Phys.org June 16, 2023
Among the four fundamental forces, only gravity does not couple to particle spins according to the general theory of relativity. Researchers in China tested this principle by searching for an anomalous scalar coupling between the neutron spin and the Earth’s gravity on the ground. They developed an atomic gas comagnetometer to measure the ratio of nuclear spin-precession frequencies between 129Xe and 131Xe, and searched for a change of this ratio to the precision of 10−9 as the sensor is flipped in Earth’s gravitational field. The null results of this search set an upper limit on the coupling energy between the neutron spin and the gravity on the ground at 5.3×10−22eV (95% confidence level)resulting in a 17-fold improvement over the previous limit. According to the researchers the results can also be used to constrain several other anomalous interactions. In particular, the limit on the coupling strength of axion-mediated monopole-dipole interactions at the range of Earth’s radius are improved by a factor of 17… read more. TECHNICAL ARTICLEÂ
(a) Illustration of the experimental setup… Credit: Phys. Rev. Lett. 130, 201401, 15 May 2023Â