Underground detectors search for neutrinos and relics of dark matter.
Neutrinos are elementary particles somewhat like electrons, only they have zero charge and hardly any mass. Many believe that neutrinos contribute to some of the dark matter mentioned earlier in this booklet. Other earth-based detectors aim to directly detect the dark matter that may be all around us. These include WIMP and axion detectors. Axions, theoretical exotic particles thought to contribute to dark matter, may burst into detectable microwaves when they encounter very strong magnetic fields.