Dual role could solve the mystery
emitted, when a neutrino collides with a proton. The collision produces a neutron and a positron, which is immediately destroyed and converted into radiation, because it is an antiparticle.
Neutrinos keep to themselves
Since Frederick Reines’ and Clyde Cowan’s experiment, many experiments have been made with neutrinos, but they remain poorly described, as they are so extremely difficult to measure. Although the scientists’ measuring equipment by the nuclear reactor was struck by 50 billion neutrions per cm2 per second, a collision between a neutrino and a neutron only happened three times an hour. That is because the particles only interact with other particles via gravity, which is very weak, and the weak nuclear force. The weak nuclear force decreases so quickly with distance that it is almost only interesting inside an atomic nucleus and in the close vicinity.
This means that the likelihood of a neutrino influencing another particle is very limited. Almost all the neutrinos that the Sun is constantly emitting – some 1038 neutrinos per second – pass freely through Earth at a speed close to that of light, and tens of thousands of them pass through your body every second, without you noticing. So, the neutrino is known as a ghost particle.
Scientists know that neutrinos are some of the most common particles in the universe. They have no charge and exist in a minimum of three different versions. At least one of them has a mass, which is millions of times smaller than an electron’s. Physicists also talk about it that both neutrinos and antineutrinos must exist as two different particles. All the particles that physicists know today have a known, particular antiparticle – except for the neutrino. So, physicists increasingly suspect that the neutrino might be its own antiparticle – and if it is, the tiny particle could solve the mystery about how a universe of matter could be born in the Big Bang.
Scientists’ theory is that heavy hermaphrodite particles, i.e. particle and antiparticle in one, formed immediately after the Big Bang. Due to their duality, they could decay into much more matter than antimatter, creating the universe.
Today, such particles would be long gone – they could only exist in the very early, energyrich universe. But if the neutrino proves to be its own antiparticle, scientists know, that the early, heavy particles could also be both.
Zero neutrinos is the key
The Cuore detector is to try to reveal the dual role of the neutrino as its own antiparticle. Cuore is short for “Cryogenic Underground Observatory for Rare Events”.
The rare events are a special type of decay of the radioactive isotope of the tellurium element, which is known as 130Te. In a high concentration, the matter is betaradioactive, but in another way than the beta decay that Wolfgang Pauli studied. Instead of a neutron decaying into a proton, an electron, and a neutrino, two neutrons of 130Te decay into two protons, two electrons, and two neutrinos in double beta decay.
If the neutrino is its own antiparticle, there will sometimes be a very special neutrinoless double beta decay, by which the two neutrinos neutralize each other, the moment they occur. So, the electrons emitted in the decay must carry the energy that equals the mass difference between the two neutrons and the two protons. And that is the very energy that Cuore is looking for.
Initially, Cuore was active for two months in 2017 to determine the half-life period of 130Te, so scientists know how many neutrinoless decays to expect from the quantity in the detector. The result shows that they cannot find any more than one a year or five in the five years that the experiment is active, making the experiment the world’s slowest, but it is worth waiting for. If Cuore captures the rare decay, it has also revealed how the entire universe could have been formed.