Glueball
Encyclopedia
In particle physics
, a glueball is a hypothetical composite particle
. It consists solely of gluon
particles, without valence quark
s. Such a state is possible because gluons carry color charge
and experience the strong interaction
. Glueballs are extremely difficult to identify in particle accelerator
s, because they mix
with ordinary meson
states.
Theoretical calculations show that glueballs should exist at energy ranges accessible with current collider
technology. However, due to the aforementioned difficulty, they have so far not been observed and identified with certainty.
provides a way to study the glueball spectrum theoretically and from first principles. Morningstar and Peardon have computed the masses of the lightest glueballs in QCD without dynamical quarks. The three lowest states are tabulated below. The presence of dynamical quarks would slightly alter these data, but also makes the computations more difficult.
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
, a glueball is a hypothetical composite particle
Subatomic particle
In physics or chemistry, subatomic particles are the smaller particles composing nucleons and atoms. There are two types of subatomic particles: elementary particles, which are not made of other particles, and composite particles...
. It consists solely of gluon
Gluon
Gluons are elementary particles which act as the exchange particles for the color force between quarks, analogous to the exchange of photons in the electromagnetic force between two charged particles....
particles, without valence quark
Quark
A quark is an elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. Due to a phenomenon known as color confinement, quarks are never directly...
s. Such a state is possible because gluons carry color charge
Color charge
In particle physics, color charge is a property of quarks and gluons that is related to the particles' strong interactions in the theory of quantum chromodynamics . Color charge has analogies with the notion of electric charge of particles, but because of the mathematical complications of QCD,...
and experience the strong interaction
Strong interaction
In particle physics, the strong interaction is one of the four fundamental interactions of nature, the others being electromagnetism, the weak interaction and gravitation. As with the other fundamental interactions, it is a non-contact force...
. Glueballs are extremely difficult to identify in particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...
s, because they mix
Quantum superposition
Quantum superposition is a fundamental principle of quantum mechanics. It holds that a physical system exists in all its particular, theoretically possible states simultaneously; but, when measured, it gives a result corresponding to only one of the possible configurations.Mathematically, it...
with ordinary meson
Meson
In particle physics, mesons are subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometer: 10−15 m, which is about the size of a proton...
states.
Theoretical calculations show that glueballs should exist at energy ranges accessible with current collider
Collider
A collider is a type of a particle accelerator involving directed beams of particles.Colliders may either be ring accelerators or linear accelerators.-Explanation:...
technology. However, due to the aforementioned difficulty, they have so far not been observed and identified with certainty.
In lattice simulations
Lattice field theoryLattice field theory
In physics, lattice field theory is the study of lattice models of quantum field theory, that is, of field theory on a spacetime that has been discretized onto a lattice. Although most lattice field theories are not exactly solvable, they are of tremendous appeal because they can be studied by...
provides a way to study the glueball spectrum theoretically and from first principles. Morningstar and Peardon have computed the masses of the lightest glueballs in QCD without dynamical quarks. The three lowest states are tabulated below. The presence of dynamical quarks would slightly alter these data, but also makes the computations more difficult.
| J P Parity (physics) In physics, a parity transformation is the flip in the sign of one spatial coordinate. In three dimensions, it is also commonly described by the simultaneous flip in the sign of all three spatial coordinates:... C |
mass Mass Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:... |
|---|---|
| 0++ | 1730(50)(80) MeV Electronvolt In physics, the electron volt is a unit of energy equal to approximately joule . By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt... |
| 2++ | 2400(25)(120) MeV |
| 0−+ | 2590(40)(130) MeV |