The discovery and observation of up and down quarks, which are fundamental particles that make up protons and neutrons, did not occur through direct observation of their radiation. Instead, their existence was inferred indirectly through a combination of experimental results and theoretical considerations.
In the 1960s, experiments studying the scattering of high-energy electrons off protons and neutrons revealed a consistent pattern of behavior that couldn't be explained solely by the known particles at the time. These experiments provided evidence for the existence of smaller constituents within protons and neutrons, which were later identified as quarks.
The concept of quarks was introduced independently by Murray Gell-Mann and George Zweig in 1964. They proposed that quarks were the fundamental building blocks of hadrons (particles made of quarks, such as protons and neutrons) and carried fractional electric charges. Gell-Mann named the proposed subatomic particles "quarks" after a line from James Joyce's Finnegans Wake.
However, due to a phenomenon called confinement, which is a property of the strong nuclear force, quarks cannot exist in isolation. They are always found bound together in composite particles, such as protons and neutrons, forming color-neutral combinations.
The subsequent development of quantum chromodynamics (QCD), the theory that describes the strong nuclear force, provided a theoretical framework to understand the behavior of quarks within hadrons. QCD explained why quarks couldn't be observed directly but only inferred through their effects on experimental measurements.
Over time, further experiments, such as deep inelastic scattering experiments, precision measurements, and studies of particle collisions at high energies, provided strong evidence for the existence of quarks and their properties. The collective body of experimental evidence and the theoretical consistency of the quark model led to the acceptance of up and down quarks as fundamental constituents of matter.
To summarize, the existence and properties of up and down quarks were inferred indirectly from experimental observations and theoretical developments in the field of particle physics. Direct observation of their radiation is not possible due to the phenomenon of confinement.