Rotatable-Torsion-Balance Equivalence Principleexperiment for the Spin-Polarized Hofe_{3}

Abstract

We use a rotatable torsion balance to perform an equivalence principle test on a magnetically shielded spin-polarized body of HoFe_{3}. With a rotation period of one hour, the period of possible signal is reduced from one solar day by 24 times, and hence the 1/f noise is greatly reduced. Our present experimental results gives a limit (0.25 +- 1.26) X 10^{-9} on the Eotvos parameter \eta of equivalence of the polarized body compared with unpolarized aluminium-brass cylinders in the solar gravitional field, and a limit (0.34 +- 0.52) X 10^{-9} in the earth gravitional fields. This improves the previous limit on polarized bodies by a factor of 45 for solar field and by a factor of 11 for earth field.