Another impressive one: Ultra high energy cosmic rays have been detected to 3e20 eV (300 EeV; detected by the Fly's Eye Collaboration). They're nuclei, however, so the rest mess is at least about 10000x higher.

https://en.m.wikipedia.org/wiki/Ultra-high-energy_cosmic_ray

If you're interested in popular science but haven't read about this before, consider following the link to the GZK cutoff from that page. It's super cool.

I used to work for the Pierre Auger Observatory. Happy to try to answer any questions if folks are curious. :)