Gluon facts for kids
Diagram 1: In Feynman diagrams, emitted gluons are represented as helices. This diagram depicts the annihilation of an electron and positron.
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| Composition | Elementary particle |
|---|---|
| Statistics | Bose–Einstein statistics |
| Interactions | Strong interaction |
| Symbol | g |
| Theorized | Murray Gell-Mann (1962) |
| Discovered | First evidence in 1978 at DESY by PLUTO experiments. Confirmed in 1979 at PETRA by TASSO, MARK-J, JADE, and PLUTO experiments. |
| Types | 8 |
| Mass | 0 (theoretical value) < 1.3 MeV/c2 (experimental limit) |
| Electric charge | 0 e |
| Color charge | octet (8 linearly independent types) |
| Spin | 1 ħ |
| Parity | −1 |
A gluon (pronounced GLOO-on) is a tiny, fundamental particle that helps hold matter together. Think of it as the "glue" that binds even smaller particles called quarks. Gluons are responsible for the strongest force in the universe, known as the strong interaction.
These special particles are like messengers that carry the strong force between quarks. They are massless, meaning they have no weight, and they have a property called spin of 1.
Gluons make quarks stick together to form larger particles called hadrons. The most famous hadrons are protons and neutrons, which make up the center of every atom.
Unlike other force-carrying particles, gluons also carry a "color charge" themselves. This means they not only pass on the strong force but also feel it. This makes the strong force very unique and powerful.
The name "gluon" was created by scientist Murray Gell-Mann in 1962. He chose the name because gluons act like an adhesive, or glue, keeping the tiny parts of atoms tightly bound.
Contents
What Makes a Gluon Special?
Gluons are a type of particle called a vector boson. This means they have a specific kind of spin, which is a bit like how a planet spins. For gluons, this spin is 1.
Because gluons are massless, they travel at the speed of light. Scientists have done experiments to check if gluons have any mass, and they found that if gluons have any mass at all, it must be incredibly tiny, almost zero.
Another interesting property is their "parity," which is a way scientists describe how a particle behaves when its mirror image is considered. Gluons have a negative intrinsic parity.
How Many Types of Gluons Are There?
You might think there's just one type of gluon, but scientists have discovered there are actually eight different kinds! This is quite different from the photon, which carries the electromagnetic force and only has one type.
Gluons carry something called "color charge". This isn't like the colors you see, but a special property that quarks and gluons have. Quarks come in three "colors": red, green, and blue. Antiquarks have "anticolors": anti-red, anti-green, and anti-blue.
Gluons are unique because they carry both a color and an anticolor at the same time. For example, a gluon could be red-anti-green. If you combine all the possible colors and anticolors, you get nine combinations. However, one of these combinations is "colorless" and doesn't exist as a free gluon. This leaves us with the eight types of gluons that we observe.
Why Hadrons Are "Colorless"
Particles like protons and neutrons, which are made of quarks, always appear "colorless" to the outside world. This means their internal color charges balance out perfectly, similar to how mixing red, green, and blue light can make white light. This "colorless" state is called a "color singlet."
Because hadrons are colorless, the strong force doesn't reach out far from them. This is why you don't feel the strong force from a proton or neutron directly, only the nuclear force (which is a leftover effect).
Gluons: The Ultimate Binders
Because gluons carry color charge, they interact strongly with each other, not just with quarks. Imagine the strong force as a super-strong rubber band connecting quarks. When you try to pull two quarks apart, this "rubber band" (called a flux tube) gets stronger and stronger.
This incredible strength means that quarks are always "confined" or trapped inside larger particles like hadrons. You can never find a single, free quark on its own! The strong force is so powerful that it's limited to a very tiny range, about the size of an atomic nucleus.
If you try to pull quarks apart with enough energy, instead of breaking the connection, new quark-antiquark pairs are created from the energy. It's like trying to break a rubber band, but instead, it just creates more rubber bands!
Glueballs and Quark-Gluon Plasma
Scientists believe that particles made entirely of gluons, called glueballs, might exist. These would be very exotic and interesting particles.
Under extreme conditions, like those found in the early universe or inside powerful particle accelerators, matter can reach incredibly high temperatures and pressures. In these conditions, quarks and gluons can break free from their confinement and form a special state of matter called quark–gluon plasma. In this plasma, quarks and gluons move around freely, almost like a liquid.
Discovering Gluons: A Scientific Journey
Scientists first found evidence of gluons in experiments during the late 1970s.
Early Discoveries at DESY
In 1978, the PLUTO detector at the DORIS particle accelerator in DESY, Germany, found the first hints of gluons. They observed a special event where a particle decayed into three "jets" of other particles. This was interpreted as a sign that three gluons were involved. Later studies confirmed that gluons have a spin of 1.
A year later, in 1979, at a more powerful accelerator called PETRA (also at DESY), scientists saw similar three-jet patterns. Experiments like TASSO, MARK-J, and PLUTO clearly showed these jets, which were understood as a quark, an antiquark, and a gluon being produced. These findings further confirmed the gluon's spin of 1.
Gluons in Protons and Extreme Conditions
Later, experiments at the HERA collider at DESY, from 1996 to 2007, helped scientists learn more about gluons inside protons. They measured how many gluons are in a proton and how they move. The HERMES experiment also studied how gluons contribute to the proton's spin.
The idea that quarks are always confined by gluons has been proven because scientists have never found a free quark.
In 2000, at CERN, scientists observed a new state of matter called quark–gluon plasma during heavy-ion collisions. This plasma is where quarks and gluons are no longer confined inside hadrons. This exciting discovery was confirmed by several experiments at the Relativistic Heavy Ion Collider (RHIC) in the United States between 2004 and 2010. The CERN Large Hadron Collider (LHC) also confirmed the existence of quark-gluon plasma in 2010 with its ALICE, ATLAS, and CMS experiments.
Future Research
The Jefferson Lab in Virginia, USA, is one of the facilities researching gluons. In December 2019, the US Department of Energy chose the Brookhaven National Laboratory in New York to host a new electron-ion collider. This new machine will help scientists study gluons and the strong force even more closely.
See also
In Spanish: Gluon para niños
- Quark
- Hadron
- Meson
- Gauge boson
- Quark model
- Quantum chromodynamics
- Quark–gluon plasma
- Color confinement
- Glueball
- Standard Model
- Three-jet event
- Color charge
