EXPERIMENTAL TEST OF EQUIVALENCE PRINCIPLE WITH POLARIZED MASSES

A torsion pendulum having masses with 1022 and 1023 polarized electrons is used to search for an anomalous spin interaction of macroscopic range. Competition from magnetic forces is reduced by using Dy-Fe masses (which exhibit orbital compensation of the electron intrinsic spin), combined with light magnetic shielding, so that the sensitivity is better than one-tenth of a percent of the gravitational force. Fluctuations set the overall experimental limit at about 8 times this level. Interpretation of our null result sets limits on electron spin interactions and on moments which are not of electromagnetic origin. In terms of a standard dipole-dipole form the result is (1.6 6.9) × 10-12 of the interaction strength between the magnetic moments of the electrons. Comparisons are made with theoretical predictions for very light exchange particles. © 1990 The American Physical Society.