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Subatomic

Introduction, Important Definitions and Related Concepts:

A subatomic particle is an elementary or composite particle smaller than an atom. Particle physics and nuclear physics are concerned with the study of these particles, their interactions, and non-atomic matter. Subatomic particles include the atomic constituents electrons, protons, and neutrons. Protons and neutrons are composite particles, consisting of quarks. In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which all other particles are made. In the Standard Model, the quarks, leptons, and gauge bosons are elementary particles.^[1][2] Historically, the hadrons (mesons and baryons such as the proton and neutron) and even whole atoms were once regarded as elementary particles. Beyond the elementary fermions, leptons, and bosons, are the composite particles which are made up of these elementary particles. Baryons are a class of particles that are usually composed of three quarks, or three antiquarks. Nucleons are a special type of baryon that have three first generation quarks, either the proton (uud) or the neutron (udd). Sometimes, one of the down quarks in the neutron will decay into an up quark, and a neutron will be transmuted into a proton. An atom is the smallest particle that comprises a chemical element. An atom consists of an electron cloud that surrounds a dense nucleus. This nucleus contains positively charged protons and electrically neutral neutrons, whereas the surrounding cloud is made up of negatively charged electrons. When the number of protons in the nucleus equals the number of electrons, the atom is electrically neutral; otherwise it is an ion and has a net positive or negative charge. A point particle (or point-like, often spelt pointlike) is an idealized object heavily used in physics. Its defining feature is that it lacks spatial extension: being zero-dimensional, it does not take up space. A point particle is an appropriate representation of any object whose size, shape, and structure is irrelevant in a given context. For example, from far away an object of any shape will look and behave as a point-like object.

Physics is the science of matter^[1] and its motion,^[2][3] as well as space and time^[4][5] — the science that deals with concepts such as force, energy, mass, and charge. Physics is an experimental science;^[6] it is the general analysis of nature, conducted in order to understand how the world around us behaves.^[7] Physics is one of the oldest academic disciplines, having emerged as a modern science in the 17th century,^[8] and through its modern subfield of astronomy, it may be the oldest of all.^[9] Those who work professionally in the field are known as physicists. Nuclear physics is the branch of physics concerned with the nucleus of the atom. It has three main aspects: probing the fundamental particles (protons and neutrons) and their interactions, classifying and interpreting the properties of nuclei, and providing technological advances. Nuclei are bound together by the strong force. The strong force acts over a very short range and causes an attraction between nucleons (protons and neutrons). In science, matter is commonly defined as the substance of which physical objects are composed, not counting the contribution of various energy or force-fields, which are not usually considered to be matter per se (though they may contribute to the mass of objects). Matter constitutes much of the observable universe, although again, light is not ordinarily considered matter. Unfortunately, for scientific purposes, "matter" is somewhat loosely defined. It is normally defined as anything that has mass and takes up space. The electron is a fundamental subatomic particle that carries a negative electric charge. It is a spin ½ lepton that participates in electromagnetic interactions, and its mass is approximately 1 / 1836 of that of the proton. Together with atomic nuclei, which consist of protons and neutrons, electrons make up atoms. Their interaction with adjacent nuclei is the main cause of chemical bonding. In physics, the proton (Greek πρώτον / proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1.602 × 10⁻¹⁹ coulomb), a diameter of about 1.6 to 1.7×10⁻¹⁵ m ^[1], and a mass of 938.27231(28) MeV/c² (1.6726 × 10⁻²⁷ kg), 1.007 276 466 88(13) u or about 1836 times the mass of an electron. Protons are spin-1/2 fermions and are composed of three quarks^[2], making them baryons. The two up quarks and one down quark of the proton are held together by the strong force, mediated by gluons. Protons and neutrons are both nucleons, which may be bound by the nuclear force into atomic nuclei. In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939.573 MeV/c² or 1.008 664 915 (78) u (1.6749 × 10⁻²⁷ kg, slightly more than a proton). Its spin is ½. Its antiparticle is called the antineutron. The neutron, along with the proton, is a nucleon. A quark (IPA: /kwɔrk/) is a generic type of physical particle that forms one of the two basic constituents of matter, the other being the lepton. Various species of quarks combine in specific ways to form protons and neutrons, in each case taking exactly three quarks to make the composite particle in question. There are six different types of quark, usually known as flavours: up, down, charm, strange, top, and bottom. (Their names were chosen arbitrarily based on the need to name them something that could be easily remembered and used.) The up and down varieties survive in profusion, and are distinguished by (among other things) their electric charge. The Universe is most commonly defined as everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. However, the term "universe" may be used in slightly different contextual senses, denoting such concepts as the cosmos, the world or Nature. Astronomical observations indicate that the universe is 13.73 ± 0.12 billion years old and at least 93 billion light years across. The event that started the universe is called the Big Bang. A technical standard is an established norm or requirement. It is usually a formal document that establishes uniform engineering or technical criteria, methods, processes and practices. A technical standard can also be a controlled artifact or similar formal means used for calibration. Reference Standards and certified reference materials have an assigned value by direct comparison with a reference base. An abstract model (or conceptual model) is a theoretical construct that represents something, with a set of variables and a set of logical and quantitative relationships between them. Models in this sense are constructed to enable reasoning within an idealized logical framework about these processes and are an important component of scientific theories. Idealized here means that the model may make explicit assumptions that are known to be false (or incomplete) in some detail. Such assumptions may be justified on the grounds that they simplify the model while, at the same time, allowing the production of acceptably accurate solutions, In physics, a lepton is a particle with spin 1/2 that does not experience the strong interaction (that is, the strong nuclear force). The leptons form a family of fermions that are distinct from the other known family of fermions, the quarks. There are three known flavors of lepton: the electron, the muon, and the tau lepton or tau. Each flavor is represented by a pair of particles called a weak doublet. In physics, gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. This idea applies not only to field theories, but to finite-dimensional systems as well (i.e., systems described by ordinary differential equations). The earliest field theory which had a gauge symmetry was Maxwell's formulation of electrodynamics in 1864. However, the importance of this symmetry remained unnoticed in the earliest formulations. In particle physics, bosons are particles with an integer spin, as opposed to fermions which have half-integer spin. From a behaviour point of view, fermions are particles that obey the Fermi-Dirac statistics while bosons are particles that obey the Bose-Einstein statistics. They may be either elementary, like the photon, or composite, as mesons. All force carrier particles are bosons.

