Subject: energetic cosmic ray
This particle was in the EeV range. That is just crazy (the technical term ;-)

This was actually related to my thesis research. We did TeV gamma rays. We would filter out hadronic showers, which this appears to have been (they aren't sure). The energy involved would have generated a Cherenkov shower that would have saturated our instrument, and therefore would have been discarded (i.e. we couldn't glean any information from it if every tube was maxed-out). Our instrument filled the range from ~500MeV to about 1.5TeV. Lower than that wouldn't generate a signal, and higher than that saturated the electronics. EeV is way beyond that.

https://www.universetoday.com/...

When the Amaterasu particle entered Earth's atmosphere, the TAP array in Utah recorded an energy level of more than 240 exa-electronvolts (EeV). Such particles are exceedingly rare and are thought to originate in some of the most extreme cosmic environments. At the time of its detection, scientists were not sure if it was a proton, a light atomic nucleus, or a heavy (iron) atomic nucleus.