Hadron

	Email		Print
	Bookmark		Link

Hadron

In particle physics

Particle physics

Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
, a hadron (from the , hadrós, "stout, thick") is a bound state

Bound state

In physics, a bound state is a composite of two or more building blocks that behaves as a single object. In quantum mechanics , a bound state is a state in the Hilbert space that corresponds to two or more particles whose interaction energy is negative, and therefore these particles cannot be separated unless energy is spent....
of quark

Quark

Quarks are a type of elementary particle and major constituents of matter. They are the only particles in the Standard Model to experience all four fundamental interaction, which are also known as fundamental interactions....
s. Hadrons are held together by the strong force

Strong interaction

In particle physics, the strong interaction, or strong force, or color force, holds quarks and gluons together to form protons, neutrons and other particles....
, similarly to how molecules are held together by the electromagnetic force

Electromagnetic force

In physics, the electromagnetic force is the force that the electromagnetic field exerts on electrically charged particles. It is the electromagnetic force that holds electrons and protons together in atoms, and which hold atoms together to make molecules....
. There are two subsets of hadrons: baryons and mesons; the most well known baryons are proton

Proton

The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom but is also stable by itself and has a second identity as the hydrogen ion, H+....
s and neutron

Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s.

rding to the quark model

Quark model

In physics, the quark model is a classification scheme for hadrons in terms of their valence quarks, i.e., the quarks which give rise to the quantum numbers of the hadrons....
, the properties of hadrons are primarily determined by their so-called valence quarks.

Discussion

Ask a question about 'Hadron'

Start a new discussion about 'Hadron'

Answer questions from other users

Full Discussion Forum

Encyclopedia

In particle physics

Particle physics

Bound state

Quark

Strong interaction

Electromagnetic force

Proton

Neutron

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton.Neutrons are usually found in atomic nucleus....
s.

Introduction

According to the quark model

Quark model

Proton

Up quark

The up quark is a particle described by the Standard Model theory of physics. It is a first-generation quark with a charge of +elementary charge....
s (each with electric charge

Electric charge

Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. Electrically charged matter is influenced by, and produces, electromagnetic fields....
+2/3) and one down quark

Down quark

The down quark is a first-generation quark with a charge of - elementary charge. It is the second-lightest of all the six flavour of quarks, the lightest being the up quark....
(with electric charge -1/3). Adding these together yields the proton charge of +1. Although the constituent quarks also carry color charge

Color charge

In particle physics, color charge is a property of quarks and gluons which are related to their strong interactions in the context of quantum chromodynamics ....
(nothing to do with visual color

Color

Color or colour is the visual perception property corresponding in humans to the categories called red, yellow, blue and others....
), a property of the strong nuclear force called color confinement requires that any composite state carry no residual color charge. That is, hadrons must be colorless. There are two ways to accomplish this: three quarks of different colors, or a quark of one color and an anti-quark

Antimatter

In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles....
carrying the corresponding anticolor. Hadrons based on the former are called baryons

Hadron

In particle physics, a hadron is a bound state of quarks. Hadrons are held together by the strong interaction, similarly to how molecules are held together by the electromagnetic force....
, and those based on the latter are called mesons

Hadron

Subatomic particle

A subatomic particle is an elementary particle or composite particle particle smaller than an atom. Particle physics and nuclear physics are concerned with the study of these particles, their interactions, and non-atomic QCD matter....
s, hadrons are assigned quantum numbers corresponding to the representations

Representation theory

Representation theory is a branch of mathematics that studies abstract algebra algebraic structures by representing their element as linear transformations of vector spaces....
of the Poincaré group

Poincaré group

In physics and mathematics, the Poincar? group, named after Henri Poincar?, is the group of isometry of Minkowski spacetime. It is a 10-dimensional compact space Lie group....
: J^PC(m), where J is the spin

Spin (physics)

In quantum mechanics, spin is a fundamental property of atomic nucleus, hadrons, and elementary particles. For particles with non-zero spin, spin direction is an important intrinsic degrees of freedom ....
quantum number, P, the intrinsic (or P) parity

Parity

Parity is a concept of equality of status or functional equivalence. It has several different specific definitions.* Parity , the name of the symmetry of interactions under spatial inversion...
, and C, the charge conjugation, or C parity

C parity

In physics, C parity or charge parity is a multiplicative quantum number of some particles that describes its behavior under a symmetry operation of charge conjugation ....
, and the particle four-momentum

Four-momentum

In special relativity, four-momentum is the generalization of the classical three-dimensional momentum to four-dimensional spacetime. Momentum is a vector in three dimensions; similarly four-momentum is a four-vector in spacetime....
, m, (i.e., its mass

Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
). Note that the mass of a hadron has very little to do with the mass of its valence quarks; rather, due to mass–energy equivalence, most of the mass comes from the large amount of energy associated with the strong nuclear force. Hadrons may also carry flavor

Flavour (particle physics)

In particle physics, flavour or flavor is a quantum number of elementary particles. In quantum chromodynamics flavour is a global symmetry....
quantum numbers such as isospin

Isospin

In physics, and specifically, particle physics, isospin is a quantum number related to the strong interaction. This term was derived from isotopic spin, but the term is confusing as two isotopes of a nucleus have different numbers of nucleons; in contrast, rotations of isospin maintain the number of nucleons....
(or G parity), and strangeness. All quarks carry an additive, conserved quantum number called a baryon number

Baryon number

In particle physics, the baryon number is an conservation laws quantum number of a system. It is defined as:whereWhy one third? According to the laws of strong interaction there cannot be any bare color charge, i.e....
(B), which is +1/3 for quarks and -1/3 for antiquarks. This means that baryons --which are groups of three quarks-- have B=1 while mesons have B=0.

