A tale of two mysteries: ghostly neutrinos and the proton decay puzzle

AT SOME point in our lives, most of us learn that atoms are comprised of three types of particle: neutrons, protons and electrons. Each has distinct properties. The electron and proton have opposite electrical charge from one another, while the neutron lacks an electrical charge entirely. The electron is also an elementary particle – not comprised of any other entities – while the proton and neutron are both composite particles, each made of three quarks (which are themselves elementary).

From a category standpoint, protons and…