With this free course of 153 video lessons you will learn about the most important concepts of Elementary Particles
Elementary particles are the elementary constituents of matter; more precisely they are particles that are not made up of smaller particles nor are they known to have internal structure.
Originally the term elementary particle was used for any subatomic particle such as protons and neutrons, electrons and other types of exotic particles that can only be found in cosmic rays or in large particle accelerators, such as pions or muons. However, from the 1970s it became clear that protons and neutrons are particles composed of simpler ones. Currently the name elementary particle is used for particles that, as far as is known, are not made up of simpler particles.
When john Dalton postulated his atomic theory in the early nineteenth century, he considered atoms to be indivisible and therefore, in a way, elementary particles. Advances in the knowledge of atomic structure revealed that atoms were far from indivisible and were made up of more elementary particles: protons, neutrons and electrons. The study of the particles that make up the atomic nucleus revealed that these were not elementary, but were made up of simpler particles. In turn, neutrons, protons and other particles are composed of hadrons and mesons. Both hadrons and mesons are made up of smaller particles, called quarks and antiquarks, and "clouds" of gluons that hold them together.
The list of subatomic particles that are currently known consists of hundreds, a situation that surprised physicists, until they were able to understand that many of these particles were not really elementary but composed of simpler elements called quarks and leptons that interact with each other through the exchange of bosons. In the standard model, which reflects our state of knowledge about the ultimate constituents of matter, quarks, leptons, and exchange bosons are considered elementary particles, since there is no evidence that they were in turn made up of other, "smaller" particles.
While heavier particles (hadrons) and intermediate-mass particles (mesons) that responded to the strong interaction were considered elementary, they are now known to be composite particles. Only the lightest particles (leptons) that were not affected by the strong interaction turned out to be elementary. The two most common types of leptons are electrons and neutrinos, which as has been said are thought to be really elementary. Neutrinos, entities that began their existence as mathematical artifices, have already been detected and are part of all physical theories of the composition of matter, cosmology, astrophysics and other disciplines.
It is currently believed that leptons, quarks (these first two types are fermions) and gauge bosons, are all the smallest constituents of matter and therefore would be properly elementary particles. There is an interesting problem regarding these properly elementary particles, since, for example, leptons seem to be grouped into homofunctional series, each generation being similar to the previous one but formed by more massive particles:
Generation 1: electron, electron neutrino, up quark, down quark.
Generation 2: muon, muon neutrino, strange quark, enchanted quark.
Generation 3: tauon, tauonic neutrino, bottom quark, top quark.
Although there are not many ideas as to why these three generations exist, in string theory the number of existing generations has to do with the topology of the Calabi-Yau manifold that appears in its formulation. Specifically, the number of generations would coincide in this theory with half the absolute value of the Euler number of the Calabi-Yau manifold.3 However, this is not strictly a prediction since in the current study of string theory Calabi-Yau spaces of different Euler number can be constructed. It is known that if you want to build a string theory that gives rise to only three generations, euler's number must be ±6.
It is hypothesized that quarks in turn are made up of preons.
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