Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session FB: Weak Processes and Symmetry Tests |
Hide Abstracts |
Chair: Michael Gericke, University of Manitoba Room: Kohala 2 |
Friday, October 10, 2014 9:00AM - 9:15AM |
FB.00001: Nab: precise experimental study of unpolarized neutron beta decay Dinko Pocanic Nab, a program of experimental study of unpolarized neutron decays at the Spallation Neutron Source, Oak Ridge, TN, aims to determine $a$, the electron--neutrino correlation with precision of $\delta a/a = 10^{-3}$, and $b$, the Fierz interference term, with uncertainty $\delta b \simeq 3\times 10^{-3}$. Neutron beta decay's simple theoretical description in the Standard Model (SM) is overconstrained by the set of available observables, providing opportunities to search for evidence of SM extensions. Planned Nab results will lead to a new precise determination of the ratio $\lambda=G_A/G_V$, and to significant reductions in the allowed limits for both right- and left-handed scalar and tensor currents. Alternatively, the experiment may detect a discrepancy from SM predictions consistent with certain realizations of supersymmetry. An optimized, asymmetric spectrometer has been designed to achieve the narrow proton momentum response function required to meet the physics goals of the experiment. The apparatus is to be used in a follow-up measurement (ABba) of asymmetry observables $A$ and $B$ in polarized neutron decay. Nab is funded, now in the construction stage, with planned beam readiness in 2016. We discuss the experiment's motivation, expected reach, design and method. [Preview Abstract] |
Friday, October 10, 2014 9:15AM - 9:30AM |
FB.00002: Measurement of the $\beta$-asymmetry in the decay of magneto-optically trapped, spin-polarized $^{37}\mathrm{K}$ Benjamin Fenker, Melissa Anholm, Daniel Ashery, Spencer Behling, John Behr, Iuliana Cohen, Alexandre Gorelov, Gerald Gwinner, Michael Mehlman, Dan Melconian, Praveen Shidling, Claire Warner We have performed a measurement of the $\beta$-asymmetry parameter ($A_{\beta}$) in the isobaric-analogue $\frac{3}{2}^+\rightarrow\frac{3}{2}^+$ $\beta^+$ decay of $^{37}\mathrm{K}$ by observing the angular distribution of the decay positrons with respect to the nuclear polarization axis. The value of this parameter is sensitive to a possible ($V+A$) admixture in the weak interaction and is a sensitive probe of physics beyond the standard model. Atoms delivered from ISAC, the radioactive ion beam facility at TRIUMF, were cooled and confined in a magneto-optical trap, providing a localized source of atoms decaying nearly from rest. Furthermore, the decaying atoms were highly spin-polarized by optical pumping techniques and monitored by photoionization, with a preliminary analysis giving a nuclear polarization near 99\% with statistical uncertainty of 0.4\%. Here, I will present the current status of the analysis of our recent 2014 run, from which we have the statistics necessary for a $\la$ 0.5\% measurement. [Preview Abstract] |
Friday, October 10, 2014 9:30AM - 9:45AM |
FB.00003: Development of a Position Sensitive Beta and Recoil Ion Detectors for the $^6$He $\beta-\nu$ Angular Correlation Measurement Ran Hong, Yelena Bagdasarova, Alejandro Garcia, Derek Storm, Matthew Sternberg, Erik Swanson, Frederik Wauters, David Zumwalt, Kevin Bailey, Arnaud Leredde, Peter Mueller, Thomas O'Connor, Xavier Fl\'echard, Etienne Liennard, Andreas Knecht, Oscar Naviliat-Cuncic In order to measure the $\beta-\nu$ angular correlation coefficient {\em a} and put more stringent limits on exotic tensor type weak currents, we constructed a system which detects $\beta$ particles in coincidence with recoil ions from the $\beta$-decay of laser trapped $^6$He atoms. The $\beta$ particles are detected by a scintillator and a multi-wire proportional chamber (MWPC) with a capacitive charge division anode. The recoil ions are detected by a microchannel plate (MCP) with delay-line anodes. The coefficient {\em a} is extracted by fitting the coincidence data to GEANT4 based Monte Carlo simulations, which are also used to study systematic uncertainties related to the detector system. A new method of calibrating the MWPC using a cathode focusing effect will be presented. This work is supported by DOE, Office of Nuclear Physics, under contract nos. DE-AC02-06CH11357 and DE-FG02-97ER41020. [Preview Abstract] |
