Short-range, spin-dependent interactions of electrons: a sensitive probe for exotic pseudo-Goldstone bosons

We used a torsion pendulum and rotating attractor with 20-pole electron-spin distributions to probe dipole-dipole interactions mediated by exotic pseudo-Goldstone bosons with $m_{\rm b}c^2\leq 500 \; \mu$eV and coupling strengths up to 14 orders of magnitude weaker than electromagnetism. Our 95\% confidence result indicates that any hidden global symmetry involving electrons must have a symmetry-breaking scale $F \geq 70$ TeV, the highest reached in any laboratory experiment. We used an attractor with a 20-pole unpolarized mass distribution to improve laboratory bounds on $CP$-violating monopole-dipole forces with $1.5\:\mu$eV$