Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session CH: Neutron Decay and Electroweak Physics |
Hide Abstracts |
Sponsoring Units: DNP JPS Chair: Christopher Morris, Los Alamos National Laboratory Room: Ritz-Carlton Hotel Plantation 1 |
Tuesday, September 20, 2005 2:00PM - 2:15PM |
CH.00001: Simulation of the ``little a'' Neutron Beta Decay Experiment at the SNS Emil Frlez We present the GEANT4 Monte Carlo simulation of an experimental apparatus being developed to measure the electron-antineutrino correlation in the free neutron beta decay (``little a'') at the SNS. The proposed method relies on the measurement of the proton time-of-flight distribution using a pair of large area Silicon detectors. The design calls for systematic uncertainties of a few parts in a thousand. We address the practical issues related to a MC simulation of $\simeq 10^9$ events in the 4$\pi$ hermetic magnetic spectrometer. We discuss modeling the required precision of the electromagnetic field maps, p-e coincidence trigger efficiencies, TOF timing spreads due to neutron beam size and position, charged particle detector energy thresholds and backscattering processes. [Preview Abstract] |
Tuesday, September 20, 2005 2:15PM - 2:30PM |
CH.00002: Polarized Neutron $\beta$-decay: the Proton Asymmetry and Recoil-Order Currents Sky Sjue, Alejandro Garc\'ia We present an analytic calculation of the proton asymmetry from polarized neutron $\beta$-decay, including recoil-order effects. The differential decay rate in terms of electron energy and proton direction follows, parametrized in terms of the most general Lorentz-invariant hadron current coupled to a left-handed lepton current. Implications for experimental efforts to measure recoil-order currents are discussed. [Preview Abstract] |
Tuesday, September 20, 2005 2:30PM - 2:45PM |
CH.00003: Performance of the beta-spectrometer for a precision measurement of the neutron beta-decay asymmetry Junhua Yuan, Bradley Plaster, Bradley Filippone, Takeyasu Ito, Jeffery Martin A precise value for the neutron beta-decay asymmetry will be extracted from measurements of the angular correlation between the neutron spin and the direction of emission of the decay electron in polarized ultracold neutron decay. Ultracold neutrons polarized via transport through a 7.0 Tesla field will be directed into the center of our beta-spectrometer, consisting of a 10-cm diameter, 3-m long open-ended decay trap situated within a highly-uniform 1.0 Tesla solenoidal field. Spiraling decay electrons will be detected at both ends of the decay trap in identical detector arrays consisting of a multi-wire proportional chamber backed by plastic scintillator. Initial results of various performance tests of our beta-spectrometer and electron detector system will be presented. [Preview Abstract] |
Tuesday, September 20, 2005 2:45PM - 3:00PM |
CH.00004: Measurement of Electron Backscattering for Neutron $\beta$-Decay J.W. Martin, M.J. Betancourt, B.W. Filippone, T.M. Ito, J. Yuan, S.A. Hoedl, A.R. Young Electron backscattering from the surfaces of detectors complicates accurate beta spectroscopy in nuclear beta-decay experiments. For example, an upcoming measurement of the beta-asymmetry in neutron decay (the UCNA experiment at Los Alamos) will require an understanding of backscattering at the 20\% level. The beta-asymmetry, when combined with the neutron lifetime, can be used to extract the standard model parameter $V_{ud}$ governing weak transitions between $u$ and $d$ quarks. The existing measurements of electron backscattering are not detailed enough in the relevent energy range to make assessments of models of electron transport. We report on recent progress of measurements of electron backscattering at normal incidence from low $Z$ bulk targets in the energy range 40 to 120 keV. The total backscattered fraction, and the energy and angular distributions of the backscattered electrons were measured for scattering from beryllium, silicon, and scintillator targets. In particular, the scintillator target data presented several additional interesting systematic effects which have now been characterized. Accuracy better than the experimental requirement has been achieved. The measurements have been compared with electron transport models based on the Geant4 and Penelope Monte Carlo codes. [Preview Abstract] |
Tuesday, September 20, 2005 3:00PM - 3:15PM |
CH.00005: Neutron Beam Polarization with $^{3}$He Polarizing and Modulating Cells Robert Cooper, Timothy Chupp, Thomas Gentile, Fred Wietfeldt Precision experiments with polarized neutrons provide data on beta-decay correlation coefficients and particle physics of neutron decay. They rely upon large numbers of decays to achieve the desired level of statistical precision. High flux polychromatic neutron sources are used. This presents difficulties in characterizing the properly weighted polarization for all neutron wavelengths in the beam spectrum. Time of flight with a chopped beam typically characterizes the spectrum and wavelength dependent polarization. Our approach uses the well-known properties of a $^{3}$He polarizer with an added thin $^{3}$He cell to modulate the polarization. With the appropriate combination of thick and thin detectors, the beam polarization can be estimated with high precision. This real- time measurement properly weights the polarization by the decay probability (i.e. the capture-flux polarization), but does require precise knowledge of the thin $^{3}$He cell properties. This alternative can provide a check on beam-chopping methods. [Preview Abstract] |
