Search for anomalous long-range spin-spin interaction

A search for a unique non-electromagnetic interaction between intrinsic spins has been completed. A cryogenic torsion balance was built to measure the torque between two polarized ferromagnets. Each magnet was enclosed in a superconducting lead shield to suppress magnetic interactions, while allowing penetration of anomalous spin-spin fields. The effectiveness of the shields in blocking magnetic fields was determined to be sufficient to allow a significant improvement in the existing limit on the strength of any anomalous spin-spin interaction. The torsion balance measurements indicate no anomalous spin-spin interaction between our spin polarized bodies. Assuming an anomalous interaction of the same functional form as the magnetic interaction, this null result demonstrates that the anomalous interaction must be at least 109.7 times weaker than the magnetic interaction, compared to the pre-existing limit of 107.2