proton

In physics, a positively charged elementary particle, a constituent of the nucleus of all atoms. It 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. 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.

In January 2001, scientists at the Kamioka Observatory, Tokyo, Japan, proposed plans for a US$326 million project to study whether protons decay over time. The experiment would involve setting up a tank containing one million tons of water, that would show up decaying protons as faint flashes. Protons are believed by many scientists to have a half-life 20 times the age of the universe.