Search for Anomalous Spin-Like Gravitational Interactions Using a Torsion Pendulum.

A torsion pendulum is used in the time-of-swing method to search for weak anomalous spin-dependent forces between test masses containing polarized electrons. The large attracting masses have 2 times 10^{23} aligned electrons and the small beam masses have one-tenth as many. In order to avoid the problems associated with superconducting shields, the masses were fabricated from a Dy-Fe compound. This compound has internal orbital compensation of the magnetic moment of the aligned spins. With this internal compensation of the magnetic moments, a minimum amount of shielding is needed to account for the imperfectly compensated moment at room temperature. The unique features of this experiment include the spin-polarized masses fabricated from the Dy-Fe compound, the novel use of a modified Fast Fourier Transform algorithm, and the use of the highly sensitive relative precision mode of the torsion pendulum. In terms of the limit on the anomalous spin-coupling constant, alpha _{rm s}, consider that there exists a spin-dependent potential of the form V _{rm a} = alpha _{rm s}S(vec sigma_1, vecsigma _2), where alpha_{ rm s} is the constant which determines the strength of the interaction and S is a tensor interaction of the dipole-dipole form. Given a potential of this form, alpha_{rm s} can be written asalpha_ {s} = {anomalous^in torque over magnetic^in torque}. This experiment places a value on alpha _{rm s} of alpha _{rm s} = (-0.7 +/- 7.1) times 10^{-12}.