What is the weak interaction in physics?

Weak interaction is one of the four fundamental forces that govern all matter in the universe. The other three are gravity, electromagnetism and strong interaction. While other forces hold things together, a weak force plays a big role in their destruction.

Weak interaction is stronger than gravity, but it is effective only at very small distances. The force acts on a subatomic level and plays a decisive role in providing the energy of stars and creating elements. It is also responsible for most of the natural radiation in the universe.

The Fermi theory

The Italian physicist Enrico Fermi in 1933 developed a theory for explaining beta decay - the process of converting a neutron into a proton and displacing an electron, which is often referred to in this context as a beta particle. He defined a new type of force, the so-called weak interaction, which was responsible for the decay, the fundamental process of the conversion of a neutron into a proton, a neutrino and an electron, which was subsequently defined as an antineutrino.

Fermi originally assumed that there was zero distance and grip. Two particles had to come into contact, so that the force worked. Since then, it has been found that a weak interaction is in fact an attractive force that manifests itself at an extremely short distance equal to 0.1% of the proton diameter.

Electroweak strength

In radioactive decays, a weak force is approximately 100,000 times smaller than the electromagnetic one. Nevertheless, it is now known that it is internally equal to the electromagnetic one, and these two clearly different phenomena are believed to represent the manifestations of a single electroweak force. This is confirmed by the fact that they combine at energies above 100 GeV.

Sometimes it is said that a weak interaction is manifested in the decay of molecules. However, intermolecular forces have an electrostatic nature. They were discovered by Van der Waals and bear his name.

Standard Model

Weak interaction in physics is part of the standard model - the theory of elementary particles, which describes the fundamental structure of matter, using a set of elegant equations. According to this model, elementary particles, that is, what can not be divided into smaller parts, are the building blocks of the universe.

One such particle is a quark. Scientists do not expect the existence of something less, but they are still looking. There are six types, or varieties of quarks. We place them in order of increasing mass:

• upper;
• lower;
• strange;
• charmed;
• charming;
• true.

In various combinations, they form a variety of different types of subatomic particles. For example, protons and neutrons-large particles of the atomic nucleus -consist of three quarks each. The two upper and lower constitute the proton. The upper and the two lower form a neutron. Changing the grade of the quark can change the proton into a neutron, thereby converting one element into another.

Another type of elementary particles is a boson. These particles are carriers of interaction, which consist of energy beams . Photons are one type of boson, gluons are another. Each of these four forces is the result of an exchange of vectors of interaction. Strong interaction is carried out by a gluon, and electromagnetic interaction by a photon. Graviton is theoretically a carrier of gravity, but it was not found.

W and Z bosons

The weak interaction is carried by W and Z bosons. These particles were predicted by Nobel Prize winners Steven Weinberg, Sheldon Salam and Abdus Gleshaw in the 60s of the last century, and they were discovered in 1983 by the European Organization for Nuclear Research CERN.

W-bosons are electrically charged and are denoted by the symbols W ⁺ (positively charged) and W ^- (negatively charged). The W-boson changes the composition of the particles. By emitting an electrically charged W-boson, a weak force changes the type of quark, converting the proton into a neutron or vice versa. This is what causes nuclear fusion and makes the stars burn.

This reaction creates heavier elements that are ultimately thrown into space by supernova explosions to become a building material for planets, plants, humans and everything else on Earth.

Neutral current

The Z-boson is neutral and carries a weak neutral current. Its interaction with particles is difficult to detect. Experimental searches for W- and Z-bosons in the 1960s led scientists to a theory that combines electromagnetic and weak force into a single electroweak. However, the theory required the carrier particles to be weightless, and the scientists knew that theoretically the W-boson should be heavy to explain its short range. Theorists attributed the mass of W to an invisible mechanism called the Higgs mechanism, which provides for the existence of the Higgs boson.

In 2012, CERN reported that scientists using the world's largest accelerator - the Large Hadron Collider - observed a new particle "corresponding to the Higgs boson."

Beta decay

Weak interaction manifests itself in β-decay - a process in which a proton is converted into a neutron and vice versa. It occurs when in a nucleus with too many neutrons or protons, one of them is converted into another.

Beta decay can be carried out in one of two ways:

1. In the case of a minus beta decay, sometimes written as β ^- decay, the neutron splits into a proton, antineutrinos, and an electron.
2. Weak interaction manifests itself in the decay of atomic nuclei, sometimes written as β ⁺ decay, when a proton is split into a neutron, a neutrino, and a positron.

One of the elements can turn into another when one of its neutrons spontaneously turns into a proton through a minus beta decay, or when one of its protons spontaneously turns into a neutron through β ⁺ decay.

Double beta decay occurs when 2 protons in a nucleus simultaneously transform into 2 neutrons or vice versa, as a result of which 2 electron-antineutrinos and 2 beta particles are emitted. In a hypothetical neutrinoless double beta decay, neutrinos do not form.

Electronic Capture

The proton can turn into a neutron through a process called electron capture or K-capture. When there is an excessive number of protons in the nucleus with respect to the number of neutrons, the electron, as a rule, falls from the inner electron shell into the nucleus. The electron of the orbital is captured by the mother nucleus, the products of which are the daughter nucleus and the neutrino. The atomic number of the obtained daughter nucleus decreases by 1, but the total number of protons and neutrons remains the same.

Thermonuclear reaction

Weak interaction takes part in nuclear synthesis - a reaction that supplies energy to the sun and thermonuclear (hydrogen) bombs.

The first stage in the fusion of hydrogen is the collision of two protons with sufficient force to overcome the mutual repulsion they experience because of their electromagnetic interaction.

If both particles are placed close together, a strong interaction can bind them. This creates an unstable form of helium ( ² He), which has a nucleus with two protons, in contrast to the stable form ( ⁴ He), which has two neutrons and two protons.

At the next stage, a weak interaction enters the game. Due to the overabundance of protons, one of them undergoes beta decay. After this, other reactions, including intermediate formation and fusion of ³ He, ultimately form a stable ⁴ He.