Subatomic particles

Subatomic particle. It is a particle smaller than the atom. It can be an elementary particle or a compound, in turn, by other subatomic particles, such as quarks, which make up protons and neutrons. However, there are other subatomic particles, both composite and elemental, that are not part of the atom, as is the case with neutrinos and bosons.

Particle physics and nuclear physics are concerned with the study of these particles, their interactions, and the matter that forms them and does not aggregate in atoms. Most of the elementary particles that have been discovered and studied cannot be found under normal conditions on Earth , generally because they are unstable (break down into already known particles), or they are difficult to produce anyway.

These particles, both stable and unstable, are produced randomly by the action of cosmic rays when they collide with atoms in the atmosphere, and in the processes that occur in particle accelerators, which imitate a process similar to the first, but under controlled conditions. In these ways, dozens of subatomic particles have been discovered, and hundreds of others are theorized. Examples of theoretical particles are the graviton and the Higgs boson; however, these and many others have not been observed in modern particle accelerators, nor in natural conditions in the atmosphere (by the action of cosmic rays).

Virtual particles are also classified as subatomic particles, which are particles that represent an intermediate step in the disintegration of an unstable particle, and therefore last a very short time.


[ hide ]

  • 1 Atomic models
    • 1 Properties
  • 2 History
  • 3 Elementary Particles
    • 1 Boson
    • 2 Fermion
    • 3 Quarks
    • 4 Lepton
    • 5 Hadrons
    • 6 Neutrino
    • 7 Inn
  • 4 Sources

Atomic models

The first atomic models basically considered three types of subatomic particles: protons, electrons, and neutrons. Later the discovery of the internal structure of protons and neutrons revealed that these were compound particles. Furthermore, the usual quantum treatment of the interactions between the particles implies that the cohesion of the atom requires other bosonic particles such as pions, gluons or photons.

The protons and neutrons for their part are made up of quarks. Thus a proton is made up of two quarks up and one quark down. Quarks are united by particles called gluons. There are six different types of quarks (up, down, bottom, top, weird, and charm). Protons are held together with neutrons by the effect of pions, which are compound mesons made up of pairs of quark and antiquark (in turn linked by gluons). There are also other elementary particles that are responsible for the electromagnetic (photons) and weak (neutrinos and W and Z bosons) forces.

The electrons, which are negatively charged, have a mass 1/1836 of that of the hydrogen atom, with the rest of their mass coming from the proton. The atomic number of an element is the number of protons (or the number of electrons if the element is neutral). For their part, neutrons are neutral particles with a mass very similar to that of the proton. Different isotopes of the same element contain the same number of protons but different numbers of neutrons. The mass number of an element is the total number of protons plus neutrons it has in its nucleus.


The most interesting properties of the 3 constituent particles of matter existing in the universe are:

  • It is located in the nucleus. Its mass is 1.6 × 10-27 kg. [1] It has a positive charge equal in magnitude to the charge of the electron. The atomic number of an element indicates the number of protons it has in the nucleus. For example, the nucleus of the hydrogen atom contains a single proton, so its atomic number (Z) is 1.
  • It is found in the cortex. Its mass is approximately 9.1 × 10-31 kg. It has a negative electric charge (-1,602 × 10-19 C). [2]
  • It is located in the nucleus. Its mass is almost equal to that of the proton. It has no electric charge.

The concept of elementary particle is somewhat darker today due to the existence of quasiparticles that, although they cannot be detected by a detector, constitute quantum states whose phenomenological description is very similar to that of a real particle.


In classical Greece, an atom was conceived as the smallest and most indivisible part of matter, provided with hooks that held them together with other atoms.

It was the development of chemistry that managed to establish a certain number of constituents of all the existing and medibe matter on Earth. Their findings yielded their greatest fruit thanks to Dmitri Mendeléyev , by concretizing in a simple way all the possible atoms (in fact defining the existence of some undiscovered until some time later).

Later it was discovered that, although the newly defined atoms fulfilled the condition of being the constituents of all matter, they did not fulfill any of the other two conditions. They were neither the smallest part nor indivisible. However, it was decided to keep the term atom for these constituents of matter.

Electrochemistry led by G. Johnstone Stoney led to the discovery of electrons (e-) in 1874 , observed in 1897 by Joseph John Thomson . These electrons gave rise to the different configurations of atoms and molecules. For his part, in 1907 Ernest Rutherford’s experiments revealed that much of the atom was really empty, and that almost all of the mass was concentrated in a relatively small nucleus.

