Baryon number

Tiny bits make up everything. Some bits join in groups. These groups have a special count. This count helps us know them.

Some groups have three bits. These are called baryons. They have a count of one. Other groups have zero. They are called mesons.

Some bits are not in groups. An electron is one of these. They have a count of zero.

Scientists think this count stays the same. It is like a rule. But some ideas say the rule might break.

No one has seen this break yet. It would be a big find. We are still looking for it.

Everything in our world is made of tiny bits. Some bits are called quarks. Quarks have a special number called a baryon number. This number helps us group the bits together.

Baryons are groups with three quarks. They have a baryon number of +1. Antibaryons have three antiquarks. They have a number of -1. Mesons are different. They have one quark and one antiquark. Their number is 0.

There are even more strange groups. A pentaquark has five parts. It has four quarks and one antiquark. A tetraquark has four parts. It has two quarks and two antiquarks.

Some bits have no baryon number at all. We call these leptons. An electron is a lepton. Photons are also leptons. They all have a number of 0.

Scientists use a rule called conservation. This rule says the total number stays the same. It is like a balance scale. If one side changes, the other must change too. No one has seen this rule break yet. Some big ideas say it might break. We are still looking for these changes.

Scientists study the tiny parts of our universe using special rules. One important rule involves the baryon number. This is a number used to group tiny particles called hadrons. Hadrons are made of even smaller bits called quarks. The baryon number tells us how many quarks are in a group. It also looks at antiquarks, which are the opposite of quarks. This number helps us understand how matter is built.

To find the baryon number, we follow a simple way it works. A baryon is a group with three quarks. These particles have a baryon number of +1. An antibaryon has three antiquarks and a number of -1. Mesons are different because they have one quark and one antiquark. Their baryon number is 0. We also find exotic hadrons like pentaquarks. A pentaquark has four quarks and one antiquark. These also follow the rules of the baryon number.

This idea was used by scientists for a long time. The baryon number was defined before we even knew about quarks. Because of this, scientists gave each quark a value of one third. This makes the math work when quarks join together. In 2015, a group called the LHCb collaboration at CERN found something special. They saw results that looked like pentaquark states. They found these during the decay of bottom Lambda baryons.

Some particles do not have a baryon number at all. These are called leptons. Examples of leptons include the electron, muon, and tauon. Neutrinos are also leptons. Other particles like photons and gluons have a number of 0 too. In the Standard Model, the baryon number is a conserved quantity. This means the total number stays the same during a reaction. The number of quarks going in must match the number coming out.

Scientists wonder if this rule ever breaks. We have never seen the baryon number change in an experiment. However, some big theories say it might happen. Ideas like Supersymmetry or String theory suggest the number could change. One example would be proton decay. We have searched for this using experiments like Kamiokande in 1985. Other searches happened at ILL in 1994 and Super-Kamiokande in 1999. We are still looking for these secrets of the universe.

In particle physics, the baryon number is an additive quantum number. This number helps scientists categorize different types of particles called hadrons. Hadrons are made of even smaller building blocks known as quarks. The baryon number is calculated by looking at the total number of quarks and antiquarks. Quarks carry a value of +1/3, while antiquarks carry a value of -1/3. This system allows physicists to track the balance of matter in a reaction.

To understand how this works, we must look at how quarks combine. Quarks possess a property called color charge, which can be red, green, or blue. Antiquarks have corresponding anticolors, such as anti-red or anti-blue. Because of a rule called color confinement, a hadron cannot have a net color charge. This means the total color must always be "white" or neutral. There are three main ways to achieve this neutral state. One way is to combine three quarks of different colors. This creates a baryon, which has a baryon number of +1. Another way is to combine three antiquarks of different anticolors. This creates an antibaryon, which has a baryon number of -1. Finally, you can combine one quark with one antiquark of the matching color. This creates a meson, which has a baryon number of 0.

Scientists have also discovered more complex groupings called exotic hadrons. These particles follow the same additive rules for their baryon number. For example, a pentaquark is made of four quarks and one antiquark. A pentaquark could have the colors red, green, blue, blue, and antiblue. This combination results in a net baryon number of +1. Another type is the tetraquark, which consists of two quarks and two antiquarks. Since the quark and antiquark values cancel out, a tetraquark has a baryon number of 0. In 2015, the LHCb collaboration at CERN reported results consistent with pentaquark states. They observed these during the decay of bottom Lambda baryons.

Not all particles in the universe are made of quarks. Many particles have a baryon number of exactly zero. These include a group called leptons, such as the electron, muon, and tauon. Neutrinos are also members of the lepton family. Other particles with a baryon number of zero are vector bosons, like the photon and gluons. The Higgs boson is a scalar boson, and the graviton is a hypothetical tensor boson. Because these particles lack quarks, they do not contribute to the total baryon number of a system.

In the Standard Model of physics, the baryon number is considered a conserved quantity. This means that in most reactions, the total baryon number stays the same. The sum of the baryon numbers of the incoming particles must equal the sum of the outgoing particles. However, this conservation is described as an "accidental symmetry." This means it appears to be a rule, but it might not be a fundamental one. Some theories suggest that the baryon number can be violated. These theories include Supersymmetry, Grand Unified Theory, and String theory.

There are specific processes that could cause the baryon number to change. In the Standard Model, nonperturbative effects like sphalerons and instantons can change these numbers. Sphalerons can change the baryon and lepton numbers by multiples of three. This is because the sum of baryon and lepton number, known as B - L, is a conserved quantity. At the very high temperatures of the early universe, these effects might explain why there is more matter than antimatter. Other theoretical processes include proton decay or neutron-to-antineutron oscillation. While these are predicted by some models, proton decay has never been observed in an experiment.

Scientists have conducted many searches to see if the baryon number actually changes. Experiments like Kamiokande in 1985 and ILL in 1994 have looked for these signs. The Super-Kamiokande experiment also conducted searches in 1999. Future projects, such as Hyper-Kamiokande and HIBEAM/NNBAR, are planned to continue this work. Finding a violation of this number would change our understanding of physics. It would link the behavior of tiny particles to the largest structures in the universe, such as black holes.