Test of Cosmic Spatial Isotropy for Polarized Electrons Using a Rotatable Torsion Balance

To test the cosmic spatial isotropy, we use a rotatable torsion balance carrying a transversely spin-polarized ferrimagnetic ${\mathrm{D}\mathrm{y}}_6{\mathrm{F}\mathrm{e}}_{23}$ mass. With a rotation period of 1 h, the period of anisotropy signal is reduced from one sidereal day by about 24 times, and hence the $1/f$ noise is reduced. Our present experimental results constrain the cosmic anisotropy Hamiltonian $H=C_1{\sigma }_1+C_2{\sigma }_2+C_3{\sigma }_3$ (${\sigma }_3$ is in the axis of earth rotation) to $(C_1^2+C_2^2{)}^{1/2}=(1.1\pm 2.0)\times {10}^{-20}\mathrm{e}\mathrm{V}$ and $|C_3|=(1.1\pm 6.0)\times {10}^{-19}\mathrm{e}\mathrm{V}$. This improves the previous limits on $(C_1^2+C_2^2{)}^{1/2}$ by 27 times.