Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session CK: Mini-Symposium on Probing Fundamental Symmetries with Nuclei, Neutrons, Muons, and Atoms I |
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Chair: Koichiro Asahi, Tokyo Institute of Technology Room: Queens 5 |
Thursday, October 15, 2009 9:00AM - 9:30AM |
CK.00001: Low-energy probes of physics beyond the Standard Model Invited Speaker: I will discuss theoretical aspects of symmetry tests with low-energy probes. I will focus mostly on (i) beta decays and gauge universality tests; (ii) lepton flavor violation in the charged lepton sector; (iii) searches for CP violating sources beyond the Standard Model and their cosmological implications. In all cases, I will emphasize the complementarity between collider searches and low-energy probes in understanding fundamental interactions at the weak scale and beyond. [Preview Abstract] |
Thursday, October 15, 2009 9:30AM - 9:45AM |
CK.00002: Neutron lifetime experiment with pulsed neutron beam at J-PARC 01 Kenji Mishima A new beam line using novel techniques of neutron optics for fundamental physics experiment, ``NOP,'' has been constructed on December 2008. In this talk, we introduce the beamline and a plan of neutron lifetime experiment. An accurate determination of neutron lifetime is important for tests of the Standard Model of Fundamental Particles, as well for the production of light mass nuclei in big ban nucleosynthesis. For the measurement of the neutron lifetime, there are two principally different approaches: one is ``In-beam'' methods, and the other is the ultracold neutron storage methods. The latest measurement of the latter methods (878.5 $\pm $ 0.7$_{stat} \quad \pm $ 0.3$_{syst.}$ sec) differs from the previous former method (886.3 $\pm $ 1.2$_{stat.} \quad \pm $ 3.2$_{syst.})$ by 7.8 sec. Thus we are planning the measurement of the lifetime with a intense pulsed neutron source at J-PARC by ``in beam'' method, and our target accuracy is 0.1{\%}, which is comparable to the ultracold neutron storage method. Our method is a relative measurement of decay electrons and $^{3}$He(n,p)$^{3}$H reactions by a time projection chamber. The neutron beam is bunched by a spin flip chopper for background reduction and definition of the fiducial volume. In this talk, we would like to introduce our method and discuss how to improve the measurement up to 0.1{\%}. [Preview Abstract] |
Thursday, October 15, 2009 9:45AM - 10:00AM |
CK.00003: Neutron lifetime experiment with pulsed neutron beam at J-PARC 02 Hidetoshi Otono For the measurement of the neutron lifetime, there are two principally different approaches: one is ``In-beam'' methods, and the other is the ultracold neutron storage methods. Nowadays the latest measurement of the latter methods (878.5 $\pm$ 0.7 stat. $\pm$ 0.3 syst. sec) differs from the previous former method (886.3 $\pm$ 1.2 stat. $\pm$ 3.2 syst. sec) by 7.8 sec. Against this problem, we are planning another ``In-beam'' experiment by detecting decay electrons from neutron beam. The apparatus of our experiment consists of a time projection chamber for the track of decay electron and plastic scintilators with MPPCs for the trigger detector. The difficulty of our experiment is expected as the discrimination between decay electron and ambient background. For this purpose, we use neutron bunched by a spin flip chopper. The bunched neutron beam makes us possible to distinguish signal in chamber and background from outside. In addition, the fiducial position of neutron decay is determined as the function of time. In this talk, we present the performance of our experimental apparatus and the results of a test experiment. [Preview Abstract] |
Thursday, October 15, 2009 10:00AM - 10:15AM |
