Evidence for muon neutrino oscillation in an accelerator-based experiment

We present results for nu(mu) oscillation in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced nu(mu) beam with a mean energy of 1.3 GeV directed at the Super-Kamiokande detector. We observed the energy-dependent disappearance of nu(mu), which we presume have oscillated to nu(tau). The probability that we would observe these results if there is no neutrino oscillation is 0.0050% (4.0 sigma).     

Analysis of atomic arrangement in magnetic Fe–Pt nanoparticles

The order parameter S of Fe–Pt nanoparticles is estimated from X-ray diffraction (XRD) patterns. The total intensity of a diffraction peak is obtained by Rietveld analysis as well as simply integrating the intensity. The Rietveld analysis is found to provide a plausible value of S even for a sample showing an XRD pattern with broad and overlapped peaks. Another order parameter Q, which is obtained from Mössbauer spectra, is introduced, and it is confirmed that Q is equivalent to the probability of Fe atoms being in the L1₀-type atomic arrangement. The coercivity of Fe–Pt nanoparticles is directly proportional to Q, while it vanishes at S=0.4, indicating that the magnetic property of Fe–Pt nanoparticles has a closer relationship to Q than S.     

Potential formation and high density plasma production on the tandem mirror GAMMA 10

GAMMA 10 experiments have advanced in high density experiments after the last EPS Workshop where we reported high density plasma production by using an ion cyclotron range of frequency heating at a high harmonic frequency and neutral beam injection in the central cell. Recently a high density plasma was obtained with much improved reproducibility than before and without degradation of diamagnetic signal. The high density plasma was attained by adjusting the spacing of the conducting plates installed in the anchor transition regions. Dependencies of particle confinement time, ion energy confinement time and plasma confining potential on plasma density were obtained for the first time in the high density region. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreus, Switzerland, June 23–24, 2002.     

Influence of radial electric field on trajectories of plug potential bounce ion in the tandem mirror

Bouncing ions between the plug potentials play an important role in improvement of the axial confinement in the tandem mirror. We examined the influence of the radial electric field on the trajectories of the ions passed through the anchor cell with nonaxisymmetric magnetic configuration on the assumption that the shape of the magnetic flux tube was shifted from the shape of the equipotential surface of the plasma at the mirror throats of the anchor cells. The discrepancy between the shapes enhanced the radial drift of the bounce ion. Radial potential profile of the core plasma was controlled by adjustment of the radially separated endplate potentials, and it was found that the flattened radial potential profile was effective for the decrease of the radial drift. Presented at 5th Workshop “Role of Electric Fields in Plasma Confinement and Exhaust”, Montreux, Switzerland, June 23–24, 2002.     

Gamma-ray spectroscopy of the neutron-rich Ni region through heavy-ion deep-inelastic collisions

Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T _1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the doubly magic ⁶⁸Ni and its neighbor ^69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed. Received: 1 May 2001 / Accepted: 4 December 2001     

1.5 mJ, 6.4 fs parametric chirped-pulse amplification system at 1 kHz

We demonstrate an optical parametric chirped-pulse amplification (OPCPA) system with the pulse energy of 1.5 mJ at a 1 kHz repetition rate. The newly developed 100 ps Ti:sapphire pump laser system, which was optically synchronized with OPCPA seed pulses, delivered 10 mJ, 400 nm pump pulses. After three-stage parametric amplification, recompression of the amplifier output from 45 ps to 6.4 fs was performed. The pulse width of 6.4 fs is, to our knowledge, the shortest ever obtained by OPCPA, and the average power of 1.5 W (1.5 mJ, 1 kHz) is believed to be the highest among few-cycle OPCPA systems.     

In-plane magnetoresistance of electron-doped superconducting thin films Pr0.9LaCe0.1CuO4

We measured the in-plane magnetoresistance of Pr_0.9LaCe_0.1CuO₄ (PLCCO) epitaxial thin films under various magnetic fields H applied parallel to the tetragonal c-axis. The measurements were performed at the superconducting state as well as the normal state. As the magnetic field is between the low critical field H_c1 and upper critical field H_c2, a critical scaling behavior of electrical resistivity is found. We analyze the electrical transport properties and show the magnetic field H dependence of glass transition temperature T_g and the characteristic temperature T^* for the PLCCO film, which may shed some light on vortex behavior in electron-doped superconductors.