New constraints on composition-dependent interactions weaker than gravity

Published data from two recent experiments testing the fifth-force hypothesis are analyzed theoretically, and new results are reported. It is suggested that both (1) the positive result of Thieberger (1987) using a hollow Cu sphere floating in water and (2) the negative result of Stubbs et al. (1987) using Cu and Be test bodies in a torsion balance operated on a hillside could be explained in terms of a single Yukawa interaction with a nonzero value of the mixing angle theta5. However, the results of a new torsion-balance experiment with Al and Be test bodies appear to rule out such an interaction, the only possible exception being an interaction coupled to q5 and limited to a narrow region with theta5 near -63 deg.