Session H4: Precision Measurements and Tests of Fundamental Physics I

Progress toward a search for a long-range spin-mass coupling

We discuss progress in our search for a hypothetical long-range coupling between rubidium (Rb) nuclear spins and the mass of the Earth. The experiment employs a dual-isotope Rb comagnetometer: the valence electron dominates magnetic interactions and serves as a precise magnetic field monitor for the nuclei in a simultaneous measurement of Rb-85 and Rb-87 spin precession frequencies, enabling accurate subtraction of magnetic perturbations. The nuclear structure of Rb makes the experiment particularly sensitive to non-magnetic, spin-dependent interactions of the proton. The majority of recent searches for similar effects limit anomalous couplings of either the neutron or electron spin, so the proposed experiment searches a parameter space to some degree, depending on the theoretical model, orthogonal to that constrained by previous experiments. We have begun to collect data and carry out in-depth analysis of systematic effects. The optimized dual-isotope Rb magnetometer has the sensitivity to improve experimental limits on long-range spin-mass couplings by an order of magnitude in general and by three orders of magnitude for the proton spin in particular.   

Using geoelectrons to search for velocity-dependent spin-spin interactions

We use the recently developed model of the electron spins within the Earth to investigate all of the six possible long-range velocity-dependent spin-spin interactions associated with the exchange of an intermediate vector boson.\footnote{B.A. Dobrescu, I. Mocioiu, J. High Energy Phys. \textbf{11}, 005 (2006).} Several laboratory experiments have established upper limits on the energy associated with various spin orientations relative to the Earth.\footnote{S.K. Peck \textit{et al}., Phys. Rev. A \textbf{86}, 012109 (2012).}$^,$\footnote{B.R. Heckel, et al., Phys. Rev. D 78, 092006 (2008).}$^,$\footnote{B.J. Veneman, P.K. Majumder, S.K. Lamoreaux, B.R. Heckel, E.N. Fortson, Phys. Rev. Lett. \textbf{68}, 135 (1992).} We combine the results from three of these experiments with the Earth-spin model to obtain bounds on the velocity-dependent interactions that couple electron spin to the spins of electrons, neutrons and protons. Five of the six possible potentials investigated were previously unbounded. The bound achieved on V$_{8}$ is about 30 orders of magnitude more restrictive in the long-range limit than the only previously established constraint.\footnote{D.F. Jackson Kimball, A. Boyd, D. Budker, Phys. Rev. A 82, 062714 (2010).}   

Precise measurement of the scalar polarizability of $^{115}$In within the $5P_{1/2} \rightarrow 6S_{1/2}$ transition using an atomic beam

In recent years, we have pursued a series of precise atomic structure measurements in Group III elements---currently thallium and indium - in order to test recent \emph{ab initio} theory calculations in these three-valance-electron systems. Such high-accuracy theory is essential for atomic physics-based tests of symmetry violation in these high-Z systems. We have recently completed a precision measurement of the indium scalar polarizability within the 410 nm $5P_{1/2} \rightarrow 6S_{1/2}$ transition using a GaN semiconductor laser interacting transversely with a collimated indium atomic beam in the presence of a large, precisely-calibrated electric field. We use laser frequency modulation and lock-in detection to obtain a high-resolution absorption signal despite indium beam optical depths of $< 0.001$. Our result for the indium scalar polarizability within this transition is 1000.2$\pm$2.7 in atomic units, and is in excellent agreement with a new atomic theory calculation\footnote{M.S. Safranova, private communication}. By combining the experimental result and theory expressions, new, precise values for the indium 6P-state lifetimes can be extracted. Details of the measurement and future plans will be presented.   

