Bulletin of the American Physical Society
2008 Annual Meeting of the Division of Nuclear Physics
Volume 53, Number 12
Thursday–Sunday, October 23–26, 2008; Oakland, California
Session GF: Electroweak Interactions |
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Chair: Robert Tribble, Texas A&M University Room: Simmons Ballroom 4 |
Saturday, October 25, 2008 10:30AM - 10:42AM |
GF.00001: Precision Determination of the Excitation Energy of the Long-Lived Isomer in the Superallowed Fermi Emitter $^{42}$Sc M. Sternberg, G. Savard, J. Clark, I. Tanihata, N. Scielzo, A.F. Levand, Y. Wang, H. Sharma, A. Hecht, A.C.C. Villari, J. Fallis, R. Segel, A. Heinz, V. Werner, J.R. Terry, E.A. McCutchan, H. Ai, B. Shoraka, E. Williams, R. Luttke, D. Frank, C.W. Beausang, P. Regen, K.S. Sharma Some Q-value measurements for superallowed Fermi emitters used in calculation of the $V_{ud}$ quark mixing matrix element came into question after measurements at ANL and confirmation of these measurements by JYFLTRAP found the Q-value for $^{46}$V to differ by more than 2 keV ($7 \sigma$) from the previous accepted value. A new precision Q-value measurement for the superallowed emitter $^{42}$Sc performed by JYFLTRAP found no substantial shift from the previous accepted Q-value. Their measurement included a new precision measurement of the excitation energy of the 7+ long-lived isomeric state of $^{42}$Sc, which did not agree with old measurements. New measurements of this excited state have been preformed at YRASTBall to within roughly 200 eV. Combined with recent measurements for the mass of this excited state preformed by the Canadian Penning Trap group of ANL, a new precision Q-value measurement has been completed and no substantial shift in the $^{42}$Sc Q-value is observed. [Preview Abstract] |
Saturday, October 25, 2008 10:42AM - 10:54AM |
GF.00002: Precise Half Life Measurement of $^{26}$Si V.E. Iacob, V. Golovko, J. Goodwin, J.C. Hardy, N. Nica, H.I. Park, L. Trache, R.E. Tribble As part of our program to test the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix \textit{via} $0^+\to 0^+$superallowed $\beta $ transitions, we recently measured the half-life of $^{26}$Si. The radioactive $^{26}$Si beam was obtained with a $^{27}$Al primary beam at 30$A~$MeV, which bombarded a cryogenic hydrogen target held at a pressure of 2.0 atm. From the reaction products, a high-purity $^{26}$Si beam at 25$A~$MeV was selected with the MARS spectrograph. The beam was then extracted in air, passed through a 0.3-mm-thick BC-404 plastic scintillator and a set of Al degraders, which had been adjusted so that the radioactive nuclei stopped in the center of the 76-$\mu $m-thick aluminized-mylar tape of our fast tape-transport system. We collected $^{26}$Si nuclei for 1.3~s; then the beam was switched off and the activity was moved in less than 0.2~s to the center of a 4$\pi $ proportional counter, located in a well-shielded region. The observed decays were then multi-scaled over a 44~s time span. To ensure an unbiased result, we split the experiment into many runs, each differing from the others in its discriminator threshold, detector bias or dominant dead-time setting. The analysis of these separate runs showed no systematic bias with these parameters. Our preliminary result agrees with the currently accepted (average) value, and the full analysis is expected to yield an uncertainty of 0.05{\%} or better. [Preview Abstract] |
Saturday, October 25, 2008 10:54AM - 11:06AM |
GF.00003: Search for Oscillation of the Electron-Capture Decay Probability of $^{142}$Pm Paul Vetter, R.M. Clark, J. Dvorak, S.J. Freedman, K.E. Gregorich, H.B. Jeppesen, D. Mittelberger, M. Wiedeking We have searched for time modulation of the electron capture decay probability of $^{142}$Pm in an attempt to confirm a claim from a group at the Gesellschaft f\"{u}r Schwerionenforschung (GSI) attributed to neutrino oscillation. We produced $^{142}$Pm via the $^{124}$Sn($^{23}$Na, 5n)$^{142}$Pm reaction at the Berkeley 88-Inch Cyclotron with a short bombardment time. Isotope selection by the Berkeley Gas-filled Separator is followed by implantation and a long period of monitoring the $^{142}$Nd K$_{\alpha}$ x-rays from the daughter. The decay time spectrum of the x-rays is well-described by a simple exponential and our measured half-life is consistent with the accepted value. We observed no decay rate oscillation at the frequency reported by Litvinov {\it et al.} (Phys.~Lett.~B {\bf 664}, 162 (2008)), and no oscillation terms at any frequency were statistically significant. A search for previous experiments that might have been sensitive to the reported modulation uncovered another example in $^{142}$Eu electron-capture decay. A reanalysis of the published data shows no decay rate oscillation. [Preview Abstract] |
Saturday, October 25, 2008 11:06AM - 11:18AM |
