- Alpha decay: It is a type of radioactive decay in which an atomic nucleus
emits an alpha particle (two protons and two neutrons bound together into
a particle identical to a helium nucleus) and transforms (or 'decays') into
an atom with a mass number 4 less and atomic number 2 less. For example:
although this is typically written as:
- Alpha particles: Alpha particles are emitted by radioactive nuclei such as uranium or radium in a process known as alpha decay. They consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are a highly ionizing form of particle radiation, and have low penetration. Their mass is 6.644656×10-27 kg, which is equivalent to the energy of 3.72738 GeV. The charge of an alpha particle is equal to +2e, (e=1.602176462x10-19C).
- Antimuon (positive muon): It is the antimatter partner of the muon; it has opposite charge but equal mass and spin. Antimuons are denoted by ?+
- Antiquarks: They are the antiparticles of quarks. The additive quantum numbers of antiquarks are equal in magnitude and opposite in sign to those of the quarks. CPT symmetry forces them to have the same spin and mass as the corresponding quark. Tests of CPT symmetry cannot be performed directly on quarks and antiquarks, due to confinement. Notation of antiquarks follows that of antimatter in general: an up quark is denoted by u, and an up antiquark is denoted by u.
- Axion: It is a hypothetical elementary particle postulated to resolve the strong-CP problem in quantum chromodynamics (QCD).
- Background radiation: It is the ionizing radiation emitted from a variety
of natural and artificial radiation sources. Primary contributions come
from:
. Sources in the Earth. These include sources in food and water, which are
incorporated in the body, and in building materials and other products that
incorporate those radioactive sources;
. Sources from space, in the form of cosmic rays;
. Sources in the atmosphere. One significant contribution comes from the
radon gas that is released from the Earth's crust and subsequent only decays
into radioactive atoms that become attached to airborne dust and particulates.
. Another contribution arises from the radioactive atoms produced in the
bombardment of atoms in the upper atmosphere by high-energy cosmic rays.
The worldwide average background dose for a human being is about 2.4 millisievert
(mSv) per year. This exposure is mostly from cosmic radiation and natural
isotopes in the Earth, far greater than human-caused background radiation
exposure, which in the year 2000 amounted to an average of about 0.01 mSv
per year from historical nuclear weapons testing, nuclear power accidents
and nuclear industry operation combined, and is greater than the average
exposure from medical tests, which ranges from 0.04 to 1 mSv per year. Older
coal-fired power plants without effective fly ash capture are one of the
largest sources of human-caused background radiation exposure. The level
of natural background radiation varies depending on location, and in some
areas the level is significantly higher than average.
- Baryons: They are the family of subatomic particles made of three quarks. The family includes the proton and neutron, which make up the atomic nucleus, but many other unstable baryons exist as well.
Particle Symbol
Rest mass
