Bulletin of the American Physical Society
2012 Fall Meeting of the APS Division of Nuclear Physics
Volume 57, Number 9
Wednesday–Saturday, October 24–27, 2012; Newport Beach, California
Session JE: Ultra Cold Neutrons |
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Chair: Takeyasu Ito, Los Alamos National Laboratory Room: Garden I |
Friday, October 26, 2012 10:30AM - 10:42AM |
JE.00001: Measurement cell development for the neutron EDM experiment W.C. Griffith, S.M. Clayton, M.D. Cooper, S.A. Currie, T.M. Ito, M.F. Makela, J.C. Ramsey, A. Saunders An experimental search for the neutron electric dipole moment is under development for installation at the Oak Ridge Spallation Neutron Source. The experiment will use ultracold neutrons (UCN) produced in superfluid helium, along with $^3$He that will act as a neutron spin analyzer and comagnetometer. The measurement will take place in two 3-liter rectangular acrylic cells coated with deuterated tetraphenyl butadiene (dTPB) in a deuterated polystyrene (dPS) matrix. It is crucial for the ultimate sensitivity of the experiment that UCN survive many ($\sim 10^5$) wall collisions without being lost. We are currently testing the UCN storage properties of dPS+dTPB coated acrylic cells at the LANSCE solid deuterium UCN source. The test cell is filled with UCN through a 1 cm diameter opening, sealed with a valve carefully designed to have very low UCN losses, and then after waiting for between 20-1000 seconds the valve is opened and the remaining UCN are counted. Measurements are carried out from room temperature to below 20 K to determine the temperature dependence of the UCN wall losses. We will discuss cell construction techniques and present recent UCN storage measurements. This work is supported by the U. S. Department of Energy. [Preview Abstract] |
Friday, October 26, 2012 10:42AM - 10:54AM |
JE.00002: Overview on the UCNtau experiment Daniel Salvat The UCN$\tau$ experiment is a precision measurement of the neutron beta-decay lifetime using ultracold neutrons (UCN) in a magneto-gravitational trap. Due to its long beta-decay lifetime (880.1 $\pm$ 1.1 s, PDG2012), neutrons are also susceptible to many other loss mechanisms, such as upscatterings, absorptions on material surface, and spin flips. These interactions could act on similar time-scale as the neutron beta-decay, making precision experimental measurements very challenging. In this talk, we will describe a new effort at Los Alamos National Laboratory to measure the beta-decay lifetime using ultracold neutrons trapped in a hybrid magnetic and gravitational trap. A Halbach array is used to levitate UCN (up to 50 neV), which are confined vertically up to 0.5 m by gravity. Such a trap minimizes the chance of neutron interactions with material walls, and furthermore its open-top geometry allows implementations of novel schemes to detect neutrons and decay particles in-situ. The experiment aims to improve on the uncertainty of the neutron lifetime measurement beyond 1 second. In this talk, we will describe the design features and discuss plans to quantify systematic effects. [Preview Abstract] |
Friday, October 26, 2012 10:54AM - 11:06AM |
JE.00003: Investigation of Vanadium foils for in situ UCN detection for the UCN$\tau$ lifetime experiment Brittney VornDick We will report on preliminary work aimed at developing a new technique for counting trapped ultra-cold neutrons (UCN) for a precision lifetime experiment, UCN$\tau$. We propose to mechanically insert a $^{51}$V foil to capture neutrons in the trap and then count the $^{52}$V decays. The negative potential of $^{51}$V; relatively short half life of $^{52}$V (3.74 minutes); and large imaginary potential makes $^{51}$V ideal for an activation/counting technique. Preliminary measurements show that high counting efficiency and low backgrounds can be obtained by counting $\gamma-\beta$ coincidences. [Preview Abstract] |
Friday, October 26, 2012 11:06AM - 11:18AM |
JE.00004: Neutron Tracking Simulations for the UCN$\tau$ experiment Evan Adamek The UCN$\tau$ experiment aims to measure the neutron beta-decay lifetime to 1 s total uncertainty and beyond by trapping ultracold neutrons (UCN) in a gravito-magnetic trap, in which UCN will undergo no material wall interactions. To study the feasibility in this experimental technique, we have built Monte-Carlo simulations of the full-scale UCN$\tau$ experiment. The simulation program consists of two major components: one focuses on simulation of the UCN flux in the guide tubes, and the other on UCN tracking inside the trap. The first simulation studies optimized delivery of UCN into the trap and evaluates the effectiveness of relative flux monitoring to infer the number of trappable UCN for each fill. The second simulation tracks UCN, originating from the trap door, over the entire accessible region. Symplectic integrators are used to integrate the equations of motion of UCN using the full potential. Focus is given to studying the phase-space evolution of marginally trapped UCN. These neutrons have a large tangential velocity component and could be leaking out of the trap slowly (due to non-harmonic components in the trapping potential) and thus skewing the accuracy of the neutron beta-decay lifetime. In this talk, we will discuss many of these subtle effects. [Preview Abstract] |
