**law of conservation of baryon number**states that:

*The sum of the baryon number of all incoming particles is the same as the sum of the baryon numbers of all particles resulting from the reaction.*

In analyzing nuclear reactions, we apply the **many conservation laws**. **Nuclear reactions** are subject to classical **conservation laws for, momentum, angular momentum, and energy **(including rest energies). Additional conservation laws, not anticipated by classical physics, are **electric charge**, **lepton number and baryon number**. Certain of these laws are obeyed under all circumstances, others are not.

**Baryon number** is a generalization of **nucleon number**, which is conserved in nonrelativistic nuclear reactions and decays. The **law of conservation of baryon number** states that:

*The sum of the baryon number of all incoming particles is the same as the sum of the baryon numbers of all particles resulting from the reaction.*

For example, the following reaction has never been observed:

even if the incoming proton has sufficient energy and charge, energy, and so on, are conserved. This reaction does not conserve baryon number since the left side has B =+2, and the right has B =+1.

On the other hand, the following reaction (proton-antiproton pair production) does conserve B and does occur if the incoming proton has sufficient energy (the threshold energy = 5.6 GeV):

As indicated, B = +2 on both sides of this equation.

From these and other reactions, the conservation of baryon number has been established as a basic principle of physics.

This principle provides basis for the **stability of the proton**. Since the proton is the lightest particle among all baryons, the hypothetical products of its decay would have to be non-baryons. Thus, the decay would violate the conservation of baryon number. It must be added some theories have suggested that protons are in fact unstable with very long half-life (~10^{30} years) and that they decay into leptons. There is currently no experimental evidence that proton decay occurs.

## What is Baryon Number

In particle physics, the **baryon number** is used to denote which particles are baryons and which particles are not. Each baryon has a baryon number of 1 and each antibaryon has a baryon number of -1. Other non-baryonic particles have a baryon number of 0. Since there are exotic hadrons like pentaquarks and tetraquarks, there is a general definition of baryon number as:

where n_{q} is the number of quarks, and n_{q} is the number of antiquarks.

The **baryon number is a conserved quantum number** in all particle reactions. The term conserved means that the sum of the baryon number of all incoming particles is the same as the sum of the baryon numbers of all particles resulting from the reaction. A slight asymmetry in the laws of physics allowed baryons to be created in the Big Bang.