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Bizarre Particles Keep Flying Out of Antarctica's Ice
- crazynick4 8y agoIf I understand correctly, these particles are entering the earth from space around, say, the North Pole, and the coming out the other side in Antarctica? If so, is it only out of Antarctica? Would that mean they are coming from a specific direction in space? Why can't we observe them simply as they come out of space? Is there something about the process of moving through the earth that makes them more detectable? These may be stupid questions, feel free to vote this down.. Edit: if I understand correctly it seems like it's happenstance and ANITA just happened to be above Antarctica when the cosmic rays shot up through it on those particular occasions, I think
- gog-ma-gog 8y agoIt’s also a matter of signal to noise. Not very many things (other than neutrinos) are detectable when you point a detector straight down into the earth. Contrariwise, you’re swamped with signal when you point a detector at space.
- Gibbon1 8y agoI think it's because both detectors are using the deep ice sheet as part of neutrino detection experiments. ANITA is listening for Askaryan radiation created by neutrino's traveling through ice (from the wiki, I know as much as you). And IceCube is looking for flashes of light created when a neutrino interacts with ice.
- cozzyd 8y agoDisclaimer: I work on ANITA. Also I need to go to bed, so I'm writing this really fast so it probably doesn't make sense. ANITA is a radio telescope attached to a balloon looking for broaband impulsive radio emission in Antarctica. The main purpose is to look for the Askaryan emission from neutrinos interacting in the ice. The Askaryan emission is just the coherent version of the same process (Cerenkov radiation) that produces the flashes of light in IceCube (basically at long wavelengths you can't resolve the charges in a cascade and see a fast moving current density-- there's a negative charge excess because positrons can annihilate with atomic electrons). To detect this Askaryan emission, you need a dense dielectric material (if not dense, no target mass, if not dielectric, then RF won't propagate). Antarctica happens to be both the place you do long duration ballooning (due to all-day sunlight and favorable wind patterns that keep you over land) and the place with the most ice. However, the events discussed here were produced by another channel. ANITA can also see RF emission from cosmic-ray extensive air showers (EAS). The RF emission here mostly comes from the splitting of charges in the showers by the Earth's magnetic field. Because in Antarctica, the magnetic field is approximately vertical, this produces horizontally polarized emission. Because ANITA is so high up (~40 km), EAS development from cosmic rays occurs below the payload, so the most common way for us to observe EAS's from cosmic rays is for the emission to bounce off the ice (because it's very forward-beamed). We can also see atmosphere-skimming showers that miss the ice entirely. As expected, the events that bounce off the ice have a polarity flip compared to the events that miss the ice. The strange events discussed here look like EAS's from air showers, but the RF emission clearly points at the ice and there is no polarity flip from reflection, so the events look like very-energetic upward going air showers. There's no good way to explain upward going air showers in the Standard Model at these energies and observed angle (at lower energies or more grazing angles, tau neutrinos make it through the earth, which can decay to make upward-going air showers). So either there is something wrong with the measurement (we can't think of anything, but we're trying!), we got really unlucky with anthropogenic backgrounds (we think this is very unlikely), or there might be some new physics. For this detection channel, there isn't too much special about Antarctica, just that we're on a balloon looking down so we can see stuff coming from below. The ice could potentially offer a slight enhancement compared to rock, but that's probably not so important. Other observatories looking for upward going showers from tau neutrinos (Pierre Auger) only look at very grazing incidence. There are proposals using fluorescence instead of radio emission (e.g. JEM-EUSO, and the SPB-EUSO balloon mission) that could do more or less the same thing.
- grey-area 8y agoThanks, that was a great explanation of what is going on. How exciting!
- Gibbon1 8y agoThank you, I've been working with microwave wireless transceivers for 20 years now and feel like you're explained what's going on. (I'm not really going to understand the physics) Also a bit gobsmacked you can get Cerenkov radiation in air. On reflection I shouldn't be.
- apankrat 8y agoUnrelated - are you accepting public pull requests for your AnitaFramework project on GH? From a quick glance there are some resource leaks and some such, should be easy to patch up.
- cozzyd 8y agoWe don't have any policy on this really. Like most experiments we are highly manpower-constrained, so I can make no general guarantees about timeliness to respond, but I don't see any problem with it. I'd probably be the one to deal with it anyway :)
- singularity2001 8y agolayman's question: how can it be ruled out that these events result from bounce particles or decay particles of the standard model?
- cozzyd 8y agoI'm not sure what you mean exactly by bounce particles, but I think the answer is probably that at these highly relativistic energies, particles don't really bounce (what would they decay off of) or decay backwards (in the lab frame).