The development of quantum theory led to consider chemistry in terms of electron distributions in that empty space. Other experiments showed that there were particles that formed the nucleus: the proton (p +) and the neutron (n) (postulated by Rutherford and discovered by James Chadwick in 1932 ). These discoveries reframed the question of the smallest and indivisible parts that made up the known universe. Subatomic particles began to be discussed.

Later still, delving further into the properties of protons, neutrons and electrons, it was concluded that neither (at least the first two) could be treated as the smallest part, nor as indivisible, since the quarks gave structure to nucleons. From here it began to speak of particles whose size was less than that of any atom. This definition included all the constituents of the atom, but also the constituents of those constituents, and also all those particles that, without being part of matter, exist in nature. From here we talk about elementary particles.

In 1897 Joseph John Thomson discovers the electron. Albert Einstein interprets the photoelectric effect as evidence of the photon’s actual existence. Previously, in 1905 , Max Planck had postulated the photon as a minimum electromagnetic energy quantum to solve the thermodynamic problem of blackbody radiation.

For his part, Ernest Rutherford discovered in 1907 in the famous gold foil experiment that almost the entire mass of an atom was concentrated in a very small part of it, which would later be called the atomic nucleus, the rest being empty. The continued development of these ideas led to quantum mechanics, some of whose early successes included explaining the properties of the atom.

Very soon a new particle, the proton, was identified as the sole constituent of the hydrogen nucleus. Rutherford also postulated the existence of another particle, called a neutron, after his discovery of the nucleus. This particle was discovered experimentally in 1932 by James Chadwick. To these particles a long list was added: Wolfgang Pauli postulated in 1931 the existence of the neutrino to explain the apparent loss of the conservation of the amount of movement that occurred in beta decay. It was Enrico Fermi who invented the name. The particle was not discovered until 1956.

It was Hideki Yukawa who postulated the existence of the pions to explain the strong force that bound the nucleons inside the nucleus. The muon was discovered in 1936, initially mistakenly thought to be a pion. In the 1950s the first kaon was discovered among cosmic rays.

The development of new particle accelerators and particle detectors in that 1950s led to the discovery of a large number of hadrons, along with compound hadrons series of particles appeared that seemed to duplicate the functions and characteristics of smaller particles. Thus another “heavy electron” was discovered, in addition to the muon, the tauon, as well as various series of heavy quarks. None of the particles in these heavier series seems to be part of the atoms of ordinary matter.

Classification of those hadrons using the quark model in 1961 was the beginning of the golden age of modern particle physics, culminating in the completeness of the unified theory called the standard model in the 1970s.

Confirmation of the existence of weak gauge bosons in the 1980s and verification of their properties in the 1990s is seen as the era of consolidation of particle physics. Among the particles defined by the standard model, the Higgs boson still remains undiscovered. Therefore, this is the primary objective of CERN’s Large Hadron Collider (LHC) accelerator. The rest of the known particles fit perfectly with the standard model.

Elementary particles

The subatomic particles of which its existence is known are: Boson Positron Electron Proton Fermion Neutrino Hadron Neutron Lepton Quark Meson

The particles are made up of atomic components like electrons, protons and neutrons, (protons and neutrons are compound particles), these are made up of quarks. Quarks are held together by gluon particles that cause interaction in quarks and are indirectly responsible for holding protons and neutrons together in the atomic nucleus.


The boson is an atomic or subatomic particle, of integer or null spin, which complies with the postulates of the Bose-Einstein statistic and violates the Paulli exclusion principle (it states that two electrons cannot occupy the same energetic state). Alpha particles, photons, and nuclides with an even number of nucleons are bosons.


It is a particle belonging to a family of elementary particles characterized by its intrinsic angular momentum or spin. Fermions are named after Enrico Fermi, in the standard model, there are two types of elemental fermions, which are: quarks and leptons. According to quantum theory, the angular momentum of particles can only adopt certain values, which can be integer multiples of a given constant h (Planck’s constant) or half-multiples of that same constant.

Fermions, including electrons, protons, and neutrons, have half-multiples of h, for example ± 1 / 2h or ± 3 / 2h. Fermions comply with the exclusion principle. The nucleus of an atom is a fermion or boson, depending on whether the total number of its protons and neutrons is odd or even, respectively. Scientists have recently discovered that this causes very strange behavior in certain atoms when subjected to unusual conditions, such as too cold helium.


