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 strongly 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.