For interested parties, here's the most recent paper on anisotropy, ie how we know the particles are extragalactic: https://arxiv.org/abs/1709.07321 https://arx

For interested parties, here's the most recent paper on anisotropy, ie how we know the particles are extragalactic: https://arxiv.org/abs/1709.07321 https://arxiv.org/abs/1709.07321 I also worked in this field (Pierre Auger Observatory in the Karlsruhe group) before I "sold out" to join a tech company in late 2010. Might we have met? Back to cosmic ray anisotropy. There was actually a big paper from the Pierre Auger collaboration in 2007 on anisotropy that made it to the cover of Science. It correlated arrival directions with a I catalog of, IIRC, AGNs. I was in my first year in the group so I didn't make the author list yet. I was quite disappointed at the time. Pretty much from the moment of publication, however, the statistical significance we got from the data started decreasing until it was no longer something we were particularly confident in. The collaboration had to publish a note on that. Ouch. We never worked out why this was happening (if other than horrible luck) before I left. Before the publication there had been interesting internal discussions about whether to publish. The astronomers typically felt the significance was plenty by astronomy standards and we were trying to do astronomy with particles after all! The particle physicists tended to want to apply the more conservative thresholds that are common in accelerator physics. After all, what was our detector if not a giant calorimeter? :)