MeV/c²
Spin
Q
S
C
B
Mean lifetime
s
Decays to
Proton
p+
938.3 1/2 +1 0 0 0 Stable Unobserved
Neutron
n0
939.6 1/2 0 0 0 0 885.7±0.8 p+ + e? + ?eDelta
?++
1232 3/2 +2 0 0 0 6×10-24 ?+ + p+Delta
?+
1232 3/2 +1 0 0 0 6×10-24 ?+ + n0
or ?0 + p+Delta
?0
1232 3/2 0 0 0 0 6×10-24 ?0 + n0
or ?- + p+Delta
?-
1232 3/2 -1 0 0 0 6×10-24 ?- + n0Lambda
?0
1115.7 1/2 0 -1 0 0 2.60×10-10 ?- + p+
or ?0 + n0charmed Lambda
?c+
2285 1/2 +1 0 +1 0 2.0×10-13
bottom Lambda
?b0
5624 1/2 0 0 0 -1 1.2×10-12
Sigma
?+
1189.4 1/2 +1 -1 0 0 0.8×10-10 ?0 + p+
or ?+ + n0Sigma
?+
3/2 +1 -1 0 0 0
Sigma
?0
1192.5 1/2 0 -1 0 0 6×10-20 ?0 + ?Sigma
?0
3/2 0 -1 0 0
Sigma
?-
1197.4 1/2 -1 -1 0 0 1.5×10-10 ?- + n0Sigma
?-
3/2 -1 -1 0 0
bottom Sigma
?b+
5807.8 ?3.9+3.7 1/2 +1 0 0 -1 ?b + ?+bottom Sigma
?b+
3/2 +1 0 0 -1
bottom Sigma
?b-
5815.2 ± 2.7 1/2 -1 0 0 -1 ?b + ?-bottom Sigma
?b0
3/2 0 0 0 -1
bottom Sigma
?b0
1/2 0 0 0 -1
bottom Sigma
?b-
3/2 -1 0 0 -1
charmed Sigma
?c++
1/2 +2 0 +1 0
charmed Sigma
?c+
1/2 +1 0 +1 0
charmed Sigma
?c0
1/2 0 0 +1 0
Xi
?0
1315 1/2 0 -2 0 0 2.9×10-10 ?0 + ?0Xi
?0
3/2 0 -2 0 0
Xi
?-
1321 1/2 -1 -2 0 0 1.6×10-10 ?0 + ?-Xi
?-
3/2 -1 -2 0 0
charmed Xi
?c+
2466 1/2 +1 -1 +1 0 4.4×10-13
charmed Xi
?c0
2472 1/2 0 -1 +1 0 1.1×10-13
double charmed Xi
?cc++
1/2 +2 0 +2 0
double charmed Xi
?cc+
1/2 +1 0 +2 0
bottom Xi or
Cascade B
?b-
5792±3 1/2 -1 -1 0 -1 1.42×10-12 ?- + J/? (seen)
bottom Xi (Cascade B?) ?b-
3/2 -1 -1 0 -1
double bottom Xi
?bb0
1/2 0 0 0 -2
double bottom Xi
?bb-
1/2 -1 0 0 -2
Omega
?-
1672 3/2 -1 -3 0 0 0.82×10-10 ?0 + K-
or ?0 + ?-charmed Omega
?c0
2698 1/2 0 -2 +1 0 7×10-14
double charmed Omega
?cc+
1/2 +1 -1 +2 0
triple charmed Omega
?ccc++
3/2 +2 0 +3 0
bottom Omega
?b-
1/2 -1 -2 0 -1
double bottom Omega
?bb-
1/2 -1 -1 0 -2
bottom Omega
?b-
3/2 -1 -2 0 -1
double bottom Omega
?bb-
3/2 -1 -1 0 -2
triple bottom Omega
?bbb-
3/2 -1 0 0 -3
- Beta decay (nuclear): In nuclear physics it is a type of radioactive
decay in which a beta particle (an electron or a positron) is emitted. In
the case of electron emission, it is referred to as "beta minus"
(??), while in the case of a positron emission as "beta plus"
(?+). In ?? decay, the weak interaction converts a neutron (n0) into a proton
(p+) while emitting an electron (e?) and an anti-neutrino ( ):
.
- Beta particles: They are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. They are emitted as ionizing radiation also known as beta rays.
- Bosons: Bosons are either elementary, like the photon, or composite,
as mesons. All force carrier particles are bosons. Most bosons are composite
particles but the four gauge bosons are elementary particles. The Higgs
boson and the graviton have not yet been discovered (February 2008). They
are particles with an integer spin, as opposed to fermions which have half-integer
spin.
. Photon (?): Electric charge, 0; mass, 0
Carrier of electromagnetism, the quantum of light acts on electrically
Charged particles over unlimited distances.
. Z boson (Z): Electric charge, 0; mass, 91 Gev
Mediator of weak reactions that do not change the identity of particles
Its range is about10R-18 metre.
. W+/W- bosons (W): Electric charge, +1 or -1; mass, 80.4 Gev
Mediators of weak reactions that change particles flavour and charge.
Their range is about only 10E-18 metre.
