New Spin-dependent Forces
Forces produced by the exchange of unnatural-parity bosons are spin-dependent,
and vanish for unpolarized bodies. Tests for new spin-dependent forces must
contend with background from the magnetization that always associated with
electron or nucleon spins. We have developed electron-spin polarized
test bodies and attractors that have no significant external magnetic
fields. This is achieved by using toroids containing two different kinds
of magnetic materials, a samarium-cobalt alloy and an iron alloy.
The magnetization in iron is due essentially entirely to aligned electron
spins, while only half of the magnetization in samarium cobalt is from
spin, the remainder from orbital angular momentum. This allows us to make
a pendulum that is a spin dipole with a negligible magnetic dipole moment.
The drawing below shows a schematic design of our ``spin pendulum''. Notice
that the net spins of the rings are parallel, while the magnetizations
of the rings alternate; in principle, the magnetization can be confined
within the individual rings. The design also minimizes gravitational couplings
from the small difference in densities of the two kinds of permanent magnet.
The internal field inside the rings is 9500 Gauss, while the field
1 cm from the surface of the pendulum is only 4 mGauss. This residual field
is further reduced by a mu-metal shield.
