Search

The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of 57Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.

We search for hidden-photon cold dark matter (HP-CDM) using a spectroscopic system in a K-band frequency range. Our system comprises a planar metal plate and cryogenic receiver. This is the first time a cryogenic receiver has been used in the search for HP-CDM. Such use helps reduce thermal noise. We recorded data for 9.3 hours using an effective aperture area of 14.8 cm$^2$. No signal was found in the data. We set upper limits for the parameter of mixing between the photon and HP-CDM in the mass range from 115.79 to 115.85 $\mu$eV, $\chi < 1.8$-$4.3 \times 10^{-10}$, at a 95% confidence level. This is the most stringent upper limit obtained to date in the considered mass range., Comment: 14 pages, 7 figures

We report on a search for hidden photon cold dark matter (HP CDM) using a novel technique with a dish antenna. We constructed two independent apparatus: one is aiming at the detection of the HP with a mass of $\sim\,\rm{eV}$ which employs optical instruments, and the other is for a mass of $\sim5\times10^{-5}\, \rm{eV}$ utilizing a commercially available parabolic antenna facing on a plane reflector. From the result of the measurements, we found no evidence for the existence of HP CDM and set upper limits on the photon-HP mixing parameter $\chi$., Comment: Contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs, Zaragoza, June 22 to 26, 2015

We searched for solar hidden photons in the visible photon energy range using a hidden photon detector add-on attached to Sumico. It consists of a parabolic mirror of dia. 0.5m and f=1m installed in a vacuum chamber, and a low noise photomultiplier tube at the focal point. No evidence for the existence of hidden photons was found in the latest measurement giving a new limit on the photon-hidden photon mixing parameter in the hidden photon mass range 0.001-1eV., Comment: 6 pages. Contributed to the 9th Patras Workshop on Axions, WIMPs and WISPs, Mainz, June 24-28, 2013

We propose a new type segmented antineutrino detector made of plastic scintillators for the nuclear safeguard application. A small prototype was built and tested to measure background events. A satisfactory unmanned field operation of the detector system was demonstrated. Besides, a detailed Monte Carlo simulation code was developed to estimate the antineutrino detection efficiency of the detector., Comment: 23 pages, 11 figures; accepted for publication in Nuclear Instruments and Methods in Physics Research A

A compact resonance ionization mass spectrometer is developed using two laser diodes and a quadrupole mass spectrometer to perform trace element analysis of potassium. With the help of a narrow linewidth of the laser diode, the isotope shifts of $^{40}{\rm K}$ and $^{41}{\rm K}$ of the 405 nm line with respect to $^{39}{\rm K}$, corresponding to the transition of $4\,^2$S$_{1/2}\rightarrow$ $5\,^2$P$^\circ_{1/2}$, are measured to be $207\pm13$ MHz and $451\pm10$ MHz, respectively, by comparing them to the known hyperfine splitting widths of the $4\,^2{\rm S}_{1/2}$ ground state of each potassium isotope. The overall detection efficiency of an order of $\sim10^{-6}$ in our setup indicates the availability of RIMS to the analysis of the trace metal impurities on or in a certain material such as the contamination assessment of semiconductor wafers., Comment: 9 pages, 4 figures

A simple resonance ionization mass spectrometer is built with a Quadrupole Mass Spectrometer (QMS) and two laser diodes aiming at trace analysis of potassium. The overall detection efficiency is estimated comparing the yields of resonance ionization and electron-impact ionization in the same QMS. A clear discrimination of $^{39}\rm K$, $^{40}\rm K$ and $^{41}\rm K$ is demonstrated with a help of isotope shifts of the atomic levels., Comment: 14 pages, 9 figures, submitted to JJAP

A preliminary result of the solar axion search experiment at the University of Tokyo is presented. We searched for axions which could be produced in the solar core by exploiting the axion helioscope. The helioscope consists of a superconducting magnet with field strength of 4 Tesla over 2.3 meters. From the absence of the axion signal we set a 95 % confidence level upper limit on the axion coupling to two photons $g_{a\gamma\gamma} < 6.0 \times 10^{-10} GeV^{-1}$ for the axion mass $m_a < 0.03$ eV. This is the first solar axion search experiment whose sensitivity to $g_{a\gamma\gamma}$ exceeds the limit inferred from the solar age consideration., Comment: 5 pages, 5 eps files included, uses espcrc2.sty, to be published in Proc. AXION WORKSHOP, Gainesville, Florida, 13-15 March 1998, ed. by P.Sikivie

We have searched for axions which could be produced in the solar core by exploiting their conversion to X rays in a strong laboratory magnetic field. The signature of the solar axion is an increase in the rate of the X rays detected in a magnetic helioscope when the sun is within its acceptance. From the absence of such a signal we set a 95% confidence level limit on the axion coupling to two photons $g_{a\gamma\gamma}\equiv 1/M < 6.0\times 10^{-10}$ GeV$^{-1}$, provided the axion mass $m_a<0.03$ eV. The limit on the coupling is factor 4.5 more stringent than the recent experimental result. This is the first experiment whose sensitivity to $g_{a\gamma\gamma}$ is higher than the limit constrained by the solar age consideration., Comment: 11 pages, REVTeX, 4 eps figures included, submitted to PLB

The First results of the Tokyo dark matter search programme using a 21-g lithium fluoride bolometer are presented. The background spectrum was measured in the surface laboratory. We derive an exclusion plot for the spin-dependently coupled Weakly Interacting Massive Particles (WIMPs) cross section., Comment: 6 pages, 4 figures, LaTeX (elsart.sty)

An x-ray detector using a liquid-helium cooled large-area silicon PIN photodiode has been developed along with a tailor-made charge sensitive preamplifier whose first-stage JFET has been cooled. The operating temperature of the JFET has been varied separately and optimized. The x- and $\gamma$-ray energy spectra for an \nuc{241}{Am} source have been measured with the photodiode operated at 13 K. An energy resolution of 1.60 keV (FWHM) has been obtained for 60-keV $\gamma$ rays and 1.30 keV (FWHM) for the pulser. The energy threshold could be set as low as 3 keV. It has been shown that a silicon PIN photodiode serves as a low-cost excellent x-ray detector which covers large area at 13 K., Comment: 6 pages, and 3 figures, Elsevier macros elsart.sty and elsart12.sty are needed