A hadron (from Greek ἁδρός, hadros, thick) , in particle physics, is any strongly interacting composite subatomic particle. All hadrons are composed of quarks. Hadrons are divided into two classes:

• Baryons, strongly interacting fermions such as a neutron or a proton, made up of three quarks. Mesons, strongly interacting bosons consisting of a quark and an antiquark.

Notice that mesons are composite bosons, but they are not composed of bosons (quarks are fermions). In particle physics, a meson is a strongly interacting boson - that is, a hadron with integral spin. In the Standard Model, mesons are composite (non-elementary) particles composed of an even number of quarks and antiquarks. All known mesons are believed to consist of a quark-antiquark pair — the so-called valence quarks — plus a "sea" of virtual quark-antiquark pairs and virtual gluons. Searches for exotic mesons that have different constituents are ongoing. In particle physics, the baryons are the family of subatomic particles which are made of three quarks. The family notably includes the proton and neutron, which make up the atomic nucleus, but many other unstable baryons exist as well. The term "baryon" is derived from the Greek βαρύς (barys), meaning "heavy," because at the time of their naming it was believed that baryons were characterized by having greater mass than other particles. Baryons are strongly interacting fermions — that is, they experience the strong nuclear force and are described by Fermi-Dirac statistics, which apply to all particles obeying the Pauli exclusion principle. A chemical substance is a material with a definite chemical composition. It is a concept that became firmly established in the late eighteenth century after work by the chemist Joseph Proust on the composition of some pure chemical compounds such as basic copper carbonate.^[1] He deduced that, "All samples of a compound have the same composition; that is, all samples have the same proportions, by mass, of the elements present in the compound." This is now known as the law of constant composition.^[2] A chemical element, or element, is a type of atom that is distinguished by its atomic number; that is, by the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.^[1] Common examples of elements are hydrogen, carbon, nitrogen, and oxygen. In total, 117 Elements have been observed as of 2007, of which 94 occur naturally on Earth. The nucleus of an atom is the very small dense region of an atom, in its center consisting of nucleons (protons and neutrons). The size (diameter) of the nucleus is in the range of 1.6 fm (10^-15 m) (for a proton in light hydrogen) to about 15 fm (for the heaviest atoms, such as uranium). These dimensions are much smaller than the size of the atom itself by a factor of about 23,000 (uranium) to about 145,000 (hydrogen). Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus with a very small contribution from the orbiting electrons. Charged means