According to our current understanding in particle physics, quarks are considered fundamental particles. They are not believed to be composed of any smaller constituents.
In the framework of the Standard Model, which is the prevailing theory describing elementary particles and their interactions, quarks are considered point-like particles with no known substructure. They are categorized as fundamental along with other elementary particles like electrons and neutrinos.
The notion of splitting quarks into smaller components is not supported by our current understanding. Quarks are subject to a phenomenon known as confinement, which means they are always found in bound states called hadrons. This confinement prevents quarks from existing in isolation and makes it impossible to observe them as free particles.
When quarks combine to form hadrons (such as protons and neutrons), they are held together by the strong nuclear force mediated by particles called gluons. The strong force becomes stronger as quarks are pulled apart, making it increasingly difficult to separate them. This phenomenon is known as asymptotic freedom, and it prevents quarks from being isolated or studied in isolation.
It's important to note that while quarks are currently considered fundamental particles, scientific understanding is always subject to revision and improvement. Future discoveries or advancements in our understanding may reveal new insights or substructure within quarks. However, as of now, quarks are considered fundamental constituents of matter.