Proton decay Totally Explained

Everything about Proton Decay totally explained

In particle physics, proton decay is a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles, usually a neutral pion and a positron. Proton decay hasn't been observed. There is currently no evidence that proton decay exists. In the Standard Model, protons, a type of baryon, are theoretically stable because baryon number is approximately conserved. That is, they won't decay perturbatively into other particles on their own because they're 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 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.

Baryogenesis

One of the outstanding problems in modern physics is the predominance of matter over antimatter in the universe. The universe, as a whole, has a nonzero baryon number density — that is, matter exists. Since it's assumed in cosmology that the particles we see were created using the same physics we measure today, it would normally be expected that the overall baryon number should be zero, as matter and antimatter should have been created in equal amounts. This has led to a number of proposed mechanisms for symmetry breaking that favour the creation of normal matter (as opposed to antimatter) under certain conditions. This imbalance would have been exceptionally small, on the order of 1 in every 10,000,000,000 (10¹⁰) particles a split second after the Big Bang, but after most of the matter and antimatter annihilated, what was left over was all the baryonic matter in the current universe, along with a much greater number of bosons.
Most grand unified theories (GUTs) explicitly break the baryon number symmetry, which would account for this discrepancy, typically invoking reactions mediated by very massive X bosons (X below) or massive Higgs bosons (T). The rate that these events occur is governed largely by the mass of the intermediate X or T particles, so by assuming these reactions are responsible for the majority of the baryon number seen today, a maximum mass can be calculated, above which the rate would be too slow to explain the presence of matter today. These estimates predict that a large volume of material will periodically exhibit spontaneous proton decay even given the much reduced energies available today.

Experimental evidence

Proton decay is one of the few observable effects of the various proposed GUTs, the other major one being magnetic monopoles. Both became the focus of major experimental physics efforts starting in the early 1980s. Proton decay was, for a time, an extremely exciting area of experimental physics research. To date, all attempts to observe these events have failed. Recent experiments at the Super-Kamiokande water Cherenkov radiation detector in Japan indicate that if protons decay at all, their half-life must be at least 10³⁵ years.

Theoretical motivation

Despite the lack of observational evidence for proton decay, some grand unification theories require it. According to some such theories, the proton has a half-life of about 10³⁶ years, and decays into a positron and a neutral pion that itself immediately decays into 2 gamma ray photons:
ť which is far too fast unless the couplings are very small.

Appearance in popular culture

An experiment that proved protons decay was a central plot to an episode of the television legal drama Law & Order.

Further Information

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