Search for Spin-Dependent Short-Range Interaction with an 3He/129Xe Clock Comparison Experiment

We performed an experiment to search for a new spin-dependent P- and T-violating nucleon–nucleon interaction σ → ⋅ r ̂ which is mediated by light pseudoscalar bosons such as axions or axionlike particles. This interaction causes a shift Δ ν in the precession frequency of nuclear spin polarized gases in the presence of an unpolarized mass. In order to measure this frequency shift a 3He/ 1 2 9 Xe comagnetometer was used which is based on the detection of free precession of 3He and 1 2 9 Xe nuclear spins using SQUIDs as detectors. For the upper limit of Δ ν sp we obtained 7.1 nHz. With this value, an upper limit of the scalar-pseudoscalar coupling of the axion to the spin of a bound neutron could be deduced within the axion mass window. For axion masses between 2 and 500 μ eV, the laboratory upper bounds were improved by up to 4 orders of magnitude.