Hadronization
Encyclopedia
In particle physics
, hadronization is the process of the formation of hadron
s out of quark
s and gluon
s. This occurs after high-energy collisions in a particle collider
in which free quarks or gluons are created. Due to postulated colour confinement
, these cannot exist individually. In the Standard Model they combine with quarks and antiquarks spontaneously created from the vacuum
to form hadrons. The QCD (Quantum Chromodynamics) dynamics of the hadronization process are not yet fully understood, but are modeled and parameterized in a number of phenomenological studies, including the Lund string model
and in various long-range QCD
approximation schemes.
The tight cone of particles created by the hadronization of a single quark
is called a jet
. Jets are observed in particle detector
s, rather than quarks, whose existence must be inferred. The models and approximation schemes and their predicted Jet hadronization, or fragmentation, have been extensively compared with measurement in a number of high energy particle physics experiments; e.g. TASSO
, OPAL
, H1
.
Hadronization also occurred shortly after the Big Bang
when the quark-gluon plasma
cooled to the temperature
below which free quarks and gluons cannot exist (about 170 MeV
). The quarks and gluons then combined into hadrons.
A top quark
, however, has a mean lifetime of 5*10^-25 seconds, which is shorter than the time scale at which the strong force of QCD acts, so a top quark decays before it can hadronize, allowing physicists to observe a "bare quark." Thus, they have not been observed as components of any observed hadron, while all other quarks have been observed only as components of hadrons.
simulation. After the Particle shower
has terminated, partons with virtualities on the order of the cut off scale remain. From this point on, the parton is in the low momentum transfer, long-distance regime in which non-perturbative effects become important. The most dominant of these effects is hadronization, which converts partons into observable hadrons. No exact theory for hadronization is known but there are two successful models for parameterization.
The scale at which partons are given to the hadronization is fixed by the Shower Monte Carlo program. Hadronization models typically start at some predefined scale of their own. This can cause significant issue if not set up properly within the Shower Monte Carlo. Common choices of Shower Monte Carlo are PYTHIA
and HERWIG. Each of these correspond to one of the two parameterization models.
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...
, hadronization is the process of the formation of hadron
Hadron
In particle physics, a hadron is a composite particle made of quarks held together by the strong force...
s out of 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 and 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....
s. This occurs after high-energy collisions in a particle 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:...
in which free quarks or gluons are created. Due to postulated colour confinement
Colour confinement
Color confinement, often simply called confinement, is the physics phenomenon that color charged particles cannot be isolated singularly, and therefore cannot be directly observed. Quarks, by default, clump together to form groups, or hadrons. The two types of hadrons are the mesons and the baryons...
, these cannot exist individually. In the Standard Model they combine with quarks and antiquarks spontaneously created from the vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
to form hadrons. The QCD (Quantum Chromodynamics) dynamics of the hadronization process are not yet fully understood, but are modeled and parameterized in a number of phenomenological studies, including the Lund string model
Lund string model
In particle physics, the Lund string model is a phenomenological model of hadronization. It treats all but the highest-energy gluons as field lines, which are attracted to each other due to the gluon self-interaction and so form a narrow tube of strong color field...
and in various long-range QCD
Quantum chromodynamics
In theoretical physics, quantum chromodynamics is a theory of the strong interaction , a fundamental force describing the interactions of the quarks and gluons making up hadrons . It is the study of the SU Yang–Mills theory of color-charged fermions...
approximation schemes.
The tight cone of particles created by the hadronization of a single 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...
is called a jet
Jet (particle physics)
A jet is a narrow cone of hadrons and other particles produced by the hadronization of a quark or gluon in a particle physics or heavy ion experiment. Because of QCD confinement, particles carrying a color charge, such as quarks, cannot exist in free form. Therefore they fragment into hadrons...
. Jets are observed in particle detector
Particle detector
In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
s, rather than quarks, whose existence must be inferred. The models and approximation schemes and their predicted Jet hadronization, or fragmentation, have been extensively compared with measurement in a number of high energy particle physics experiments; e.g. TASSO
Tasso
-People:*Torquato Tasso, the famous Italian 16th-century poet, author of Gerusalemme liberata**Tasso, Lament and Triumph, a symphonic poem by Franz Liszt based on the poet*Bernardo Tasso, his father, also a poet...
, OPAL
OPAL
OPAL is a 20 megawatt pool-type nuclear research reactor that was officially opened on 20 April 2007 at the Australian Nuclear Science and Technology Organisation Research Establishment at Lucas Heights, located in South Sydney, Australia.The main reactor uses are:* Irradiation of target...
, H1
H1 (particle detector)
H1 is a particle detector in operation at HERA in DESY, Hamburg. It began operating together with HERA in 1992. Leptons are collided with protons by HERA in the interaction point of H1. H1 is operated by an internationalcollaboration of about 400 physicists from 42 institutes in 15 countries...
.
Hadronization also occurred shortly after the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...
when the quark-gluon plasma
Quark-gluon plasma
A quark–gluon plasma or quark soup is a phase of quantum chromodynamics which exists at extremely high temperature and/or density. This phase consists of asymptotically free quarks and gluons, which are several of the basic building blocks of matter...
cooled to the temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
below which free quarks and gluons cannot exist (about 170 MeV
MEV
MeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
). The quarks and gluons then combined into hadrons.
A top quark
Top quark
The top quark, also known as the t quark or truth quark, is an elementary particle and a fundamental constituent of matter. Like all quarks, the top quark is an elementary fermion with spin-, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and...
, however, has a mean lifetime of 5*10^-25 seconds, which is shorter than the time scale at which the strong force of QCD acts, so a top quark decays before it can hadronize, allowing physicists to observe a "bare quark." Thus, they have not been observed as components of any observed hadron, while all other quarks have been observed only as components of hadrons.
Hadronization Simulation and models
Hadronization is a very important component of Monte CarloMonte Carlo method
Monte Carlo methods are a class of computational algorithms that rely on repeated random sampling to compute their results. Monte Carlo methods are often used in computer simulations of physical and mathematical systems...
simulation. After the Particle shower
Particle shower
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...
has terminated, partons with virtualities on the order of the cut off scale remain. From this point on, the parton is in the low momentum transfer, long-distance regime in which non-perturbative effects become important. The most dominant of these effects is hadronization, which converts partons into observable hadrons. No exact theory for hadronization is known but there are two successful models for parameterization.
The scale at which partons are given to the hadronization is fixed by the Shower Monte Carlo program. Hadronization models typically start at some predefined scale of their own. This can cause significant issue if not set up properly within the Shower Monte Carlo. Common choices of Shower Monte Carlo are PYTHIA
PYTHIA
PYTHIA is a computer simulation program for particle collisions at very high energies in particle accelerators.-External links:* *...
and HERWIG. Each of these correspond to one of the two parameterization models.