Italian astrophysicists have presented the first results of the experiment known as 'The cryogenic search for dark matter', the most accurate experiment so far, but for the moment they have found nothing.
There is much more matter than is seen in the universe, dark matter. That's what physicists believe, but they don't know where that matter is. Neither where it is nor how it is. Some believe that dark matter is made up of a particle that they cannot see.
On the one hand, this particle should be of great mass and, on the other, it should cause very weak interactions with other particles. It is therefore very difficult to see and detect.