Tests of the weak equivalence principle for charged particles in space

The Weak Equivalence Principle states that in a gravitational field all structureless point-like particles follow the same path. The Weak Equivalence Principle is confirmed for neutral bulk matter with an accuracy of 5 . 10(-12) and for neutral quantum matter on a level of 10(-9), rare tests for charged matter have been carried out. The experiment for freely falling electrons carried out by Witteborn and Fairbank [Witteborn, F.C., Fairbank, W.M. Experimental comparison of the gravitational force on freely falling electrons and metallic electrons. Phys. Rev. Lett., 19, 1049, 1967] with an accuracy of 0.1 is the only one cited in literature. A brief report and re-analysis of this experiment is given and the gravity induced disturbing electrical fields are discussed. We show that experimentation under conditions of stronely reduced residual accelerations (near-weightlessness) will reduce the disturbing effects considerably and will improve the results for free fall tests with charged particles by orders of magnitude. (C) 2007 Published by Elsevier Ltd on behalf of COSPAR.