In the framework of quantum field theory (QFT), the most fundamental particles are typically considered to be the elementary particles. Elementary particles are particles that are not known to have any substructure or internal constituents. They are the building blocks of matter and are described by quantum fields.
In the Standard Model of particle physics, which is the prevailing theory that describes the known elementary particles and their interactions, the most fundamental particles are divided into two categories: fermions and bosons.
Fermions are particles that obey Fermi-Dirac statistics, which means they follow the Pauli exclusion principle and have half-integer values of spin. Fermions include quarks, which are the constituents of protons and neutrons, as well as leptons such as electrons and neutrinos. There are six types of quarks and six types of leptons, each with their respective antiparticles.
Bosons, on the other hand, are particles that obey Bose-Einstein statistics, which means they do not follow the Pauli exclusion principle and have integer values of spin. Bosons include particles such as photons (particles of light), gluons (mediators of the strong nuclear force), and the W and Z bosons (mediators of the weak nuclear force). The Higgs boson, discovered in 2012, is also an elementary particle within the Standard Model.
It is important to note that while the elementary particles are considered fundamental in the context of the Standard Model, the concept of what is truly fundamental may evolve as our understanding of physics advances. The search for a more comprehensive theory, such as a theory of quantum gravity, aims to uncover a deeper level of fundamental entities and their interactions beyond the Standard Model.