Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session C6: Fundamental Symmetries I |
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Sponsoring Units: GPMFC DNP Chair: Chen-Yu Liu, Indiana University Room: Key 2 |
Saturday, April 11, 2015 1:30PM - 1:42PM |
C6.00001: A New Search for the Atomic EDM of $^{129}$Xe at FRM-II (Munich Research Reactor) Florian Kuchler, Peter Fierlinger, Eva Kraegeloh, Tobias Lins, Mike Marino, Jonas Meinel, Benjamin Niessen, Stefan Stuiber, Martin Burghoff, Isaac Fan, Wolfgang Kilian, Silvia Knappe-Grueneberg, Allard Schnabel, Frank Seifert, Lutz Trahms, Jens Voigt, Tim Chupp, Skyler Degenkolb, Fei Gong, Natasha Sachdeva, Earl Babcock, Jaideep Singh Electric dipole moments (EDMs) arise due to the breaking of time-reversal or, equivalently, CP-symmetry. Although all searches have so far only set upper limits on EDMs, the motivation for more sensitive searches is stronger than ever. The present limit of 6$\times$10$^{-27}$ e*cm (95$\%$ CL) for the $^{129}$Xe EDM helps constrain CP-violating parameters within nuclei. A new effort at FRM-II incorporating a $^3$He comagnetometer can potentially improve this limit by over three orders of magnitude. The noble gas mixture is polarized by spin-exchange optical pumping and then transferred into a high-performance magnetically shielded room. A SQUID magnetometer array measures the precession frequencies in the presence of applied electric- and magnetic-fields. Recent test runs indicate that the experiment is capable of an EDM sensitivity of 10$^{-28}$ e*cm in one day. [Preview Abstract] |
Saturday, April 11, 2015 1:42PM - 1:54PM |
C6.00002: First Measurement of the Permanent Electric Dipole Moment of Radium-225 Jaideep T. Singh, K.G. Bailey, M.N. Bishof, M.R. Dietrich, J.P. Greene, R.J. Holt, M.R. Kalita, W. Korsch, N.D. Lemke, Z.-T. Lu, P. Mueller, T.P. O'Connor, R.H. Parker Electric dipole moments (EDMs) are signatures of time-reversal ($T$), parity ($P$),\& charge-parity ($CP$) violation. $CP$-violation beyond the Standard Model is generally believed to be required to explain the observed prevalence of matter over antimatter in the universe. Radium-225 ($\tau_{1/2} = 14.7$ d, $I = 1/2$) is mostly sensitive to $T$- and $P$-violating interactions originating within the nucleus. The best limits on these types of exotic interactions are derived from the atomic EDM limit for Mercury-199. Because of its unusual nuclear structure (octupole deformation), Ra-225 is expected to have a physics sensitivity that is a few hundred to a few thousand times higher than Hg-199. Laser cooling \& trapping techniques are performed to collect \& transport the cold Ra atoms into the measurement region. An EDM measurement is then performed by searching for a linear electric field dependent shift in the nuclear spin precession frequency of Ra-225. We will report on the first measurement of the atomic EDM of Ra-225 as well as plans for future improvements. [Preview Abstract] |
Saturday, April 11, 2015 1:54PM - 2:06PM |
C6.00003: Development on cryogenic valve (V1) for the SNS nEDM experiment Zhaowen Tang, Takeyasu Ito, John Ramsey, Scott Currie The goal of the nEDM experiment at the Spallation Neutron Source (SNS) is to search for a neutron electric dipole moment (EDM) with a sensitivity below $5 \times 10^{-28}$ e-cm as a signature of Charge-Parity violation, which is $\sim 50$ times better than the current experimental limit. The experiment utilizes polarized $^3$He as a co-magnetometer and as a method to measure the precession frequency of the neutron in-situ. This method improves both the statistical and systematic sensitivity of the experiment, however, does create many technical challenges. One of these challenges is the cryogenic V1 valve operating at 0.4 K, which isolates the ultra cold neutron (UCN) cell from the $^3$He transfer system. The valve has to be UCN friendly, mechanically robust, $^3$He leak tight, friendly to polarized $^3$He, etc. We will report the progress of the R/D effort of the V1 valve. [Preview Abstract] |
Saturday, April 11, 2015 2:06PM - 2:18PM |
C6.00004: Progress on Tests of Electric Breakdown of Superfluid Liquid Helium-4 in High Electric Field for the SNS nEDM Experiment Wanchun Wei, Douglas Beck, Vince Cianciolo, Steven Clayton, Christopher Crawford, Scott Currie, William Griffith, Takeyasu Ito, John Ramsey, Amy Roberts, Richardo Schmid, George Seidel, Daniel Wagner, Steven Williamson, Weijun Yao The SNS nEDM experiment is a collaborative project under development, which aims to search for the neutron electric dipole moment (EDM) with ultracold neutrons (UCNs) stored in superfluid liquid helium-4 at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory. In general, the ultimate sensitivity of the EDM searches linearly depends on the strength of the applied electric field across the volume of superfluid liquid helium-4 in the UCN storage space. Our goal is to achieve an electric field with strength of 75 kV/cm. However, the phenomenon of electric breakdown in liquid helium-4 is poorly understood in the available literatures. We, therefore, have developed an apparatus to study it at temperatures as low as 0.4 K and pressures between saturated vapor pressure (SVP) of liquid helium and 1 atm. In this talk, we will present the latest progress on the tests of the electric breakdown of superfluid liquid helium-4 and its implications of findings that affect the design of the SNS nEDM experiment. [Preview Abstract] |
