The proton is a subatomic particle that belongs to the category of baryons. According to our current understanding in particle physics, protons are composed of smaller particles called quarks. Quarks are elementary particles and are considered the fundamental building blocks of matter.
The quark model, proposed in the 1960s by physicists Murray Gell-Mann and George Zweig, describes the proton as being composed of three quarks. Specifically, the proton is composed of two up quarks and one down quark. The up quark has a positive charge of +2/3 elementary charge, while the down quark has a negative charge of -1/3 elementary charge. The combination of these charges results in the proton's overall positive charge of +1 elementary charge.
The evidence supporting the existence of quarks and their presence within protons comes from a variety of sources:
Deep inelastic scattering: Experiments involving the scattering of high-energy electrons or other particles off protons and other atomic nuclei have provided evidence for the existence of quarks. By studying the distribution of scattered particles, scientists have observed the presence of point-like constituents within protons, which are consistent with the behavior of quarks.
Particle accelerator experiments: High-energy particle accelerators, such as the Large Hadron Collider (LHC), have allowed scientists to probe the internal structure of protons in great detail. These experiments involve colliding particles at high energies, and the resulting interactions provide evidence for the presence of quarks within protons. Measurements of particle scattering angles, energy distributions, and other properties have been consistent with the quark model.
Quark confinement: One of the key aspects of the quark model is a phenomenon known as quark confinement. According to this principle, quarks cannot exist as isolated particles in free form. Instead, they are bound together within composite particles, such as protons and neutrons. The experimental observation of confined quarks within protons and other particles supports the concept of quark confinement.
Conservation laws and quantum numbers: The quark model also provides a framework to explain the conservation of various quantities, such as electric charge, baryon number, and spin. The properties of quarks and their combinations within protons satisfy these conservation laws and quantum numbers, providing further evidence for their existence.
It's important to note that our understanding of the subatomic world is based on a combination of experimental evidence, theoretical models, and mathematical frameworks. The existence and properties of quarks within protons have been extensively studied and are supported by a wealth of experimental data and theoretical consistency.