Session H8: EDM and Fundamental Symmetries

The ACME Electron EDM Search

We recently improved the limit on the electron electric dipole moment (eEDM), $d_e$, by an order of magnitude\footnote{Science \textbf{343}, 269 (2014)}. An eEDM-induced energy shift consistent with zero implied a limit $|d_e|<9.6\times10^{-29}~e\cdot$cm$\times(\mathcal{E}_{\rm eff}^0/\mathcal{E}_{\rm eff})$ (90\% c.l.). $\mathcal{E}_{\rm eff}~(\mathcal{E}_{\rm eff}^0)$ is the true (mean calculated = 78 GV/cm\footnote{J. Chem. Phys. \textbf{139} 221103 (2013), J. Mol. Spectrosc. \textbf{300}, 16 (2014)}) value of the effective $\mathcal{E}$-field acting on $d_e$. We are implementing various upgrades to substantially enhance usable molecule flux. These include a new type of buffer gas beam source based on a high-yield thermochemical reaction, coherent state preparation via STIRAP, and electrostatic focusing of the molecular beam. Preliminary tests demonstrated significant improvement in molecule number and we anticipate an overall factor of 100 increase. This would enable a tenfold improvement in statistical sensitivity, which would probe interactions at scales up to 10 TeV. Modifications are also being made to suppress the largest systematic errors associated with our previous result to reduce these below our projected statistical sensitivity.   

Measurement of the electric dipole moment of the electron using trapped molecular ions

A permanent electric dipole moment of the electron (eEDM) at the level of $10^{-28}-10^{30}$$e$ cm is predicted by many extensions to the Standard Model. Here we present results from the first measurement of the eEDM using trapped molecular ions. The use of trapped ions -- in this case HfF$^+$ -- has enabled Ramsey-type spectroscopy with free-evolution times of 500 ms, which in turn yields high sensitivity. This time can be increased to beyond one second in future experiments by lowering the ion density. We are currently performing a thorough search for potential systematic errors and placing corresponding upper bounds. These measurements demonstrate the ability to perform precision measurements using an ensemble of ions in rotating fields and provide a route towards an order-of-magnitude increased sensitivity in the second-generation measurement.   

First Atomic Electric Dipole Moment Limit Derived from an Octupole-Deformed Nucleus

Ra-225 (half-life $=$ 15 d, nuclear spin $=$ 1/2) is a promising isotope for a measurement of the EDM of a diamagnetic atom. Due to its large nuclear octupole deformation and high atomic mass, the EDM sensitivity of Ra-225 is expected to be 2-3 orders of magnitude larger than that of Hg-199. We demonstrate an efficient multiple-stage apparatus in which radium atoms are first loaded into a MOT, then transferred into a movable optical-dipole trap (ODT) that carries the atoms over 1 m to a magnetically-shielded science chamber, loaded into a standing-wave ODT, polarized, and then allowed to precess in magnetic and electric fields. We will discuss our first measurement of the EDM of Ra-225, as well as plans for future improvements. This work is supported by DOE, Office of Nuclear Physics (DE-AC02-06CH11357).   

South Pole Lorentz Invariance Test

Searches for Lorentz and CPT violation play an important role in testing current theories of space-time. To test one of the consequences of local Lorentz invariance we have performed a precision test of spatial isotropy at the Amundsen-Scott station near the geographic South Pole. This location provides the most isotropic environment available on Earth. The experiment is a rotating atomic-spin co-magnetometer which compares energy levels of $^{21}$Ne and Rubidium atoms as a function of direction. The experimental sensitivity obtained is more than an order of magnitude better than in previous such measurements, known as Hughes-Drever experiments. By operating the experiment at the Pole we are able to eliminate background signals due to the gyroscopic interactions of spins with Earth's rotation as well as diurnal environmental effects. Here we will present final results from the experiment's 2-year data collection period. This is the first precision atomic physics experiment performed at the Pole, and we will discuss the potential for future such measurements.   

