proton

In physics, a positively charged subatomic particle, a constituent of the nucleus of all atoms. It carries a unit positive charge equal to the negative charge of an electron. Its mass is almost 1,836 times that of an electron, or 1.673 × 10^-24 g. The number of protons in the atom of an element is equal to the atomic number of that element. The diameter of the proton is approximately 1.6 × 10^-15 m.

A proton belongs to the baryon group of hadrons and is composed of two up quarks and one down quark. A proton is extremely long-lived, with a lifespan of at least 10³² years.