Comment by DavidSJ
7 years ago
I ask in ignorance, but: could these particles actually have come from space in the normal way (i.e. from above the South Pole) and then just been reflected back up from several meters or so below the surface? That would, on its face, seem to resolve the question about strong vs. weak interaction: they’d be strongly interacting particles that happened to interact and ricochet straight back.
Disclaimer: I work on ANITA
The particles can't be reflected like that. We do see reflected radio emission from (presumably) cosmic ray air showers, but the polarity of the signal undergoes a sign flip on reflection. These signals are peculiar because they are definitely coming from the ice but don't have the sign flip one would expect for a reflection.
Thanks for the answer! Apologies if this question betrays my ignorance further, but what would happen if a signal were reflected twice? Would the polarity flip back?
Yeah, or if it reflected off an interface going from high refraction index to low (e.g. reflecting off an under-ice cavern or something). These are possibilities, but 1) the reflection is far away, so for this to be coherent, it probably must be some massive feature, and 2) ANITA also had a trailing balloon with a calibration pulser from which we could observe both direct and reflected pulses, and from that pulser, we never saw evidence of the reflected pulses not being flipped in polarity. Of course, that did not probe every region of ice and all incident angles, but it seems like if such a strange reflection were likely, we likely would have seen it there.
Nonetheless, we are working on simulating reflections off various ice models to see if we can come up with a plausible optics explanation (like pathological sastrugi).
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How do you know what the original polarity was?
If the radio emission was generated by an air shower in Earth's magnetic field, it's something we can model (and we've seen many other events that are probably reflected air showers so we can check consistency).