  The PAMELA space experiment, in orbit since 2006, has measured cosmic rays
through the most recent A < 0 solar minimum activity period. During this entire
time, galactic electrons and protons have been detected down to 70 MV and 400
MV, respectively, and their differential intensity variation in time has been
monitored with unprecedented accuracy. These observations are used to show how
differently electrons and protons responded to the quiet modulation conditions
that prevailed from 2006 to 2009. It is well known that particle drifts, as one
of four major mechanisms for the solar modulation of cosmic rays, cause
charge-sign dependent solar modulation. Solar minimum activity periods provide
optimal conditions to study these drift effects. The observed behaviour is
compared to the solutions of a three-dimensional model for cosmic rays in the
heliosphere, including drifts. The numerical results confirm that the
difference in the evolution of electron and proton spectra during the last
prolonged solar minimum is attributed to a large extent to particle drifts. We
therefore present new evidence of charge-sign dependent solar modulation, with
perspective on its peculiarities for the observed period from 2006 to 2009.
