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Title: Is the proton lifetime to $e+ \pi0$ below $1e35\,\mathrm{years}$?
Plain: Grand unified theories predict a proton can decay into a positron and a neutral pion. Huge water detectors watch for this rare event.
Precise: Measure or bound $\tau(p \to e+ \pi0)/B$, currently $> 2.4e34\,\mathrm{yr}$ (Super-Kamiokande, 2020, 90 percent CL). Non-supersymmetric $\mathrm{SO}(10)$ models with intermediate scales typically predict $1e34\text{ to }1e36\,\mathrm{yr}$. An answer is a detection or a limit near $1e35\,\mathrm{yr}$.
Settled by: Hyper-Kamiokande exposure of about 1 to 2 Mt-yr reaching $\sim 1\mathrm{e}35\,\mathrm{yr}$ sensitivity.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: Hyper-Kamiokande construction is under way, with data expected late in the 2020s.
Posed since: 1974