High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPDGamma experiment, a search for the small parity-violating gamma-ray asymmetry A(gamma) in polarized cold neutron capture on parahydrogen, is one example. For the NPDGamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to rf neutron spin flippers based on adiabatic fast passage. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically polarized He-3 neutron spin filters. The efficiency of the spin rotator was measured at LANSCE to be 98.8 +/- 0.5% for neutron energies from 3 to 20 meV over the full phase space of the beam. Systematic effects that the rf spin rotator introduces to the NPDGamma experiment are considered.

Submitted for the APR06 Meeting of The American Physical Society Monte Carlo Simulation and Photon Detector Development for the Radiative Decay Experiment R.L. COOPER, T.E. CHUPP, U. Michigan, K.J. COAKLEY, M.S. DEWEY, T.R. GENTILE, H.P. MUMM, J.S. NICO, A.K. THOMPSON, NIST, B.M. FISHER, I. KREMSKY, F.E. WIETFELDT, Tulane U., E.J. BEISE, K.G. KIRILUK, U. Maryland, J. BYRNE, U. Sussex — We have recently observed the radiative decay mode of the neutron, where an electron and photon are observed in coincidence, followed by a delayed proton. A false signal can be obtained if bremsstrahlung from the electron detector reaches the photon detector. We estimate the contribution from this process to be small. The potential false signal was experimentally addressed by measuring the dependence of the radiative decay process on the available phase space of decay and comparing it to prediction. Phase space was controlled by varying the voltage on an electrostatic mirror to reflect decay protons. We discuss the simulation techniques used to study the systematic effects in the experiment. We also discuss the performance of the photon detector, which operates in a high magnetic field and at cryogenic temperatures. Additionally we present the design of a 12-element scintillation detector that will allow a precision measurement of the radiative decay spectrum. Robert Cooper University of Michigan Date submitted: 13 Jan 2006 Electronic form version 1.4

Submitted for the DNP06 Meeting of The American Physical Society An Experiment for a Precision Measurement of the Radiative Decay Spectrum of the Neutron R.L. COOPER, T.E. CHUPP, U. Michigan, K.J. COAKLEY, M.S. DEWEY, T.R. GENTILE, H.P. MUMM, J.S. NICO, A.K. THOMPSON, NIST, B.M. FISHER, I. KREMSKY, F.E. WIETFELDT, Tulane U., E.J. BEISE, K.G. KIRILUK, U. Maryland, J. BYRNE, U. Sussex — We have recently observed the radiative decay mode of the free neutron, in which a photon accompanies the usual beta decay products. Monte Carlo methods were used in the analysis of this observation, and these are being applied to optimize the apparatus for a precision measurement of the photon spectrum. The goal is to substantially increase the number of detected radiative decay events while better understanding the systematic effects. Increased statistical sensitivity is expected with a 12-element scintillation detector that is currently being constructed and modeled. These 12 independent channels for photon detection will allow a more thorough examination of our sources of background. Monte Carlo methods address subtle design issues regarding the charged particle detector and neutron transport. Direct photon detection with an avalanche photodiode as a potential photon detector will also be discussed.

The NPDGamma collaboration has constructed and commissioned an apparatus on flight path 12 at LANSCE to measure with a high precision, 5x10(-9), the small parity-violating gamma-ray asymmetry, A(gamma), 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.

The abBA collaboration is developing a new type of field‐expansion spectrometer to measure neutron beta decay angular parameters, a, b, B, and A, to the 0.1% precision level. This precision will be achieved by combining three new technical approaches; a pulsed cold neutron beam, a 3He neutron spin filter, and segmented large‐area thin‐dead layer silicon detectors. Both the electron and proton resulting from the decay will be guided by electric and magnetic fields and detected in coincidence by two 2π solid‐angle silicon detectors. For the neutron polarization‐dependent observables A and B, a novel precision neutron polarimetry technique has been developed. The parameters a and b will be obtained from the proton time‐of‐flight and the measured electron energy spectrum. Measurement of the four parameters in the same apparatus provides a redundant determination of parameter λ=gA/gV, providing a test of the standard electroweak interaction.

The NPDGamma experiment will measure with a high precision, 5x10(-9), the small parity-violating gammaray asymmetry, A. in polarized cold neutron capture in a para-hydrogen target to determine unambiguously the weak pion-nucleon coupling constant H-pi(1). 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 A(gamma) on Al, B, Cl, Cu, and In. The CI 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 A(gamma)=0 for these nuclei except for Cl. We report the status of the experiment and preliminary results of the 2004 commissioning run.