Hadrons have excited state

Excited state

Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
s known as resonances. Each ground-state hadron may have several excited states; hundreds of resonances have been observed in particle physics experiments. Resonances decay extremely quickly (within about 10⁻²⁴ second

Second

The second , sometimes abbreviated sec., is the name of a units of measurement of time, and is the International System of Units SI base unit of time....
s) via the strong nuclear force.

In other phases

Phase (matter)

In the physical sciences, a phase is a region of space , throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, refractive index, and chemical composition....
of QCD matter

QCD matter

Quark matter or QCD matter refers to any of a number of theorized phase of matter whose degrees of freedom include quarks and gluons. These theoretical phases would occur at extremely high temperatures and densities, billions of times higher than can be produced in equilibrium in laboratories....
the hadrons may disappear. For example, at very high temperature and high pressure, unless there are sufficiently many flavors of quarks, the theory of quantum chromodynamics

Quantum chromodynamics

Quantum chromodynamics is a theory of the strong interaction , a fundamental force describing the interactions of the quarks and gluons making up hadrons ....
(QCD) predicts that quarks and gluons will interact weakly and will no longer be confined within hadrons. This property, which is known as asymptotic freedom

Asymptotic freedom

In physics, asymptotic freedom is the property of some gauge theory in which the interaction between the particles, such as quarks, becomes arbitrarily weak at ever shorter distances, i.e....
, has been experimentally confirmed at the energy scales between a GeV

GEV

GEV may stand for:*Generalized extreme value distribution*Electronvolt*Wing-In-Ground effect vehicle*G.E.V., a tabletop game by Steve Jackson games, based on Ogre_...
and a TeV

TEV

TEV may refer to:* TeV, or teraelectronvolt, a measure of energy* Enterprise value, a financial measure* Total Economic Value, an economic measure...
.

All hadrons except the proton are unstable.

Baryons

All known baryons are made of three valence quarks, and are therefore fermion

Fermion

In particle physics, fermions are subatomic particle which obey Fermi-Dirac statistics; they are named after Enrico Fermi. In contrast to bosons, which have Bose-Einstein statistics, only one fermion can occupy a quantum state at a given time; this is the Pauli Exclusion Principle....
s. They have baryon number B=1, while antibaryons (composed of three antiquarks) have B=-1. In principle, some baryons could be composed of further quark-antiquark pairs in addition to the three quarks (or antiquarks) that make up basic baryons. Baryons containing a single additional quark-antiquark pair are called pentaquark

Pentaquark

A pentaquark is an hypothetical subatomic particle consisting of a group of five quarks , or more specifically four quarks and one anti-quark and is represented by T....
s. Evidence for these states was claimed by several experiments in the early 2000s, though this has since been refuted. No evidence of baryon states with even more quark-antiquark pairs has been found.

Mesons

Mesons are boson

Boson

In particle physics, bosons are subatomic particle which obey Bose-Einstein statistics; they are named after Satyendra Nath Bose and Albert Einstein....
s composed of a quark-antiquark pair. They have baryon number B=0. Examples of mesons commonly produced in particle physics experiments include pion

Pion

In particle physics, a pion is any of three subatomic particles: , and . Pions are the lightest mesons and play an important role in explaining low-energy properties of the strong nuclear force....
s and kaon

Kaon

In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called Strangeness ....
s. The former also play a role holding atomic nuclei together via the residual strong force. Hypothetical mesons have more than one quark-antiquark pair; a meson composed of two of these pairs is called a tetraquark

Tetraquark

In particle physics a tetraquark is a hypothetical meson composed of four valence quarks. In principle, a tetraquark state may be allowed in Quantum chromodynamics, the modern theory of strong interactions....
. Currently there is no evidence of their existence. Mesons that lie outside the quark model classification are called exotic meson

Exotic meson

Non-quark model mesons include#exotic mesons, which have quantum numbers not possible for mesons in the quark model;#glueballs or gluonium, which have no quark model quarks at all;...
s. These include glueball

Glueball

In particle physics, a glueball is a hypothetical composite subatomic particle. It solely consists of gluon particles, without valence quarks. Such a state is possible because gluons carry color charge and experience the strong interaction....
s and hybrid mesons (mesons bound by excited gluon

Gluon

Gluons are elementary particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei....
s).

Hadron

Introduction

Baryons

Mesons

See also