In particle physics

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...

, the Lund

Lund

-Main sights:During the 12th and 13th centuries, when the town was the seat of the archbishop, many churches and monasteries were built. At its peak, Lund had 27 churches, but most of them were demolished as result of the Reformation in 1536. Several medieval buildings remain, including Lund...

 string model is a phenomenological

Phenomenology (science)

The term phenomenology in science is used to describe a body of knowledge that relates empirical observations of phenomena to each other, in a way that is consistent with fundamental theory, but is not directly derived from theory. For example, we find the following definition in the Concise...

 model of hadronization

Hadronization

In particle physics, hadronization is the process of the formation of hadrons out of quarks and gluons. 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...

. It treats all but the highest-energy

Energy

In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...

 gluons as field lines, which are attracted to each other due to the gluon self-interaction and so form a narrow tube (or string) of strong color field

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,...

. (Compare to electric or magnetic field lines, which are spread out because the carrier of the electromagnetic force, the photon

Photon

In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

, does not interact with itself.)

String fragmentation is one of the parton

Parton (particle physics)

In particle physics, the parton model was proposed by Richard Feynman in 1969 as a way to analyze high-energy hadron collisions. It was later recognized that partons describe the same objects now more commonly referred to as quarks and gluons...

 fragmentation models used in the PYTHIA

PYTHIA

PYTHIA is a computer simulation program for particle collisions at very high energies in particle accelerators.-External links:* *...

/Jetset and UCLA event generator

Event generator

Event generators are software libraries that generate simulated high-energy particle physics events.They randomly generate events as those produced in particle accelerators, collider experiments or during the initial phases of the Universe creation....

s, and explains many features of hadronization quite well. In particular, the model predicts that in addition to the particle jets formed along the original paths of two separating 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, there will be a spray of hadron

Hadron

In particle physics, a hadron is a composite particle made of quarks held together by the strong force...

s produced between the jets by the string itself—which is precisely what is observed.

Note: this use of "string" is not the same as in string theory

String theory

String theory is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything , a manner of describing the known fundamental forces and matter in a mathematically complete system...

, in which strings are the fundamental objects of nature rather than collections of field lines.