A proton, which is a type of baryon, is composed of three valence quarks bound together by the strong nuclear force. The valence quarks in a proton are two up quarks (u) and one down quark (d). These quarks carry fractional electric charges: the up quark has a charge of +2/3e (where "e" represents the elementary charge), and the down quark has a charge of -1/3e.
While the proton is primarily composed of three valence quarks, the internal dynamics of the proton are more complex. According to the theory of quantum chromodynamics (QCD), which describes the strong force, the proton's interactions involve not only the valence quarks but also a sea of virtual quark-antiquark pairs and gluons. These virtual particles continuously fluctuate in and out of existence due to the inherent properties of the quantum vacuum.
These virtual quark-antiquark pairs and gluons are collectively referred to as the "sea quarks" and "sea gluons." However, it's important to note that these virtual particles do not significantly contribute to the proton's overall properties, such as its mass and charge. The dominant contribution to the proton's mass and charge comes from the three valence quarks.
The virtual quark-antiquark pairs in the proton are often visualized as a "cloud" of particles surrounding the valence quarks. The interactions of the valence quarks with this sea of virtual particles play a role in shaping the proton's properties, such as its spin structure and distribution of momentum. However, it's important to understand that these virtual particles do not exist as distinct, observable particles and their contributions to the proton are a result of the underlying dynamics of the strong force.