Bulletin of the American Physical Society
APS April Meeting 2011
Volume 56, Number 4
Saturday–Tuesday, April 30–May 3 2011; Anaheim, California
Session R13: Precision Measurements, Fundamental Symmetries, and Tests of the Standard Model |
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Sponsoring Units: GPMFC Chair: Blayne Heckel, University of Washington Room: Royal EF |
Monday, May 2, 2011 1:30PM - 1:42PM |
R13.00001: Precision laser spectroscopy of Li isotopes for probing the nuclear size J.D. Gillaspy, C.J. Sansonetti, C.E. Simien, S.M. Brewer, J.N. Tan, R.C. Brown, S.J. Wu, J.V. Porto We have performed a new measurement of the isotope shift of the $^{6}$Li and $^{7}$Li D lines. Our results resolve large discrepancies between theory and all other measurements of the splitting isotope shift (isotopic difference in the 2P fine structure). Our probe laser was heterodyned to a frequency comb to determine absolute transition frequencies. The laser-atom interaction was modeled to accurately determine the line centers of the hyperfine components, some of which are separated by less than their natural widths. The overall accuracy of our measured frequencies is four parts in 10$^{11}$. These results can be combined with accurate atomic theory to determine relative nuclear charge radii. [Preview Abstract] |
Monday, May 2, 2011 1:42PM - 1:54PM |
R13.00002: Towards a new study of the electron-neutrino angular correlation in the decay of magneto-optically trapped $^6$He A. Knecht, B.G. Delbridge, A. Garcia, G.C. Harper, R.G.H. Robertson, H.E. Swanson, D.I. Will, C. Wrede, D.W. Zumwalt, P. Mueller, Z.-T. Lu, W. Williams Studies of nuclear beta decay have a long standing history in testing the Standard Model of particle physics. With the dominant (V-A) structure of the weak interaction determined, measurements of the angular correlation between the electron and neutrino momenta in nuclear beta decay can be used to search for scalar and tensor contributions to the weak interaction. The current best measurement on the electron-neutrino angular correlation coefficient in the decay of $^6$He dates back to 1963 by measuring the energy spectrum of the recoiling $^6$Li nucleus and amounts to $-0.3343 \pm 0.0030$. Its compatibility with the Standard Model expectation allows to constrain tensor contributions to $(|C_T|^2+|C'_T|^2)/(|C_A|^2+|C'_A|^2) < 0.4\%$. We intend to improve on this measurement by confining $^6$He atoms in a magneto-optical trap and detecting the recoiling nucleus and emitted electron in coincidence. The foreseen sensitivity in the measurement of the angular correlation coefficient will be approximately $0.1\%$. Here, we will present the details and current status of the experiment focussing on the performance of the $^6$He production and the magneto-optical trapping of the $^6$He atoms. [Preview Abstract] |
Monday, May 2, 2011 1:54PM - 2:06PM |
R13.00003: Application of a high speed digitizer to high-precision nuclear $\beta$-decay lifetime measurements Lixin Chen, John Hardy The objective of this study is to probe the feasibility of applying a high-speed digitizer to precise lifetime measurements of super-allowed nuclear $\beta$-emitters in order to improve the achievable precision. Instead of using analogy modules to discriminate and count decay events, we have developed a digital counting method based on an 8-bit digitizer with a 1 GS/s sampling rate, which records the waveforms from our gas proportional counter for later software analysis. The digitizer and our analysis software have been extensively tested on the saved waveforms from off-line radioactive-source measurements as well as from on-line experiments. A software filter has been designed, tested and applied successfully to separate true $\beta$ events from spurious signals by pulse-shape analysis. The methods used for, and the results obtained from, our first two on-line test experiments in 2010 will be described in detail. This work demonstrates the first successful application of a high-speed digitizer and off-line digital signal processing techniques to high precision nuclear $\beta$-decay lifetime measurements. [Preview Abstract] |
Monday, May 2, 2011 2:06PM - 2:18PM |
R13.00004: Searching for the electron electric dipole moment in an electrostatic storage ring David Kawall A non-zero permanent electric dipole moment (EDM) of an electron would violate parity and time-reversal symmetries. Non-zero EDMs are predicted in the standard model, but are unobservably small. New physics incorporating new particles and new $CP$-violating phases can lead, through radiative corrections, to dramatic enhancements of the electron EDM, to within a few orders of magnitude of the current experimental limit. A new approach to electron EDM searches using molecular ions stored in a table-top electrostatic storage ring is described. Molecular ions with long-lived paramagnetic states such as WN$^{+}$ can be injected and stored in larger numbers and with longer coherence times than competing experiments, leading to high sensitivity to an electron EDM. Systematic effects mimicking an EDM such as those due to motional magnetic fields and geometric phases are found not to limit the approach in the short term. Sensitivities of $\delta|d_{e}| \approx 10^{-30}~e\cdot$cm/day, an improvement by three orders of magnitude, appear possible under conservative conditions. [Preview Abstract] |
Monday, May 2, 2011 2:18PM - 2:30PM |
