The classification of the top quark as a fundamental particle is based on its intrinsic properties and behavior within the framework of particle physics. While it is true that the top quark can decay into other quarks, this does not negate its fundamental nature. Let me explain further.
In particle physics, fundamental particles are defined as elementary particles that are not known to have any substructure or internal constituents. These particles are considered to be indivisible and are not composed of smaller particles. The top quark is one of the six known quarks and is classified as a fundamental particle because it is not known to have any substructure.
The top quark is the heaviest known elementary particle, and as such, it is very unstable. It decays rapidly before it can form bound states or hadrons. When the top quark decays, it predominantly transforms into a W boson and a bottom quark. The W boson is another fundamental particle responsible for the weak nuclear force. The bottom quark is also a fundamental particle and one of the six types of quarks.
The decay of the top quark into a W boson and a bottom quark occurs through the weak interaction, one of the fundamental forces in nature. This decay process is governed by the laws of particle physics and is consistent with the behavior expected from a fundamental particle.
It is important to note that the decay of a particle does not change its fundamental nature. Many fundamental particles can decay into other particles while still retaining their own fundamental properties. The decay process simply reflects the transformation of the original particle into different particles according to the rules of particle interactions.
In summary, the classification of the top quark as a fundamental particle is based on its intrinsic properties and its behavior within the framework of particle physics. While it can decay into other quarks, this does not undermine its fundamental status. The decay process is a natural consequence of the top quark's interaction with other particles and forces in the universe.