New limit on possible long-range parity-odd interactions of the neutron from neutron-spin rotation in liquid 4He

New Limits on Exotic Spin-Dependent Interactions at Astronomical Distances

Exotic spin-dependent interactions involving new light particles address key questions in modern physics. Interactions between polarized neutrons (n) and unpolarized nucleons (N) occur in three forms: g_{S}^{N}g_{P}^{n}σ·r, g_{V}^{N}g_{A}^{n}σ·v, and g_{A}^{N}g_{A}^{n}σ·v×r, where σ is the spin and g's are the corresponding coupling constants for scalar, pseudoscalar, vector, and axial-vector vertexes. If such interactions exist, the Sun and Moon could induce sidereal variations of effective fields in laboratories. By analyzing existing data from laboratory measurements on Lorentz and CPT violation, we derive new experimental upper limits on these exotic spin-dependent interactions at astronomical ranges. Our limits on g_{S}^{N}g_{P}^{n} surpass the previous combined astrophysical-laboratory limits, setting the most stringent experimental constraints to date. We also report new constraints on vector-axial-vector and axial-axial-vector interactions at astronomical scales, with vector-axial-vector limits improved by ∼12 orders of magnitude. We extend our analysis to Hari Dass interactions and obtain new constraints.

Search for exotic parity-violation interactions with quantum spin amplifiers

Quantum sensing provides sensitive tabletop tools to search for exotic spin-dependent interactions beyond the standard model, which have attracted great attention in theories and experiments. Here, we develop a technique based on Spin Amplifier for Particle PHysIcs REsearch (SAPPHIRE) to resonantly search for exotic interactions, specifically parity-odd spin-spin interactions. The present technique effectively amplifies exotic interaction fields by a factor of about 200 while being insensitive to spurious magnetic fields. Our studies, using such a quantum amplification technique, explore the parity-violation interactions mediated by a new vector boson in the challenging parameter space (force range between 3 mm and 1 km) and set the most stringent constraints on axial-vector electron-neutron couplings, substantially improving previous limits by five orders of magnitude. Moreover, our constraints on axial-vector couplings between nucleons reach into a hitherto unexplored parameter space. The present constraints complement the existing astrophysical and laboratory studies on potential standard model extensions.

Constraints on exotic spin-velocity-dependent interactions

Experimental searches for exotic spin-dependent forces are attracting a lot of attention because they allow to test theoretical extensions to the standard model. Here, we report an experimental search for possible exotic spin-dependent force, specifically spin-and-velocity-dependent forces, by using a K-Rb-²¹Ne co-magnetometer and a tungsten ring featuring a high nucleon density. Taking advantage of the high sensitivity of the co-magnetometer, the pseudomagnetic field from this exotic force is measured to be ≤7 aT. This sets limits on coupling constants for the neutron-nucleon and proton-nucleon interactions in the range of ≥0.1 m (mediator boson mass ≤2 μeV). The coupling constant limits are established to be [Formula: see text] and [Formula: see text], which are more than one order of magnitude tighter than astronomical and cosmological limits on the coupling between the new gauge boson such as Z' and standard model particles.

Limits on Axions and Axionlike Particles within the Axion Window Using a Spin-Based Amplifier

Searches for the axion and axionlike particles may hold the key to unlocking some of the deepest puzzles about our Universe, such as dark matter and dark energy. Here, we use the recently demonstrated spin-based amplifier to constrain such hypothetical particles within the well-motivated "axion window" (10  μeV-1  meV) through searching for an exotic dipole-dipole interaction between polarized electron and neutron spins. The key ingredient is the use of hyperpolarized long-lived ^{129}Xe nuclear spins as an amplifier for the pseudomagnetic field generated by the exotic interaction. Using such a spin sensor, we obtain a direct upper bound on the product of coupling constants g_{p}^{e}g_{p}^{n}. The spin-based amplifier technique can be extended to searches for a wide variety of hypothetical particles beyond the standard model.

Experimental Limits on Exotic Spin and Velocity Dependent Interactions Using Rotationally Modulated Source Masses and an Atomic-Magnetometer Array