CK.00004: Progress Toward a Redetermination of the Neutron Lifetime Through the Absolute Determination of Neutron Flux A. Yue, G. Greene, M. Dewey, D. Gilliam, J. Nico, A. Laptev The measurements of the neutron lifetime using ``bottled'' ultra- cold neutrons that claim the smallest experimental uncertainties are seriously discrepant with respect to each other. Given that the statistical contribution to their uncertainty is much smaller than the discrepancy, it is likely that one or more of these measurements suffers from an unidentified systematic effect. In the most precise cold neutron beam measurement of the lifetime which gives $\tau_{n} = \left(886.3 \pm 3.4\right)$ s, the largest uncertainty was attributed to the absolute determination of the capture flux of the neutron beam. A new direct measurement of the neutron lifetime flux monitor efficiency using an absolute ``black'' neutron detector could reduce this contribution to the uncertainty. A ``black'' detector that achieves 0.1\,\% statistical precision in several days of running has been put into operation at the NIST Center for Neutron Research. A 0.1\,\% calibration of the flux monitor efficiency will reduce the neutron lifetime uncertainty to approximately 0.25\,\% (2.2 s). The technique, the uncertainty budget, and the current status of the experiment will be discussed. [Preview Abstract] |
Thursday, October 15, 2009 10:15AM - 10:30AM |
CK.00005: A Gravito-Magnetic Trap for Measuring the Neutron Lifetime using Ultracold Neutrons Kevin Hickerson There continues to be a significant discrepancy amongst the most precise measurements of the neutron lifetime. To help resolve this, the lifetime experiment at the Los Alamos Neutron Science Center (LANSCE) will use polarized ultracold neutrons (UCN) trapped by gravity in an asymmetric compound toroidal trap made of permanent magnets arranged in a high field gradient configuration called a Halbach array. Progress has been made on constructing the LANL experiment which removes marginally trapped UCN, a problematic systematic effect in previous measurements, with a compound toroid and a rippled multipole field that can quickly reduce the fraction of phase space of the trap that is quasi-bound, decreasing the probability that UCN escape or have material interactions during the lifetime measuring period. [Preview Abstract] |
Thursday, October 15, 2009 10:30AM - 10:45AM |
CK.00006: Overview of the UCNA Experiment Jianglai Liu In neutron beta decay, the beta asymmetry $A$ is the angular correlation parameter between the neutron spin and the outgoing electron momentum. A measurement of $A$ allows a direct determination the ratio of the nucleon axial to vector coupling constants $g_A/g_V$. While this ratio plays a significant role in solar fusion as well as in understanding other phenomena (in many instances in which the weak interaction in nuclear decays is involved), the axial coupling constant can not presently be calculated from first principles following the Standard Model. However, in combination with the neutron half life, it can provide strigent constraints to the Standard Model. The UCNA experiment is designed to measure the neutron decay $A$ parameter to very high precision ($<$0.5\%), using the ultracold neutron (UCN) source at the Los Alamos Neutron Science Center. UCN are transported in a guide system, fully polarized, then loaded into a decay trap within a solenoidal beta spectrometer. A proof-of-principle measurement in 2007 has been published, and we are on track to produce a 1\% measurement of $A$ based on data collected in 2008. In this talk, I will present an overview of the experiment, give a status report of the data analysis and ongoing data taking, as well as provide a projection for the near future. [Preview Abstract] |
Thursday, October 15, 2009 10:45AM - 11:00AM |
CK.00007: Systematics of the UCNA Experiment Robert Pattie The UCNA experiment measures the $\beta$-asymmetry parameter in free neutron $\beta$-decay using polarized ultracold neutrons (UCN). UCN created in the spallation source at LANSCE are polarized by a 7 T magnetic field in transit to a $2\times 2\pi$ spectrometer where the emitted electrons are measured. During the 2008 run cycle the major systematics were investigated, including neutron depolarization, electron scattering and energy loss, and neutron generated backgrounds. The asymmetry was measured in three geometries designed to maximize or minimize the effect of scattering and energy loss, \textit{in situ} and \textit{ex situ} measurements of the neutron depolarization were performed, and by blocking the $\beta$'s from neutron decay, limits were placed on the gamma flux from neutron capture in the spectrometer. Results of these tests will be presented in the context of a $<1\%$ measurement of the $\beta$-asymmetry. [Preview Abstract] |
