The discovery of quarks was achieved through a combination of experimental evidence and theoretical understanding. Here's a brief overview of the process:
Early observations: In the 1960s, experiments studying the scattering of high-energy particles, such as electrons or muons, off atomic nuclei revealed that nucleons (protons and neutrons) were not elementary particles. Instead, they exhibited an internal structure, suggesting the presence of smaller constituents.
Quark model: In 1964, physicists Murray Gell-Mann and George Zweig independently proposed the quark model to explain the observed patterns in particle interactions. According to the model, quarks are fundamental particles carrying fractional electric charges (-1/3 or +2/3) and possess a property called "color" (a property related to the strong nuclear force).
Deep inelastic scattering: In the late 1960s and early 1970s, experiments involving deep inelastic scattering, particularly at the Stanford Linear Accelerator Center (SLAC) and the European Organization for Nuclear Research (CERN), played a crucial role in confirming the existence of quarks. By firing high-energy electrons or muons at protons and neutrons, scientists observed that the scattered particles revealed point-like constituents inside the nucleons, suggesting the presence of quarks.
Evidence accumulation: Over the years, a wealth of experimental evidence from particle colliders, such as the Large Hadron Collider (LHC) at CERN and its predecessors, provided further confirmation of the quark model. These experiments studied the interactions and decay processes of particles, revealing the intricate behaviors of quarks and confirming their existence.
It's important to note that quarks cannot be observed as free particles due to a phenomenon known as confinement. Quarks are always confined within larger particles (such as protons, neutrons, or mesons) due to the strong nuclear force. However, their properties and existence are inferred through the analysis of experimental data and theoretical frameworks such as quantum chromodynamics (QCD), which describes the interactions of quarks and gluons within the framework of the Standard Model of particle physics.