Various theories beyond the standard model predict new interactions mediated by new light particles with very weak couplings to ordinary matter. Interactions between polarized electrons and unpolarized nucleons proportional to g_{V}^{N}g_{A}^{e}σ[over →]·v[over →] and g_{A}^{N}g_{A}^{e}σ[over →]·v[over →]×r[over →] are two such examples, where σ[over →] is the spin of the electrons, r[over →] and v[over →] are position and relative velocity between the polarized electrons and nucleons, g_{V}^{N}/g_{A}^{N} is the vector or axial-vector coupling constant of the nucleon, and g_{A}^{e} is the axial-vector coupling constant of the electron. Such interactions involving a vector or axial-vector coupling g_{V}^{N}/g_{A}^{N} at one vertex and an axial-vector coupling g_{A}^{e} at the polarized electron vertex can be induced by the exchange of spin-1 bosons. We report new experimental upper limits on such exotic spin-velocity-dependent interactions of the electron with nucleons from dedicated experiments based on a recently proposed scheme. We rotationally modulated two ∼6  Kg source masses at a frequency of 20 Hz. We used four identical atomic magnetometers in an array form to increase the statistics and cancel the common-mode noise. We applied a data processing method based on high precision numerical integration for the four harmonic frequencies of the signal. We reverse the rotation direction of the source masses to flip the signal due to the new interactions; thus, we can apply the [+1,-3,+3,-1] weighting method to remove possible slow drifting. Our constraint on the product of vector and axial-vector couplings is |g_{V}^{N}g_{A}^{e}|<2.1×10^{-34} and on the product of axial-vector and axial-vector couplings is |g_{A}^{N}g_{A}^{e}|<2.4×10^{-22} for an interaction range of 10 m. The new constraints on vector-axial-vector interaction improved by as much as more than 4 orders of magnitude and on axial-axial interaction by as much as 2 orders of magnitude in the corresponding interaction range, respectively.

Searches for Exotic Interactions Using Neutrons

Slow neutrons possess several advantageous properties which make them useful probes for a variety of exotic interactions, including some that can form at least some components of the dark matter of interest for this issue of Symmetry. We discuss the relevant neutron properties, describe some of the recent work that has been done along these lines using neutron experiments mainly with cold and ultra-cold neutrons, and outline some interesting and exciting opportunities which can be pursued using resonant epithermal neutron interactions in heavy nuclei.

Search for exotic spin-dependent interactions with a spin-based amplifier

Development of new techniques to search for particles beyond the standard model is crucial for understanding the ultraviolet completion of particle physics. Several hypothetical particles are predicted to mediate exotic spin-dependent interactions between standard-model particles that may be accessible to laboratory experiments. However, laboratory searches are mostly conducted for static spin-dependent interactions, with a few experiments addressing spin- and velocity-dependent interactions. Here, we demonstrate a search for these interactions with a spin-based amplifier. Our technique uses hyperpolarized nuclear spins as an amplifier for pseudo-magnetic fields produced by exotic interactions by a factor of more than 100. Using this technique, we establish constraints on the spin- and velocity-dependent interactions between polarized neutrons and unpolarized nucleons for the force range of 0.03 to 100 meters, improving previous constraints by at least two orders of magnitude in partial force range. This technique can be further extended to investigate other exotic spin-dependent interactions.

Constraints on the Velocity and Spin Dependent Exotic Interaction at the Micrometer Range

We report on an experimental test of the velocity and spin dependent exotic interaction that can be mediated by new light bosons. The interaction is searched by measuring the force between a gold sphere and a microfabricated magnetic structure using a cantilever. The magnetic structure consists of stripes with antiparallel electron spin polarization so that the exotic interaction between the polarized electrons in the magnetic structure and the unpolarized nucleons in the gold sphere varies periodically, which helps to suppress the spurious background signals. The experiment sets the strongest laboratory constraints on the coupling constant between electrons and nucleons at the micrometer range with f_{⊥}<5.3×10^{-8} at λ=5  μm.

Experimental limit on an exotic parity-odd spin- and velocity-dependent interaction using an optically polarized vapor

Exotic spin-dependent interactions between fermions have recently attracted attention in relation to theories beyond the Standard Model. The exotic interactions can be mediated by hypothetical fundamental bosons which may explain several unsolved mysteries in physics. Here we expand this area of research by probing an exotic parity-odd spin- and velocity-dependent interaction between the axial-vector electron coupling and the vector nucleon coupling for polarized electrons. This experiment utilizes a high-sensitivity atomic magnetometer, based on an optically polarized vapor that is a source of polarized electrons, and a solid-state mass containing unpolarized nucleons. The atomic magnetometer can detect an effective magnetic field induced by the exotic interaction between unpolarized nucleons and polarized electrons. We set an experimental limit on the electron-nucleon coupling \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$g_{\mathrm{A}}^{\mathrm{e}}g_{\mathrm{V}}^{\mathrm{N}} \, < \, 10^{ - 30}$$\end{document}gAegVN<10-30 at the mediator boson mass below 10⁻⁴ eV, significantly improving the current limit by up to 17 orders of magnitude.

Symmetry breaking is an important process in fundamental understanding of matter and dark matter. Here the authors discuss an experimental bound on an exotic parity odd spin- and velocity-dependent interaction between electron and nucleon by using a sensitive spin-exchange relaxation-free atomic magnetometer.