. Gluons (g): Electric charge, 0; mass, 0
Eight species of gluons carry the strong interactions, acting on quarks
And other gluons. Do not feel electromagnetic or weak interactions.
. Higgs (H) (not yet observed): Electric charge, 0; mass, between 114 and
192 Gev
Believed to endow W and Z bosons, quarks and electrons with mass.
- Bremsstrahlung: It is electromagnetic radiation produced by the deceleration of a charged particle, such as an electron, when deflected by another charged particle, such as an atomic nucleus. The term is also used to refer to the process of producing the radiation. Bremsstrahlung has a continuous spectrum.
- Cosmic rays: They are energetic particles originating from space that impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are protons, about 9% are helium nuclei (alpha particles) and about 1% are electrons.
- Electromagnetic (EM) radiation: It is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. EM radiation carries energy and momentum, which may be imparted when it interacts with matter.
- Electrons: Electrons are fundamental subatomic particles that carry a negative electric charge. It is a spin-1/2 lepton that participates in electromagnetic interactions, its mass is approximately 1/1836 of the proton. With protons and neutrons, electrons make up atoms. Their interaction with adjacent nuclei is the main cause of chemical bonding.
- Electron neutrinos, muon neutrinos and tau neutrinos; these are the three types, or "flavours", of neutrinos. Each type also has an antimatter partner, called an antineutrino. Electron neutrinos or antineutrinos are generated whenever neutrons change into protons or vice versa, the two forms of beta decay. Interactions involving neutrinos are generally mediated by the weak force.
- Elementary particle: An elementary or fundamental particle is a particle not known to have substructure, not known to be made up of smaller particles. An elementary particle is one of the basic particles of the universe from which all larger particles are made. The quarks, leptons, and gauge bosons are elementary particles. The hadrons (mesons and baryons such as the proton and neutron) and even whole atoms were once regarded as elementary particles.
- Exotic baryons: If they exist, they would be bound states of 3 quarks and additional particles. These additional particles can be quarks. The pentaquark, would consist of four quarks and an anti-quark. Another exotic baryon which consists only of quarks is the H dibaryon. The H dibaryon consists of two up quarks, two down quarks and two strange quarks. Unlike the pentaquark, this particle would be long lived or even stable. There have been unconfirmed claims of detections of pentaquarks and dibaryons. Several types of exotic baryons which require physics beyond the standard model have been conjectured in order to explain specific experimental anomalies. There is no independent experimental evidence for any of these particles. One example is supersymmetric R-baryons, which are bound states of 3 quarks and a gluino. The lightest R-baryon is denoted as S0 and consists of an up quark, a down quark, a strange quark and a gluino. This particle is expected to be long lived or stable and has been invoked to explain ultrahigh energy cosmic rays. Stable exotic baryons are also candidates for strongly interacting dark matter.
- Fermions: Fermions are particles with a half-integer spin, such as protons
and electrons. There are two types of elementary fermions: quarks and leptons.
The 24 fundamental fermionic flavours are:
- 12 quarks - 6 particles (u · d · s · c · b
· t) with 6 corresponding antiparticles;
12 leptons - 6 particles (e · ? · ? · ?e · ??
· ??) with 6 corresponding antiparticles, of which 3 are neutrinos
and 3 are antineutrinos.
In contrast to bosons, only one fermion can occupy a quantum state at a given time (they obey the Pauli Exclusion Principle). Thus, if more than one fermion occupies the same place in space, the properties of each fermion (e.g. its spin) must be different from the rest. Therefore fermions are usually related with matter while bosons are related with radiation.
- Gamma rays: They are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and radioactive decay; most are generated from nuclear reactions occurring within the interstellar medium of space.
- Gauge bosons are bosonic particles which act as carriers of the fundamental forces of Nature that is elementary particles whose interactions are described by gauge theory exert forces on each other by the exchange of gauge bosons, usually as virtual particles.
