MesonIn particle physics, a meson (ˈmiːzɒn,_ˈmɛzɒn) is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles, they have a meaningful physical size, a diameter of roughly one femtometre (10^−15 m), which is about 0.6 times the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few tenths of a nanosecond.
Eta and eta prime mesonsThe eta (_eta) and eta prime meson (_eta prime) are isosinglet mesons made of a mixture of up, down and strange quarks and their antiquarks. The charmed eta meson (_charmed eta) and bottom eta meson (_bottom eta) are similar forms of quarkonium; they have the same spin and parity as the (light) _eta defined, but are made of charm quarks and bottom quarks respectively. The top quark is too heavy to form a similar meson, due to its very fast decay. The eta was discovered in pion–nucleon collisions at the Bevatron in 1961 by Aihud Pevsner et al.
PionIn particle physics, a pion (or a pi meson, denoted with the Greek letter pi: _Pion) is any of three subatomic particles: _Pion0, _Pion+, and _Pion-. Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more generally, the lightest hadrons. They are unstable, with the charged pions _Pion+ and _Pion- decaying after a mean lifetime of 26.033 nanoseconds (2.6033e-8 seconds), and the neutral pion _Pion0 decaying after a much shorter lifetime of 85 attoseconds (8.
Belle experimentThe Belle experiment was a particle physics experiment conducted by the Belle Collaboration, an international collaboration of more than 400 physicists and engineers, at the High Energy Accelerator Research Organisation (KEK) in Tsukuba, Ibaraki Prefecture, Japan. The experiment ran from 1999 to 2010. The Belle detector was located at the collision point of the asymmetric-energy electron–positron collider, KEKB.
J/psi mesonThe _J/psi (J/psi) meson ˈdʒeɪ_ˈsaɪ_ˈmiːzɒn is a subatomic particle, a flavor-neutral meson consisting of a charm quark and a charm antiquark. Mesons formed by a bound state of a charm quark and a charm anti-quark are generally known as "charmonium" or psions. The _J/Psi is the most common form of charmonium, due to its spin of 1 and its low rest mass. The _J/Psi has a rest mass of 3.0969GeV/c2, just above that of the _charmed eta (2.9836GeV/c2), and a mean lifetime of 7.2e-21s.
LHCb experimentThe LHCb (Large Hadron Collider beauty) experiment is a particle physics detector experiment collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the parameters of CP violation in the interactions of b-hadrons (heavy particles containing a bottom quark). Such studies can help to explain the matter-antimatter asymmetry of the Universe. The detector is also able to perform measurements of production cross sections, exotic hadron spectroscopy, charm physics and electroweak physics in the forward region.
B mesonIn particle physics, B mesons are mesons composed of a bottom antiquark and either an up (_B+), down (_B0), strange (_Strange B0) or charm quark (_Charmed B+). The combination of a bottom antiquark and a top quark is not thought to be possible because of the top quark's short lifetime. The combination of a bottom antiquark and a bottom quark is not a B meson, but rather bottomonium, which is something else entirely. Each B meson has an antiparticle that is composed of a bottom quark and an up (_B-), down (_AntiB0), strange (_Strange antiB0) or charm (_Charmed b-) antiquark respectively.
Pseudoscalar mesonIn high-energy physics, a pseudoscalar meson is a meson with total spin 0 and odd parity (usually notated as J^P = 0^− ). Pseudoscalar mesons are commonly seen in proton-proton scattering and proton-antiproton annihilation, and include the pion (π), kaon (K), eta (η), and eta prime () particles, whose masses are known with great precision. Among all of the mesons known to exist, in some sense, the pseudoscalars are the most well studied and understood.
Rho mesonIn particle physics, a rho meson is a short-lived hadronic particle that is an isospin triplet whose three states are denoted as _Rho+, _Rho0 and _Rho-. Along with pions and omega mesons, the rho meson carries the nuclear force within the atomic nucleus. After the pions and kaons, the rho mesons are the lightest strongly interacting particle, with a mass of 775.45MeV for all three states. The rho mesons have a very short lifetime and their decay width is about 145MeV with the peculiar feature that the decay widths are not described by a Breit–Wigner form.