"Radiation Damping" in gas spin comagnetometers

We report a new kind of interaction between overlapping Rb-Xe spin ensembles polarized by spin-exchange optical pumping. The Rb acts as both a medium to optically polarize the Xe spins and as a magnetometer to probe the precession of Xe spins. When Xe spins precess, they result in the precession of Rb spins. Like the radiation damping effect caused by the coil in conventional NMR systems, the precessing Rb spins lead to damping and a frequency-shift for the precessing Xe spins. When Xe spins are operated in a free-induction decay mode, the transverse relaxation time and oscillating frequency of Xe spins change due to the "radiation damping" effect of Rb spins. When Xe spins are operated in the self-oscillating mode, its transverse relaxation time and oscillating frequency will also be changed. These effects will influence the accuracy of NMR probes, which are widely used in the search for CPT- and Lorentz-invariance violations, the fifth force, etc. If this problem is solved or compensated for, the limit of the aforementioned search may be improved.

Experimental upper bound and theoretical expectations for parity-violating neutron spin rotation in 4He

Neutron spin rotation is expected from quark-quark weak interactions in the standard model, which induce weak interactions among nucleons that violate parity. We present the results from an experiment searching for the effect of parity violation via the spin rotation of polarized neutrons in a liquid 4He medium. The value for the neutron spin rotation angle per unit length in 4He, d ϕ / d z = [ + 2.1 ± 8.3 (stat.) - 0.2 + 2.9 (sys.) ] × 10 - 7 rad/m, is consistent with zero. The result agrees with the best current theoretical estimates of the size of nucleon-nucleon weak amplitudes from other experiments and with the expectations from recent theoretical approaches to weak nucleon-nucleon interactions. In this paper we review the theoretical status of parity violation in then → + 4He system and discuss details of the data analysis leading to the quoted result. Analysis tools are presented that quantify systematic uncertainties in this measurement and that are expected to be essential for future measurements.

Searching for an exotic spin-dependent interaction with a single electron-spin quantum sensor

Searching for new particles beyond the standard model is crucial for understanding several fundamental conundrums in physics and astrophysics. Several hypothetical particles can mediate exotic spin-dependent interactions between ordinary fermions, which enable laboratory searches via the detection of the interactions. Most laboratory searches utilize a macroscopic source and detector, thus allowing the detection of interactions with submillimeter force range and above. It remains a challenge to detect the interactions at shorter force ranges. Here we propose and demonstrate that a near-surface nitrogen-vacancy center in diamond can be utilized as a quantum sensor to detect the monopole-dipole interaction between an electron spin and nucleons. Our result sets a constraint for the electron-nucleon coupling, [Formula: see text], with the force range 0.1-23 μm. The obtained upper bound of the coupling at 20 μm is [Formula: see text] < 6.24 × 10-15.

Searching for New Spin- and Velocity-Dependent Interactions by Spin Relaxation of Polarized ^{3}He Gas

We have constrained possible new interactions which produce nonrelativistic potentials between polarized neutrons and unpolarized matter proportional to ασ[over →]·v[over →] where σ[over →] is the neutron spin and v[over →] is the relative velocity. We use existing data from laboratory measurements on the very long T_{1} and T_{2} spin relaxation times of polarized ^{3}He gas in glass cells. Using the best available measured T_{2} of polarized ^{3}He gas atoms as the polarized source and the Earth as an unpolarized source, we obtain constraints on two new interactions. We present a new experimental upper bound on possible vector-axial-vector (V_{VA}) type interactions for ranges between 1 and 10^{8} m. In combination with previous results, we set the most stringent experiment limits on g_{V}g_{A} ranging from ~μm to ~10^{8} m. We also report what is to our knowledge the first experimental upper limit on the possible torsion fields induced by the Earth on its surface. Dedicated experiments could further improve these bounds by a factor of ~100. Our method of analysis also makes it possible to probe many velocity dependent interactions which depend on the spins of both neutrons and other particles which have never been searched for before experimentally.

A slow neutron polarimeter for the measurement of parity-odd neutron rotary power

We present the design, description, calibration procedure, and an analysis of systematic effects for an apparatus designed to measure the rotation of the plane of polarization of a transversely polarized slow neutron beam as it passes through unpolarized matter. This device is the neutron optical equivalent of a crossed polarizer/analyzer pair familiar from light optics. This apparatus has been used to search for parity violation in the interaction of polarized slow neutrons in matter. Given the brightness of existing slow neutron sources, this apparatus is capable of measuring a neutron rotary power of dϕ/dz = 1 × 10(-7) rad/m.