Research is underway at NIST and IU to develop neutron polarizers that are based on polarized {sup 3}He. Such polarizers rely on the strong spin dependence of the cross section for neutron capture by polarized {sup 3}He. Two methods can produce the high density of polarized {sup 3}He gas (10{sup 19}-10{sup 20} cm{sup -3}) required for an effective neutron polarizer: spin-exchange optical pumping, which is performed directly at high pressure (1-10 bar), and metastability-exchange optical pumping, in which the gas is polarized at low pressure (1 mbar) and then compressed. While we are pursuing both methods, progress in the metastable method will be discussed. The features of the metastable method are the high rate at which the gas can be polarized and the inherent separation of the optical pumping and target cells. In a landmark achievement, researchers at the Univ. of Mainz have developed a piston compressor that can fill a 130 cm{sup 3} cell to a pressure of 7 bar of 45% polarized {sup 3} He gas in 2 hours. We plan to develop a compressor and test it at the NIST Cold Neutron Research Facility. We have constructed a metastable-pumping apparatus at NIST and have obtained 76% polarizationmore » with a pumping rate of 1.2 x 10{sup 18} atoms/sec in a 0.4 mbar, 270 cm{sup 3} cell.« less

The tau lifetime has been measured with the OPAL detector at LEP, from analyses using the impact parameters in decays to single charged tracks, and the decay lengths from tau decays to three charged tracks. The 1991 sample of approximately 12300 tau-pair events, of which 70% contain silicon microvertex detector information, has been combined with a re-analysis of the 5100 events recorded during 1990. The two statistically-independent determinations give: tau (one-prong) = 296.4 +/- 7.1 (stat) +/- 3.8 (sys) fs, tau (three-prong) = 286.3 +/- 7.4 (stat) +/- 5.2 (sys) fs. The weighted average of these results after combination of the uncorrelated systematic errors is: tau(tau) = 291.9 +/- 5.1 (stat) +/- 3.1 (sys) fs.

Several recent theories suggest the existence of massive stable particles that might exist in nature as remnants of the big bang. Such particles could be hidden in ordinary terrestrial matter as anomalous-mass isotopes of ordinary nuclei. A search for massive isotopes of hydrogen, lithium, beryllium, boron, carbon, oxygen, and fluorine was performed using an electrostatic charged-particle spectrometer in conjunction with a tandem accelerator. A variety of materials was sampled, including some that had heavy-particle concentrations enriched by various means. No evidence for stable isotopes with masses between 100 and 10 000 amu was found. The sensitivity of the search was greater by several orders of magnitude than the expected concentration levels, limiting the types of stable particles that could exist in this mass range.

By studying lepton-kaon angular correlations in \ensuremath{\Upsilon}(4S) decays, we have measured the branching ratios for B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${K}^{+}$X, B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${K}^{\mathrm{\ensuremath{-}}}$X, B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${K}^{0}$/K${\ifmmode\bar\else\textasciimacron\fi{}}^{0}$X, B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${l}^{\mathrm{\ensuremath{-}}}$${K}^{+}$X, B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${l}^{\mathrm{\ensuremath{-}}}$${K}^{\mathrm{\ensuremath{-}}}$X, and B\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}${l}^{\mathrm{\ensuremath{-}}}$${K}^{0}$/K${\ifmmode\bar\else\textasciimacron\fi{}}^{0}$X. Their values imply that (b\ensuremath{\rightarrow}c)/(b\ensuremath{\rightarrow}all)=0.98\ifmmode\pm\else\textpm\fi{}0.16\ifmmode\pm\else\textpm\fi{}0.12.

We present the results of a search for anomalously heavy isotopes of light elements using an electrostatic charged particle spectrometer in conjunction with the MP tandem accelerator facility at the Nuclear Structure Research Laboratory of the University of Rochester. New limits for the abundance of anomalously heavy isotopes (100–10000 amu) in ordinary terrestrial H, Li, Be, B, and F samples and enriched 2H, 13C, and 18O samples are reported.

Limits are set on ${B}^{0}$B${\ifmmode\bar\else\textasciimacron\fi{}}^{0}$ mixing by use of dilepton events from \ensuremath{\Upsilon}(4S) decay. On the assumption that the charged- and neutral-B semileptonic branching ratios are equal and that 41% of the B mesons from the \ensuremath{\Upsilon}(4S) are neutral, a 90%-confidence-level upper limit of 24% is set on ${B}^{0}$B${\ifmmode\bar\else\textasciimacron\fi{}}^{0}$ mixing. Limits are also given for the ratio of the lifetimes of neutral and charged B mesons. The 90%-confidence-level limits are 2.05.

We have investigated the transitions \ensuremath{\Upsilon}(3S)\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\Upsilon}(1S) and \ensuremath{\Upsilon}(3S)\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\Upsilon}(2S) and the cascade process \ensuremath{\Upsilon}(3S)\ensuremath{\rightarrow}\ensuremath{\Upsilon}(2S)+X, \ensuremath{\Upsilon}(2S)\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\Upsilon}(1S), both in the exclusive decay mode where the daughter \ensuremath{\Upsilon} state decays into two leptons, and in the inclusive decay mode where the daughter \ensuremath{\Upsilon} state decays hadronically. Results are presented on branching fractions and the properties of the ${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ system. Possible evidence for the transition \ensuremath{\Upsilon}(3S)\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\Upsilon}${(1}^{1}$${P}_{1}$) is presented.