Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session D10: Precision Measurements on Atomic and Subatomic Systems |
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Sponsoring Units: GPMFC Chair: Jeff Nico, National Institute of Standards & Technology Room: Maryland B |
Saturday, February 13, 2010 1:30PM - 1:42PM |
D10.00001: Blackbody-radiation shifts in optical frequency standards with trapped ions Dansha Jiang, Bindiya Arora, Marianna Safronova, Charles W. Clark The SI unit of time, the second, is defined in terms of the microwave transition frequency between the two hyperfine levels of the ground state of $^{133}$Cs. Recent advancements in experimental techniques such as laser frequency stabilization, atomic cooling and trapping, etc. have made possible the realization of the second to a precision that is six decades higher than that of the existing standard, by use of optical {\it v.s.} microwave transitions. At optical frequencies, the transition levels are members of different electronic configurations, and one of the largest contributors to the uncertainty budget is the blackbody radiation (BBR) frequency shift. We report BBR shifts of the Ca$^+ 4s - 3d_{5/2}$ and Sr$^+ 5s - 4d_{5/2}$ clock transitions as calculated by the relativistic all-order method, in which all single and double excitations of the Dirac-Fock wave function are included to all orders of perturbation theory. Additional calculations are conducted for the dominant contributions in order to evaluate some omitted high-order corrections and estimate the uncertainty of our final values. Our results for these shifts are an order of magnitude more accurate than previous estimates and are of sufficient accuracy at the present stage of development of trapped-ion optical frequency standards. [Preview Abstract] |
Saturday, February 13, 2010 1:42PM - 1:54PM |
D10.00002: Preparation of the anapole moment measurement in a chain of isotopes Dong Sheng, Jonathan Hood, Luis Orozco We present the current status of the experimental effort towards the measurement of the anapole moment in different isotopes of francium. The anapole is a parity violating, time reversal conserving nuclear moment that arises from the weak interaction among nucleons, and should be sensitive to the changes in the nuclear structure configuration among the isotopes. The anapole is a unique probe of the weak interaction in the presence of the strong interaction. The system is currently being tested with rubidium and we have analyzed the sensitivity to measurements with a chain of Rb isotopes. Our experimental scheme involves a collection of cold atoms in a blue-detuned dipole trap located at the anti-node of a microwave cavity. The standing wave would drive a parity forbidden E1 transition between hyperfine ground states, interfering with an allowed transition. The rate of transitions depends on the positive or negative handedness of the apparatus and the measurement of their difference is proportional to the anapole moment. The experiment will use of the ISAC radioactive beam facility at TRIUMF. [Preview Abstract] |
Saturday, February 13, 2010 1:54PM - 2:06PM |
D10.00003: $^3$He comagnetometer readout for the neutron electric dipole moment (nEDM) experiment at SNS Steven Clayton The nEDM collaboration is developing a new experiment to measure the neutron's electric dipole moment to $~\sim 10^{-28}$~e--cm. A non-zero neutron EDM would be the first observation of CP violation in a baryon containing only light quarks, while a null result would be inconsistent with predictions from most variants of supersymmetry. The experiment will measure the difference in spin precession, of polarized ultracold neutrons (UCN) produced and stored in a superfluid-helium-filled cell, when the magnetic and electric fields are parallel and antiparallel. A key feature of the experimental method is the use of polarized $^3$He atoms within the cell acting as both spin analyzer and comagnetometer to the UCN. In one mode of running, the $^3$He precession signal is detected by SQUID gradiometers adjacent to the cell. This talk will cover the efforts of the nEDM collaboration towards practical implementation of SQUIDs for the $^3$He comagnetometer readout, with a goal of $\leq 1\ {\rm fT/\sqrt{Hz}}$ noise level (referred to one gradiometer loop), low enough to be a small contribution to the overall uncertainty of the final nEDM result. [Preview Abstract] |
Saturday, February 13, 2010 2:06PM - 2:18PM |
D10.00004: Neutron interferometric precision measurement of the n-$^3$He incoherent scattering length M.G. Huber, M. Arif, W.C. Chen, T.R. Gentile, D.S. Hussey, D.A. Pushin, L. Yang, F.E. Wietfeldt, T.C. Black A new high precision measurement of the incoherent neutron-$^3$He scattering length was recently done at the NIST Neutron Interferometry and Optics Facility. Precision measurements of neutron scattering lengths are an important test of nucleon-nucleon (NN) and three nucleon interaction (3NI) models. In general, theoretical models have failed to agree with experimentally determined scattering lengths for systems with greater than two nucleons. The scattering length for the n-$^3$He system is particularly interesting because large spin-dependent effects make it a unique test of three-nucleon and four-nucleon interactions. Our result of $b_i^\prime = -2.429 \pm$ 0.012 (stat.) $\pm$ 0.014 (syst.) fm was obtained by comparing the phase shift caused by a polarized $^3$He sample for two different neutron spin states using an interferometer. This result and other recent experimental measurements of n-$^3$He scattering lengths will be compared with current NN+3NI models. [Preview Abstract] |
Saturday, February 13, 2010 2:18PM - 2:30PM |
