Session N2: Focus Session: EDM and Fundamental Symmetry Tests

Order of Magnitude Smaller Limit on the Electron's Electron Dipole Moment

Proposed extensions to the Standard Model of particle physics typically predict that the electron would naturally have a small but potentially measurable electric dipole moment (EDM). The Standard Model, known to be incomplete, instead predicts that the electron EDM is much too small to measure. The ACME collaboration [1] used the enormous electric field that electrons experience within a ThO molecule, the unique structure of this molecule, and a cryogenic buffer gas beam of molecules to search for an electron EDM. The new search was sensitive enough to detect an EDM that is ten times smaller than the previously measured upper limit [2] -- well within the range of predictions from various proposed extensions to the Standard Model. We did not detect such an EDM, however. Instead, we set a new upper limit on the electron EDM at a 90\% confidence limit, $|d_e|<8.7 \times 10^{-29}$, making use of the effective electric field calculated for ThO [3]. The new limit stringently constrains the parameters of proposed extensions to the Standard Model to values that predict an electron EDM smaller than the new limit. The TeV energy scale being probed is comparable to that being investigated at CERN's Large Hadron Collider (LHC).\\[4pt] [1] J. Baron, W. C. Campbell, D. DeMille, J. M. Doyle, G. Gabrielse, Y. V. Gurevich, P. W. Hess, N. R. Hutzler, E. Kirilov, I. Kozyryev, B. R. O'Leary, C. D. Panda, M. F. Parsons, B. Spaun, A. C. Vutha, and A. D. West, Science {\bf 343}, 269 (2014).\\[0pt] [2] J. J. Hudson, D. M. Kara, I. J. Smallman, B. E. Sauer, M. R. Tarbutt, and E. A. Hinds, Nature {\bf 473}, 493 (2011).\\[0pt] [3] L.V. Skripnikov, A.N. Petrov and A.V. Titov, J. Chem. Phys. {\bf 139}, 221103 (2013).   

Precision Spectroscopy of Polarized Molecules in an Ion Trap

To realize the advantages that molecules offer to a measurement of the electron's electric dipole moment (eEDM), one must apply an electric field large enough to polarize the molecule in the lab frame. We show that via the use of a rotating bias field, this can be accomplished for trapped molecular ions. We observe coherence times in excess of 150 ms on the science transition in trapped ionic hafnium fluoride. We characterize some of effects limiting the realization of still longer coherence times. We discuss the implications for an improved eEDM measurement. The work was done in collaboration with Will Cairncross, Kevin Cosell, Dan Gresh, Matt Grau, Huanqian Loh, Ed Meyer, Kang-Kuen Ni, Yiqi Ni, John Bohn and Jun Ye.   

Progress in the Radium EDM Experiment

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 the results of our first attempt to measure 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).   

Coherence time in the JILA eEDM measurement using trapped molecular ions

Trapped molecular ions provide several significant potential advantages in precision measurement experiments due to the ease with which they can be trapped and the long coherence time possible in ground or metastable states. Current precision measurement experiments using ions, such as atomic clocks, typically use a single ion, which limits the signal-to-noise possible. In some cases, it would be beneficial to work with an ensemble of ions to improve the count rate, but ion-ion interactions may also lead to potential sources of systematic errors or decoherence. For example, we have recently demonstrated the feasibility of a measurement of the electric dipole moment of the electron using a collection of trapped HfF$^+$, with a coherence time of 100ms. Here we discuss the effects limiting this coherence time.   

South Pole Lorentz Invariance Test

Atomic spin co-magnetometers are among the most sensitive instruments to test for violations of CPT and Lorentz symmetry. Our rotating co-magnetometer has, in recent years, set the most stringent limits for such violations in fermions with measurements conducted in Princeton. In order to eliminate the gyroscopic pickup of Earth's rotation as a major limiting background, we now operate a Rb-$^{21}$Ne co-magnetometer at the Amundsen-Scott South Pole Station. We discuss the current status of our ongoing South Pole experiment along with the latest results.   

Laboratory Search for a Long-Range, scalar-pseudoscalar Interaction Using Dual-Species NMR with Polarized Xe129 and Xe131 Gas

Various theories for physics beyond the Standard Model predict the presence of new weak forces of ``mesoscopic'' range (mm-$\mu$m). One possibility is a new spin-dependent scalar-pseudoscalar interaction mediated by a spin-0 boson with a small mass.\footnote{Moody/Wilczek, PRD 30, 130 (1984)} The strength of this interaction would be the product of the scalar (gs) coupling at the unpolarized vertex and the pseudoscalar (gp) coupling at the polarized vertex and is proportional to ${\bf s \cdot r}$ where s is the spin of the source particle and r is the interaction distance. Using a test station for an NMR gyroscope at Northrop Grumman Corp., we conducted a search\footnote{Bulatowicz et al., PRL 111, 102001 (2013)} for this interaction by measuring NMR frequency shifts in a vapor cell containing polarized $^{129}$Xe and $^{131}$Xe as a non-magnetic zirconia rod is moved near and far from the cell. The vapor cell features a long T2 spin relaxation time for both polarized species, allowing for very precise frequency measurements and a new laboratory limit to be set on this monopole-dipole interaction between the polarized neutrons in the nuclei and unpolarized matter at distances near 1mm.   

Spectroscopy of Francium, recent developments at TRIUMF

We present the current results of our program of precision spectroscopy on Francium using the recently commissioned Francium Trapping Facility at TRIUMF during two runs. The measurements include $7P_{1/2}$ state hyperfine splitting of isotopes $^{206-213, 221}$Fr as well as isotope shift measurements on the $7S_{1/2} \rightarrow 7P1_{1/2}$ ($D1$) transition. The statistical and systematic errors are small enough that measurements can provide information needed to understand future work on weak interaction physics using microwave and optical excitation of parity non conserving transitions.