Scientists call this the "ghost particle." It has almost no mass, develops a speed close to the speed of light and has been hiding from researchers around the world for three decades in a row. We are talking about neutrinos, which physicists are now beating over in laboratories from Pakistan to Switzerland. Neutrinos are formed when radioactive elements decay. They are in the sun, other stars, and even in our own bodies. A neutrino passes through a huge amount of matter without difficulty. So how do scientists study this elusive particle?
GERDA
This sophisticated apparatus, the GERmanium Detector Array (GERDA), helps scientists understand why we exist at all. GERDA searches for neutrinos by monitoring electrical activity inside pure germanium crystals isolated deep under a mountain in Italy. Scientists working with GERDA hope to find a very rare type of radioactive decay. When the Big Bang spawned our universe (13.7 billion years ago), an equal amount of matter and antimatter should have formed. And when matter and antimatter collide, they destroy each other, leaving behind nothing but pure energy. So where did we come from? If scientists can detect those signs of decay, then this would mean that the neutrino is a particle and an antiparticle at the same time. Of course, such an explanation will remove most of the questions of interest to us.
SNOLAB
The Canadian Sudbury Neutrino Observatory (SNO) is buried about two kilometers underground. The SNO + division investigates neutrinos from the Earth, the Sun, and even supernovae. The heart of the laboratory is a huge plastic sphere filled with 800 tons of a special liquid called a liquid scintillator. The sphere is surrounded by a shell of water and held in place by ropes. The whole thing is controlled by an array of 10,000 extremely sensitive light detectors called photomultiplier tubes (PMTs). When neutrinos interact with other particles in the detector, the liquid scintillator is illuminated and the PMT reads the data. Thanks to the original SNO detector, scientists now know that at least three different kinds, or "flavors," of neutrinos are capable of being transported back and forth through spacetime.
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IceCube
And this is the largest neutrino detector in the world. IceCube, located at the South Pole, uses 5,160 sensors spread across over a billion tons of ice. The goal is to obtain high-energy neutrinos from extremely violent cosmic sources such as exploding stars, black holes and neutron stars. When neutrinos slam into water molecules in ice, they release high-energy eruptions of subatomic particles that can travel several kilometers. These particles move so fast that they emit a short cone of light called the Cherenkov cone. Scientists hope to use the information received to reconstruct the path of neutrinos and determine their source.
Daya bay
The neutrino experiment takes place in three huge halls at once, buried in the hills of Daya Bay, China. Six cylindrical detectors, each containing 20 tons of liquid scintillator, are grouped in halls and surrounded by 1000 PMTs. They drown in pools of clean water, blocking out any surrounding radiation. A nearby group of six nuclear reactors churns out millions of quadrillions of harmless electronic antineutrinos every second. This stream of antineutrino interacts with a liquid scintillator to emit short flashes of light that are picked up by the PMT. Daya Bay was built to study neutrino oscillations.