Friday, October 10, 2014 9:45AM - 10:00AM |
FB.00004: Status update on the measurement of the $\beta$-$\nu$ angular correlation with trapped $^{8}$B ions Adrian Perez Galvan Measurements of the $\beta$-$\nu$ angular correlation coefficient ($a_{\beta \nu}$) in $\beta$-decay provide information on the presence of possible exotic interactions beyond the Standard Model. The $^{8}$Li-$^{8}$B radioactive mirror nuclei represent a particularly attractive system for these studies due to their small masses, large $Q$-value, and a triple-correlation that enhance the sensitivity to detect so-called ``New Physics.'' Furthermore, it is possible to search for the existence of second-class-currents in the Standard Model and to test the Conserved-Vector-Current hypothesis by comparing correlation measurements in $^{8}$Li and $^{8}$B. Our collaboration has already performed a measurement of $a_{\beta \nu}$ with trapped $^{8}$Li ions using the Beta-Decay Paul Trap at Argonne National Laboratory with an uncertainty of approximately 1 percent. Tests with a small sample of $^{8}$B decays obtained during a preliminary run showed that a measurement of comparable sensitivity is feasible. In this talk we present the current status on the ongoing effort to achieve a high statistics measurement using trapped $^{8}$B ions. [Preview Abstract] |
Friday, October 10, 2014 10:00AM - 10:15AM |
FB.00005: Measuring $\beta $-$\nu $ angular correlation with laser trapped $^{6}$He Arnaud Leredde, Kevin Bailey, Peter Mueller, Thomas O'Connor, Yelena Bagdasarova, Alejandro Garcia, Ran Hong, Matthew Sternberg, Derek Storm, Erik Swanson, Frederik Wauters, David W. Zumwalt, Xavier Flechard, Etienne Lienard, Andreas Knetch, Oscar Naviliat-Cuncic Exotic current contributions to the weak interaction can be constrained through measuring the beta-neutrino angular correlation parameter $a_{\beta \nu }$ in nuclear beta decay - providing opportunities to find evidence for physics beyond the Standard Model. Our goal is to measure $a_{\beta \nu }$ with a precision of 0.1{\%} for the beta decay of $^{6}$He (t$_{1/2}=$807ms) which is particularly sensitive to the exotic tensor currents. For this purpose, we have built a double magneto-optical trap (MOT) system to provide a cold and point-like source of $^{6}$He. Of the 1x10$^{10}$ $^{6}$He atoms/s produced via the $^{7}$Li(d,$^{3}$He)$^{6}$He nuclear reaction, roughly 1000 atoms/s are captured in the first MOT and periodically transferred to the second, low background MOT that is surrounded by a detector system. Coincidence detection of the beta particle and the recoiling ion offers kinematic reconstruction of $a_{\beta \nu }$ in combination with high statistic numerical simulations of the detector setup. The performance of the trap setup, preliminary coincidence data, and studies of systematic uncertainties will be presented. This work is supported by DOE, Office of Nuclear Physics, under contract nos. DE-AC02-06CH11357 and DE-FG02-97ER41020. [Preview Abstract] |
Friday, October 10, 2014 10:15AM - 10:30AM |
FB.00006: High-Precision Half-Life Measurements for the Superallowed $\beta^+$ emitter $^{10}$C Michelle Dunlop High precision measurements of superallowed Fermi beta transitions between 0$^+$ isobaric analogue states allow for stringent tests of the electroweak interaction described by the Standard Model. These transitions provide an experimental probe of the unitary of the Cabibbo-Kobayashi-Maskawa matrix, the Conserved-Vector-Current hypothesis, as well as set limits on the existence of scalar currents in the weak interaction. Half-life measurements for the lightest of the superallowed emitters are of particular interest as the low-Z superallowed decays are most sensitive to a possible scalar current contribution. The half-life of $^{10}$C can be measured by directly counting the $\beta$ particles or measuring the $\gamma$-ray activity following $\beta$ decay. Previous results for the $^{10}$C half-life measured via these two methods differ at the 1.5$\sigma$ level, motivating further independent measurements of the $^{10}$C half-life using both techniques. Recent $^{10}$C half-life measurements via both gamma-ray photo-peak and direct beta counting were performed at TRIUMF's Isotope Separator and Accelerator facility. This presentation will highlight the importance of these measurements and preliminary half-life results will be presented. [Preview Abstract] |
