Extensive experimental searches have been carried out to find these hypothetical particles, usually called “Weakly interacting massive particles,” or “WIMPs.” Direct detection experiments, located deep underground to filter out the myriad other particles streaming in from space, look for evidence of dark matter particles bumping into regular matter.
Another theory also fit the data: could it be that dark matter particles were colliding, annihilating, and producing positrons in the process? The answer was yes – but only if the dark matter particles were light enough.
“When there is light dark matter, there must also be a light particle that mediates interactions between dark matter and Standard Model matter,” explains Pospelov.
The possibility of a mediator particle for dark matter carried an intriguing correlation: perhaps dark matter could interact more than just gravitationally, through some new, long-range “Dark force.” Though it might sound like something straight out of a science fiction novel, the existence of a dark force fit well into theories describing the production of dark matter in the early universe.
“Unfortunately, there is no guarantee we will ever discover dark matter. On the other hand, there is no other method to make progress on the basic question. The nature of dark matter is one of the outstanding mysteries in physics, and we are obliged as scientists to explore and experimentally test, to the extent of our abilities, all motivated ideas and hypotheses.”
“And dark matter particles would fly into the detector and scatter off. So we would be able to search for light dark matter in neutrino experiments.”
“Direct detection experiments are good at searching for heavy dark matter particles, but not so good at searching for light dark matter particles,” explains Batell.