The fundamental particles of the universe are the building blocks of matter and are categorized into two main types: elementary particles and composite particles.
Elementary particles: These are particles that are not composed of smaller constituents. The Standard Model of particle physics, which is our current framework for understanding particle physics, identifies several types of elementary particles:
Quarks: Quarks are the building blocks of protons and neutrons, which are found in the atomic nucleus. There are six types, or flavors, of quarks: up, down, charm, strange, top, and bottom.
Leptons: Leptons are particles that include electrons, muons, and taus, as well as their associated neutrinos. Electrons are familiar as the negatively charged particles surrounding atoms, while neutrinos are neutral and have very little interaction with matter.
Gauge Bosons: These are particles that mediate the fundamental forces in nature. They include photons (associated with electromagnetism), W and Z bosons (associated with the weak nuclear force), and gluons (associated with the strong nuclear force).
Higgs Boson: The Higgs boson is a particle associated with the Higgs field, which gives other particles mass according to the mechanism known as the Higgs mechanism.
Composite particles: These are particles that are composed of combinations of elementary particles. The most well-known composite particles are protons and neutrons, which are made up of quarks held together by the strong nuclear force. Atoms, which form the basis of ordinary matter, are composed of a nucleus (made of protons and neutrons) surrounded by electrons.
The interactions between particles are mediated by the fundamental forces in nature:
Electromagnetic Force: It is carried by photons, and charged particles (such as electrons and protons) interact through the exchange of photons.
Weak Nuclear Force: It is responsible for processes like radioactive decay. The W and Z bosons mediate this force, allowing particles to change their types (for example, a neutron decaying into a proton, electron, and an electron antineutrino).
Strong Nuclear Force: This force binds quarks together to form protons and neutrons within atomic nuclei. Gluons mediate this force, and it is responsible for the stability of atomic nuclei.
Gravitational Force: This force is associated with the interaction of mass and energy, as described by Einstein's general theory of relativity. It acts on all particles with mass and is responsible for the attraction between objects in the universe.
Understanding how these fundamental particles interact with each other and the forces they experience is a fundamental goal of particle physics. Scientists study these interactions through particle accelerators and detectors, aiming to deepen our understanding of the fundamental nature of the universe.