Tau (particle)The tau (τ), also called the tau lepton, tau particle, tauon or tau electron, is an elementary particle similar to the electron, with negative electric charge and a spin of 1/2. Like the electron, the muon, and the three neutrinos, the tau is a lepton, and like all elementary particles with half-integer spin, the tau has a corresponding antiparticle of opposite charge but equal mass and spin. In the tau's case, this is the "antitau" (also called the positive tau). Tau particles are denoted by the symbol _Tau- and the antitaus by _Tau+.
Beta decayIn nuclear physics, beta decay (β-decay) is a type of radioactive decay in which an atomic nucleus emits a beta particle (fast energetic electron or positron), transforming into an isobar of that nuclide. For example, beta decay of a neutron transforms it into a proton by the emission of an electron accompanied by an antineutrino; or, conversely a proton is converted into a neutron by the emission of a positron with a neutrino in so-called positron emission.
Eightfold way (physics)In physics, the eightfold way is an organizational scheme for a class of subatomic particles known as hadrons that led to the development of the quark model. Working alone, both the American physicist Murray Gell-Mann and the Israeli physicist Yuval Ne'eman proposed the idea in 1961. The name comes from Gell-Mann's (1961) paper and is an allusion to the Noble Eightfold Path of Buddhism. By 1947, physicists believed that they had a good understanding of what the smallest bits of matter were.
Radioactive decayRadioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay, all of which involve emitting particles. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetism and nuclear force.
D mesonThe D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called "F mesons" prior to 1986. The D mesons were discovered in 1976 by the Mark I detector at the Stanford Linear Accelerator Center. Since the D mesons are the lightest mesons containing a single charm quark (or antiquark), they must change the charm (anti)quark into an (anti)quark of another type to decay.
Vector mesonIn high energy physics, a vector meson is a meson with total spin 1 and odd parity (usually noted as JP = 1−). Vector mesons have been seen in experiments since the 1960s, and are well known for their spectroscopic pattern of masses. The vector mesons contrast with the pseudovector mesons, which also have a total spin 1 but instead have even parity. The vector and pseudovector mesons are also dissimilar in that the spectroscopy of vector mesons tends to show nearly pure states of constituent quark flavors, whereas pseudovector mesons and scalar mesons tend to be expressed as composites of mixed states.
Quark modelIn particle physics, the quark model is a classification scheme for hadrons in terms of their valence quarks—the quarks and antiquarks which give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)", or the Eightfold Way, the successful classification scheme organizing the large number of lighter hadrons that were being discovered starting in the 1950s and continuing through the 1960s. It received experimental verification beginning in the late 1960s and is a valid effective classification of them to date.
SignalIn signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The IEEE Transactions on Signal Processing includes audio, video, speech, , sonar, and radar as examples of signals. A signal may also be defined as observable change in a quantity over space or time (a time series), even if it does not carry information.
Digital signalA digital signal is a signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog signal, which represents continuous values; at any given time it represents a real number within a continuous range of values. Simple digital signals represent information in discrete bands of analog levels. All levels within a band of values represent the same information state.
Decay chainIn nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". The typical radioisotope does not decay directly to a stable state, but rather it decays to another radioisotope. Thus there is usually a series of decays until the atom has become a stable isotope, meaning that the nucleus of the atom has reached a stable state. Decay stages are referred to by their relationship to previous or subsequent stages.
Eta CarinaeEta Carinae (η Carinae, abbreviated to η Car), formerly known as Eta Argus, is a stellar system containing at least two stars with a combined luminosity greater than five million times that of the Sun, located around distant in the constellation Carina. Previously a 4th-magnitude star, it brightened in 1837 to become brighter than Rigel, marking the start of its so-called "Great Eruption". It became the second-brightest star in the sky between 11 and 14 March 1843 before fading well below naked-eye visibility after 1856.
