Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
Volume 71, Issue 9
Displaying 1-27 of 27 articles from this issue
70 Challenges and Mysteries in Physics
  • Tsunefumi Mizuno, Horoyasu Tajima
    Article type: Researches
    2016 Volume 71 Issue 9 Pages 617-622
    Published: September 05, 2016
    Released on J-STAGE: January 09, 2017

    About 25% of energy density of the universe today is in the form of non-baryonic cold dark matter, and Weakly Interacting Massive Particles (WIMPs) are one of the most promising candidates. Annihilation of WIMPs could produce detectable gamma-ray signal depending on their mass and number density. The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope is sensitive to GeV gamma rays and is suitable for indirect search of WIMP signals. Recent studies of gamma rays in the direction of Galactic center reveal an extended excess emission in 1–10 GeV energies over the standard Galactic diffuse gamma-ray emission. Although the excess can be explained by annihilation of WIMPs with the mass of a few 10s GeV, the spectrum is strongly affected by the uncertainty of the Galactic diffuse emission. No significant gamma-ray excess was found coincident with known dwarf spheroidal galaxies which are known to be dark matter rich and lack of non-thermal astrophysical processes. Instead, WIMP mass less than 100 GeV are excluded by 95% confidence. If the most of the Galactic center excess is not due to WIMP annihilation, more observations by Fermi-LAT with future observations in TeV gamma rays by Cherenkov Telescope Array, will enable us to search for WIMP signal of mass range from 10 GeV up to a few TeV.

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  • Reika Kanya, Yuya Morimoto, Kaoru Yamanouchi
    Article type: Researches
    2016 Volume 71 Issue 9 Pages 623-627
    Published: September 05, 2016
    Released on J-STAGE: January 09, 2017

    The first observation of the light-dressing effect in the laser-assisted elastic electron scattering process, which was predicted more than 30 years ago, is reported. This phenomenon will be of use for probing the ultrafast evolution of the electron density distribution in atoms and molecules.

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Experimental Developments
  • Manabu Saito, Yoichi Haruyama
    Article type: Experimental Developments
    2016 Volume 71 Issue 9 Pages 628-635
    Published: September 05, 2016
    Released on J-STAGE: January 09, 2017

    An electrostatic ion beam trap confines the keV energy ion beam in a finite space using only electrostatic force. This device has a simple structure in which the ions oscillate between the two electrostatic reflectors located on opposite sides. The space between the two reflectors is a field-free region so that the kinetic energy of the ions in this region is equal to their injection energy. Therefore, the device allows us to study interactions of mono-energetic ions with atoms, ions, electrons, and photons. An advantage of the electrostatic ion beam trap is that the electric field for the storage of the ions is independent of the ion mass at a given energy. This opens the possibility of experiments using ion beams of heavier molecular ions, such as cluster ions and biomolecular ions. In this article, we provide an overview of the design and operation of the electrostatic ion beam trap. After this we will present our recent experimental results briefly.

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