D10.00005: Precision neutron polarimetry for a measurement of the n-$^3$He incoherent scattering length of $^3$He Thomas Gentile, M. Arif, W.C. Chen, D.S. Hussey, D.A. Pushin, L. Yang, M.G. Huber, F.E. Wietfeldt, T.C. Black In a recent experiment, we performed a precision measurement of the incoherent scattering length for neutrons in $^3$He at the Neutron Interferometry and Optics Facility (NIOF) at the National Institute of Standards and Technology (NIST). As part of this experiment, the neutron polarization produced by a supermirror in a monochromatic neutron beam and the efficiency of a precession coil spin flipper were measured to better than 0.1\% relative standard uncertainty using polarized $^3$He spin filter analyzers. Two related, but not identical, approaches were employed: the asymmetry method, in which we determined the asymmetry in the transmission of neutrons through the $^3$He, and the \textquotedblleft normalized transmission\textquotedblright method, in which we determined the transmission asymmetry for polarized vs. unpolarized neutrons. (The latter is often referred to as the shim method in neutron scattering, in which a ferromagnetic shim is typically employed to depolarize the beam.) In both cases we employed reproduceable translation of the supermirror so as to permit determination of the $^3$He analyzing power via neutron transmission measurements, and adiabatic fast passage nuclear magnetic resonance to invert the $^3$He polarization. Results from the two methods will be discussed. [Preview Abstract] |
Saturday, February 13, 2010 2:30PM - 2:42PM |
D10.00006: Decoherence Free Neutron Interferometery Dmitry Pushin, Michael Huber, Muhammad Arif, David Cory Matter wave optics provide deep insights into quantum mechanics, and in particular matter wave interferometers have served as important examples of macroscopic quantum coherence. Here we show that matter wave optics can benefit from concepts of quantum information processing. We show that a Decoherence Free (DF) matter wave interferometer that was designed based on a quantum error correction code is much less sensitive to mechanical vibrations than is the standard Mach-Zehnder (MZ) interferometer. Matter wave interferometers in general are extremely sensitive to environmental noise, including vibrations, and as a result are only rarely used. The sensitivity to vibrations is a result of the slow velocities of matter waves. Just as neutron interferometer assisted in the development of our current understanding of foundational issues in quantum mechanics, it is well suited to leading the practical implementation of improved coherent control through quantum information theory. We foresee that these changes can make neutron interferometry more available and extend applications in important fields such as soft condensed matter and spintronics. [Preview Abstract] |
Saturday, February 13, 2010 2:42PM - 2:54PM |
D10.00007: Spin Dependent Absorption Cross Section of Neutron $^3He$ C.B. Fu, T.R. Gentile, T.G. Walker, F.E. Wietfeldt, M.G. Huber Measurement of neutron scattering lengths for light nuclei provides a good opportunity to test theories of nucleon-nucleon and three-nucleon forces. The largest systematic uncertainty for recent measurements of the neutron-$^3He$ incoherent scattering length originates from lack of precise knowledge of the spin dependent abosorption cross section (SDACS). To measure the SDACS to $\sim$0.1\%, the primary experimental challenge is to measure the $^3He$ polarization to the same precision. We are developing a new approach to measure the polarization based on the free induction decay (FID) method. The $^3He$ gas, sealed in a special T-shape cell, is polarized with the spin exchange optical pumping method. The polarized $^3He$ nuclei, which are magnetic dipoles, can induce a classical magnetic field. By using the $^3He$ itself as a magnetometer, the Larmor frequency of the $^3He$ can be measured with FID method. We have chosen a special T-shape for the cell that allows for a calculable magnetic field from the $^3He$ gas while also permitting acceptable neutron transimission. If we flip the polarized $^3He$ 1$80^{\circ}$, the magnetic field will change and therefore the Larmor frequency of $^3He$ will change also. With this method, the polarization of $^3He$, and then the SDACS of n+$^3He$ can be measured to high precision. [Preview Abstract] |
Saturday, February 13, 2010 2:54PM - 3:06PM |
D10.00008: Search For Dinucleon Decay Into Kaon Modes Using Multivariate Techniques Michael Litos The final results of a search for dinucleon decay into kaon modes ($\it{e.g.}$ pp $\rightarrow$ K$^{+}$K$^{+}$, in $^{16}$O) in the Super-Kamiokande detector, are presented. Multivariate techniques are used to maximize search sensitivity. These dinucleon decay modes are motivated by R-Parity violating modes of Supersymmetry, and can be used to constrain the parameter $\lambda''_{uds}$. [Preview Abstract] |
Saturday, February 13, 2010 3:06PM - 3:18PM |
D10.00009: A New Beam Modulation Strategy for the Q$^{p}_{weak}$ Experiment F.N.U. Nuruzzaman A new, robust strategy is presented for beam modulation in the Q-weak experiment. The objective of the Q-weak experiment is to measure the weak charge of the proton via the parity violating asymmetry ($<$ 1ppm) in elastic e-p scattering. The e-p scattering rate largely depends on five beam parameters: horizontal position (X), angle (X), vertical position (Y), angle (Y), and beam energy (E). Changes in these beam parameters when the beam polarization is reversed will create false asymmetries. Although we will attempt to keep changes in beam parameters during reversal as small as possible, we will also measure beam parameter differences and correct the false asymmetries. To do this, we will modulate X, X, Y, Y using four air-core dipoles in the Hall C beamline and measure the beam sensitivities. (We will also modulate beam energy using an SRF cavity.) Two air-core dipoles separated by $\sim $10m will be pulsed at a time to produce relatively pure position or angle changes at the target, for virtually any tune of the beamline. Some preliminary tests of the air-core coils and the associated control instrumentation will be discussed. [Preview Abstract] |
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