Limits on exotic long-range spin-spin interactions of electrons

Area of Science:

• Experimental Physics
• Particle Physics
• Quantum Mechanics

Background:

• Fundamental forces and particle interactions are described by the Standard Model.
• Searches for new physics often involve looking for deviations from predicted interactions or searching for new mediating particles.
• Spin-dependent interactions are particularly sensitive probes of new physics.

Purpose of the Study:

• To search for new, hypothetical spin-dependent interactions mediated by low-mass bosons.
• To set new experimental limits on the coupling strengths of such hypothetical forces.
• To constrain parameters of beyond-Standard-Model physics.

Main Methods:

• A rotating torsion pendulum experiment was conducted.
• The pendulum contained polarized electrons and was surrounded by stationary sources of polarized electrons.
• The experiment was designed to detect hypothetical dipole-dipole, spin-dot-spin, and spin-cross-spin interactions.

Main Results:

• Null results were obtained for the searched-for interactions.
• New 1σ upper limits were placed on (g(P)(e))^2/(ħc), (g(A)(e))^2/(ħc), and (g(V)(e)g(A)(e))/(ħc) for bosons with masses up to 0.1 μeV.
• New constraints were established for static spin-spin interactions.

Conclusions:

• The experiment did not find evidence for the hypothetical forces.
• The results constrain models of new physics, particularly those involving light, weakly interacting bosons.
• The study advances the search for physics beyond the Standard Model through precise measurements of fundamental interactions.