- Gluino: It is the hypothetical supersymmetric partner of the gluon. Gluinos are Majorana fermions and interact via the strong nuclear force as an octet of colour. Gluinos have a lepton number 0, baryon number 0, and spin 1/2. Gluinos decay via strong interaction to a squark and a quark provided that an appropriate mass relation is satisfied. The squark subsequently decays to another quark and the lightest supersymmetric particle, LSP. However if gluinos are lighter than squarks, 3-body decay of a gluino to a neutralino and a quark antiquark pair is kinematically accessible through an off-shell squark.
- Gluons: They are elementary particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. In technical terms, they are vector gauge bosons that mediate strong colour charge interactions of quarks in quantum chromodynamics (QCD). Unlike the neutral photon of quantum electrodynamics (QED), gluons themselves participate in strong interactions. The gluon has the ability to do this as it carries the colour charge and so interacts with itself, making QCD significantly harder to analyze than QED.
- Goldstone bosons or Nambu-Goldstone bosons: They are bosons that appear in models with spontaneously broken symmetry. The Goldstone bosons correspond to the broken symmetry generators -they can be thought of as the excitations of the field in the symmetric "directions"- and are massless if the spontaneously broken symmetry is not also broken explicitly. If the symmetry is not exact, i.e., if it is explicitly broken as well as spontaneously broken, then the Goldstone bosons are not massless, though they typically remain light; these are called pseudo-Goldstone bosons or pseudo-Nambu-Goldstone bosons (abbreviated PNGBs).
- Graviscalar (also known as a radion): It is a hypothetical particle that emerges as an excitation of the metric tensor (i.e. gravitational field) but whose physical properties are virtually indistinguishable from a scalar in four dimensions, as shown in Kaluza-Klein theory. The new scalar field ? comes from a component of the metric tensor g55 where the figure 5 labels an additional, fifth dimension. It can be thought of as a measure of the size of the extra dimension, with variations in the scalar field representing variations in the size of the extra dimensions. In models with multiple extra dimensions, there exist several such particles.
- Gravitino: It is the supersymmetric partner of the graviton, as predicted by theories combining general relativity and supersymmetry; i.e. supergravity theories. If it exists it is a fermion of spin 3/2 and therefore obeys the Rarita-Schwinger equation. The gravitino field is conventionally written as ??? with ? = 0,1,2,3 a four-vector index and ? = 1,2 a spinor index. For ? = 0 one would get negative norm modes, as with every massless particle of spin 1 or higher. Thus the gravitino is the fermion mediating supergravity interactions, just as the photon is mediating electromagnetism, and the graviton is presumably mediating gravitation. Whenever supersymmetry is broken in supergravity theories, it acquires a mass which is directly the supersymmetry breaking scale.
- Graviton: It is a hypothetical elementary particle that mediates the force of gravity in the framework of quantum field theory. If it exists, the graviton must be massless (because the gravitational force has unlimited range) and must have a spin of 2 (because gravity is a second-rank tensor field).
- Hadron: It 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.
Mesons are composite bosons, but they are not composed of bosons (quarks are fermions). Like all subatomic particles, hadrons have quantum numbers corresponding to the representations of the Poincaré group: JPC(m), where J is the spin, P, the parity, C, the C parity, and m, the mass. In addition they may carry flavour quantum numbers such as isospin (or G parity), strangeness etc. Moreover, Baryons always carry an additive conserved quantum number called baryon number (B). B=1 for nucleons (the proton and the neutron), which are part of the atomic nucleus; Mesons have B=0. Most hadrons can be classified by the quark model which posits that all the quantum numbers are derived from those of the valence quarks (the quarks which form the hadron). For instance, since each quark has B=1/3, each baryon, composed of three quarks, has B=1.
- Higgs boson: It is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. It is the only Standard Model particle not yet observed, but would help explain how otherwise massless elementary particles still manage to construct mass in matter. In particular, it would explain the difference between the massless photon and the relatively massive W and Z bosons. Elementary particle masses, and the differences between electromagnetism (caused by the photon) and the weak force (caused by the W and Z bosons), are critical to many aspects of the structure of microscopic (and hence macroscopic) matter; thus, if it exists, the Higgs boson has an enormous effect on the world around us.
