Parity violating electron scattering on the proton and deuteron at backward angles

The parity violating asymmetry in quasielastic electron scattering from the deuteron at backward scattering angles has been recently measured for the first time. Combined with the previously performed similar measurement on the proton, this measurement provides a determination of both the proton's strange magnetic form factor G^(a)_(M) and the axial vector e-N form factor G^(a)_(A). A preliminary analysis indicates that G^(a)_(M) is slightly positive but consistent with zero and that G^(e)_(A)(T=1) is in substantial disagreement with the theoretical estimate

Hybrid Simulation between Molecular Dynamics and Binary Collision Approximation Codes for Hydrogen injection onto Carbon Materials

Molecular dynamics (MD) simulation with modified Brenner's reactive empirical bond order (REBO) potential is a powerful tool to investigate plasma wall interaction on divertor plates in a nuclear fusion device. However, MD simulation box's size is less than several nm for the performance of a computer. To extend the size of the MD simulation, we develop a hybrid simulation code between MD code using REBO potential and binary collision approximation (BCA) code. Using the BCA code instead of computing all particles with a high kinetic energy for every step in the MD simulation, considerable computation time is saved. By demonstrating a hydrogen atom injection on a graphite by the hybrid simulation code, it is found that the hybrid simulation code works efficiently in a large simulation box.Comment: 5 pages, 5 figure

Efficient Implementations of Molecular Dynamics Simulations for Lennard-Jones Systems

Efficient implementations of the classical molecular dynamics (MD) method for Lennard-Jones particle systems are considered. Not only general algorithms but also techniques that are efficient for some specific CPU architectures are also explained. A simple spatial-decomposition-based strategy is adopted for parallelization. By utilizing the developed code, benchmark simulations are performed on a HITACHI SR16000/J2 system consisting of IBM POWER6 processors which are 4.7 GHz at the National Institute for Fusion Science (NIFS) and an SGI Altix ICE 8400EX system consisting of Intel Xeon processors which are 2.93 GHz at the Institute for Solid State Physics (ISSP), the University of Tokyo. The parallelization efficiency of the largest run, consisting of 4.1 billion particles with 8192 MPI processes, is about 73% relative to that of the smallest run with 128 MPI processes at NIFS, and it is about 66% relative to that of the smallest run with 4 MPI processes at ISSP. The factors causing the parallel overhead are investigated. It is found that fluctuations of the execution time of each process degrade the parallel efficiency. These fluctuations may be due to the interference of the operating system, which is known as OS Jitter.Comment: 33 pages, 19 figures, add references and figures are revise

Neutrino mass constraints on beta decay

Using the general connection between the upper limit on the neutrino mass and the upper limits on certain types of non-Standard Model interaction that can generate loop corrections to the neutrino mass, we derive constraints on some non-Standard Model $d\to ue^-\bar{\nu}$ interactions. When cast into limits on $n\to pe^-\bar{\nu}$ coupling constants, our results yield constraints on scalar and tensor weak interactions improved by more than an order of magnitude over the current experimental limits. When combined with the existing limits, our results yield |C_S/C_V|\alt 5\times 10^{-3}, |C'_S/C_V|\alt 5\times 10^{-3}, |C_T/C_A| \alt 1.2\times 10^{-2} and |C'_T/C_A| \alt 1.2\times 10^{-2}.Comment: 4 pages, 3 figures; revised to reflect referee comments; accepted for publication in Physical Review Letter

On the Magnetic Excitation Spectra of High Tc Cu Oxides up to the Energies far above the Resonance Energy

Magnetic excitation spectra c"(q,w) of YBa2Cu3Oy and La214 systems have been studied. For La1.88Sr0.12CuO4, c"(q,w) have been measured up to ~30 meV and existing data have been analyzed up to the energy w~150 meV by using the phenomenological expression of the generalized magnetic susceptibility c(q,w)=c0(q,w)/{1+J(q)c0(q,w)}, where c0(q,w) is the susceptibility of the electrons without the exchange coupling J(q) among them. In the relatively low energy region up to slightly above the resonance energy Er, it has been reported by the authors' group that the expression can explain characteristics of the q- and w-dependence of the spectra of YBa2Cu3Oy (YBCO or YBCOy). Here, it is also pointed out that the expression can reproduce the rotation of four incommensurate peaks of c"(q,w) within the a*-b* plane about (p/a, p/a) {or so-called (p, p)} point by 45 degree, which occurs as w goes to the energy region far above Er from E below Er. For La2-xSrxCuO4 and La2-xBaxCuO4, agreements between the observed results and the calculations are less satisfactory than for YBCO, indicating that we have to take account of the existence of the "stripes" to consistently explain the observed c"(q,w) of La214 system especially near x=1/8.Comment: 14 pages, 5 figure

Determination of Trace Levels of Uranium and Thorium in High Purity Gadolinium Sulfate Using ICP-MS with Solid-Phase Chromatographic Extraction Resin

The new Super-Kamiokande-Gadolinium (SK-Gd) project is an upgrade of the Super-Kamiokande (SK) detector. In the SK-Gd project, 0.2\% Gd$_2$(SO$_4$)$_3$ is loaded into the 50 kton water tank of the SK. One of the main purposes of the project is to discover Supernova Relic Neutrinos. Neutrino measurements and proton decay searches will also be performed in the SK-Gd. In order to measure solar neutrinos with a low energy threshold of $\sim$3.5 MeV in the SK-Gd, the main radioactive contaminations, $^{238}$U and $^{232}$Th, in Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O, should be minimized before loading. Our maximum levels for U and Th are 5 mBq (U)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) and 0.05 mBq (Th)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O). In order to measure such low concentrations of U and Th in Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O, we developed the solid-phase extraction technique. Using this method, about 90\% or more U and Th could be efficiently extracted while Gd was reduced by a factor of about $10^{4}$. This allowed these radioactivity contaminations to be measured precisely as 0.04 mBq/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) for U and 0.01 mBq/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) for Th. We measured three pure Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O samples using this method and estimated that the purest one contained $<0.04$ mBq (U)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) and 0.06 $\pm$ 0.01 mBq (Th)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) by ICP-MS.Comment: 13 pages, 11 figure