GF.00004: Central Particle Tracking Detectors in the PEN Experiment Emil Frlez The PEN Collaboration is conducting a new measurement of the $\pi^+\to e^+\nu(\gamma)$ ($\pi_{e2}$ decay) branching ratio at the Paul Scherrer Institute, with the goal uncertainty of $\Delta B/B \simeq 5\times 10^{-4}$ or lower. At present, the combined accuracy of all published $\pi_{e2}$ decay measurements lags behind the theoretical calculation by a factor of 40. In this contribution we describe the redesigned central region tracking detectors of the PEN detector. The design and performance of a pair of two-piece wedge degraders for simultaneous horizontal and vertical tracking of the $\pi^+$ beam particles are presented in detail. After passing through the tracking degrader, the $\pi^+$ beam is stopped in the center of an active target scintillator. The positrons from $\pi^+$ and $\mu^+$ decays are tracked in a pair of cylindrical MWPC's, and detected in a thin plastic scintillator hodoscope and a pure CsI electromagnetic calorimeter. [Preview Abstract] |
Saturday, October 25, 2008 11:18AM - 11:30AM |
GF.00005: Waveform Analysis for a Precision Pion Decay Measurement Anthony Palladino The PEN experiment aims to measure the $\pi^+$ $\rightarrow$ $e^+\nu(\gamma)$ ($\pi_{\rm e2}$ decay) branching ratio at PSI, with an uncertainty of $\Delta B/B \simeq 5\times 10^{-4}$, or better, using a large-angle detector system featuring a pure CsI calorimeter. A critical element of the data analysis requires distinguishing $\pi\to$ $e \nu$ events from the $\pi\to\mu\to e$ decay chain. A digitized waveform for a large subset of pion decay events must be reliably sorted into one of the two categories in order to reveal the low-energy ``tail'' of the calorimeter response to the $\pi_{\rm e2}$ 69\,MeV $e^+$'s, otherwise masked by the muon decay positrons. Most events contain pulses which overlap. An analysis program was designed to distinguish between the different decay types with a high resolution extraction of closely spaced peaks. The peak to peak (or overlapping pulse) separation methods and their relative merits will be discussed. [Preview Abstract] |
Saturday, October 25, 2008 11:30AM - 11:42AM |
GF.00006: Prospects for a High Sensitivity Lepton Flavor-Violating Search at Fermilab James Miller The Mu2e collaboration is proposing to search for coherent, neutrino-less conversion of muons into electrons in the field of a nucleus, with a sensitivity improvement of a factor of 10,000 over existing limits. Such a lepton flavor-violating reaction probes new physics at a scale unavailable by direct searches at either present or planned high energy colliders. The physics motivation for mu2e will be presented, as well as the design of the muon beamline and spectrometer. A scheme by which the experiment can be mounted in the present Fermilab accel-erator complex will be described. Prospects for increased sensitivity from the Project X linac that is being proposed by Fermilab will be discussed. [Preview Abstract] |
Saturday, October 25, 2008 11:42AM - 11:54AM |
GF.00007: Muon radiative decay and limits on non-(V-A) weak interaction Maxim Bychkov Using the PIBETA detector in its original form and, more recently, as configured for the PEN experiment, we have recorded the world largest sample of radiative muon decay events $\mu^+ \to {\rm e}^+ \nu_e \overline{\nu}_\mu \gamma$, resulting from secondary muons produced by a stopped pion beam. Theoretical predictions of the muon radiative decay branching ratio depend on the Michel parameters $\rho$ and $\overline{\eta}$ which, along with other muon decay parameters, can be used to set limits on the possible extensions of the V-A form of the electroweak interactions. We will report the branching ratio for this process in a wide kinematic region of phase space, and a new, improved value of the parameter $<$eta-bar$>$, which, coupled with other results, provide comprehensive limits on non-standard contributions to the electoweak interaction. [Preview Abstract] |
Saturday, October 25, 2008 11:54AM - 12:06PM |
GF.00008: Future Prospects for a Muon g-2 Experiment David Hertzog, Chris Polly The final results from the muon g-2 experiment at Brookhaven National Laboratory were published in 2004.~ The difference between the final experimental result and the current theoretical prediction for a$_{\mu }$ reveals a 3.4$\sigma $ discrepancy with the Standard Model, hinting at the possibility of new particles entering via quantum fluctuations.~ The experiment ended in a statistical error dominated regime, thus enabling a future generation muon g-2 experiment to be pursued with a higher muon flux and relatively minor modifications to the basic technique.~ The motivation for a new experiment will be discussed along with a description of design improvements and siting considerations for a new effort at BNL, FNAL, or JPARC. [Preview Abstract] |
Saturday, October 25, 2008 12:06PM - 12:18PM |
GF.00009: Isospin-symmetry-breaking corrections to superallowed Fermi beta decay Gerald A. Miller, Achim Schwenk We study the formalism to include isospin-symmetry-breaking corrections when extracting the up-down Cabibbo-Kobayashi-Maskawa matrix element from superallowed $0^+\rightarrow 0^+$ nuclear beta decay. We show that there are no first order isospin-symmetry-breaking corrections to the relevant nuclear matrix elements. We find corrections to the treatment of Towner and Hardy, and assess these using schematic models of increasing complexity. [Preview Abstract] |
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