What distinguishes baryons from other particles in terms of structure?

Baryons are distinguished from other particles by their unique structural composition, which is defined as being made up of three quarks. This characteristic is fundamental to their classification within the broader category of hadrons, which also includes mesons—particles that are formed from a quark and an antiquark pair.

Baryons specifically exhibit properties such as being fermions with half-integer spin and following the Pauli exclusion principle, which arises due to their three-quark makeup. Examples of baryons include protons and neutrons, which are essential building blocks of atomic nuclei.

The other information provided in the question clarifies how baryons differ fundamentally from other particles such as leptons—which are a separate class of particles not made of quarks, and mesons, which contain one quark and one antiquark. Baryons can also exist independently, but this characteristic alone does not define their structure, as other types of particles can also exist in isolation. Additionally, baryons made of four quarks do not exist in the standard classification of subatomic particles and are generally not recognized as baryons. Thus, the defining structural feature of baryons remains their composition of three quarks.