Friday, October 10, 2014 10:30AM - 10:45AM |
FB.00007: Precise branching-ratio measurement for the superallowed Fermi beta decay of $^{34}$Ar at NIRS-HIMAC Shumpei Kinno The precise measurement of the $ft$ values for superallowed Fermi beta decays is a valuable tool to explore weak interactions. The resulting $ft$ values can confirm the CVC hypothesis, the unitarity of CKM matrix, and the existence of large isospin-symmetry breaking. Recently, the mirror superallowed Fermi beta decays, $^{38}$Ca $\to$ $^{38m}$K and $^{38m}$K $\to$ $^{38}$Ar, have been reported as a sensitive test of the isospin-symmetry breaking. In order to study the mirror superallowed Fermi beta decays in $A$ = 34 systems, the precise measurement for the branching ratios of $^{34}$Ar emitter has been performed.The experiment was carried out at NIRS-HIMAC. The secondary beam including $^{34}$Ar was produced with the projectile fragmentation of a 500-MeV/u $^{36}$Ar beam on a CH$_2$ target. The secondary beam was separated and identified by passing through the secondary beam line. After decreasing the beam energy with an Al degrader of variable thickness, the beam was implanted in the center of a 6-mm thick GSO scintillator surrounded by four clover Ge detectors. The beta and gamma rays were detected by the GSO stopper and the clover Ge detectors, respectively. By analyzing the beta- and gamma-rays energy and time spectra, the branching ratios of $^{34}$Ar have been determined. [Preview Abstract] |
Friday, October 10, 2014 10:45AM - 11:00AM |
FB.00008: Precision $Q_{EC}$-value measurement of $^{23}$Mg for testing the CKM matrix unitarity Maxime Brodeur, Brad Schultz, Jens Dilling We report a new direct measurement of the $^{23}$Mg $\beta^+$-decay transition energy $Q_{EC}$ using the TITAN Penning trap mass spectrometer. This value agrees with the latest atomic mass evaluation while being four times more precise. The increase in precision changes the uncertainty contribution of the $Q_{EC}$-value on the statistical rate function $f_v$ from 11$\%$ to 0.6$\%$, an improvement by a factor of 18. This enables a more robust determination of the corrected $Ft$-value of this mirror transition to the required precision, making possible further test of the CKM matrix unitarity. [Preview Abstract] |
Friday, October 10, 2014 11:00AM - 11:15AM |
FB.00009: Branching-ratio measurement for superallowed emitter 30S at NIRS-HIMAC Yoshimasa Taguchi The corrected $Ft$ values with some radiative corrections and the isospin-symmetry breaking correction for the most precisely determined 13 decays are consistent within 0.3 \%. However, the $Ft$ value for the superallowed beta emitter 30S significantly deviates from the average $Ft$ value, even through it still has a large experimental uncertainty of a few \% which mainly comes from the measured branching ratio. On the other hand, the isospin-symmetry breaking correction has been predicted in several theoretical calculations. Especially, theoretical results for 30S decay differ from each other. In order to resolve this discrepancy of Ft value and to confirm the reliability of these calculations, the branching ratio for 30S has been measured. The secondary beam of 30S was produced by the fragmentation of a 500-MeV/u 36Ar beam on (CH2 )n target. After passing through the separator, it was implanted in the center of 6-mm-thick GSO scintillator. Around the GSO scintillator, four clover-type HPGe detectors were located at an angle of 45 degrees symmetrically with respect to the beam axis. The beta and gamma rays emitted from 30S were detected by the GSO active stopper and the HPGe detectors, respectively. The results of branching ratio for 30S will be presented. [Preview Abstract] |
Friday, October 10, 2014 11:15AM - 11:30AM |