$7P_{1/2}$ hyperfine splitting in $^{206,207,209,213}$Fr and the hyperfine anomaly

We perform precision measurements on francium, the heaviest alkali with no stable isotopes, at the recently commissioned Francium Trapping Facility at TRIUMF. A combination of RF and optical spectroscopy allows better than 10 ppm (statistical) measurements of the $7P_{1/2}$ state hyperfine splitting for the isotopes $^{206,207,209,213}$Fr, in preparation for weak interaction studies. Together with previous measurements of the ground state hyperfine structure, it is possible to extract the hyperfine anomaly. This is a correction to the point interaction of the nuclear magnetic moment and the electron wavefunction, known as the Bohr Weisskopf effect. Our measurements extend previous measurements\footnote{Grossman {\it et al} Phys. Rev. Lett. 83, 935 (1999).} to the neutron closed shell isotope (213) as well as further in the neutron deficient isotopes (206, 207).   

Isotope shift measurements on the D1 line in francium isotopes at TRIUMF

Francium is the heaviest alkali and has no stable isotopes. The longest-lived among them, with half-lives from seconds to a few minutes, are now available in the new Francium Trapping Facility at TRIUMF, Canada, for future weak interaction studies. We present isotope shift measurements on the $7S_{1/2} \rightarrow 7P_{1/2}$ ($D1$) transition on three isotopes, 206, 207 and 213 in a magneto-optical trap. The shifts are measured using a c.w. Ti:sapphire laser locked to a stabilized cavity at the mid-point between two hyperfine transitions of the reference isotope $^{209}$Fr. Scanning tunable microwave sidebands locate transitions in the other isotopes. In combination with the $D2$ isotope shifts, analysis can provide a separation of the field shift, due to a changing nuclear charge radius, and specific mass shift, due to changing electron correlations, in these isotopes.   

Kinetic Energy and Hidden Violations of the Equivalence Principle

A major challenge for modern tests of the Einstein equivalance principle (EEP) is to verify that gravity couples equally to both normal matter and antimatter particles. While the EEP has been validated to high precision in tests on normal matter, experimental tests on antimatter are ongoing. We consider the state of experimental constraints on ``hidden,'' spin-independent, EEP-violation that do not manifest for free elementary particles, but do for their antimatter counterparts. We work in the context of the standard model extension, an energy and momentum-conserving effective field theory that describes multiple mechanisms for EEP-violation. We find that such hidden violations of EEP are nevertheless revealed in the gravitational acceleration of bound systems of normal matter, e.g., nuclei. This results from the interplay between EEP-violation and the internal kinetic energy of bound systems of particles. We calculate the kinetic energies of nucleons within nuclei using a Woods-Saxon potential, and estimate the sensitivities of a wide range of atomic species to EEP violation, hidden or otherwise. We make a survey of existing and planned experimental tests of EEP, and report limits on the degree to which the EEP can be violated for antimatter relative to normal matter.   

Limits on violations of Lorentz symmetry and variation of the fine-structure constant using radio-frequency spectroscopy of atomic dysprosium

Atomic dysprosium (Dy) has been found to be a useful system to look for new physics beyond the Standard Model and General Relativity. Large relativistic corrections to electron energies, owing to the high nuclear charge ($Z = 66$), make the energies of atomic states in Dy highly sensitive to proposed variations of the fine-structure constant, $\alpha$. Due to the reduced screening of the nuclear charge, the relative energy of excited states in Dy are also sensitive to violations of Local Lorentz Invariance (LLI) and the Einstein Equivalence Principle (EEP) as parametrized by the Standard Model Extension. The existence of an electric-dipole transition between a pair of nearly-degenerate excited states in Dy allows us to place some of the best limits on these effects with relatively low precision radio-frequency spectroscopy. We present the results of our analyses of over two years of data to constrain variation of $\alpha$ at the level of $|\dot{\alpha}/\alpha|<10^{-16}$~yr$^{-1}$. In the context of the Standard Model Extension we bound violation of LLI for electrons at the level of $10^{-17}$ for the $c_{\mu\nu}$ tensor that modifies the kinetic term in the electronic QED Lagrangian.