Which particle is NOT a lepton?

The particle identified as a quark is not classified as a lepton. Leptons are a category of fundamental particles that do not undergo strong interactions, and they include particles such as electrons, muons, and neutrinos.

Electrons, muons, and neutrinos are all examples of leptons, characterized by their half-integer spin and the fact that they are not subject to the strong nuclear force, which is responsible for holding the nucleus of an atom together. In contrast, quarks are the building blocks of protons and neutrons, participating in the strong force, making them fundamentally different from leptons. Quarks possess a different set of properties, including fractional electric charges, which further distinguishes them from the lepton family.

Understanding the distinction between leptons and quarks is essential in the study of particle physics, as it helps in comprehending how matter is constructed at a fundamental level.