- ynniv 8y agoMods, can we make this a toplevel comment?
- garmaine 8y ago> If so, is it only out of Antarctica? That's the only place there are detectors.
- DavidSJ 8y agoI 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.
- cozzyd 8y agoDisclaimer: 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.
- DavidSJ 8y agoThanks 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?
- cozzyd 8y agoYeah, 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).
- 8y ago
- jakeogh 8y agopaper: https://arxiv.org/pdf/1603.05218.pdf https://arxiv.org/pdf/1603.05218.pdf
- mhandley 8y agoThat's the 2016 Anita paper. There's also a newer Anita paper: https://arxiv.org/abs/1803.05088 https://arxiv.org/abs/1803.05088. The new paper described in the article is this one: https://arxiv.org/abs/1809.09615 https://arxiv.org/abs/1809.09615
- M_Bakhtiari 8y agoUltraghiaccio, perhaps? Romano Scarpa fans should know what I'm talking about.
- M_Bakhtiari 8y agoHmm...looks like I'd better stick to yankee cultural references in the future.
- audunw 8y agoAh, must be the second Stargate ;)
- negamax 8y agoIsn't Earth like a giant rotating magnet? That should create some weird things. Wears sci-fi cap!
- fabatka 8y ago> and it could break physics as we know it. Stopped reading there. I hate that a lot of pop-science articles suggest that the foundations of natural sciences are so shaky that a new finding can turn them upside-down. I've lived together with 50-60 social scientists in a small community during my student years, and I found that they don't have the slightest idea about how thoroughly e.g. special and general relativity have been tested in controlled experiments and every day when they use gps in their smartphones. For them these theories may be true, but who knows? I find it really sad that media that are supposed to bring sciences closer to non-scientists fail this way. EDIT: added last sentence
- crispyambulance 8y ago> and it could break physics as we know it. It's just a case of provocative phrasing to hook the reader. The rest of the article is interesting, does NOT make out-sized claims and even references source material in arxiv for those who are interested. You're expecting too much from a popular science article!
- Moodles 8y agoI agree. It is frustrating. These journalists have an incentive to make their articles as sensational as possible.
- baq 8y agothis writeup by cozzyd just below https://news.ycombinator.com/item?id=18082370 https://news.ycombinator.com/item?id=18082370 is much better and is exactly why I start reading HN links comments first :)
- garmaine 8y agoWell, maybe you shouldn't have stopped reading. A particle that is not described by the standard model DOES "break physics as we know it." That phrasing is typical of science journalism hyperbole, but it is accurate in this case.
- fabatka 8y agoPerhaps my exact point didn't get through well. I find that exactly this kind of phrasing is what's bad, because I fear that it isn't interpreted as "new physics" or "overhalued physics" as in cozzyd's or SideburnsOfDoom's comments, but rather "look, scientists from Newton through Einstein were proved wrong". And the big issue is when this is followed by the thought "How can we know scientists aren't wrong about [insert issue here]?"
- nosjwshere 8y agohttps://en.wikipedia.org/wiki/Hollow_Earth https://en.wikipedia.org/wiki/Hollow_Earth
- deytempo 8y agoIt’s obviously a UFO buried under the ice. Molder proved they are down there.
- torgian 8y agoMaybe it's alien transmissions that are using the Earth as a gigantic radio booster. XD one can dream...
- JBReefer 8y agoRogue ICMP packets performing a reflection attack on those schmucks on Mars
- Zenst 8y agoWhat angle are these particles hitting the detector as it may well be possible these are particles are not traveling thru the entire planet and just a traveling in a chord (a line thru a circle that does not pass thru the centre) and as such, traveling thru far less of the planet. Then there is the aspect that due to the size and the stated interaction with other matter that they are deflected from their original trajectory and could very well appear to be arising from directly below, giving the appearance of passing right thru the planet when they are not. So very much possibly explained with what we already know about said particles.
- Iem6gaoc 8y agoDo you think the scientists overlooked the geometries involved?
- cozzyd 8y agoDisclaimer: I work on ANITA The two relevant events had RF emission from 27 and 35 degrees below the horizontal. If interpreted as emission from upward-going EAS, then the particle would be within a degree or so of that. So they don't go all the way through the Earth, but through a chord long enough that, if our shower energy estimate (which, admittedly, is fraught with peril, we have an order of magnitude errors on that), no standard model particle could have made it through (yes, at high energies, the Earth is opaque to neutrinos).