ABOVEGROUND OBSERVATION OF DARK MATTER USING A CRYOGENIC PARTICLE DETECTOR

我们用一个由344，000个重0.0354克的锡微球（每个直径30微米）组成的低温探测器对宇宙线中的暗物质候选粒子进行了初步观测。在温度30 mK，外加场326高斯的条件下，利用带有阻尼谐振电路（谐振频率约为1 MHz）的信号读出系统，通过对信号时间间隔和脉冲高度的分析，证实了：（1）当入射粒子同时引起多个球翻转时，它肯定是带电的宇宙粒子;然而，对于一个单一的跃迁信号，我们无法推断它是否是由于通常的宇宙射线或暗物质粒子，而不采取事件符合程序。(2)对于所使用的锡球的尺寸的5微米变化，在30 mK下，过热超导场从250 G变化到400 G，这降低了靶的有效质量。对于较窄的场容限，希望直径的精度在1微米以内。(3)微球在填料中的均匀分布也是至关重要的。一个球的跃迁，一个目标球彼此非常接近，可以触发最近的邻居，连锁反应发生连续。假设第一次跃迁是由暗物质粒子引起的，那么由此产生的链式反应是由带电粒子引起的。总之，基于过热超导球相变的粒子探测器还存在一些问题需要克服，如球尺寸的精确选择、更高灵敏度的读出系统的发展以及球的均匀分布等。

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.