Progress toward the Cosmic Axion Spin Precession Experiments (CASPEr)

We discuss progress on the design and construction of a new set of experiments to search for the QCD axion and axionlike-particle dark matter [Graham and Rajendran, Phys. Rev. D {\textbf{88}}, 035023 (2013); Budker et al., Phys. Rev. X {\textbf{4}}, 021030 (2014)]. Nuclei that interact with an oscillating background axion field acquire time-varying nuclear moments (for example, electric and magnetic dipole moments). Magnetic resonance techniques can be applied to search for precession of nuclear spins induced by the oscillating axion field. An initial phase of these experiments will cover many orders of magnitude in axionlike-particle parameter space beyond the current astrophysical and laboratory limits. It is anticipated that future versions of the experiments will offer sensitivity to QCD axions with masses $m_a < 10^{-9}$ eV.   

Search for Lorentz symmetry violation with entangled Yb$^+$ ions

Recent breakthrough in application of quantum information techniques for test of fundamental physics [T. Pruttivarasin et al., Nature, v.517, 592 (2015)] opened a pathway toward improved probes of Lorentz symmetry violation in electron-photon sector. Here, we describe a detailed scheme based on Yb$^+$ entangled ions that we find to be the best system for such tests that can be carried out with already existing technologies. We estimate the factor of $2.5\times 10^4$ improvement in Lorentz-violation limits with the new scheme.   

Weak interaction studies with trapped $^{6}$He in a double-MOT apparatus

The short-lived isotope $^{\mathrm{6}}$He (half-life 0.8s) is an interesting atom to search for exotic tensor-like contributions to the weak interaction. A double-MOT apparatus has been set up to capture 6He and to precisely measure the beta-neutrino angular correlation parameter a$_{\mathrm{\beta \nu }}$ in its radioactive decay with the aim to search for or constrain potential physics beyond the Standard Model. a$_{\mathrm{\beta \nu }}$ is extracted from an analysis of momentum distribution of the $^{\mathrm{6}}$Li daughter nuclei detected in coincidence with the $\beta $ particles. $^{\mathrm{6}}$He atoms are produced on-line by nuclear reactions at a rate of 2x10$^{\mathrm{10}}$ atoms/s using the Tandem Van de Graaff accelerator at the University of Washington in Seattle. To achieve the precision goal of measuring a$_{\mathrm{\beta \nu }}$ to 0.1{\%}, high trapping and detection efficiency are required along with low background rates from untrapped atoms. Our setup is optimized to overcome these technical challenges; its details will be presented along with preliminary results. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under contract numbers DE-AC02-06CH11357 and DE-FG02-97ER41020   

New Atomic Methods for Dark Matter Detection

We propose to exploit P and T violating effects in atoms, nuclei, and molecules to search for dark matter (eg axions) and various other cosmic fields. We perform calculations of electric dipole moments (EDMs) that a dark matter field would induce in atoms. Crucially, the effects we consider here are linear in the small parameter that quantifies the dark matter interaction strength; most current searches rely on effects that are at least quadratic in this parameter. The induced oscillating EDMs have the potential to be measured with very high accuracy, and experimental techniques in this field are evolving fast. Pairs of closely spaced opposite parity levels that are found in diatomic molecules will also lead to a significant enhancement in these effects. We are also interested in a possible explanation for the anomalous DAMA dark matter detection results based on DM-electron scattering. Our calculations may provide a possible mechanism for dark matter induced ionisation modulations that are not ruled out by other experiments. Alternatively, they could further reduce the available parameter space for certain dark matter models. Phys. Rev. Lett. 113, 081601 (2014); Phys. Rev. D 90, 096005 (2014) [Editors' Suggestion].   

Penning-Trap Signals for Lorentz and CPT Violation

Prospective signals for Lorentz and CPT violation are studied for Penning-trap experiments. The general effective field theory known as the Standard-Model Extension is used to identify observable signals in measurements of anomaly and cyclotron frequencies of trapped particles and antiparticles. Constraints are obtained from existing data on coefficients controlling Lorentz- and CPT-violating operators of arbitrary dimension, and sensitivities in future experiments are discussed.   

Signals for Lorentz violation in atomic spectroscopy

A breakdown of Lorentz and CPT symmetry has been proposed as a possible signal in several candidate theories of quantum gravity. This talk discusses the prospects for detecting Lorentz and CPT violation via atomic spectroscopy, using the effective field theory known as the Standard-Model Extension and including operators of both renormalizable and nonrenormalizable mass dimensions. The discussion targets commonly measured atomic transitions in experiments with conventional matter and with more exotic atoms such as antihydrogen, muonium, and muonic hydrogen. Potential signals are identified and constraints from existing data are obtained.