Do leptons generate gravity? First laboratory constraints obtained from some G experiments and possibility of a new decisive constraint

The equivalence of the active and passive gravitational masses has been tes ted in the laboratory to an accuracy of about 5 parts in 10(5). However, th is level of sensitivity is not enough to answer the important question whet her leptons generate gravity. We point out that some of the contemporary ex periments aimed at re-determining the Newtonian gravitational constant, G, have reached the level of sensitivity required to provide the first meaning ful result from a direct experiment on this important issue. Stronger const raints on the hypothesis that leptons do not generate gravity could be more decisively provided by still other G experiments if their aimed sensitivit ies are maintained in experiments with different sets of source masses. (C) 2001 Published by Elsevier Science B.V.