Abstract:The influence of nitrogen (N) pre-implantation on the deuterium (D) retention in tungsten (W) at different temperatures was investigated. Bulk W samples were exposed to D plasma with a fluence of 110 24 D/m 2 with or without nitrogen pre-implantation at 300 K and 500 K, respectively. Nuclear reaction analysis was applied for the determination of N content and D retention in the near surface. Optical microscopy was used to investigate the surface modification by blistering after implantation. It is shown that, the W:N layers formed during the N preimplantation play very different roles on D retention and blistering in the samples at different temperatures. At 500 K, the W:N layer seems to enhance D diffusion into the bulk by suppressing D loss from the surface, which results in a much higher D concentration in the bulk and larger blisters than without N pre-implantation. At 300 K, the effect of this layer is much less pronounced than that at 500 K.

We report the first measurement of the charm-mixing parameter y CP in D 0 decays to the CP-odd final state K 0 S ω. The study uses the full Belle e þ e − annihilation data sample of 976 fb −1 taken at or near the ϒð4SÞ centre-of-mass energy. We find y CP ¼ ð0.96 AE 0.91 AE 0.62 þ0.17 −0.00 Þ%, where the first uncertainty is statistical, the second is systematic due to event selection and background, and the last is due to possible presence of CP-even decays in the data sample.