Monopole search with SQUID fluxmeters and with metastable superconducting granules

First, our experiments of monopole search in ferromagnetic materials are recapitulated which have been performed with SQUID fluxmeters KOBE I and II in our laboratory. An upper limit of monopole density in old iron ore and that of flux in cosmic ray are given as 3.2 x 10-6 monopoles/gram (95 % C.L.) and 5.9 x 10-10 cm-2sec-1str-1 (90 % C.L.), respectively. Second, a report is made on the progress of preparing our next experiment. By using a larger-scale fluxmeter KOBE III with two sensing parts, each containing a two-turn, 20-cm-diam search coil, we intend to search for magnetic monopoles in this summer in large under a conveyer of sintering furnace at a commercial ore processing plant. Last, we will briefly discuss on a feasible detector based on the flipping mechanism of metastable superconducting granules. It is one of the most favorable as a large-area monopole detector, since the signal in magnetic flux change not only is expected in β-independent way but also may be read by conventional electronics and expensive SQUID systems are not needed. (author)