Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session S6: Mini-symposium on Recent Results with Cold and Ultracold Neutrons |
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Sponsoring Units: DNP Chair: Pieter Mumm, National Institute of Standards and Technology Room: Key 2 |
Monday, April 13, 2015 1:30PM - 2:06PM |
S6.00001: The scattering length difference between the $b_1$ and $b_0$ states of $n$-$^3$He using a neutron interferometer Invited Speaker: M.G. Huber We report a determination of the $n-$$^3$He scattering length difference $\Delta b^{\prime} = b_{1}^{\prime}-b_{0}^{\prime}= $($-5.411\pm0.051$) fm between the triplet and singlet states using a neutron interferometer. This revises our previous result $\Delta b^{\prime}=$($-5.610\pm0.042$) fm obtained using the same technique in 2008. A sample placed in one of the beam paths of the interferometer causes a phase shift that is proportional to sample's scattering length density, thickness and $n$ wavelength. For this experiment, polarized neutrons were incident on the interferometer and the relative phase shift caused by a spin-dependent interaction with a polarized $^3$He target was measured. The neutron polarization and spin flipper efficiency were determined separately using helium-3 analyzers to $<$ 0.1 \% relative uncertainty. This re-evaluation comes from new phase shift data taken in 2013 and a partial reanalysis of the 2008 data that includes a systematic correction caused by magnetic field gradients which was previously underestimated. Scattering lengths of low Z materials are important for both providing inputs into effective field theories and testing nuclear models. This result along with other measured values of $b$ for $^3$He will be compared to nucleon models.\\[4pt] In collaboration with M. Arif, W.C. Chen, T.R. Gentile, D.S. Hussey, NIST; T.C. Black, University of North Carolina-Wilmington; D.A. Pushin, University of Waterloo; C.B. Shahi, F.E. Wietfeldt, Tulane University; and L. Yang, University of Illinois at Urbana-Champaign. [Preview Abstract] |
Monday, April 13, 2015 2:06PM - 2:18PM |
S6.00002: Status of The NPDGamma Analysis Jason Fry The NPDGamma Experiment was performed to measure the parity violating gamma asymmetry from polarized neutrons captured on protons at the Spallation Neutron Source at ORNL. The parity-violating (PV) neutron spin asymmetry $A_{\gamma}$ of gammas from neutron capture on protons is proportional to the $\Delta I = 1$ long range weak meson coupling $h_{\pi}^1$ between nucleons in the hadronic weak interaction (HWI). Liquid para-hydrogen production data finished in April 2014 and the preliminary result for the PV asymmetry $A_{\gamma}$ is that it is small with a statistical error of about 13 ppb, which can help constrain the HWI coupling space. Various aspects of the analysis will be discussed and $h_{\pi}^1$ will be compared to previous results. [Preview Abstract] |
Monday, April 13, 2015 2:18PM - 2:30PM |
S6.00003: Analysis of the aCORN NG-6 Dataset Michael Mendenhall The aCORN experiment is designed to measure the angular correlation ``$a$'' between electron and neutrino momenta in free neutron decay. Measurement of the $a$ correlation constrains the Standard Model weak interaction coupling constants ratio $g_A/g_V$, in a complementary manner to the current best constraints which come from the ``$A$'' polarized neutron beta decay asymmetry. Along with pinning down Standard Model parameters, comparison between high-precision measurements of multiple neutron decay observables probes Beyond-Standard-Model interactions. aCORN collected data over the previous two years on the NG-6 cold neutron beamline at the NIST Center for Neutron Research. aCORN has since re-located to the new, higher-flux NG-C beamline. This talk describes the present status of analysis of the aCORN NG-6 dataset, outlining the main systematics and corrections for the measurement. [Preview Abstract] |
Monday, April 13, 2015 2:30PM - 2:42PM |
