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Original: "Search for proton decay via $$p \to e^{+}\pi^{0}\pi^{0}$$ and $$p \to \mu^{+}\pi^{0}\pi^{0}$$ in 0.401 megaton-years exposure of Super-Kamiokande I-V"
Physicists have peered deep into matter and set a new record: the proton lives longer than previously thought possible.
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Inside every atom lives a proton. For a long time, it was considered as eternal as matter itself. But theories that unify all forces of nature predict that, sooner or later, the proton will decay. The only question is how long we have to wait.
In the Japanese detector Super-Kamiokande — a giant tank of ultra-pure water — physicists searched for signs of such a decay. They monitored protons for 0.4 megaton-years (that's like watching a million tons of water for a whole year). They were looking for a rare scenario: a proton transforming into a positron and two neutral particles called pions. No one has ever seen this decay.
During the entire run, only one suspicious event was found. But it is indistinguishable from the usual background noise — neutrinos constantly passing through the detector.
This means the proton is even more durable than we thought. The new limit: it lives at least 7.2×$10^{33}$ years. That's a number with 33 zeros — billions of times the age of the universe. If the proton does die, we'll have to wait an unimaginably long time.