- Ion: It is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion due to its attraction to anodes. Conversely, a positively-charged ion, which has fewer electrons than protons, is known as a cation due to its attraction to cathodes.
- Hadrons are any strongly interacting composite subatomic particles. 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.
- Hawking radiation (also known as Bekenstein-Hawking radiation): In physics it is a thermal radiation with a black body spectrum predicted to be emitted by black holes due to "quantum effects". Stephen Hawking provided the theoretical argument for its existence in 1974 the Israeli physicist Jacob Bekenstein predicted that black holes should have a finite, non-zero temperature and entropy. Because Hawking radiation allows black holes to lose mass, black holes which lose more matter than they gain through other means are expected to evaporate, shrink, and ultimately vanish. Smaller 'micro' black holes are currently predicted by theory to be larger net emitters of radiation than larger black holes, and to shrink and evaporate faster. However, the existence of Hawking radiation has never been observed.
- Ionizing radiation: It is energetic particles or waves that have the potential to ionize an atom or molecule through atomic interactions. Examples of ionizing radiation are energetic Beta particles, neutrons, alpha particles and energetic photons (UV and above). The amount of energy required to ionize an atom or molecule may widely vary. X-rays and gamma rays will ionize almost any molecule or atom; Far ultraviolet, near ultraviolet and visible light are ionizing to very few molecules; microwaves and radio waves are non-ionizing radiation.
- Leptons are particles with spin-1/2 (a fermion) that do not experience
the strong interaction that is, the strong nuclear force. The leptons form
a family of elementary particles that are distinct from the other known
family of fermions, the quarks. There are three known flavours of lepton:
the electron, the muon, and the tau. Each flavour is represented by a pair
of particles called a weak doublet. One is a massive charged particle that
bears the same name as its flavour (like the electron). The other is a nearly
massless neutral particle called a neutrino (such as the electron neutrino).
All six of these particles have corresponding antiparticles (such as the
positron or the electron antineutrino). All known charged leptons have a
single unit of negative or positive electric charge (depending on whether
they are particles or antiparticles) and all of the neutrinos and antineutrinos
have zero electric charge. The charged leptons have two possible spin states,
while only one helicity is observed for the neutrinos (all the neutrinos
are left-handed, and all the antineutrinos are right-handed).
. Electron neutrino (Ve); electric charge, 0
Immune to electromagnetism and strong force; barely interact; essential
to
Radioactivity.
. Electron (e): Electric charge, -1; mass, 0.511 Mev
Lightest charged particle; carrier of electric currents; particles orbiting
the
Nucleus.
. Muon neutrino (Vµ): Electric charge, 0.
Appears in weak reactions involving the muon
. Muon (?): Electric charge, -1; mass, 106 Mev
Heavier electron; lifetime 2.2 microsec; found in cosmic ray shower.
. Tau neutrino (V ?): Electric charge, 0.
Appears in weak reactions involving the Tau lepton.
. Tau (?): Electric charge, -1; mass, 1.78 Gev
Unstable particle still a heavier version of the electron; lifetime, 0.3
picosec.
- Lightest Supersymmetric Particle (LSP): It is the generic name given to the lightest of the additional hypothetical particles found in supersymmetric models. In models with R-parity conservation, the LSP is stable. There is extensive observational evidence for an additional component of the matter density in the Universe that goes under the name dark matter. The LSP of supersymmetric models is a dark matter candidate and is a weakly interacting massive particle (WIMP). Dark matter particles must be electrically neutral; otherwise they would scatter light and thus not be "dark". They must also almost certainly be non-coloured. With these constraints, the LSP could be the lightest neutralino, the gravitino, or the lightest sneutrino. Sneutrino dark matter is ruled out because the sneutrino interacts via Z boson exchange and would have been detected by now if it makes up the dark matter. Neutralino dark matter is the favoured possibility. Gravitino dark matter is a possibility in supersymmetric models where the gravitino is very light, of order an eV. As dark matter, the gravitino is sometimes called a super-WIMP because its interaction strength is much weaker than that of other supersymmetric dark matter candidates.