S6.00004: Status of the UCNA Experiment Michael Brown The UCNA Experiment at the Los Alamos Neutron Science Center (LANSCE) is the first measurement of the $\beta$-decay asymmetry parameter $A_0$ using polarized ultracold neutrons (UCN). $A_0$, which represents the parity-violating angular correlation between the neutron spin and the decay electron's momentum, determines $\lambda=g_{A}/g_{V}$, the ratio of the weak axial-vector and vector coupling constants. Measurements of the $\beta$-asymmetry presently provide the most precise determination of $\lambda$, which, together with the lifetime, permits the extraction of the CKM matrix element $V_{ud}$ solely from neutron decay. At LANSCE, UCN are produced in a solid deuterium source and polarized via transport through a 7 T magnetic field. Their spins can then be flipped in an Adiabatic Fast Passage spin flipper prior to storage within a 1 T solenoidal spectrometer with electron detectors at each end. Previous UCNA results (data from 2010 and earlier) were limited by systematic uncertainties, in particular those from the UCN polarization, calibration of the electron energy, and electron backscattering. This talk will present the status of the analysis of data obtained during run periods in 2011-2013, particularly focusing on updated work on the UCN polarization and energy calibration. [Preview Abstract] |
Monday, April 13, 2015 2:42PM - 2:54PM |
S6.00005: The overview and early measurements from the n3He experiment Garishvili Garishvili The main goal of the n3He experiment at the Spallation Neutron Source (SNS) at ORNL is to perform a precise measurement of the parity violating (PV) weak amplitude of the reaction $\vec{n}+3He \rightarrow T + p + 765$ KeV. In particular, the goal is to measure the spatial asymmetry of emitted protons with respect to the neutron spin direction. This asymmetry is expected to be very small ($< 10^{-7}$) since the NN interaction is dominated by the parity conserving (PC) strong amplitude. The final goal is to measure the asymmetry in the n3He experiment with an accuracy of $\sim 2\times 10^{-8}$ to isolate the I=0 components of the hadronic weak interaction, which is vital for constraining weak coupling constants predicted by theory. The n3He detector was installed and commissioned in December 2014 on the Fundamental Neutron Physics Beamline at the SNS. Production data taking is expected to start by the end of January 2015 and planned to run until the end of 2015. The status of the experiment will be presented, including early data. [Preview Abstract] |
Monday, April 13, 2015 2:54PM - 3:06PM |
S6.00006: New Results from the UCN$\tau$ Experiment Evan Adamek A precise measurement of the free neutron beta decay lifetime provides a test of the weak interaction and is a significant input for the prediction of primordial light element abundances. The UCN$\tau$ experiment at the Los Alamos Neutron Science Center employs an open-top 600L volume lined by a NdFeB Halbach array to magnetically and gravitationally trap polarized ultracold neutrons (UCN). The decay constant is calculated by measuring the activity of a vanadium foil which is activated by absorbing trapped UCN. The UCN flux is monitored during loading using a newly developed boron-coated ZnS scintillator. Magneto-gravitational trapping mitigates systematic effects that can occur in material and other magnetic storage experiments, while in situ UCN detection mitigates those induced by the draining of UCN into external detectors for counting. Here we provide an overview of the experiment, discuss recent improvements in neutron transport and detection methods, and present new results from the 2014/2015 run cycle. [Preview Abstract] |
Monday, April 13, 2015 3:06PM - 3:18PM |
S6.00007: Analysis of hadronic parity violation in the context of beyond the standard model physics using results from the NPDGamma collaboration Chris Haddock Various theories beyond the Standard Model predict new particles with masses in the sub-eV range that couple very weakly to ordinary matter. A parity-odd interaction between polarized nucleons and unpolarized matter equal to $\frac{g_{A}g_{V}}{2\pi}\frac{e^{-r/\lambda}}{r} \vec{s} \cdot {\vec{v}}$ is one such possibility(B. Dobrescu and I. Mocioiu, 2006), where ${\vec{s}}$ and ${\vec{v}}$ are the spin and velocity of the polarized nucleon, $r$ is the separation between the nucleon and unpolarized matter, $\lambda$ is the interaction range, and $g_{A}$ and $g_{V}$ are the axial and vector couplings of an interaction induced by the exchange of a new light vector boson. We analyze how the presence of such an interaction would manifest itself in the parity violating up-down asymmetry $A_{\gamma}$ with respect to the neutron spin direction of $\gamma$ rays emitted in the reaction $\vec{n}+p\rightarrow d + \gamma$ measured by the NPDGamma Collaboration (M.T. Gericke et al., 2011). The result from this experiment in combination with some assumptions about the Standard Model hadronic weak interaction can be used to set model-independent constraints on the product $g_{A}^ng_{V}^p$ for interaction ranges large compared to the nucleon size. [Preview Abstract] |
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