> The energy of this particle was some 40 million times that of the highest-energy protons that have been produced in any terrestrial particle accelerator.

If it were me observing this, and I didn't observe it again, I would attribute it to something else. However rare, I would consider some phenomenon as part of the sensor (for example decay causing a release of energy), or two particles arriving at the same time, some localised event, etc.

I'm sure they already addressed this, but I would be considering some other source of such a high energy particle. It's just too perfect, why would we see such a high energy particle and nothing inbetween?