The generic name by which the constituents of hadrons are designated. The theory about quarks started from the work of Gell-Mann and Zweig (1966) and its existence was confirmed in 1977 (By Fairbank et al.).

Physics dedicated to the study of the fundamental nature of matter has formulated a standard model, capable of explaining a series of facts and unable to respond to others. This model is currently based on the hypothesis that ordinary matter is made up of two classes of particles, quarks (which combine to form larger particles) and leptons, in addition to the fact that the forces acting between them are transmitted by a third class of particles called bosons, which we already explained earlier. The spin of the quarks is ½, there are six different types of quarks that physicists have named as follows: up, down, charm, strange, top, and bottom in addition to the corresponding antiquarks.


Name given to each of the elementary particles of spin equal to +1/2 and a mass less than that of the mesons. Leptons are fermions between which weak interactions are established, and only electromagnetic interactions if they have an electric charge. Furthermore, electrically charged leptons are almost always attached to an associated neutrino.

There are three types of leptons: the electron, the muon, and the tau. Each one is represented by a pair of particles. One is a massively charged particle, which bears the same name as its particle, (like the electron). The other is a nearly massless neutral particle called a neutrino (such as the neutrino electron). All of these 6 particles have corresponding antiparticles (such as the positron or the antineutrino electron).

All charged leptons have a single unit of positive or negative energy (depending on whether they are particles or antiparticles) and all neutrinos and antineutrinos have zero electric charge. Charged leptons have 2 possible spin turns while a single helicity is observed for neutrinos (All neutrinos are left-handed and antineutrinos right-handed).

Leptons obey a simple relationship known as the Koide formula. When the particles interact, the number of leptons of the same type (electrons and neutrino electrons, muons and neutrino muons, tau and tau neutrino leptons) generally remain the same. This principle is known as the conservation of the lepton number.


The hadron is a subatomic particle made up of quarks, characterized by relating through strong interactions. Although they can also show weak and electromagnetic interactions, strong interactions predominate in hadrons, which are those that maintain internal cohesion in the atomic nucleus.

These particles have two categories: the baryons formed by three quarks, such as the neutron and the proton, and the mesons, formed by a quark and an antiquark, such as the pion. Most hadrons can be classified with the quark model which implies that all quantum numbers of baryons are derived from those of valence quark.


An electrically neutral elementary nuclear particle with a mass much less than that of the electron (possibly null). The neutrino is a fermion; its spin is 1/2. Before the discovery of the neutrino, it appeared that the total energy, momentum, and spin of the process were not conserved in the beta decay electron emission. To explain this inconsistency, the Austrian physicist Wolfgang Pauli deduced the properties of the neutrino in 1931 .

With no charge and a negligible mass, the neutrino is extremely difficult to detect; Research confirmed its peculiar properties by measuring the recoil it causes in other particles. Billions of neutrinos traverse Earth every second, and only a tiny proportion of them interact with any other particle. American physicists Frederick Reines and Clyde Lorrain Cowan Jr. obtained conclusive evidence of their existence in 1956 .

The neutrino’s antiparticle is emitted in electron-producing beta decay processes, while neutrinos are emitted along with positrons in other beta decay reactions. Some physicists conjecture that in a strange form of radioactivity, called double beta decay, two neutrinos can sometimes fuse to form a particle they call a “majoron.” Another type of high-energy neutrino, called a muonic neutrino, is emitted along with a muon when a pion decays.

When a pion decays, a neutral particle must be emitted in the opposite direction to that of the muon to preserve momentum. The initial assumption was that that particle was the same neutrino that retains momentum in beta decay. In 1962, however, research showed that the neutrino that accompanies pion decay is of a different type. There is also a third type of neutrino, the tau neutrino (and its antiparticle).

Currently, the possibility that neutrinos can oscillate between one form and another is of great interest. So far, the evidence in this regard is indirect, but if confirmed it would suggest that the neutrino has a certain mass, which would have profound implications for cosmology and physics in general: this additional mass in the universe could mean that the universe does not follow expanding indefinitely but eventually contracting. Although there are different interpretations, some scientists believe that the information on neutrinos obtained from the SN 1987A supernova supports the idea that the neutrino has mass.


Name given to each of the elementary particles subjected to strong interactions, of null or integer spin and null baryonic charge.

The mesons, identified by Powell in 1947 in cosmic rays and whose existence had been postulated by Yukawa in 1935, are unstable particles, with a mass generally between that of electrons and that of neutrons. The most stable, whose half-lives are on the order of a hundred millionth of a second, are pions and kaons.


Leave a Comment