In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. There is currently no experimental evidence that proton decay occurs.
In the Standard Model, protons, a type of baryon, are theoretically stable because baryon number (quark number) is conserved (under normal circumstances; however, see chiral anomaly). Therefore, protons will not decay into other particles on their own, because they are the lightest (and therefore least energetic) baryon.
Some beyond-the-Standard Model grand unified theories (GUTs) explicitly break the baryon number symmetry, allowing protons to decay via the Higgs particle, magnetic monopoles or new X bosons. Proton decay is one of the few observable effects of the various proposed GUTs. To date, all attempts to observe these events have failed.
Read more about Proton Decay: Baryogenesis, Experimental Evidence, Theoretical Motivation
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