What is a Hadron?
A hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Unlike leptons (like electrons) which are fundamental particles, hadrons have internal structure. They are the only particles that experience the strong force directly.
Types and Composition
Hadrons are primarily divided into two categories: baryons and mesons. Baryons are made of three quarks (or three antiquarks), such as protons and neutrons. Mesons are made of a quark and an antiquark pair, such as pions and kaons. Each quark carries a fractional electric charge and a 'color charge' which is mediated by gluons, the carriers of the strong force.
An Everyday Example: Protons and Neutrons
The most common examples of hadrons are protons and neutrons, which make up the nuclei of all atoms. A proton consists of two up quarks and one down quark (uud), while a neutron consists of one up quark and two down quarks (udd). These familiar particles are baryons, a class of hadrons.
Role in Atomic Structure and Forces
Hadrons are crucial for the stability of matter, as protons and neutrons form atomic nuclei. The strong nuclear force, which binds quarks together within hadrons and, residually, binds protons and neutrons within the nucleus, is one of the four fundamental forces of nature. Understanding hadrons is essential for comprehending the fundamental building blocks and forces of the universe.
Key Characteristics of Hadrons
Hadrons are always color-neutral, meaning their combination of quarks results in no net color charge. They have a measurable size and internal structure, unlike fundamental particles like leptons. Their interactions are governed by Quantum Chromodynamics (QCD), the theory of the strong interaction.