Saturday, April 11, 2015 2:18PM - 2:30PM |
C6.00005: Search For CP Violation in Positronium Chelsea Bartram We propose to search for CP violation in the charged lepton sector by studying positronium decays. Positronium, a bound state of an electron and positron, occurs in both a singlet and triplet state. The triplet state, orthopositronium, decays primarily into three gamma rays. CP violation could potentially manifest itself in angular correlations between the directions of the three gamma rays. We will use the APEX annular array of NaI detectors, combined with a tagged source and a novel, conventional electromagnet. This array will increase the angular acceptance by a factor of 25 over previous experiments. We will present the current status of the experiment. This work is supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics. [Preview Abstract] |
Saturday, April 11, 2015 2:30PM - 2:42PM |
C6.00006: Developments in Ultracold Neutron Measurement for the UCN$\tau$ experiment Nathan Callahan The UCN$\tau$ experiment at Los Alamos National Laboratory (LANL) has constructed and tested a new iteration of its $\beta$ particle detectors for its $\textit{in-situ}$ vanadium-based neutron detector as well as tested a novel scintillating Ultracold Neutron (UCN) monitor. This talk will discuss developments and results since 2013. Previously the $\beta$ detector used scintillating paddles coupled to acrylic lightguides of comparable volume and a photomultiplier tube (PMT). The volume of light guide was reduced by using edge-coupled wavelength shifting fibers, providing three benefits: better-shielded PMTs, reduction of background from the light guides, and reduction of dark counts due to smaller PMTs. Data will be presented to characterize these improvements. A novel UCN detector for monitoring was also tested. The new detectors consist of a thin layer of boron coated zinc sulfide scintillator coupled to an acrylic lightguide and a PMT. Boron has a negative material potential, a large cross-section for neutron capture, and decays promptly into an $\alpha$ and a Li ion, allowing high efficiency absorption and detection and low background. Tests to determine the optimal thickness of the boron layer will be discussed as well as comparisons to existing UCN detector performance. [Preview Abstract] |
Saturday, April 11, 2015 2:42PM - 2:54PM |
C6.00007: Progress toward a new measurement of the neutron lifetime Kyle Grammer Free neutron decay is the simplest nuclear beta decay. A precise value for the neutron lifetime is valuable for standard model consistency tests and Big Bang Nucleosynthesis models. There is a disagreement between the measured neutron lifetime from cold neutron beam experiments and ultracold neutron storage experiments. A new measurement of the neutron lifetime using the beam method is planned at the National Institute of Standards and Technology Center for Neutron Research. Experimental improvements should result in a 1s uncertainty measurement of the neutron lifetime. The technical improvements and the path towards the new measurement will be discussed. This work is supported by DOE Office of Science, NIST, and NSF. [Preview Abstract] |
Saturday, April 11, 2015 2:54PM - 3:06PM |
C6.00008: Precision neutron flux measurements and applications using the Alpha Gamma device Eamon Anderson The Alpha Gamma device [1] is a totally-absorbing ${}^{10}B$ neutron detector designed to measure the absolute detection efficiency of a thin-film lithium neutron monitor on a monoenergetic neutron beam. The detector has been shown to measure neutron fluence with an absolute accuracy of 0.06\%. [2] This capability has been used to perform the first direct, absolute measurement of the ${}^6Li(n,t){}^4He$ cross section at sub-thermal energy, improve the neutron fluence determination in a past beam neutron lifetime measurement by a factor of five, and is being used to calibrate the neutron monitors for use in the upcoming beam neutron lifetime measurement BL2 (NIST Beam Lifetime 2) [3]. The principle of the measurement method will presented and the applications will be discussed.\\[4pt] [1] D. M. Gilliam, G. L. Greene, and G. P. Lamaze, Nucl. Instrum. Methods A 284, 220 (1989)\\[0pt] [2] A.T. Yue et al, Phys. Rev. Lett. 111, 222501 (2013)\\[0pt] [3] http://arxiv.org/abs/1410.5311 [Preview Abstract] |
Saturday, April 11, 2015 3:06PM - 3:18PM |
C6.00009: Measuring the free neutron lifetime to $\leq$ 0.3s via the beam method Nadia Fomin, Jonathan Mulholland Neutron beta decay is an archetype for all semi-leptonic charged-current weak processes. A precise value for the neutron lifetime is required for consistency tests of the Standard Model and is needed to predict the primordial $^4$He abundance from the theory of Big Bang Nucleosynthesis. An effort has begun for an in-beam measurement of the neutron lifetime with an projected $\leq$0.3s uncertainty. This effort is part of a phased campaign of neutron lifetime measurements based at the NIST Center for Neutron Research, using the Sussex-ILL-NIST technique. Recent advances in neutron fluence measurement techniques as well as new large area silicon detector technology address the two largest sources of uncertainty of in-beam measurements, paving the way for a new measurement. The experimental design and projected uncertainties for the 0.3s measurement will be discussed. [Preview Abstract] |
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