Tuesday, September 20, 2005 3:15PM - 3:30PM |
CH.00006: Search for Radiative Beta-Decay of the Neutron J.S. Nico, M.S. Dewey, T.R. Gentile, H.P. Mumm, A.K. Thompson, B.M. Fisher, F.E. Wietfeldt, E.J. Beise, K. Kiriluk, J. Byrne, T.E. Chupp, R.L. Cooper Beta decay of the neutron into a proton, electron, and antineutrino is occasionally accompanied by the emission of a photon. Despite decades of detailed experimental studies of neutron beta-decay, this rare branch of a fundamental weak decay has never been measured. An experiment to study the radiative beta-decay of the neutron is currently being developed for the NG6 fundamental physics beam line at the NIST Center for Neutron Research. The experimental approach looks for electron-photon coincidences followed by a delayed proton. The need for a large solid-angle photon detector that can operate in a strong magnetic field and at low temperature has led us to employ a photon detector consisting of scintillating crystals coupled to avalanche photodiodes. A single silicon detector is used for registering both electron and proton events. The apparatus has been installed at the NG6 beam line and initial measurements have begun. Analysis of the data indicate that electron-proton rates are as expected and photon background rates are acceptable. [Preview Abstract] |
Tuesday, September 20, 2005 3:30PM - 3:45PM |
CH.00007: Progress toward a measurement of parity violation in $\vec n + p \rightarrow d + \gamma$ Rob Mahurin The weak part of the nucleon-nucleon interaction produces small parity-violating asymmetries in the gamma rays emitted during polarized neutron capture. The asymmetry for capture on hydrogen is directly related to the nucleon-pion coupling, without complication from nuclear structure, and has an estimated size $50\times 10^{-9}$. With its installation in fall 2005 of a liquid parahydrogen target at the Los Alamos Neutron Science Center, the NPDGamma collaboration can begin to measure this asymmetry directly. I will report the status of the target system and the run plan for the next year, and discuss our plans to achieve our design sensitivity $5\times 10^{-9}$ using the higher flux at the Spallation Neutron Source. [Preview Abstract] |
Tuesday, September 20, 2005 3:45PM - 4:00PM |
CH.00008: Measurement of Parity Violation in Radiative Neutron Capture Mikayel Dabaghyan The NPDGamma experiment aims to measure parity violating directional gamma-ray asymmetry, $A_\gamma$ in the $\vec n + p \rightarrow d + \gamma $ reaction using para-hydrogen, with sensitivity of $5 \times 10^{-9}$, $10\%$ of its predicted value. The experiment is currently under comissioning at LANSCE at Los Alamos National Laboratory. We have measured $A_\gamma$ in a series of elements with $ 35 \leq A \leq 59 $ as well as B, Al, In and Cu. From the results we will extract the upper limit for the weak spreading width in hadronic weak interaction. Experiment and results will be presented. [Preview Abstract] |
Tuesday, September 20, 2005 4:00PM - 4:15PM |
CH.00009: Precision \textit{$\beta $}-decay studies in a RFQ ion trap N. Scielzo, A. Levand, G. Savard, I. Tanihata, B. Zabransky, J. Clark, H. Sharma, K. Sharma, Y. Wang, A. Hecht A linear RFQ ion trap has been constructed and brought online at Argonne for precise measurements of \textit{$\beta $}-decay angular correlations to test the $V-A$ description of the weak interaction. The open geometry of the trap allows four sets of charged particle and $\gamma $-ray detectors to be brought close to the trapped radioactive ions. The first experiment will be a measurement of the \textit{$\beta -\nu $} correlation coefficient in $^{14}$O. The recoil nucleus momentum can be inferred from the Doppler shift of the $\gamma $-rays emitted from the first excited state of $^{14}$N. Recent progress towards a measurement of the \textit{$\beta -\nu $} correlation will be discussed. This work was supported in part by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. W-31-109-ENG-38. [Preview Abstract] |
Tuesday, September 20, 2005 4:15PM - 4:30PM |
CH.00010: $\Sigma^{+}\to p \mu^{+}\mu^{-}$ in the Standard Model German Valencia The HyperCP collaboration has recently reported the observation of three events for the mode $\Sigma^{+}\to p \mu^{+}\mu^{-}$. They have suggested that new physics may be required to understand the implied decay rate and the observed $M_{\mu\mu}$ distribution. Motivated by this result, we re-examine this mode within the Standard Model. The result is long distance dominated and we estimate it with the aid of chiral perturbation theory. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700