Search for Monopole-Dipole Interactions at the Submillimeter Range with a ${}^{129}\mathrm{Xe}\text{−}{}^{131}\mathrm{Xe}\text{−}\mathrm{Rb}$ Comagnetometer

Monopole-dipole interactions involving scalar couplings between a spin and a massive particle violate both $P$ and $T$ symmetry, and can be mediated by axions. We use a ${}^{129}\mathrm{Xe}\text{−}{}^{131}\mathrm{Xe}\text{−}\mathrm{Rb}$ atomic cell comagnetometer to measure the ratio of precession frequencies between the two xenon isotopes, and search for changes of the ratio correlated with the distance between the atomic cell and a nonmagnetic bismuth germanate crystal. A modulated Rb polarization scheme is used to suppress systematic effects by 2 orders of magnitude. The null results of this search improve the upper limit on the coupling strength $g_s^N{g}_p^n$ over the interaction range 0.11–0.55 mm, and by a maximum improvement factor of 30 at 0.24 mm. The corresponding propagator mass range of this new excluded region covers 0.36–1.80 meV.

Figure 1

(a) Experiment setup. (b) Three types of switches are made in a single measurement round: the bias field direction (${\mathrm{B}}_{+}$ and ${\mathrm{B}}_{-}$), the pumping beam polarization (corresponding to the 0° and 45° angle setting of the rotatable half-wave plate), and the position of the BGO mass (near and far).

Figure 2

(a) A typical precession signal of Xe atoms at a bias field of 20.6 mG, with an amplified view of the data in the inset. (b) The amplitude spectrum of the signal in plot (a). (c) $\delta {\omega }_{129}$, deviation of ${\omega }_{129}$ as a function of the pumping beam power, when probed by Rb magnetometers using dc pumping beams with different pump polarizations (square and circle points). (d) $\delta {\omega }_{129}$ when probed by modulated Rb magnetometers with different rotatable half-wave plate settings (triangle points) as illustrated in Fig. 1. The horizontal dashed lines in plot (c) and (d) correspond to $\delta {\omega }_{129}/2\pi =0\mathrm{Hz}$.

Figure 3

(a) $\mathrm{\Delta }X$ is found to be independent of the pumping beam power; (b) $\mathrm{\Delta }X$ is found to be independent of the bias field strength. Each data point corresponds to the average result of about 30 measurement rounds, and all the data are taken at the cell temperature of $105°\mathrm{C}$. (c) Results collected over the course of two months. The reduced ${\chi }^2$ for this set of data is 1.03. The dashed line in each plot corresponds to the weighted average result of the demonstrated data.

Figure 4

Plot of constraints (95% C.L.) on $|g_s^N{g}_p^n|$ from different experiment efforts. Line 1: ${}^3\mathrm{He}$ depolarization rate measurements [37], line 2: ${}^3\mathrm{He}$ magnetometer [38], line 3: ${}^3\mathrm{He}$ depolarization rate measurement [22], line 4: ${}^{129}\mathrm{Xe}\text{−}{}^{131}\mathrm{Xe}\text{−}\mathrm{Rb}$ comagnetometer [19, 39], line 5: this Letter, line 6: ${}^3\mathrm{He}\text{−}{}^{129}\mathrm{Xe}$ comagnetometer [20].