Search

We describe a setup of time-, spin-, and angle-resolved photoemission spectroscopy (tr-SARPES) employing a 10.7-eV ($\lambda$=115.6 nm) pulse laser at 1-MHz repetition rate as a probe photon source. This equipment effectively combines technologies of a high-power Yb:fiber laser, ultraviolet-driven harmonic generation in Xe gas, and a SARPES apparatus equipped with very-low-energy-electron-diffraction (VLEED) spin detectors. A high repetition rate (1 MHz) of the probe laser allows experiments with the photoemission space-charge effects significantly reduced, despite a high flux of 10$^{13}$ photons/s on the sample. The relatively high photon energy (10.7 eV) also brings the capability of observing a wide momentum range that covers the entire Brillouin zone of many materials while ensuring high momentum resolution. The experimental setup overcomes a low efficiency of spin-resolved measurements, which gets even more severe for the pump-probed unoccupied states, and affords for investigating ultrafast electron and spin dynamics of modern quantum materials with energy and time resolutions of 25 meV and 360 fs, respectively., Comment: 11 pages, 7 figures

We report the diffusion of water molecules confined in the pores of folded silica materials (FSM-12 with average pore diameter of $\sim$ 16 \AA), measured by means of quasielastic neutron scattering using the cold neutron chopper spectrometer (CNCS). The goal is to investigate the effect of electric field on the previously observed fast component of nano-confined water. The measurements were taken at temperatures between 220 K and 245 K, and at two electric field values, 0 kV/mm and 2 kV/mm. Similar to the recently observed electric field induced enhancement of the slow translational motion of confined water, there is a an equally important impact of the field on the faster diffusion., Comment: 6 pages, 4 figures and one table, to appear in the QENS/WINS proceedings as a special edition of Japanese Journal Physics Society (2013)

We report on results of a search for the decay mode K_L -> pi^0 gamma e^+ e^- conducted by the E162 experiment at KEK. We observed no events and set a 90% confidence level upper limit of Br(K_L -> pi^0 gamma e^+ e^-)< 7.1x10^{-7} for its branching ratio. This is the first published experimental result on this decay mode., Comment: 10 pages, 4 figures, submitted to Physics Letters B

In order to study photomultiplier's short-term gain stability at high counting rate, we constructed an LED pulsed light source and its output monitor system. For the monitor system, we employed a photon counting method using a photomultiplier as a monitor photon detector. It is found that the method offers a simple way to monitor outputs from a pulsed light source and that, together with an LED light source, it provides a handy way to investigate photomultiplier's rate effects., Comment: 13 pages, 7 eps-figures, LaTeX2e, graphicx package, submitted to Nucl. Instr. and Meth. A

We report on results of an experimental search for the K_L -> pi^+ pi^- e^+ e^- decay mode. We found 13.5 +- 4.0 events and determined its branching ratio to be (4.4 +- 1.3(stat) +- 0.5(syst))*10^{-7}. The result agrees well with the theoretical prediction., Comment: 9 pages, 6 eps-figures, LaTeX2e, graphicx package, submitted to Physics Letters B

A new type of photodiode + scintillator (1 m2 x 1 cm) detector is developed to detect the large electro-magnetic burst under an EX-chamber. The threshold burst size is found to be 4.3 x 10 the 5 particles at the center of the scintillator. Therefore a gamma-ray family of 10 TeV is detectable by it, when it is set under 14 r.1. of iron. In addition, a very fast (2.4 nsec width) and very bright (correspond to 10 to the 6 particles) scintillation pulse has become avarable for this study.