Limits on new long range nuclear spin-dependent forces set with a K-3He co-magnetometer (0809.4700v2)

Abstract: A magnetometer using spin-polarized K and $^3$He atoms occupying the same volume is used to search for anomalous nuclear spin-dependent forces generated by a separate $^3$He spin source. We measure changes in the $^3$He spin precession frequency with a resolution of 18 pHz and constrain anomalous spin forces between neutrons to be less than $2 \times 10^{-8}$ of their magnetic or less than $2\times 10^{-3}$ of their gravitational interactions on a length scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar and vector particles, including torsion, and constraints on recently proposed models involving unparticles and spontaneous breaking of Lorentz symmetry.

• The paper establishes new constraints on nuclear spin-dependent forces using a co-magnetometer with an exceptional 18 pHz frequency resolution.
• The study limits neutron coupling to light pseudoscalar particles to below 5.8×10⁻¹⁰, tightening bounds on potential new interactions.
• Enhanced sensitivity, improved by a factor of 500 over prior xenon-based experiments, marks a significant advancement in precision measurement techniques.

Limits on New Long-Range Nuclear Spin-Dependent Forces

The paper by Vasilakis et al. explores the domain of long-range nuclear spin-dependent forces using a co-magnetometer setup consisting of spin-polarized potassium (K) and helium-3 ($^{3}$He) atoms. The experiment is designed to probe anomalous interactions that could be mediated by novel particles beyond the standard model, such as pseudoscalar and vector bosons, unparticles, and Goldstone bosons associated with spontaneous Lorentz symmetry breaking.

Methodology and Experimental Setup

The researchers employed a co-magnetometer configuration in which both K and $^{3}$He atoms share the same spatial volume, allowing the system to effectively cancel out ordinary magnetic field influences. This arrangement benefits from a combined magnetic field sensitivity reduction, enabling precise measurement of shifts in the $^{3}$He spin precession frequency with a resolution of 18 pHz. The setup includes a dense nuclear spin-polarized $^{3}$He gas source placed approximately 50 cm from the co-magnetometer. The sensitivity of the device reached 0.6 aT, providing a robust tool for detecting potential anomalous fields acting on neutrons.

Results and Constraints

The paper presents stringent limits on the existence of long-range forces that could couple to nuclear spins. Specifically, constraints on neutron coupling to light pseudoscalar particles with $1/r^3$ interaction potentials have been established, with the results suggesting that such forces must be weaker than $2 \times 10^{-8}$ of the magnetic interaction or $2 \times 10^{-3}$ of the gravitational interactions at the specified length scale. These results represent a significant advancement over prior experiments, offering a sensitivity improvement by a factor of 500 compared to similar studies involving a $^{3}$He-$^{129}$Xe maser.

For massless pseudoscalar bosons, the authors provide a limit on the pseudoscalar-neutron coupling strength $(g^{n}_{p})^{2}/4\pi$ at less than $5.8\times10^{-10}$. This surpasses constraints set by gravitational experiments for derivative couplings expected from axion-like particles, thus narrowing the parameter space for theories involving such mediators.

Theoretical Implications

The paper also discusses implications for theories involving para-photons, unparticles, and large mass scale ($M$) suppressed interactions mediated by a spin-1 vector boson. For a hypothetical dimension-four vector boson coupling to fermions, additional potential forms are analyzed, including those associated with axial-vector and vector-axial enhancements.

In the case of unparticle physics where non-integer scaling dimensions ($d$) produce unconventional force laws, the experiment sets limits on the effective coupling scale. These limits are comparable to those obtained from gravitational tests and highlight the sensitivity of the employed methodologies to novel physical phenomena.

Conclusion and Future Outlook

The research utilizes a sophisticated experimental setup to impose new limits on the interactions of neutrons with hypothetical particles. By achieving an energy resolution of $10^{-25}$ eV, this paper not only helps to constrain a variety of theoretical models but also demonstrates the potential of co-magnetometers as powerful instruments in precision measurement science.

Future developments in this area could focus on enhancing the sensitivity and range of co-magnetometer setups, possibly extending the search into unexplored regions of coupling strengths and interaction ranges. This could lead to groundbreaking discoveries concerning the fundamental forces in nature and further inform theoretical models of particle physics beyond the standard model.