 The Moon's cosmic ray shadow, as seen in secondary muons detected 700m below ground, at the Soudan II detector. Soudan 2 was a particle detector located in the Soudan Mine in Northern Minnesota United States |
|
| Composition | Elementary particle |
|---|---|
| Family | Fermion |
| Group | Lepton |
| Generation | Second |
| Interaction | Gravity, Electromagnetic, Weak |
| Antiparticle | Antimuon |
| Discovered | Carl D. Anderson, 1936 |
| Symbol | μ − |
| Mass | 105. 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 In Particle physics, fermions are particles which obey Fermi-Dirac statistics; they are named after Enrico Fermi. Leptons are a family of fundamental Subatomic particles comprising the Electron, the Muon, and the Tauon (or tau particle as well as their In Particle physics, a generation is a division of the Elementary particles Between generations particles differ only by their Mass. In Physics, a fundamental interaction or fundamental force is a mechanism by which particles interact with each other and which cannot be explained in terms Gravitation is a natural Phenomenon by which objects with Mass attract one another In Physics, the electromagnetic force is the force that the Electromagnetic field exerts on electrically charged particles The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four Fundamental interactions of nature to most kinds of particles, there is an associated antiparticle with the same Mass and opposite Electric charge. Carl David Anderson ( 3 September 1905 &ndash 11 January 1991) was an American Physicist. Year 1936 ( MCMXXXVI) was a Leap year starting on Wednesday (link will display the full calendar of the Gregorian calendar. 658369(9) MeV/c2 |
| Mean lifetime | 2. Given an assembly of elements the number of which decreases ultimately to zero the lifetime (also called the mean lifetime) is a certain number that characterizes the rate 19703(4)×10−6s[1] |
| Electric charge | −1 e |
| Color charge | None |
| Spin | ½ |
The muon (from the letter mu (μ)--used to represent it) is an elementary particle with negative electric charge and a spin of 1/2. The elementary charge, usually denoted e, is the Electric charge carried by a single Proton, or equivalently the negative of the electric charge carried The elementary charge, usually denoted e, is the Electric charge carried by a single Proton, or equivalently the negative of the electric charge carried In Particle physics, color charge is a property of Quarks and Gluons which are related to their Strong interactions in the context of Quantum In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin Mu (uppercase Μ, lowercase μ; Μι or el Μυ) is the 12th letter of the Greek alphabet. 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 Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction. In Quantum mechanics, spin is a fundamental property of atomic nuclei, Hadrons and Elementary particles For particles with non-zero spin It has a mean lifetime of 2. Given an assembly of elements the number of which decreases ultimately to zero the lifetime (also called the mean lifetime) is a certain number that characterizes the rate 2μs, longer than any other unstable lepton, meson, or baryon except for the neutron. Leptons are a family of fundamental Subatomic particles comprising the Electron, the Muon, and the Tauon (or tau particle as well as their In Particle physics, a meson is a strongly interacting Boson &mdashthat is a Hadron with integer spin. Baryons are the family of Subatomic particles with a Baryon number of 1 This article is a discussion of neutrons in general For the specific case of a neutron found outside the nucleus see Free neutron. Together with the electron, the tau, and the neutrinos, it is classified as a lepton. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The tau lepton (often called the tau, tau particle, or occasionally the tauon; symbol) is a negatively charged Elementary particle with Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost Leptons are a family of fundamental Subatomic particles comprising the Electron, the Muon, and the Tauon (or tau particle as well as their Like all fundamental particles, the muon has an antimatter partner of opposite charge but equal mass and spin: the antimuon, also called a positive muon. In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object Muons are denoted by μ− and antimuons by μ+.
For historical reasons, muons are sometimes referred to as mu mesons, even though they are not classified as mesons by modern particle physicists (see History). In Particle physics, a meson is a strongly interacting Boson &mdashthat is a Hadron with integer spin. Muons have a mass of 105. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 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. Bremsstrahlung ( pronounced, from German de ''bremsen'' "to brake" and de ''Strahlung'' "radiation" i
As with the case of the other charged leptons, there is a muon-neutrino which has the same flavor as the muon. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost In Particle physics, flavour or flavor (see spelling differences) is a Quantum number of Elementary particles related to their Muon-neutrinos are denoted by νμ.
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Muon sources
Since the production of muons requires an available center of momentum frame energy of over 105 MeV, neither ordinary radioactive decay events nor nuclear fission and fusion events (such as those occurring in nuclear reactors and nuclear weapons) are energetic enough to produce muons. A center of momentum frame (or zero-momentum frame or COM frame of a system is any Inertial frame in which the Center of mass is at rest (has zero velocity Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. Only nuclear fission produces single-nuclear-event energies in this range, but due to conservation constraints, muons are not produced.
