Yes, the existence of quarks has been experimentally established through a wide range of experiments conducted over several decades. While quarks themselves cannot be observed directly due to color confinement, their existence is inferred from the evidence obtained through high-energy particle physics experiments.
One of the key experimental pieces of evidence for quarks came from deep inelastic scattering experiments conducted at the Stanford Linear Accelerator Center (SLAC) in the 1960s and 1970s. These experiments involved firing high-energy electrons at protons and neutrons to probe their internal structure. The scattering patterns observed in these experiments provided clear indications that protons and neutrons possess point-like constituents, which were identified as quarks.
Furthermore, a series of experiments at various particle accelerators, including the Stanford Linear Collider (SLC), the Large Electron-Positron Collider (LEP), and the Large Hadron Collider (LHC), have provided extensive evidence for the existence of quarks. These experiments have studied the properties and interactions of quarks and have consistently confirmed the predictions made by the Standard Model of particle physics, which incorporates quarks as fundamental particles.
Additionally, the theory of quantum chromodynamics (QCD), which is the fundamental theory describing the interactions of quarks and gluons via the strong nuclear force, has been highly successful in explaining and predicting the behavior of quarks and their interactions. The precision of experimental measurements and the agreement between theoretical predictions and experimental results provide strong evidence for the existence of quarks.
It's worth noting that the discovery of quarks was a cumulative effort involving multiple experiments, theoretical developments, and the convergence of evidence from different sources. The experimental confirmation of quarks and the subsequent development of the Standard Model have greatly advanced our understanding of the fundamental particles and their interactions.