USING A PENNING TRAP TO WEIGH ANTIPROTONS

A method for measuring the Earth's gravitational acceleration g on antiprotons is proposed. The value of g is obtained by measuring the gravity-induced shift of the center of the radial orbits of antiprotons that are stored in a Penning trap. Such a shift is a measurable effect for particles of very low energy (congruent-to 1 mueV) if the point of injection lies near the axis of a big Penning trap in which the magnetic field is perpendicular to the direction of g. A possible experimental setup is described and several sources of error are analyzed. A comparison with a time-of-flight method, originally proposed to measure g on antiprotons (and now under experimental investigation by an international collaboration), indicates the advantages of the present proposal. The experimental feasibility of the method of measurement that we propose relies on the practical limit that can be achieved in minimizing the antiprotons' energy and on controlling the radial coordinates of the particles before injection into the g-sensitive trap.