On earth, all naturally occurring muons are apparently created by cosmic rays, which consist mostly of protons, many arriving from deep space at very high energy. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on
About 10,000 muons reach every square meter of the earth's surface a minute; these charged particles form as by-products of cosmic rays colliding with molecules in the upper atmosphere. Traveling at relativistic speeds, muons can penetrate tens of meters into rocks and other matter before attenuating as a result of absorption or deflection by other atoms.
—Mark Wolvertron, science writer, Scientific American magazine, September 2007, page 26 "Muons for Peace"
When a cosmic ray proton impacts atomic nuclei of air atoms in the upper atmosphere, pions are created. In Particle physics, pion (short for pi meson) is the collective name for three Subatomic particles, and. These decay within a relatively short distance (meters) into muons (the pion's preferred decay product), and neutrinos. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost The muons from these high energy cosmic rays, generally continuing essentially in the same direction as the original proton, do so at very high velocities. Although their lifetime without relativistic effects would allow a half-survival distance of only about 0. 66 km at most, the time dilation effect of special relativity allows cosmic ray secondary muons to survive the flight to the earth's surface. This article discusses a concept in physics For the concept in sociology see Time displacement. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial Indeed, since muons are unusually penetrative of ordinary matter, like neutrinos, they are also detectable deep underground and underwater, where they form a major part of the natural background ionizing radiation. Like cosmic rays, as noted, this secondary muon radiation is also directional. See the illustration above of the moon's cosmic ray shadow, detected when 700 m of soil and rock filters secondary radiation, but allows enough muons to form a crude image of the moon, in a directional detector.
The same nuclear reaction described above (i. e. , hadron-hadron impacts to produce pion beams, which then quickly decay to muon beams over short distances) is used by particle physicists to produce muon beams, such as the beam used for the muon g-2 gyromagnetic ratio experiment (see link below). In Physics, the gyromagnetic ratio (also sometimes known as the magnetogyric ratio in other disciplines of a particle or system is the Ratio of its In naturally-produced muons, the very high-energy protons to begin the process are thought to originate from acceleration by electromagnetic fields over long distances between stars or galaxies, in a manner somewhat analogous to the mechanism of proton acceleration used in laboratory particle accelerators.
Muon decays
Muons are unstable elementary particles and are heavier than the electron and neutrinos but lighter than all other matter particles. They decay via the weak interaction to an electron, two neutrinos and possibly other particles with a net charge of zero. Nearly all of the time, they decay into an electron, an electron-antineutrino, and a muon-neutrino. Antimuons decay to a positron, an electron-neutrino, and a muon-antineutrino:
. The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron.
The tree level muon decay width is
where 
.
A photon or electron-positron pair is also present in the decay products about 1. In Physics, the photon is the Elementary particle responsible for electromagnetic phenomena 4% of the time.
The mean lifetime of the muon is 2. 197019±0. 000021 μs[1]. The equality of the muon and anti-muon lifetimes has been established to better than one part in 104.
The decay distributions of the electron in muon decays have been parametrized using the so-called Michel parameters. The Michel parameters, usually denoted by \rho \eta \xi and \delta are four parameters used in describing the leptonic decays of charged Leptons The values of these five parameters can be predicted unambiguously in the Standard Model of particle physics—no deviation with respect to these predictions has yet been found. The Standard Model of Particle physics is a theory that describes three of the four known Fundamental interactions together with the Elementary particles Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them
Certain neutrino-less decay modes are kinematically allowed but forbidden in the Standard Model. Examples are
and 
.
Observation of such decay modes would constitute clear evidence for physics beyond the Standard Model (BSM). In Physics, the Standard Model of Particle physics is currently the best description of all experimental data Upper limits for the branching fractions of such decay modes are in the range 10−11 to 10−12.
Muonic atoms
The muon was the first elementary particle discovered that does not appear in ordinary atoms. 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 History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Negative muons can, however, form muonic atoms by replacing an electron in ordinary atoms. An exotic atom is a normal Atom in which one or more sub-atomic particles have been replaced by other particles of the same charge Muonic atoms are much smaller than typical atoms because the larger mass of the muon gives it a smaller ground-state wavefunction than the electron. In Quantum mechanics, a stationary state is an Eigenstate of a Hamiltonian, or in other words a state of definite energy A wave function or wavefunction is a mathematical tool used in Quantum mechanics to describe any physical system
A positive muon, when stopped in ordinary matter, can also bind an electron and form an exotic atom known as muonium (Mu) atom, in which the muon acts as the nucleus. Muonium particles are Exotic atoms made up of an Antimuon and an Electron, and are given the chemical symbol. The positive muon, in this context, can be considered a pseudo-isotope of hydrogen with one ninth of the mass of the proton. Because the reduced mass of muonium, and hence its Bohr radius, is very close to that of hydrogen, this short lived "atom" behaves chemically — to a first approximation — like hydrogen, deuterium and tritium. Reduced mass is the "effective" Inertial mass appearing in the Two-body problem of Newtonian mechanics. In the Bohr model of the structure of an Atom, put forward by Niels Bohr in 1913 Electrons orbit a central nucleus. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Deuterium, also called heavy hydrogen, is a Stable isotope of Hydrogen with a Natural abundance in the Oceans of Earth Tritium (ˈtɹɪtiəm symbol or, also known as Hydrogen-3) is a radioactive Isotope of Hydrogen.