R13.00005: Measurements of UCN storage times versus temperature in a deuterated-polystyrene coated acrylic cell W.C. Griffith, Y. Bagdasarova, S.M. Clayton, M.D. Cooper, S.A. Currie, T. Ito, M.F. Makela, C. Morris, M.S. Rahaman, J.C. Ramsey, A. Saunders, R. Rios It is planned that the Oakridge SNS neutron electric dipole moment (nEDM) search will utilize an acrylic neutron storage cell with a deuterated-polystyrene (dPS) wall coating. The ultimate sensitivity of the nEDM measurement strongly depends on the storage cell having a long neutron storage time at cryogenic temperatures. We have built an apparatus to test the storage time of ultra-cold neutrons (UCN) in a dPS coated acrylic cell, at temperatures from 15--300 K. The cell is constructed from half inch thick acrylic plates that are bonded together with acrylic solvent cement, and the dPS coating is applied by ``sloshing'' a solution of dPS dissolved in d-toluene inside the cell. UCN generated at the LANSCE super-thermal deuterium source are used to test the storage time of the cell. After filling the cell with UCN, a valve specially designed to minimize UCN losses seals the cell for between 60 and 1200 seconds, and the remaining UCN are counted after opening the valve. We will discuss the apparatus and measurements made with it at 18, 40, 65, 100, and 295 K. This work is supported by the U.S. Department of Energy. [Preview Abstract] |
Monday, May 2, 2011 2:30PM - 2:42PM |
R13.00006: The Temperature Dependence of UCN Wall Losses in Material Bottles Coated with Deuterated Polystyrene M.D. Cooper, Y. Bagdasarova, S.M. Clayton, S.A. Currie, W.C. Griffith, T. Ito, M.F. Makela, C. Morris, M.S. Rahaman, J.C. Ramsey, A. Saunders, R. Rios Ultra-cold neutrons (UCN) from the LANSCE super-thermal deuterium source were used to fill an acrylic bottle coated with deuterated polystyrene. The bottle was constructed to minimize losses through the filling valve. The storage time was extracted from a series of measurements where the number of neutrons was counted after they were held in the bottle for durations varying from 60-1200 s. The data were collected at temperatures of 18, 40, 65, 105, and 295 K. The data has been analyzed in terms of the ratio of the imaginary to real part of the wall potential. The analysis considers the velocity dependence of the probability per bounce of wall loss. The implication of these measurements for the SNS electric dipole moment search will be presented. [Preview Abstract] |
Monday, May 2, 2011 2:42PM - 2:54PM |
R13.00007: Muon Decay Parameters from TWIST: Results and Limiting Systematic Uncertainties Richard Mischke The TRIUMF Weak Interaction Symmetry Test (TWIST) collaboration has completed a simultaneous measurement of the muon decay parameters $\rho $, $\delta $, and P$_{\mu }\xi $, [1] which tests the standard model (SM) in a purely leptonic process and provides improved limits for relevant extensions to the SM. The final results along with implications for physics beyond the SM will be summarized. The talk will focus on the successes and surprises in trying to reduce systematic uncertainties to the level of 10$^{-4}$ of the parameter values. \\[4pt] [1] R. Bayes et al., Phys. Rev. Lett. (to be published); arXiv:1010.4998v2 [hep-ex] [Preview Abstract] |
Monday, May 2, 2011 2:54PM - 3:06PM |
R13.00008: The Mu2e Experiment at Fermilab James Miller The Mu2e goal is to improve on the existing limit for the neutrinoless conversion of a muon to a monoenergetic electron by four orders of magnitude. This reaction is an example of Charged Lepton Flavor Violation, so far not observed in any reaction. The existence of neutrino oscillations leads to a Standard Model prediction of the rate for mu to e that is far smaller than foreseeable experimental limits, consequently observation of mu-e conversion is a clean indication of new physics. Moreover, some models of new physics outside the Standard Model (SM) predict a signal just beyond current limits. The proposed measurement will either see a signal or place dramatic limits on the flavor conservation properties of new physics models. We give a brief account of the theoretical motivation. The experiment is being developed at Fermilab. A pulsed negative muon beam is stopped in an aluminum target. Each stopped muon forms a muonic atom. The goal is to measure the the rate of conversion of a muon into an electron relative to the rate of ordinary nuclear muon capture, with a single event sensitivity of 2e-17. A new low energy, high-flux muon beam line using solenoids is being designed. The planned methods of detection of the conversion electron and of background suppression are described. [Preview Abstract] |
Monday, May 2, 2011 3:06PM - 3:18PM |
R13.00009: The TREK program at J-PARC Michael Kohl The TREK program at J-PARC in Japan consists of a series of experiments that have been proposed to use the new, recently commissioned kaon beamline K1.1BR at the new J-PARC Hadron Facility. A beam of low-energy positively charged kaons will be stopped, and their decays observed with a large acceptance toroidal spectrometer capable of tracking charged particles with high resolution, combined with a photon calorimeter and additional instrumentation with muon polarimeters. The first two experiments, requiring less beam intensity, aim to test lepton universality in the $K_{e2}/K_{\mu2}$ ratio with 0.2\% statistical uncertainty, and to search for heavy sterile neutrinos in two-body kaon decays. Ultimately, the Time Reversal Experiment with Kaons (TREK) aims to find New Physics beyond the Standard Model by a precision measurement of the T-violating transverse polarization $P_T$ of muons in the $K^{+}_{\mu3}$ decay of stopped kaons with a sensitivity of $10^{-4}$. An overview of the planned experiments, results from recent R\&D activities, and the current project status will be presented. [Preview Abstract] |
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