ABOVEGROUND OBSERVATION OF DARK MATTER USING A CRYOGENIC PARTICLE DETECTOR

通过使用低温探测器，目标由大约344,000个质量为0.0354克的锡微球(每个球的直径为30微米)组成，我们对宇宙线中的暗物质候选粒子进行了初步观察。在温度为30mK、外加磁场为326高斯的条件下，利用带阻尼谐振电路的信号读出系统(谐振频率约为1 MHz)，通过对信号的时间间隔和脉冲高度的分析，证实了以下结论：(1)当入射粒子同时引起多个球体翻转时，它肯定是带电的宇宙粒子。然而，对于单一的跃迁信号，如果不采取事件符合过程，我们就无法推断它是由于常见的宇宙射线还是暗物质粒子。(2)对于所用的TiN球体大小的5微米变化，在30mK时，过热超导磁场从250克到400克变化很大，这降低了目标的有效质量。微球在填充物中的均匀分布也是非常重要的。单个球体的跃迁可能会触发最近的相邻球体，连锁反应就会相继发生。假设第一个转变是由非常暗物质粒子引起的，由此产生的链式反应是由带电粒子引起的。综上所述，基于过热超导球体相变的粒子探测器在球体尺寸的精确选择、高灵敏度读出系统的进展以及球体均匀分布的目标等方面存在一些有待克服的问题。

By using a cryogenic detector with the target composed of about 344,000 tinmicrospheres of 0.0354g weight (in 30 micron diameter each), we have carried out a preliminary observation of dark-matter candidate particles in cosmic rays. It was performed at the temperature of 30mK and the applied field of 326 Gauss by use of the signal-readout system with a damped resonance circuit (the resonant frequency of about 1 MHz).By analysing the temporal spacings of signals and the pulse height, we confirmed what follows :(1) When an incident particle causes multiple spheres flip at a time, it is a charged cosmic one with certainty. For a single transition signal, however, we are unable to infer it whether due to the usual cosmic ray or a dark-matter particle without taking an event-coincidence procedure.(2) For the 5-micron variance of the size of the tin spheres used the super-heating superconducting field varies widely from 250 to 400G at 30mK,which reduces the effective mass of the target. The precision of the diameter within 1 micron is desired for the narrower allowance of the field.(3) The uniform distribution of the microspheres in the filling stuff is also critically important. A transition of a single sphere, one of the target ones in close vicinity each other, may trigger the nearest neighbor one and the chain reaction occurs successively. Provided that the first transition has owed to the very dark-matter particle, the resultant chain reaction is inferred to be caused by a charged particle.In conclusion, the particle detector based on the phase transition of the superheated superconducting spheres has some issues yet to overcome, the precise selection of the sphere size, the progress of the readout system with a higher sensitivity and the target of unifomly distributed spheres.