A Search for Light Z′ Boson Exchange Using Neutron Spin Rotation*

An exotic axial vector interaction mediated via exchange of a light Z′ boson can appear in some extensions of the Standard Model [1]. A neutron spin rotation experiment searching for an exotic interaction from this exchange of the form V₅ = (g_A²/4πm)(e^-m₀r/r)(1/r + 1/λ_c)σ^→ · (v^→ × r^→) in the mm-μm range was performed at the LANSCE FP-12 beamline using polarized slow neutrons passing through a target of parallel slotted glass and copper plates [2,3]. We describe the status of an upgraded experiment which can improve on the sensitivity of φ′ = [2.8 ± 4.6(stat.) ± 4.0(sys.)] × 10⁻⁵ rad/m achieved in [3] by at least two orders of magnitude at the NIST NG-C beamline. We will also compare our existing and projected sensitivity to the recent claim of an observation of Z′ boson exchange using polarized electrons in NV centers in diamond [4]. 

[1] F. M. Piegsa and G. Pignol, Phys. Rev. Lett. 108 (2012)

[2] C. Haddock et al., Nucl. Inst. Meth. A 885 (2018)

[3] C. Haddock et al., Phys. Lett. B 783 (2018)

[4] X. Rong et al., arXiv:2010.15667v2 (2020)