HEP In the literature: open

Is the proton lifetime to $e+ \pi0$ below $1e35\,\mathrm{years}$?

In plain words

Grand unified theories predict a proton can decay into a positron and a neutral pion. Huge water detectors watch for this rare event.

Precise statement

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 $1e35\,\mathrm{yr}$.

What would settle it

Hyper-Kamiokande exposure of about 1 to 2 Mt-yr reaching $\sim 1\mathrm{e}35\,\mathrm{yr}$ sensitivity.

Status in the literature

Hyper-Kamiokande construction is under way, with data expected late in the 2020s.