Anomalous magnetic dipole moment
The anomalous magnetic dipole moment is the difference between the experimentally observed value of the magnetic dipole moment and the theoretical value predicted by the Dirac equation. In Quantum electrodynamics, the anomalous magnetic moment of a particle is a contribution of effects of Quantum mechanics, expressed by Feynman diagrams In Physics, the Dirac equation is a relativistic quantum mechanical wave equation formulated by British physicist Paul Dirac in 1928 and provides The measurement and prediction of this value is very important in the precision tests of QED (quantum electrodynamics). Quantum electrodynamics ( QED) a relativistic quantum field theory of electrodynamics is among the most stringently tested theories in Physics. Quantum electrodynamics ( QED) is a relativistic Quantum field theory of Electrodynamics. The E821 experiment at Brookhaven National Laboratory (BNL) studied the precession of muon and anti-muon in a constant external magnetic field as they circulated in a confining storage ring. Brookhaven National Laboratory ( BNL) is a United States national laboratory located in Upton New York on Long Island, and was formally established The E821 Experiment reported the following average value (from the July 2007 review by Particle Data Group)
where the first errors are statistical and the second systematic.
The difference between the g-factors of the muon and the electron is due to their difference in mass. For the acceleration-related quantity in mechanics see ''g''-force. Because of the muon's larger mass, contributions to the theoretical calculation of its anomalous magnetic dipole moment from Standard Model weak interactions and from contributions involving hadrons are important at the current level of precision, whereas these effects are not important for the electron. The Standard Model of Particle physics is a theory that describes three of the four known Fundamental interactions together with the Elementary particles The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four Fundamental interactions of nature In Particle physics, a hadron ( from the ἁδρός hadrós, " stout, thick " ( The muon's anomalous magnetic dipole moment is also sensitive to contributions from new physics beyond the Standard Model, such as supersymmetry. In Physics, the Standard Model of Particle physics is currently the best description of all experimental data In Particle physics, supersymmetry (often abbreviated SUSY) is a Symmetry that relates elementary particles of one spin to another particle that For this reason, the muon's anomalous magnetic moment is normally used as a probe for new physics beyond the Standard Model rather than as a test of QED (Phys.Lett. B649, 173 (2007)).
History
| Antimatter | |
| Overview | |
| Annihilation | |
| Devices | |
| Antiparticles | |
| Uses | |
| Bodies | |
People
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Muons were discovered by Carl D. Anderson in 1936 while he studied cosmic radiation. In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed Annihilation is defined as "total destruction" or "complete obliteration" of an object having its root in the Latin nihil (nothing Penning traps are devices for the storage of charged particles using a constant static Magnetic field and a spatially inhomogeneous static Electric field. to most kinds of particles, there is an associated antiparticle with the same Mass and opposite Electric charge. The positrons or antielectron is the Antiparticle or the Antimatter counterpart of the Electron. The antiproton ( pronounced p-bar) is the Antiparticle of the Proton. The antineutron is the Antiparticle of the Neutron. It was discovered (in proton-proton collisions in the Bevatron at Berkeley by Bruce Cork in Positron emission tomography ( PET) is a Nuclear medicine imaging technique which produces a three-dimensional image or map of functional processes in the In Particle physics and Quantum chemistry, antimatter is the extension of the concept of the Antiparticle to Matter, where antimatter is composed An antimatter weapon is a hypothetical device using Antimatter as a power source a propellant or an explosive for a Weapon. The ALPHA Collaboration (Antihydrogen Laser PHysics Apparatus consists of scientists from a number of scientific institutions whose goal it is to trap neutral Antimatter in ATHENA was an Antimatter research project that took place at the AD Ring at CERN. The ATRAP collaboration at CERN developed out of TRAP a collaboration whose members pioneered cold Antiprotons cold Positrons and first made the ingredients The European Organization for Nuclear Research (Organisation Européenne pour la Recherche Nucléaire known as CERN Carl David Anderson ( 3 September 1905 &ndash 11 January 1991) was an American Physicist. Carl David Anderson ( 3 September 1905 &ndash 11 January 1991) was an American Physicist. Year 1936 ( MCMXXXVI) was a Leap year starting on Wednesday (link will display the full calendar of the Gregorian calendar. For the 1962 Bruce Conner film see Cosmic Ray (film Cosmic rays are energetic particles originating from space that impinge on He had noticed particles that curved in a manner distinct from that of electrons and other known particles, when passed through a magnetic field. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges In particular, these new particles were negatively charged but curved to a smaller degree than electrons, but more sharply than protons, for particles of the same velocity. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive It was assumed that the magnitude of their negative electric charge was equal to that of the electron, and so to account for the difference in curvature, it was supposed that these particles were of intermediate mass (lying somewhere between that of an electron and that of a proton).