Thursday, October 15, 2009 11:00AM - 11:15AM |
CK.00008: Measuring the Parity-Violating Neutron Spin Rotation in Helium: The Neutron Spin Rotation Experiment C.D. Bass, T.D. Bass, B.E. Crawford, J.M. Dawkins, K. Gan, B.R. Heckel, J.C. Horton, C.R. Huffer, D. Luo, D.M. Markoff, A.M. Micherdzinska, H.P. Mumm, J.S. Nico, A.K. Opper, M.G. Sarsour, E. Sharapov, W.M. Snow, H.E. Swanson, S.C. Walbridge, V. Zhumabekova We have performed a precision measurement of the parity-violating neutron spin rotation in helium due to the nucleon-nucleon weak interaction at the NIST Center for Neutron Research. The measurement employed a beam of low energy neutrons passing through a liquid helium target system located between a neutron polarizer--analyzer pair. The parity-violating spin rotation magnitude was determined from measured count asymmetries in the analyzer. The expected parity-violating spin rotation of order $10^{-6}$ rad placed severe constraints on the apparatus design. In particular, isolation of the parity-odd component of the spin rotation from the much larger Larmour precession required use of a nonmagnetic target system that allowed movement of the target helium upstream or downstream of a vertical precession coil, which enabled us to take asymmetry differences to subtract background rotations. We describe the design and performance of the apparatus used for this experiment. [Preview Abstract] |
Thursday, October 15, 2009 11:15AM - 11:30AM |
CK.00009: A Measurement of the Parity-Violating Neutron Spin Rotation in 4He W. Snow, C. Bass, T. Bass, B. Crawford, M. Dawkins, K. Gan, B. Heckel, J. Horton, C. Huffer, D. Luo, D. Markoff, A. Micherdzinska, P. Mumm, J. Nico, M. Sarsour, E. Sharapov, E. Swanson, S. Walbridge, V. Zhumabekova, P. Huffman A weak interaction between nucleons is induced by the quark-quark weak interaction in the Standard Model. At present the NN weak interaction is poorly constrained by experiment. We conducted an experiment to search for parity violation in the rotation of the plane of polarization of slow neutrons in liquid 4He at the Center for Neutron Research at the National Institute of Standards and Technology. In this talk we will report a preliminary result for a measurement of parity-violating neutron spin rotation in 4He. We will also discuss the prospects for follow-on experiments with reduced statistical and systematic errors. [Preview Abstract] |
Thursday, October 15, 2009 11:30AM - 11:45AM |
CK.00010: Testing Supersymmetry with Neutron Decay W.S. Wilburn, V. Cirigliano, A. Klein, P.L. McGaughey, M.F. Makela, C.L. Morris, J. Ramsey, A. Salas-Bacci, A. Saunders, L.J. Broussard, A.R. Young It has been recently realized that the neutrino correlation parameter $B$ in neutron decay is sensitive to Minimal Supersymmetric Models for the case of maximal mixing. $B$ is currently known to a precision of $3\times10^{-3}$, but a precision of better than $1\times10^{-3}$ is required to test these models. Improvements in experimental techniques developed for the ongoing UCNA experiment and the planned abBA experiment may allow an improved measurement of $B$ with a precision approaching $1\times10^{-4}$. An emerging concept for combining these techniques into an experiment to measure $B$ using ultracold neutrons and large-area silicon detectors will be discussed. [Preview Abstract] |
Thursday, October 15, 2009 11:45AM - 12:00PM |
CK.00011: R-parity violating supersymmetric contribution to the nuclear beta decay Nodoka Yamanaka, Toru Sato, Takahiro Kubota The R-parity violating supersymmetric extension of the Standard Model is known to contribute to the neutron beta decay by the scalar coupling of the hadron and lepton currents. Among its decay distribution, the Fierz interference term and the coefficient of the triple product of the initial neutron's polarization, the momentum and polarization of the emitted electron, are observables sensitive to the scalar coupling. We investigate them within R-parity violating MSSM by constructing the hadronic matrix elements and find that new bounds on the R- violating couplings can be deduced from recent new measurement of the transverse polarization of the final electron. We also find contributions to additional angular correlation coefficients. [Preview Abstract] |
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