- Magnetic monopole or Dirac monopole: It is a hypothetical particle that may be loosely described as "a magnet with only one pole". In more technical terms, it would have a net "magnetic charge". Modern interest in the concept stems from particle theories, notably Grand Unified Theories and superstring theories that predict either the existence or the possibility of magnetic monopoles. None have been found yet. It therefore remains possible that monopoles do not exist at all.
- Mesons are strongly interacting bosons, hadrons with integral spin. 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.
- Mu mesons: For historical reasons, muons are sometimes referred to as Mu mesons, even though they are not classified as mesons by modern particle physicists.
- Muon: It is an elementary particle with negative electric charge and a spin of 1/2. It has a mean lifetime of 2.2?s, longer than any other unstable lepton, meson, or baryon except for the neutron. It is classified as a lepton. Muons are denoted by ??. Muons have a mass of 105.7 MeV/c2, which is 206.7 times the electron mass. Since their interactions are very similar to those of the electron, a muon can be thought of as a much heavier version of the electron. Due to their greater mass, muons do not emit as much bremsstrahlung radiation; consequently, they are highly penetrating, much more so than electrons.
- Muon-neutrino: it is an elementary particle which has the same flavour as the muon. Muon-neutrinos are denoted by ??.
- Neutralino: It is a hypothetical particle, part of the doubling of the particles predicted by supersymmetric theories. The standard symbol for neutralinos is , where i runs from 1 to 4.
- Neutrinos are elementary particles that travel close to the speed of light, lack an electric charge, are able to pass through ordinary matter almost undisturbed, and are thus extremely difficult to detect. Neutrinos have a minuscule, but non-zero, mass too small to be measured as of 2007. Neutrinos are created in radioactive decay, or nuclear reactions, such as those in the sun, in nuclear reactors, or when cosmic rays hit atoms. There are three types, or "flavours", of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos; each type also has an antimatter partner, called an antineutrino. Electron neutrinos are generated whenever protons change into neutrons, while electron antineutrinos are generated whenever neutrons change into protons. These are the two forms of beta decay. Interactions involving neutrinos are generally mediated by the weak nuclear force.
- Neutrons are subatomic particle with no net electric charge and a mass of 939.573 MeVc² 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. The nuclei of all atoms (except the lightest isotope of hydrogen, which has only a single proton) consists of protons and neutrons. The number of neutrons determines the isotope of an element. A neutron consists of two down quarks and one up quark. Since it has three quarks, it is classified as a baryon.
- Nucleon: it is a collective name for two baryons: the neutron and the proton.
- Photino: It is the superpartner of the photon.
- Photon: It is the elementary particle responsible for electromagnetic
phenomena. It is the carrier of electromagnetic radiation of all wavelengths,
including gamma rays, X-rays, ultraviolet light, visible light, infrared
light, microwaves, and radio waves. The photon has zero rest mass, therefore
it travels (in vacuum) at the speed of light. Like all quanta, the photon
has both wave and particle properties ("wave-particle duality").
Photons show wave-like phenomena, such as refraction by a lens; however,
as a particle, it can only interact with matter by transferring the amount
of energy
where h is Planck's constant, c is the speed of light, and ? is its wavelength.
- Pion (short for pi meson): It is the collective name for three mesons: ?0, ?+ and ??. Pions are the lightest mesons (excluding the misnamed "Mu Meson" or muon) and play an important role in explaining low-energy properties of the strong nuclear force. Pions have zero spin and are composed of first-generation quarks. In the quark model, an up and an anti-down quark compose a ?+, while a down and an anti-up quark compose the ??, its antiparticle. The neutral combinations of up with anti-up and down with anti-down have identical quantum numbers, so they are only found in superpositions. The lowest-energy superposition is the ?0, which is its own antiparticle. Together, the pions form a triplet of isospin; each pion has isospin-1 (I = 1) and third-component isospin equal to its charge (Iz = +1, 0 or ?1). The ? ± mesons have a mass of 139.6 MeV/c2 and a mean life of 2.6×10?8 seconds. They decay due to weak processes. The main decay mode (99.9877%) is into a muon and its neutrino. The second largest decay mode (0.0123%) is into an electron and the corresponding neutrino: The ?0 meson has a slightly smaller mass of 135.0 MeV/c2 and a much shorter mean life of 8.4×10?17 seconds. It decays due to electromagnetic force. The main decay mode (98.798%) is into two photons. Its second largest decay mode (1.198%) decay into a photon and an electron-positron pair.
