Well, they don’t really know what kind of particles this theoretical “dark matter” would be, since they have never been able to detect or observe any of it. They have some guesses, but that is all they are at this point.
The answer is they were looking for Weakly Interacting Massive Particles or WIMPs. It will take more sensitive detectors and about 10 to 15 more years to completely eliminate all WIMP models for dark matter.
Zineta seems particularly brilliant. A question for you is what other types of particles are theorized to make up dark matter besides WIMPs?