For this reason, Anderson initially called the new particle a mesotron, adopting the prefix meso- from the Greek word for "mid-". Shortly thereafter, additional particles of intermediate mass were discovered, and the more general term meson was adopted to refer to any such particle. Faced with the need to differentiate between different types of mesons, the mesotron was in 1947 renamed the mu meson (with the Greek letter μ (mu) used to approximate the sound of the Latin letter m).
However, it was soon found that the mu meson significantly differed from other mesons; for example, its decay products included a neutrino and an antineutrino, rather than just one or the other, as was observed in other mesons. Neutrinos are Elementary particles that travel close to the Speed of light, lack an Electric charge, are able to pass through ordinary matter almost In Physics, antineutrinos, the Antiparticles of Neutrinos are neutral particles produced in nuclear Beta decay. Other mesons were eventually understood to be hadrons—that is, particles made of quarks—and thus subject to the residual strong force. In Particle physics, a hadron ( from the ἁδρός hadrós, " stout, thick " ( In Physics, a quark (kwɔrk kwɑːk or kwɑːrk is a type of Subatomic particle. The nuclear force (or nucleon-nucleon interaction or residual strong force) is the force between two or more Nucleons It is responsible for In the quark model, a meson is composed of exactly two quarks (a quark and antiquark), unlike baryons which are composed of three quarks. Mu mesons, however, were found to be fundamental particles (leptons) like electrons, with no quark structure. Thus, mu mesons were not mesons at all (in the new sense and use of the term meson), and so the term mu meson was abandoned, and replaced with the modern term muon. In Particle physics, a meson is a strongly interacting Boson &mdashthat is a Hadron with integer spin.
See also
External links
- Muon anomalous magnetic moment and supersymmetry
- g-2 (muon anomalous magnetic moment) experiment
- muLan (Measurement of the Positive Muon Lifetime) experiment
- The Review of Particle Physics
- The TRIUMF Weak Interaction Symmetry Test
References
- ^ W. Muonium particles are Exotic atoms made up of an Antimuon and an Electron, and are given the chemical symbol. Muon spin spectroscopy is an experimental technique based on the implantation of spin polarized Muons in matter and on the detection of the influence of the atomic Muon-catalyzed fusion ( μCF) is a process allowing Nuclear fusion to take place at Temperatures significantly lower than the temperatures required for This is a list of the different types of particles known and hypothesized -M. Yao et al. (Particle Data Group), J. The Particle Data Group is an international collaboration of particle Physicists that compiles and reanalyzes published results related to the properties of particles Phys. G 33, 1 (2006)
- S. H. Neddermeyer and C. D. Anderson, "Note on the Nature of Cosmic-Ray Particles", Phys. Rev. 51, 884–886 (1937). Full text available in PDF.
- J. C. Street and E. C. Stevenson, "New Evidence for the Existence of a Particle of Mass Intermediate Between the Proton and Electron", Phys. Rev. 52, 1003-1004 (1937). Full text available in PDF.
- Serway & Faughn, College Physics, Fourth Edition (Fort Worth TX: Saunders, 1995) page 841
- Emanuel Derman, My Life As A Quant (Hoboken, NJ: Wiley, 2004) pp. 58-62.
- Marc Knecht ; The Anomalous Magnetic Moments of the Electron and the Muon, Poincaré Seminar (Paris, Oct. 12, 2002), published in : Duplantier, Bertrand; Rivasseau, Vincent (Eds. ) ; Poincaré Seminar 2002, Progress in Mathematical Physics 30, Birkhäuser (2003) [ISBN 3-7643-0579-7]. Full text available in PostScript.
Dictionary
muon
-noun
- (physics) An unstable elementary particle in the lepton family, having similar properties to the electron but with a mass 209 times greater.
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