Search for Macroscopic CP Violating Forces Using a Neutron EDM Spectrometer

The search for CP violating forces between nucleons in the so-called axion window of force ranges lambda between 2 x 10(-5) m and 0.02 m is interesting because only little experimental information is available there. Axion-like particles would induce a pseudo-magnetic field for neutrons close to bulk matter. A laboratory search investigates neutron spin precession close to a heavy mirror using ultracold neutrons in a magnetic resonance spectrometer. From the absence of a shift of the magnetic resonance we established new constraints on the coupling strength of axion-like particles in terms of the product g(s)g(p) of scalar and pseudo-scalar dimensionless constants, as a function of the force range lambda,g(s)g(p)lambda(2) <= 2 x 10(-21) [cm(2)] (C.L.95%) for 10(-4) cm < lambda < 1 cm. For 0.1 cm < lambda < 1 cm previous limits are improved by 4 to 5 orders of magnitude.