Apparatus for measuring the force of gravity on freely falling electrons

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Abstract
An apparatus and data analysis technique for measuring the gravitational force on freely falling electrons are described. The measurement required that all forces acting on the electrons be uniform and measurable to about 10−11 eV/m. The electrical force along the axis of the 5‐cm‐diam, vertical copper tube used in the experiment was found to be about 6×10−11 eV/m±9% when the tube was cooled to 4.2 K. Forces on electrons due to magnetic field gradients were reduced well below the electrical ones by selecting only ground state electrons for measurement. Other forces were reduced sufficiently by careful attention to the vacuum and thermal environment. The absence, at 4.2 K, of much stronger electric fields, which were expected to arise from the patch effect and from differential lattice components, contrasts strongly with measurements of electric fields near metal surfaces made at room temperature.