Bulletin of the American Physical Society
40th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 54, Number 7
Tuesday–Saturday, May 19–23, 2009; Charlottesville, Virginia
Session C2: Permanent EDM Searches |
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Chair: Z.T. Lu, Argonne National Laboratory Room: Gilmer Hall 130 |
Wednesday, May 20, 2009 2:00PM - 2:30PM |
C2.00001: Probing the electron electric dipole moment with cold molecules Invited Speaker: The search for an electron EDM is a search for new particle physics. We are measuring the electron EDM using a beam of cold YbF. The present version of our experiment has the statistical sensitivity to make a measurement at the level of a few times $10^{-28}$ e.cm. and this is in progress. Several upgrades now in preparation, will give a further tenfold improvement in sensitivity. I will discuss the present status of this programme and future prospects. [Preview Abstract] |
Wednesday, May 20, 2009 2:30PM - 3:00PM |
C2.00002: A New Limit on the Permanent Electric Dipole Moment (EDM) of $^{199}$Hg Invited Speaker: A finite permanent electric dipole moment (EDM) of a particle or atom would violate time reversal symmetry ($T$), and would also imply violation of the combined charge conjugation and parity symmetry ($CP$) through the $CPT$ theorem. EDMs are suppressed in the standard model of particle physics (SM), lying many orders of magnitude below current experimental sensitivity. It is generally accepted, however, that extra sources of $CP$ violation are needed to account for baryogenesis and many theories beyond the SM, such as supersymmetry, naturally predict EDMs within experimental reach. To date, EDM searches have yielded null results. The most precise and significant limits have been set on the EDM of the neutron\footnote{C.A. Baker, {\it et al}., Phys. Rev. Lett. {\bf {97}}, 131801 (2006).}, the electron\footnote{B.C. Regan, {\it et al}., Phys. Rev. Lett. {\bf{88}}, 071805 (2002).}, and the $^ {199}$Hg atom\footnote{M.V. Romalis, {\it et al}., Phys. Rev. Lett. {\bf{86}}, 2505 (2001).}, leading to tight constraints on sypersymmetric extensions of the SM. I will describe the results from a new experimental search for the EDM of $^{199} $Hg. We find $d(^{199}\mbox{Hg}) = (0.49 \pm 1.29_{stat} \pm 0.76_{syst}) \times 10^{-29}$ {\it e} cm, and interpret this as a new upper bound, $d(^{199}\mbox{Hg})$ $<$ 3.1$\times$10$^{-29} $ {\it e} cm (95$\%$ C.L.)\footnote{W.C. Griffith, {\it et al}., ArXiv:0901.2328v1.}. This result improves our previous $^ {199}$Hg limit by a factor of 7 and offers a yet more exacting probe of possible new sources of CP violation. The experiment utilizes a stack of four spin-polarized Hg vapor cells in a common $B$-field. The middle two cells have oppositely directed $E$-fields, resulting in EDM-sensitive Larmor shifts of opposite sign; the outer two cells, enclosed by the high voltage (HV) electrodes and thus placed at $E = 0$, are free of EDM effects and instead allow cancelation of $B$- field gradient noise and checks for spurious HV-correlated $B$- field shifts. The dataset consists of 166 runs, with each run lasting roughly 24 hours and comprising several hundred $E$- field reversals. Measurements were performed for nine different vapor cells, four electrodes, two cell-containing vessels, and multiple vapor cell and electrode orientations. An unknown, HV- correlated, EDM-mimicking offset was added to the fitted values of the middle cell precession frequencies. This fixed blind offset masked the measured EDM and was revealed only after the data collection, data cuts, and error analysis were complete. In addition to experimental results, I will briefly outline the resulting new upper bounds on fundamental CP violating parameters. [Preview Abstract] |
Wednesday, May 20, 2009 3:00PM - 3:30PM |
C2.00003: Electric Dipole Moment of the Neutron Invited Speaker: The search for an electric dipole moment (EDM) of the neutron has been underway for nearly 60 years. The absence of a signal for the neutron EDM has provided serious constraints, and challenges, to our understanding of elementary particle interactions. The most recent constraints have come from measurements with very slow neutrons (so-called Ultra-Cold Neutrons), and recent technical developments suggest that the sensitivity could be improved by several orders-of-magnitude. These experiments and their potential physics reach will be discussed. [Preview Abstract] |
Wednesday, May 20, 2009 3:30PM - 4:00PM |
C2.00004: Solid state-based searches for violation of parity and time-reversal symmetries Invited Speaker: We are conducting two novel searches for parity and time reversal invariance-violating permanent electric dipole moments (EDMs), using ferroelectric solids. We have identified, synthesized, and characterized Eu$_{1-x}$Ba$_x$TiO$_3$ ceramics to be used for the electron EDM search. The search for the Schiff moment of $^{207}$Pb nucleus is conducted using PbTiO$_3$ ceramics, in which we have demonstrated decoupling of the nuclear spins from the lattice. The sensitivity gains in these materials originate from large densities $n\approx 10^{22}$~cm$^{-3}$, and from large effective electric fields $E^*\approx 10$~MV/cm due to the ferroelectric displacement of the ions in the crystal lattice field. These experiments aim to achieve factor of 100 improvements to the current limits on the electron EDM and the nuclear Schiff moment. [Preview Abstract] |
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