We report a search for exotic spin-spin interactions between neutrons and electrons which could signal new physics beyond the standard model using slow neutron polarimetric imaging through a dense medium of polarized electrons. Our dense polarized electron target is a ferrimagnet held at its magnetic compensation temperature, which realizes a polarized electron ensemble with zero net magnetization. We sought the spin rotation of transversely polarized neutrons from a neutron-spin–electron-spin interaction of the form $V_2=-g_A^e{g}_A^n(\hslash c/4\pi ){\overrightarrow{\sigma }}_e·{\overrightarrow{\sigma }}_n(e^{-r/{\lambda }_c}/r)$, where $g_A^e$ and $g_A^n$ are the electron and neutron axial couplings, $\overrightarrow{{\sigma }_e}$ and $\overrightarrow{{\sigma }_n}$ are the electron and neutron spin, and ${\lambda }_c$ is the interaction range for an exotic axial vector interaction from massive spin-1 boson exchange of mass $\hslash c/{\lambda }_c$. The resulting average neutron-spin-rotation angle per unit length, $(d{\overline{\varphi }}_{F5}/dz)=[0.41\pm 6.3(\mathrm{stat})\pm 4.4(\mathrm{sys})]\times {10}^{-3}\mathrm{rad}/\mathrm{m}$, is consistent with zero. Our novel approach improves the previous upper limits on the coupling constant product $g_A^e{g}_A^n$ by several orders of magnitude in the poorly explored ${10}^{-8}\le {\lambda }_c\le {10}^{-2}\mathrm{m}$ range.

Close

PrevNext

View figure in article

• Neutron physics
• Particle interactions
• Signatures with new bosons
• Hypothetical particles
• Neutron techniques