- Positron (positif electron, anti-electron): It is the antiparticle or the antimatter of the electron. The positron has an electric charge of +1, a spin of 1/2, and the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two gamma ray photons.
- Proton: It 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 , 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, making them
baryons. The two up quarks and one down quark of the proton are also held
together by the strong nuclear force, mediated by gluons.
- Quarks: They are one of the two basic constituents of matter (the other
are the leptons). Three quarks make up protons and neutrons. There are six
different types of quark known as flavours: up, down, charm, strange, top,
and bottom. The strange, charm, bottom and top varieties are highly unstable
and died out within a fraction of a second after the Big Bang. The up and
down varieties survive in profusion, and are distinguished by their electric
charge. A proton is made up of two up quarks and one down quark, yielding
a net charge of +1; while a neutron contains one up quark and two down quarks,
yielding a net charge of 0. Quarks are the only fundamental particles that
interact through all four of the fundamental forces. Antiparticles of quarks
are called antiquarks. Isolated quarks are never found naturally; they are
almost always found in groups of two (mesons) or groups of three (baryons)
called hadrons.
. Up quark (u): electric charge, +2/3; mass, 2MeV
Two Up and one Down Quark make a proton.
. Down quark (d): electric charge, -1/3; mass, 5MeV
Two Down and one Up Quarks make a neutron.
. Charm quark (C=c): electric charge, +2/3; mass, 1.25 GeV
Unstable heavier cousin of the Up quark; constituent of the J/Ý particle.
. Strange quark (s): electric charge, -1/3; mass, 95MeV
Unstable heavier cousin of the Down quark; constituent of the kaon particle.
. Top quark (t): electric charge, +2/3; mass, 171 GeV
Heaviest known particle; very short lived.
. Bottom quark (b): electric charge, -1/3; mass, 4.2 GeV
Unstable still heavier cousin of the Down quark; constituent of the B-meson.
- Radioactive decay: It is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide.
- Selectron: It is a slepton which is the hypothetical supersymmetric partner of an electron.
- Sfermion: It is any of the class of spin-0 superpartners of ordinary fermions appearing in supersymmetric extensions to the Standard Model. Thus, the sfermions include the squarks and the sleptons.
- Slepton: It is a sfermion which is hypothetical boson superpartner of a lepton whose existence is implied by supersymmetry. Sleptons have the same flavour and electric charge as corresponding leptons and their spin is zero. In an exactly supersymmetric world they also must have the same mass. If they exist, supersymmetry must be broken and their mass is beyond current experimental reach.
- Sparticle, a merging of the words supersymmetric and particle. Supersymmetry predicts the existence of these "shadow" particles. According to the theory, when the more familiar leptons, photons, and quarks were produced in the Big Bang, each one was accompanied by a matching sparticle: sleptons, photinos and squarks. This state of affairs occurred at a time when the universe was undergoing rapid phase change, and theorists believe this state of affairs lasted only some ten trillionth of a ten trillionth of a nanosecond (10 e-35 seconds) before the particles we see now "condensed" out and froze into space-time. Sparticles have not existed naturally since that time.
- Squark: It is a hypothetical boson partner of a quark whose existence is suggested by supersymmetry.
- Subatomic particles are elementary or composite particles smaller than an atom. Subatomic particles include the atomic constituent's electrons, protons, and neutrons. Protons and neutrons are composite particles, consisting of quarks.
