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

We performed an experiment to search for a new spin-dependent P- and T-violating nucleon–nucleon interaction [Formula: see text] which is mediated by light pseudoscalar bosons such as axions or axionlike particles. This interaction causes a shift [Formula: see text] in the precession frequency of nuclear spin polarized gases in the presence of an unpolarized mass. In order to measure this frequency shift a 3 He/[Formula: see text]Xe comagnetometer was used which is based on the detection of free precession of 3 He and [Formula: see text]Xe nuclear spins using SQUIDs as detectors. For the upper limit of [Formula: see text] we obtained 7.1[Formula: see text]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[Formula: see text][Formula: see text]eV, the laboratory upper bounds were improved by up to 4 orders of magnitude.