The Sun is one of the sources of neutrinos.
The notion of neutrino is used in the field of physics . This is the name given to a particle of imperceptible mass that is neutral in terms of its electrical charge.
Subatomic particles
Neutrinos are subatomic particles : that is, they are smaller than an atom . Although it was discovered that they have mass, it is so tiny that its measurement is almost impossible.
It is interesting to note that neutrinos travel at a speed close to the speed of light . That is why they are considered hot dark matter .
Lacking electrical charge and having negligible mass, neutrinos establish almost no interactions with matter . This particularity makes them difficult to detect.
For science , neutrinos are very important since they provide information about places that are inaccessible to humans. Particles travel through the universe and pass through matter without difficulty.
Discovery
The Austrian physicist Wolfgang Pauli ( 1900 – 1958 ) was the one who, in 1930 , postulated the existence of neutrinos. This statement remained in the realm of hypotheses for more than two decades. It was not until 1956 that the Americans Frederick Reines ( 1918 – 1998 ) and Clyde Cowan ( 1919 – 1974 ) managed to demonstrate that neutrinos existed through an experiment.
Six years after Reines and Cowan 's neutrino experiment, three other scientists ( Jack Steinberger , Melvin Schwartz and Leon Max Lederman ) verified that there are several types of neutrinos. Today we know that it is possible to distinguish between tauon neutrinos , muon neutrinos and electron neutrinos , each belonging to different lepton families. Through a process called neutrino oscillation , these subatomic particles can move from one group to another.
electron neutrino
In the group of so-called leptons ( elementary particles that do not combine, which is why they are considered "solitary") we find the electron neutrino . It is a particle whose spin is 1/2 and its mass is at least ten thousand times smaller than that of the electron, but does not reach zero. Let us remember that the spin of a particle is a physical property and refers to the fact that its intrinsic angular momentum is fixed.
Given the magnitude of its mass, the electron neutrino moves at a speed that is always close to that of light, which is why the scientific community believed that it had no mass. Over time they discovered their oscillation , a phenomenon that allows them to change their flavor (the attribute that allows one quark to be distinguished from another), something impossible without mass, which is why they updated their information.
The electron neutrino does not have an electrical charge and its detection is difficult. The latter is because their interaction is always weak . Furthermore, because of the aforementioned oscillation phenomenon, it is not easy to distinguish it from muon and tauon neutrinos, which in principle have an equivalent description.
In 1956 the first detection of neutrinos took place, in a nuclear plant.
Detection
As we mentioned above, detecting these particles is not easy. It is believed that billions of neutrinos pass through us every second without us being aware of it. The first experiment through which it was possible to detect neutrinos was carried out by Clyde Cowan and Frederick Reines , at the Savannah River plant in the United States in 1956. At that time, they were able to observe electron antineutrinos coming from the nuclear reactor .
In 1967, physicist Raymond Davis achieved an effective system to detect neutrinos using chlorine-37 , which can absorb these particles and become argon-37 . Although it is not a foolproof method, the characteristics of this material make it very prone to reacting with neutrinos; Added to this is that it is easy to obtain . Furthermore, since argon-37 is radioactive, its emissions can be detected.
Expert word
We consulted the physicist Juan José Gómez-Cadenas , IKERBASQUE professor at the Donostia International Physics Center (DIPC) and director of the NEXT experiment , about the importance of the study of neutrinos and the project he directs.
The universe should not exist.
For a very simple reason. At first glance, nature does not distinguish between matter and antimatter. If we collide two high-energy particles, as is done in the large LHC accelerator at CERN, and we count the number of electrons (e-) and positrons (e+) that are emitted in that “little Big Bang”, the number is identical. This leads us to think that in the original Big Bang they were also produced in identical quantities.
But when an electron and a positron meet, they annihilate each other, producing two high-energy quanta of light. That is, by the way, the principle of operation of the PET scanner.
In the Big Bang, all the matter electrons should have annihilated with the antimatter positrons. The universe we know, composed primarily of matter, should not have existed.
Except if in that primitive universe there existed a special particle, a double agent, capable of behaving, as the occasion required, as matter or antimatter. That double agent could have been a primitive neutrino, with no electrical charge that would force it to choose sides.
Like any double agent, the neutrino had an agenda that favored matter over antimatter. Their decays injected a small excess of electrons into the universe. That small excess (the remains of a cosmic shipwreck in which most of the navigators perished, like the sailors of Ulysses' ships) is the universe we know.
If that really happened like that, there is a way to prove it. Find a very rare nuclear reaction, called double beta decay (without neutrinos). It is called double beta because two betas (electrons) are emitted. It is called “neutrino-free” because the two neutrinos that should accompany them annihilate each other (before being produced). That is only possible if the neutrino is its own antiparticle.
NEXT seeks to detect double beta decay without neutrinos using xenon (a noble gas, present in small traces in the atmosphere) as a target and as a detector.
To do this, we operate a high-pressure xenon gas chamber inside the Canfranc underground laboratory. In the last 15 years we have gone from building detectors with one kilogram of gas, to the current one, with 100 kg. If we don't find the signal we're looking for, we plan to go up to a ton of xenon gas.
If double beta decay (without neutrinos) occurs in xenon, we expect to observe the appearance of two electrons in the middle of the detector. Our device is, in essence, a device to film the history of those electrons.
The experiment is very difficult. The signal we are looking for is very rare and the background noise due to natural radioactivity is very high. That is why it has taken us 15 years to develop the technology to search for the signal and that is why we operate under the Tobazo mountain, safe from cosmic rays. Finding the signal could take us another 5, 10, or 20 years. We do high-risk research. We throw ourselves into the sea without knowing if we will see the coast of Ithaca.
About a hundred physicists from various universities in Europe and the United States participate in the NEXT experiment.
Like the doors of Moira under the great mountain, those of our laboratory open to visitors with a simple formula.
Say friend and come in.
Juan José Gómez-Cadenas