LIMITS ON SPIN-MASS COUPLINGS WITHIN THE AXION WINDOW

We compare the relative precession frequencies of Hg and Cs magnetomet ers as a function of the position of two 475 kg lead masses with respe ct to an applied magnetic field. Our observations limit the size of a possible monopole-dipole interaction expected to be produced by a pseu doscalar particle such as the axion. For a range of 20 cm, the product s of the scalar and pseudoscalar couplings (g(s)g(p)/HBARc) are found to be less than 2.3 x 10(-29) and 3.6 x 10(-29) for couplings to the e lectron and neutron spins, respectively. The e (n) limits are approxim ately 3 (4) orders of magnitude better than earlier experiments.