through the polarity reversal of theheliospheric magnetic field which took place between 2013 and 2014. Thepositron to electron ratio measured in this time period clearly shows asign-charge dependence of the solar modulation introduced by particle drifts.These results provide the first clear and continuous observation of how drifteffects on solar modulation have unfolded with time from solar minimum to solarmaximum and their dependence on the particle rigidity and the cyclic polarityof the solar magnetic field.

Time dependence of the electron and positron components of the cosmic
  radiation measured by the PAMELA experiment between July 2006 and December
  2015

Time dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015