Friday, October 26, 2012 11:18AM - 11:30AM |
JE.00005: Advanced guide coating techniques for Ultra-Cold Neutron transport Xinjian Ding The UCNA experiment utilizes Ultra-Cold Neutrons (UCN) to measure angular correlations in beta-decay. UCN are produced in a solid deuterium source and then transported to the experimental decay volume through a sequence of guide tubes. Requirements for the UCNA guides include smooth surfaces, high Fermi potentials, and also a very low depolarization probability per bounce. We review the UCNA guide system and the pulsed-laser deposition process we use to produce diamond like carbon (DLC) coatings on Cu and quartz tubes. Several improvements (magnetic field shaping of the plasma plume from the laser target and better guide mounting) over previous coating techniques will be described and their effectiveness presented. [Preview Abstract] |
Friday, October 26, 2012 11:30AM - 11:42AM |
JE.00006: UCNA Systematic Uncertainties: Developments in Analysis and Method Bryan Zeck The UCNA experiment is an effort to measure the beta-decay asymmetry parameter $A$ of the correlation between the electron momentum and the neutron spin, using bottled polarized ultracold neutrons in a homogenous 1 T magnetic field. Continued improvements in both analysis and method are helping to push the measurement uncertainty to the limits of the current statistical sensitivity (less than 0.4\%). The implementation of thinner decay trap windows will be discussed, as will the use of a tagged beta particle calibration source to measure angle-dependent scattering effects and energy loss. Additionally, improvements in position reconstruction and polarization measurements using a new shutter system will be introduced. A full accounting of the current systematic uncertainties will be given. [Preview Abstract] |
Friday, October 26, 2012 11:42AM - 11:54AM |
JE.00007: Searching for Fierz Interference in Beta-Decay of Ultracold Neutrons Kevin Hickerson It is theorized that contributions from scalar and tensor interactions from physics beyond the Standard Model could be detectable in the spectrum of neutron beta-decay, manifest as a nonzero value for the so-called neutron Fierz interference parameter, denoted as $b_n$. Some models have $b_n$ as large as $10^{-3}$, which is within reach for measurement, but below the current limits set for the Fermi component $b_F$ measured by superallowed $0+ \to 0+$ nuclear $\beta$-decays. We present progress on the UCNb experiment that uses the Ultracold Neutron (UCN) source at LANSCE to trap UCN in a $4\pi$ beta calorimeter. We also report limits on $b_n$ extracted from data collected from the 2010 run of the UCNA experiment. [Preview Abstract] |
Friday, October 26, 2012 11:54AM - 12:06PM |
JE.00008: Status of the UCNB Experiment at LANSCE Syed Hasan The goal of the UCNB experiment is to measure the neutrino asymmetry parameter B, the angular correlation between the neutron spin and the decay neutrino momentum, via the detection of electron-proton coincidences in the decay of polarized ultracold neutrons (UCN). The UCNB experiment builds upon the existing infrastructure for the UCNA experiment, where the UCN from the LANL source are polarized via transport through a 7-T field and then stored in a cylindrical decay trap situated within a 1-T solenoidal spectrometer. Several modifications to the hardware are necessary for the detection of electron-proton coincidences, however, including the requirement of a windowless decay trap, a 30-kV bias system for electrostatic acceleration of the protons, and a novel Si detector system for a precise measurement of the energy dependence of the asymmetry. This talk will present an overview of the status of the UCNB experiment. [Preview Abstract] |
Friday, October 26, 2012 12:06PM - 12:18PM |
JE.00009: A next generation neutron-antineutron oscillations experiment using very cold and ultracold neutrons Robert Pattie Neutron-antineutron oscillation experiments with free neutrons are sensitive to new interactions which violate baryon number by 2 units. As such, this phenomenon can be connected to some of the central issues in particle physics: the origin of the baryon-antibaryon asymmetry and the origin of neutrino mass. Experiments with free neutrons promise roughly three orders of magnitude improvement in the discovery potential for this phenomenon, exceeding current or planned limits for neutron-antineutron oscillations in underground experiments. We review the motivation for neutron-antineutron oscillation measurements and some strategies for a next generation neutron-antineutron oscillation experiment with very cold and ultracold neutrons. [Preview Abstract] |
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