Search

We have measured the triple correlation D · (pe × pv) with a polarized cold-neutron beam at the NIST Center for Neutron Research by observing proton-electron coincidences in the decay of polarized neutrons. A non-zero value of D can arise due to parity-even-time-reversal-odd interactions that imply CP violation due to the CPT theorem. Final-state effects also contribute to D at the level of 10-5 and can be calculated with precision of 1% or better. The D coefficient is sensitive to the phase, of λ the ratio of axial-vector and vector amplitudes as well as to scalar and tensor interactions that could arise due to beyond-Standard-Model physics such as leptoquarks. Over 300 million proton-electron coincidence events were used in a blind analysis with the result D = [-0.96±1.89(stat)±1.01(sys)]×10-4. [ABSTRACT FROM AUTHOR]

The NPDGamma collaboration has constructed and commissioned an apparatus on flight path 12 at LANSCE to measure with a high precision, 5×10-9, the small parity-violating gamma-ray asymmetry, Aγ, in polarized neutron capture on protons. This asymmetry can be determined unambiguously the weak pion-nucleon coupling constant. To study the hadronic weak interaction at low energy, the collaboration has used the NPDGamma apparatus to measure parity-violating gamma-ray asymmetries in compound nuclei with cold neutrons. Using the statistical model of compound nuclei and spectroscopic information of the target nuclei, we can set upper limit on the spreading width of the hadronic weak interaction for intermediate-mass nuclei. We describe the experiment and the preliminary results of measured gamma-ray asymmetries of Al, Sc, Ti, Mn, and Co. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

We have built a CsI(Tl) γ-ray detector array for the NPDGamma experiment to search for a small parity-violating directional asymmetry in the angular distribution of 2.2 MeV γ-rays from the capture of polarized cold neutrons by protons with a sensitivity of several ppb. The weak pion-nucleon coupling constant can be determined from this asymmetry. The small size of the asymmetry requires control of systematic errors at the ppb level, and the use of current-mode γ-ray detection with vacuum photo diodes and low-noise solid-state preamplifiers. The detectors were tested for noise performance, sensitivity to magnetic fields, pedestal stability, and cosmic background. False asymmetries due to gain changes and electronic pickup in the detector system were measured to be consistent with zero to an accuracy of 10-9 in a few hours. We show that the detector array operates at counting statistics and present asymmetry results for B4C , CCl4 , 27Al, Cu, and In. B4C , 27Al, Cu, and In are used throughout the experimental apparatus. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The NPDGamma experiment will measure with a high precision, 5×10-9, the small parity-violating gamma-ray asymmetry, Aγ, in polarized cold neutron capture in a para-hydrogen target to determine unambiguously the weak pion-nucleon coupling constant Hπ1. For the experiment the collaboration has built a new high-flux pulsed cold neutron beam line at LANSCE. In 2004, we first commissioned the beam line and then the apparatus with exception of the hydrogen target. The sensitivity of the apparatus was tested by measuring Aγ on Al, B, Cl, Cu, and In. The Cl has a well-known large parity-violating gamma-ray asymmetry that was used to verify the performance of the apparatus. The other nuclei that were studied during the commissioning run are present in materials used for construction of the experiment and are, therefore, possible sources of the false asymmetries since backgrounds are expected to be about 10% of the signal from the neutron capture on hydrogen. We measured Aγ≈0 for these nuclei except for Cl. We report the status of the experiment and preliminary results of the 2004 commissioning run. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

At the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory we have developed an intense low energy [sup 14]O ion beam. During the last development run, an average beam intensity of 2×10[sup 7] particles per second (pps) was achieved with a peak intensity of 3×10[sup 7] pps. The [sup 14]O will be used to measure the shape of the beta decay spectrum of the Garnow-Teller branch as a test of the Conserved Vector Current Hypothesis. The half-life will also be measured and used to determine the Vud element of the Cabibbo-Kobayashi-Maskawa mixing matrix. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Recent and ongoing experiments testing various fundamental discrete symmetries are discussed, including search for parity nonconservation in dysprosium and ytterbium, investigation of possibilities of searches for parity and time-reversal invariance violation in samarium, and a test of permutation properties of photons in a two-photon transition in barium. [ABSTRACT FROM AUTHOR]

By confining up to 500,000 radioactive [sup 21]Na atoms in a magneto-optic trap, we have studied the beta-neutrino correlation. The [sup 21]Na is produced on-line at the Lawrence Berkeley National Laboratory 88" Cyclotron and trapped using common laser cooling techniques. We detect the low-energy recoil [sup 21]Ne daughter nucleus in coincidence with the decay positron. Using the recoil's time-of-flight, we determine the initial momentum of the recoil nucleus and infer the β-ν correlation. Our current data set has a statistical uncertainty to determine the correlation parameter a to better than 2%, and we are studying potential systematic errors at the few percent level. Other beta decay correlations can be studied using magneto-optically trapped radioactive atoms. Precise measurements of correlation parameters can provide limits on non-Standard Model scalar and tensor interactions, or anomalous induced form factors. [ABSTRACT FROM AUTHOR]

The NPDγ experiment at the Los Alamos Neutron Science Center (LANSCE) is dedicated to measure with high precision the parity violating asymmetry in the γ emission after capture of spin polarized cold neutrons in para-hydrogen. The measurement will determine unambiguously the weak pion-nucleon-nucleon (πNN) coupling constant fπ1. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]