The standard model of particle physics is a theoretical model that was formalized to describe the fundamental forces (except gravity) and predict the many unknown particles of the universe. The standard model altogether has 19 particles. These particles help explain the mechanism of the forces of the universe.
The theory had predicted many unknown particles whose existence were successfully confirmed experimentally later on. For example, the quarks and the bosons. The first quarks were discovered in the 1970s and the neutrino in 2000. The most recent addition to this model was made in 2012 – the discovery of the Higgs boson. The standard model is divided into 2 major groups – the Fermions and the Bosons.
All the particles that have a half-integer spin (+1/2 or -1/2) are classified as Fermions. The Fermions are again divided into two groups, namely the Leptons and the Quarks. The Leptons include the Electron and its heavier versions, the Tau and Muon and their respective neutrino forms – the Electron-Neutrino, the Tau-Neutrino and the Muon-Neutrino. The quarks are of six types namely Top, Bottom, Up, Down, Strange and Charm. The Up and Down quarks are known to form the protons (2 Ups and 1 Down) and neutrons (2 Downs and 1 Up) of the atom. The electrons neutralize the atom and the Tau and Muons exist for a short span before they decay into electrons.
All particles that have a spin of 1 or 2 are classified as a Boson. The bosons include 5 particles. They are the gluons (8 types), the W and Z bosons, the photons and the Higgs Boson. The gluons are responsible for the strong nuclear force which holds the nucleus of an atom together, similar to gluing them together (thus the name gluons). The W and Z bosons are responsible for weak nuclear force (responsible for radioactive decay) and the Higgs boson is responsible for giving all the particles their mass. The photon is responsible for the production of the electromagnetic force.
Even though very successful, the standard model has many limitations. The standard model has failed to interweave gravity into itself. It also failed to explain the phenomenon of the expansion of the universe and the existence of dark matter and energy. To solve the mystery of gravity, another particle has been predicted, the Graviton- the particle that conveys gravity. The particle has not been discovered yet, but, a lot of research and experiments are being done to prove the existence of this particle.
The standard model is an amazing theory that relates all the fundamentals forces to the Elementary particles of the universe.