Neutrinos: Everything You Need To Know
What exactly are they?
With a neutral charge and nearly zero mass, neutrinos are the shadiest of particles, rarely interacting with ordinary matter and slipping through our bodies, buildings and the Earth at a rate of trillions per second.
First predicted in 1930 by Wolfgang Pauli, who won a Nobel prize for this work in 1945, they are produced in various nuclear reactions: fusion, which powers the sun; fission, harnessed by humans to make weapons and energy; and during natural radioactive decay inside the Earth.
If they are so stealthy, how do we know they are there at all?
Wily neutrinos usually avoid contact with matter, but every so often, they crash into an atom to produce a signal that allows us to observe them. Fredrick Reines first detected them in 1956, garnering himself a Nobel prize in 1995.
Most commonly, experiments use large pools of water or oil. When neutrinos interact with electrons or nuclei of those water or oil molecules, they give off a flash of light that sensors can detect.
Where are these experiments found?
These days, a lot of expense and extreme engineering go into detectors that are sunk into the ground to shield them from extraneous particles that might interfere with them. For instance, OPERA, which detected the apparently faster-than-light neutrinos beamed from CERN, lies inside the Gran Sasso mountain in Italy. This works because neutrinos shoot straight through such shields.
Other detectors pick up naturally-produced neutrinos. One such detector – ANTARES – is miles under the Mediterranean Sea, while another, IceCube, is buried under Antarctic ice.
What’s cool about neutrinos?
Their stealth belies their potential importance. Take extra dimensions. Most particles come in two varieties: ones that spin clockwise and ones that spin anticlockwise. Neutrinos are the only particles that seem to just spin anticlockwise. Some theorists say this is evidence for extra dimensions, which could host the “missing”, right-handed neutrinos.
Unseen right-handed neutrinos may also account for mysterious dark matter. This is thought to make up 80 per cent of all matter in the universe and to stop galaxies from flying apart. The idea is that right-handed neutrinos might be much heavier than left-handed ones and so could provide the requisite gravity.
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