Tabletop Equivalence Tests with Spin-Polarised Test Masses: Differential Acceleration Bounds

This paper examines what differential-acceleration sensitivity for a spin-polarised test mass implies for a spin-dependent component of free fall. The system considered is a 10 gram polarised test mass carrying 10^23 aligned spins in a tabletop equivalence test, and the observable is Eotvos parameter, differential acceleration and the spin-fraction normalisation. Evaluating the ordinary behaviour of the system and the spin-torsion contribution under explicit assumptions about polarisation and uniformity, and inverting the comparison at the stated laboratory precision, gives a quantitative bound rather than a qualitative assertion of smallness. The computed record is: eta = 1.000e-13; differential_acceleration_m_s2 = 9.810e-13; spin_fraction = 0.01661; bound_per_unit_spin_fraction_m_s2 = 5.908e-11; test_mass_kg = 0.01. The torsion-related contribution is far below the level that would alter the ordinary behaviour of the system at current precision, and the value that would have produced a visible residual is stated so that future improvements can be assessed against it directly. No new measurement is reported. This study is simulated and computed from stated assumptions, not measured.