- Superpartner: It is a particle related to a more standard particle by supersymmetry. In this physical theory, it is proposed that every fermion should have a "partner" boson (the fermion's superpartner), and vice versa. Exact unbroken supersymmetry would predict that a particle and its superpartners would have the same mass. No superpartners of the Standard Model particles have yet been found because supersymmetry is not an exact, unbroken symmetry of nature. If a superpartner is found, its mass would determine the scale at which supersymmetry is broken.
- Ttachyon: It is any hypothetical particle that travels at superluminal speed. Tachyonic fields have appeared theoretically in a variety of contexts, such as the Bosonic string theory. In the language of special relativity, a tachyon is a particle with space-like four-momentum and imaginary proper time. A tachyon is constrained to the space-like portion of the energy-momentum graph. Therefore, it cannot slow down to subluminal speeds. Even if tachyons were conventional, localisable particles, they would still preserve the basic tenets of causality in special relativity and not allow transmission of information faster than light. In the framework of quantum field theory, tachyons are understood as signifying an instability of the system and treated using tachyon condensation, rather than as real faster-than-light particles, and such instabilities are described by tachyonic fields. Tachyon particles are too unstable to be treated as existing.
- Thermal radiation: It is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature. Infrared radiation from a common household radiator or electric heater is an example of thermal radiation, as is the light emitted by a glowing incandescent light bulb. Thermal radiation is generated when heat from the movement of charged particles within atoms is converted to electromagnetic radiation. The emitted wave frequency of the thermal radiation is a probability distribution depending only on temperature, and for a genuine black body is given by Planck's law of radiation. Wien's law gives the most likely frequency of the emitted radiation, and the Stefan-Boltzmann law gives the heat intensity.
- Ultraviolet (UV) light: It is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. It is so named because the spectrum starts with wavelengths slightly shorter than the wavelengths humans identify as the colour violet (purple).
- Vector boson is a boson with spin equal to one unit of (Planck's constant divided by 2?). In elementary particle physics, the vector bosons currently considered to be fundamental particles are all gauge bosons. The most familiar vector boson is the photon, or quantum of light, which is a gauge boson.
- Vector mesons: They are composite particles that are vector bosons made of a quark and antiquark with a total angular momentum of one unit.
- Virtual particles or Vacuum Fluctuations: They are particles that exist for a limited time and space, introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty Principle. Virtual particles exhibit some of the phenomena that real particles do, such as obedience to the conservation laws. The number of particles in an area of space is not a well-defined quantity, but like other quantum observables is represented by a probability distribution. Since these particles do not have a permanent existence, they are called virtual particles or vacuum fluctuations of vacuum energy. In a certain sense, they can be understood to be a manifestation of the time-energy uncertainty principle in the vacuum.
- Visible Light or spectrum (sometimes optical spectrum): It is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. A typical generally has its maximum sensitivity at around 555 nm, in - WIMP: A weakly interacting massive particle, a hypothetical class of matter.
- W and Z bosons: They are the elementary particles that mediate the weak force. Their discovery was a major success for the Standard Model of particle physics. The W particle is named after the weak nuclear force. The Z particle was semi-humorously given its name because it was said to be the last particle to need discovery. The Z particle has zero electric charge.
- W+, W?, and Z0: They are weak gauge bosons that mediate the weak interaction. The massless photon mediates the electromagnetic interaction.
- WIMPs or weakly interacting massive particles: They are hypothetical particles serving as one possible solution to the dark matter problem. These particles interact through the weak nuclear force and gravity, and possibly through other interactions no stronger than the weak force. Because they do not interact with electromagnetism they cannot be seen directly, and because they do not interact with the strong nuclear force they do not react strongly with atomic nuclei.
- X-rays (or Röntgen rays) are a form of electromagnetic radiation
with a wavelength in the range of 10 to 0.01 nanometers, corresponding to
frequencies in the range 30 PHz to 30 EHz. X-rays are a form of ionizing
radiation and as such can be dangerous.