Bulletin of the American Physical Society
2013 Fall Meeting of the APS Division of Nuclear Physics
Volume 58, Number 13
Wednesday–Saturday, October 23–26, 2013; Newport News, Virginia
Session JE: Mini-Symposium on Fundamental Symmetries with Neutrons III |
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Chair: Brad Plaster, University of Kentucky Room: Grand Ballroom V |
Friday, October 25, 2013 10:30AM - 11:06AM |
JE.00001: Improved Determination of the Neutron Lifetime Invited Speaker: A. Yue The most precise determination of the neutron lifetime using the beam method reported a result of $\tau_n = (886.3 \pm 3.4)$ s. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was determined with a monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized $^6$Li deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the ENDF/B-VI $^6$Li(n,t)$^4$He thermal neutron cross section. We have used a second, totally-absorbing neutron detector to directly measure the detection efficiency of the monitor on a monochromatic neutron beam of precisely known wavelength. This method does not rely on the $^6$Li(n,t)$^4$He cross section or any other nuclear data. The monitor detection efficiency was measured to an uncertainty of 0.06\,\%, which represents a five-fold improvement in uncertainty. We have verified the temporal stability of the monitor with ancillary measurements, and the measured neutron monitor efficiency has been used to improve the fluence determination in the past lifetime experiment. An updated neutron lifetime based on the improved fluence determination will be presented.\\[4pt] Work done in collaboration with M. Dewey, D. Gilliam, J. Nico, National Institute of Standards and Technology; G. Greene, University of Tennessee / Oak Ridge National Laboratory; A. Laptev, Los Alamos National Laboratory; W. Snow, Indiana University; and F. Wietfeldt, Tulane University. [Preview Abstract] |
Friday, October 25, 2013 11:06AM - 11:18AM |
JE.00002: Measuring The Neutron Lifetime to One Second Using in Beam Techniques Jonathan Mulholland The decay of the free neutron is the simplest nuclear beta decay and is the prototype for charged current semi-leptonic weak interactions. A precise value for the neutron lifetime is required for consistency tests of the Standard Model and is an essential parameter in the theory of Big Bang Nucleosynthesis. A new measurement of the neutron lifetime using the in-beam method is planned at the National Institute of Standards and Technology Center for Neutron Research. The systematic effects associated with the in-beam method are markedly different than those found in storage experiments utilizing ultracold neutrons. Experimental improvements, specifically recent advances in the determination of absolute neutron fluence, should permit an overall uncertainty of 1 second on the neutron lifetime. The technical improvements in the in-beam technique, and the path toward improving the precision of the new measurement will be discussed. [Preview Abstract] |
Friday, October 25, 2013 11:18AM - 11:30AM |
JE.00003: Overview of the UCN Neutron Lifetime Experiment UCN$\tau$ A.T. Holley Determination of the free neutron lifetime with a precision at or better than one second ($\sim$0.1\%) is a challenging but important measurement. It plays an essential role in determining the implications of other precision free neutron decay measurements, as well as in models of Big Bang Nucleosynthesis, which are being constrained by increasingly high-precision astrophysical results. The UCN$\tau$ collaboration is currently studying the systematics of an ultracold neutron (UCN) magneto-gravitational trap in an effort both to better understand previous storage experiments as well as to develop a trap capable of measuring the free neutron lifetime to better than 0.1\%. Our prototype trap utilizes the potential from a Halbach array of high-field permanent magnets and the earth's gravitational field to confine UCN of one spin state in an asymmetric storage volume of $\sim$670~L, and provides the capability to count UCN remaining after a variable storage time by emptying into a $^{10}$B UCN detector or by counting the activity of a natural vanadium foil which when introduced into the storage volume quickly absorbs the UCN. The general configuration of our current experiment and the nature of the leading systematic effects we are studying will be discussed. [Preview Abstract] |
Friday, October 25, 2013 11:30AM - 11:42AM |
JE.00004: Analysis of the first data from the UCN$\tau$ experiment Daniel Salvat The UCN$\tau$ experiment is designed to measure the lifetime of the free neutron using a 670 liter permanent magnet trap which stores ultracold neutrons (UCN). Here we summarize the results of the first experimental campaign at the Los Alamos Neutron Science Center. We present a determination of the storage time of the apparatus by filling the trap with UCN and emptying the surviving UCN into a counter, including the analysis methods and background subtraction techniques. We show preliminary measurements of the UCN up-scattering rates from a low density polyethylene sheet which is designed to remove marginally trapped UCN. We have also tested a new method of counting the surviving UCN by activating a vanadium foil within the trap and measuring the activation with a plastic scintillator and NaI $\gamma$-ray detector. Initial results of the vanadium activation measurements are presented, and future improvements to increase the signal-to-noise of this measurement technique are discussed. [Preview Abstract] |
Friday, October 25, 2013 11:42AM - 11:54AM |
JE.00005: Continued Analysis of the NIST Neutron Lifetime Measurement Using Ultracold Neutrons Craig Huffer, P.R. Huffman, K.W. Schelhammer, M.S. Dewey, M.G. Huber, P.P. Hughes, H.P. Mumm, A.K. Thompson, K. Coakley, A.T. Yue, C.M. O'Shaughnessy, L. Yang The neutron lifetime is an important parameter for constraining the Standard Model and providing input for Big Bang Nucleosynthesis. The current disagreement in the most recent generation of lifetime experiments suggests unknown or underestimated systematics and motivates the need for alternative measurement methods as well as additional investigations into potential systematics. Our measurement was performed using magnetically trapped Ultracold Neutrons in a 3.1 T Ioffe type trap configuration. The decay rate of the neutron population is recorded in real time by monitoring visible light resulting from beta decay. ~Data collected in late 2010 and early 2011 is being analyzed and systematic effects are being investigated. An overview of our current work on the analysis, Monte Carlo simulations, and systematic effects will be provided. [Preview Abstract] |
Friday, October 25, 2013 11:54AM - 12:06PM |
JE.00006: Frequency shifts in gravity resonance spectroscopy Stefan Baessler In this talk, I will discuss the GRANIT setup which is intended to perform gravity resonance spectroscopy with ultracold neutrons. The measurements serve to search for new short-range interactions. My talk will focus on frequency shifts that could be responsible for false effects if not taken into account correctly. [Preview Abstract] |
Friday, October 25, 2013 12:06PM - 12:18PM |
JE.00007: A New Neutron Interferometry Facility at NCNR Chandra Shahi, Fred Wietfeldt, Michael Huber, Dmitry Pushin, Muhammad Arif A neutron interferometer splits an incoming neutron beam into two coherent partial beams, which travel on different paths and then recombine to form an interference pattern. This pattern is used to precisely determine the phase shift of a sample in one of the paths, thus the neutron interaction potential in the sample can be measured with high precision. A new neutron interferometry setup (NIOFa) has been constructed at the NIST Center for Neutron Research (NCNR). This new facility is mainly focused on spin based interferometry, which will expand its applications in both quantum computation and material research. New spin-control mechanisms are being tested; including thin-film spin flippers and efficient polarizing double cavity super mirrors. Doubling the neutron's degrees of freedom inside the interferometer promises exciting new quantum mechanical experiments and research capabilities. [Preview Abstract] |
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