Search of spin-dependent fifth forces with precision magnetometry

Spin-dependent fifth forces are associated with particles beyond the standard model. In particular, light pseudoscalar bosons mediate long-range forces, allowing mass to interact with spins. The search of these interactions can be performed by periodically varying the distance between a source mass and a spin ensemble, in order to modulate the force intensity and detect it with precision magnetometry techniques. In our setup the force arises from room temperature lead masses and is detected in a paramagnetic crystal at 4.2 K, whose magnetization is monitored by a superconducting quantum interference device (SQUID)-based magnetometer with the sensitivity of 53 aT/Hz. Our measurement places the most stringent constraints on spin-mass interactions in the ranges 1 cm to 10 m and 10 to 300 km, with couplings gepgNs≤5.7X10−32 and gepges≤1.6×10−31 at 95% C.L., improving existing limits up to more than 2 orders of magnitude. We show that this experimental technique may be further leveraged to explore a vast region of the fifth force’s parameter space, with an interaction range longer than a few centimeters.