Overview
An elementary particle (素粒子, soryūshi) is the basic unit of composition into which matter cannot be further divided into smaller components, classically treated as a particle.
In current physics, it is widely accepted that elementary particles are the 17 elementary particles and their antiparticles predicted by the Standard Model. All of the elementary particles predicted by the Standard Model have been discovered by 2013. However, due to obvious deficiencies in the Standard Model, such as the absence of gravity, a fundamental interaction whose existence is clear, there are some subatomic particles whose existence is predicted by the framework and theory beyond the Standard Model. At present, no subatomic particles beyond the Standard Model have been discovered.
List of Elementary Particles in the Standard Model
Quarks and leptons
Quarks and leptons are the particles that form matter itself. For example, all atoms that exist around us are made up of a combination of up quarks, down quarks, and electrons. In the high-energy region, there is also matter composed of other elementary particles. All are fermions that obey fermion statistics, and all have 1/2 spin.
Quarks are further subdivided into up-type quarks and down-type quarks, and leptons into charged leptons and neutral leptons (or neutrinos). There are six types of quarks and six types of leptons, each of which is classified into three generations. This was predicted by the Cabibbo–Kobayashi–Maskawa matrix. By the year 2000, all elementary particles had been discovered.
Gauge and Scalar Particles
Gauge and scalar particles are quantized fields that are responsible for the transmission of the fundamental interaction, the fundamental force of nature. All are Bose particles subject to Bose statistics, with gauge particles having a spin of 1 or more and scalar particles having a spin of 0.
All currently discovered gauge particles have a spin of 1, and are also called vector particles as opposed to scalar particles, which are currently synonymous with gauge particles. Only the gauge particle of gravity is not described in the Standard Model category, and the graviton, discussed below, may have spin 2. The only scalar particle currently discovered is the Higgs boson. All of the elementary particles have been discovered by 2013.
List of Predicted Elementary Particles
All of the currently discovered subatomic particles are within the scope of the Standard Model. However, the Standard Model is a completely inadequate framework from the viewpoint of current physics, and extended theories that cover what is not described are found to be indispensable. Some of these theories predict the existence of new subatomic particles.
Graviton
The Standard Model does not incorporate gravity, which is even the most familiar of the fundamental interactions. It is so difficult to incorporate gravity into the world of quantum mechanics that it is said to be one of the greatest challenges and even a difficult problem in physics. Under such circumstances, one of the predicted quantized versions of gravity is the graviton.
See graviton for more information.
Axion
An axion is an elementary particle classified as a pseudo-Nanbu/Goldstone particle, which was predicted to solve the strong CP problem unsolved by the Standard Model.
The operation is to swap a particle with its antiparticle and place it in a mirror image of its position. Quantum mechanics shows that when this operation is performed, the before and after positions are not the same as in the mirror image. This is called CP symmetry breaking. The theory suggests that the CP violation discovered initially in weak interactions is also broken in strong interactions, but in reality, no matter how many experiments are performed, no violation has been discovered. The axion exists to resolve this discrepancy.
An axion is a spin 0 quasi-scalar particle classified as a Bose particle and is presumed to have zero charge. Their mass is very low, though probably not zero, and is estimated to be less than one-ten-billionth of that of an electron based on observations to date. The interaction between the axion and matter is so low that it has escaped observation to date, but indirect observations have been made because axions are estimated to transform into photons under strong magnetic fields. If axions have a mass above a certain level, they are also candidates for cold dark matter with very low radiation.
Sterile Neutrino
Particles have a spin-like property called spin, and are divided into "left-handed" and "right-handed" particles based on the direction in which they travel and the direction of their spin. Most elementary particles have been discovered to be left-handed and right-handed, but right-handed neutrinos have not been discovered.
Assuming the existence of right-handed neutrinos, their interaction is expected to be even lower than that of (normal) left-handed neutrinos, which have a lower interaction. Left-handed neutrinos can sense the gravitational interaction and weak interaction, while right-handed neutrinos can sense only the gravitational interaction, which is extremely difficult to observe. For this reason, right-handed neutrinos are called sterile neutrinos, meaning sterile.
Stellar neutrinos are predicted to have extremely high masses and are expected to observe the radiation associated with their decay. There are candidates for this, although they have not yet been recognized. We are also taking advantage of the fact that direct observation is practically impossible, and are searching for examples of radioactive nuclei in which neutrinos are expected to be emitted but are not observed. Sterile neutrinos, which are expected to have mass, are also candidates for cold dark matter.
External Links
English
Elementary particle - Wikipedia