FB.00010: Half-life and Branching ratio measurements of T $=$ 1/2 Mirror Nuclei P.D. Shidling, D. Melconian, S. Behling, B. Fenker, J.C. Hardy, V. Horvat, V.E. Iacob, E. McCleskey, M. McCleskey, M. Mehlman, H.I. Park, B. Roeder The $\beta$-decay transitions between T$=$1/2 isospin doublets in mirror nuclei requires the measurement of decay rate and angular correlation to measure the comparative half-life. The motivation for improving the precision of the \textit{ft} value is to determine the standard-model prediction for the correlation parameters with better precision. We have measured the half-life of $^{21}$Na and $^{37}$K, and the ground-state branching ratio of $^{37}$K to improve the precision of the \textit{ft} value. For $^{37}$K, the \textit{ft} value was limited by 0.6{\%} uncertainty in the half-life and 0.14{\%} uncertainty in the ground-state branching ratio. The precision of the present half-life measurement is nearly an order of magnitude improvement over the previously accepted world average. In case of $^{21}$Na, the \textit{ft} value was limited by 0.13{\%} uncertainty in the half-life. Another motivation for the half-life measurement comes from the fact that the half-life has only been measured thrice nearly 40 years ago. The measurements were carried out at the Cyclotron Institute, Texas A{\&}M University. An overview of both experiments and results will be presented. [Preview Abstract] |
Friday, October 10, 2014 11:30AM - 11:45AM |
FB.00011: $A\ge62$ Superallowed Fermi $\beta$-decays and Future Prospects with GRIFFIN Ryan Dunlop Superallowed Fermi $\beta$ decays of $A\ge62$ nuclei involve relatively large nucleus dependent isospin-symmetry-breaking corrections. The magnitudes of these corrections are of great interest, and the $A\ge62$ decays provide a demanding test of theoretical models. Branching ratio measurements for these decays involve a unique challenge as they have large $Q_{EC}$, and hence a high density of available states in the daughter nucleus, resulting in the Pandemonium effect in which weak feeding is distributed over a large number of states and is difficult to observe. Therefore, high-efficiency detectors are of paramount importance in determining the branching ratio for these decays. The 8$\pi$ spectrometer at TRIUMF's Isotope Separator and Accelerator (ISAC), has been used to establish high-precision branching ratios for $^{62}$Ga and $^{74}$Rb. The newly commissioned GRIFFIN spectrometer at ISAC provides an efficiency 17 times higher than the $8\pi$ for 1 MeV $\gamma$-rays, and larger gains at higher energies which are of particular importance in resolving the Pandemonium effect. The recent branching ratio measurement for the superallowed Fermi $\beta$-decay of $^{74}$Rb will be discussed, as well as the importance of GRIFFIN for future superallowed $\beta$ decay studies at ISAC. [Preview Abstract] |
Friday, October 10, 2014 11:45AM - 12:00PM |
FB.00012: Determination of $\mu d$ chemistry kinetic parameters for the MuSun Experiment Nandita Raha The MuSun experiment at PSI will measure the muon doublet capture rate $\Lambda_d$ in ultra pure deuterium gas to 1.5\% precision from the measured decay-electron time distribution. This reaction cleanly determines the strength of the two-nucleon weak axial current interaction. The kinetic parameters of the $\mu d$ chemistry are essential for extracting $\Lambda_d$, which in turn are determined from the process of muon catalyzed fusion in deuterium. This process yields $^{3}He$ recoils and 2.45~MeV monoenergetic neutrons from the reaction $d d\mu \rightarrow$ $^{3}He+n+\mu$. Encoded in the time dependence of the fusion products are the $dd \mu $ molecular formation rates from the $F = 1/2,~3/2$ hyperfine states ($\lambda_d$ and $\lambda_q$) and the hyperfine transition rate ($\lambda_{qd}$) from the higher-energy $F = 3/2$ state to the lower-energy $F = 1/2$ state. This work concentrates on the analysis of the fusion neutrons, which are detected by an array of eight neutron detectors. Pulse shape discrimination was used to distinguish neutrons from background gamma rays. A least squared fit to the time spectrum of the fusion neutrons determines the $\mu d$ chemistry kinetic parameters $\lambda_{qd}$ and the ratio $\lambda_q$ / $\lambda_d$. [Preview Abstract] |
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