In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules, which are held together by the electric force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron, while most of the mass of the protons and neutrons is in turn due to the binding energy of their constituent quarks, due to the strong force.
In particle physics, a meson 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. Heavier mesons decay to lighter mesons and ultimately to stable electrons, neutrinos and photons.
A muon is an elementary particle similar to the electron, with an electric charge of −1 e and spin-1/2, but with a much greater mass. It is classified as a lepton. As with other leptons, the muon is not thought to be composed of any simpler particles.
In particle physics, a pion or pi meson, denoted with the Greek letter pi, is any of three subatomic particles:
π0
,
π+
, and
π−
. 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
π+
and
π−
decaying after a mean lifetime of 26.033 nanoseconds, and the neutral pion
π0
decaying after a much shorter lifetime of 85 attoseconds. Charged pions most often decay into muons and muon neutrinos, while neutral pions generally decay into gamma rays.
In theoretical physics, a chiral anomaly is the anomalous nonconservation of a chiral current. In everyday terms, it is equivalent to a sealed box that contained equal numbers of left and right-handed bolts, but when opened was found to have more left than right, or vice versa.
In nuclear physics and particle physics, isospin (I) is a quantum number related to the up- and down quark content of the particle. Isospin is also known as isobaric spin or isotopic spin. Isospin symmetry is a subset of the flavour symmetry seen more broadly in the interactions of baryons and mesons.
In quantum physics, Regge theory is the study of the analytic properties of scattering as a function of angular momentum, where the angular momentum is not restricted to be an integer multiple of ħ but is allowed to take any complex value. The nonrelativistic theory was developed by Tullio Regge in 1959.
The relativistic Breit–Wigner distribution is a continuous probability distribution with the following probability density function,
In particle physics, neutral particle oscillation is the transmutation of a particle with zero electric charge into another neutral particle due to a change of a non-zero internal quantum number, via an interaction that does not conserve that quantum number. Neutral particle oscillations were first investigated in 1954 by Murray Gell-mann and Abraham Pais.
In physics, a Fano resonance is a type of resonant scattering phenomenon that gives rise to an asymmetric line-shape. Interference between a background and a resonant scattering process produces the asymmetric line-shape. It is named after Italian-American physicist Ugo Fano, who in 1961 gave a theoretical explanation for the scattering line-shape of inelastic scattering of electrons from helium; however, Ettore Majorana was the first to discover this phenomenon. Fano resonance is a weak coupling effect meaning that the decay rate is so high, that no hybridization occurs. The coupling modifies the resonance properties such as spectral position and width and its line-shape takes on the distinctive asymmetric Fano profile. Because it is a general wave phenomenon, examples can be found across many areas of physics and engineering.
In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these then interacts, in the same way, a process that continues until many thousands, millions, or even billions of low-energy particles are produced. These are then stopped in the matter and absorbed.
In particle physics, a rho meson is a short-lived hadronic particle that is an isospin triplet whose three states are denoted as
ρ+
,
ρ0
and
ρ−
. 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 775.45±0.04 MeV for all three states.
The Delta baryons are a family of subatomic particle made of three up or down quarks, the same constituent quarks that make up the more familiar protons and neutrons.
In spectroscopy, the Autler–Townes effect, is a dynamical Stark effect corresponding to the case when an oscillating electric field is tuned in resonance to the transition frequency of a given spectral line, and resulting in a change of the shape of the absorption/emission spectra of that spectral line. The AC Stark effect was discovered in 1955 by American physicists Stanley Autler and Charles Townes.
The Roper resonance, also known as P11(1440) or N(1440)1/2+, is an unstable nucleon resonance with a mass of about 1,440 MeV/c2 and with a relatively wide full Breit-Wigner width Γ ≈ 300 MeV/c2. It contains three quarks (up (u) or down (d)) with total spin J = 1/2 and total isospin I = 1/2. In the quark model it is considered to be a radially excited three-quark state with radial quantum number N = 2 and positive parity. The Roper Resonance has been a subject of many studies because its mass is actually lower than three-quark states with radial quantum number N = 1. Only in the late 2000s was the lower-than-expected mass explained by theoretical calculations, revealing a quark core shielded by a dense cloud of mesons.
The sigma baryons are a family of subatomic hadron particles which have two quarks from the first flavour generation, and a third quark from a higher flavour generation, in a combination where the wavefunction sign remains constant when any two quark flavours are swapped. They are thus baryons, with total isospin of 1, and can either be neutral or have an elementary charge of +2, +1, 0, or −1. They are closely related to the lambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange.
The 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.
This page is a glossary of terms in string theory, including related areas such as supergravity, supersymmetry, and high energy physics.
In quantum mechanics, resonance cross section occurs in the context of quantum scattering theory, which deals with studying the scattering of quantum particles from potentials. The scattering problem deals with the calculation of flux distribution of scattered particles/waves as a function of the potential, and of the state of the incident particle. For a free quantum particle incident on the potential, the plane wave solution to the time-independent Schrödinger wave equation is:
