8 ms·
The physics anomaly no one talks about: What’s up with those neutrinos?
- hprotagonist 5y agoThe probable boring answer, mentioned near the end, is that at a detection rate of 500 events per 15 years of experiment runtime, statistical power comes slowly.
- ncmncm 5y agoBut, as noted, that already happened. Six sigma is six sigma. To demand better than that amounts to special pleading. It looks like people just wish this would go away, like the failure of the galactic rotation curves. What is strange is that this might be a place to park dark matter, catnip nowadays. Usually when this sort of thing happens in cosmology, astrophysics, or particle physics, it is because most physicists hate working with the mathematics required, and hope somebody else will tell them they were right to ignore it.
- contravariant 5y agoI suppose we should be a bit careful about limits like that when an experiment is run continuously, but 6 sigma is a pretty high bar to clear.
- hprotagonist 5y agowe have a confirmed discrepancy at six sigma, sure. wanna bet how long it'll take to figure out _how_, at such a low detection rate? We're at "we've confirmed there's a bug", not "here's the repro, traceback, and by the way if you fix these four lines it'll work again".
- Iolaum 5y agoComing up with potential "tracebacks" is how theoretical physicists make papers and get citations. And then you use them to design a proper experiment that will shed light to other aspects of this anomaly. But for some reason this process ain't starting.
- hprotagonist 5y ago> But for some reason this process ain't starting. or, 2.5 years, one of which was a global pandemic, is not enough time to design, begin, and publicize a series of experiments that take a few decades to produce data in quantity to continue investigating new physics.
- ncmncm 5y agoAgain: the next step is not more experiments. The experiments are done, and confirmed the discrepancy. The next step is theorizing, which can be done in isolation, relatively unaffected by pandemic. That is what is now neglected. After hypotheses have been shown to be plausible, i.e. account for the result correctly, yet consistent with other results, it will be time to design experiments to choose among them. So, no, the silence is not consistent with normal process AIUI.
- zzt123 5y agoThere are theories. Such as the discrepancy being due to sterile neutrinos (also explaining dark matter). Confirming or rejecting through data is currently underway, is not at six sigma, and won’t be for years due to rareness and difficulty of detecting events. So it isn’t being talked about since we are in the lurch.
- ncmncm 5y agoWe have sketches of hypotheses. What we lack are detailed predictions; and refereed papers to exposite them, and to compete. Absent such predictions, it doesn't much matter how much more data you collect.
- techdragon 5y agoNot a professional physicist but… Given the absurdly low rate of detection, it feels like a focused experiment designed explicitly to maximise detection is warranted. Difficulty of neutrino experiments aside, this is physics! If we want more detection events we just need to make more particles and/or build a bigger detection apparatus. I don’t necessarily think there’s much benefit to a “larger volume” detector in this particular experiment (MiniBooNE) due to beam width and spreading rate, but I don’t see how having one or two more identical detectors lined up along the generated neutrino‘s path wouldn’t help. Building a more “powerful” neutrino production system, even as simply as just having an accelerator with a higher particle flux would likely increase this factor. If people are arguing over possible issues in the experiment design (which there do appear to be concerns here, but grain of salt as IANAP) then dialling the experiment parameters up will should make any experiment specific effects more obvious as there will now be two sets of data points that can be correlated by the experiment parameters to fill out such effects.
- deleted 5y ago[deleted]
- mrfusion 5y agoIt’s weird I submitted this yesterday. I wonder why it let the same submission in. Different urls somehow?
- frumiousirc 5y agoI'm surprised Sabine did not bring her usual drama and controversy to this one and talk about the fact that there is, shall we say, "extreme tension" between the results from LSND/MiniBooNE and those of other experiments. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.151801 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.11... The 4th figure is the money shot.
- ncmncm 5y agoIt is rare to see two-sigma results like this reported in physics. Or did I misunderstand?
- tsimionescu 5y agoThere was a 2 sigma result, that has later been confirmed by a 4.9 sigma result from a new experiment with a new detector, giving now a combined 6 sigma confidence.
- ncmncm 5y agoThe paper I asked about reports a 2 σ result. That is distinct from the other 4.7 σ and 3.8 σ results mentioned in TFA, which combined yield a 6. AFICS nobody has suggested this one may be combined with anything. So, my question remains open: why did a 2 σ result merit publication?
- maxnoe 5y agoBecause outcomes of (in this case even large, complex, expensive) experiments should be published independent of outcome?
- civilized 5y agoUnpaywalled https://escholarship.org/content/qt496002sb/qt496002sb.pdf https://escholarship.org/content/qt496002sb/qt496002sb.pdf I don't have the background to interpret these figures, and based on a quick search for MiniBooNE mentions in the paper, the authors don't seem to say that MiniBooNE is an outlier relative to all the other experiments. Where does the paper talk about the tension? EDIT: based on the comments below, it sounds like the tension is between appearance-based and disappearance-based experiments, and isn't necessarily about a single experiment being an outlier relative to others?
- neurtrinosfake 5y agoNeutrons ain't real therefore neutrinos ain't real https://www.youtube.com/watch?v=gYHGdBqI7z4 https://www.youtube.com/watch?v=gYHGdBqI7z4
- deleted 5y ago[deleted]
- fuzzfactor 5y ago>Maybe people just don’t like neutrinos? My sentiment exactly.
- tim333 5y agoThere's a poem about that https://www.symmetrymagazine.org/article/february-2011/deconstruction-cosmic-gall https://www.symmetrymagazine.org/article/february-2011/decon...
- fuzzfactor 5y agoI appreciate that. It was truly as uplifting as it could be.
- LatteLazy 5y agoTo be fair, they are sort of boring. They don't do anything, there is no use for them really, they don't even have many properties... The only real effect they have is making physicists' maths a little more complex (or slightly wrong if they forget them).
- rpz 5y agoWhy do we need a particle accelerator to run experiments on neutrinos, given their apparent abundance? Is there any other way to observe neutrinos without a particle accelerator?
- ISL 5y agoThat's a good and subtle question, with multiple relevant answers: 1) As _Microft says in a sibling reply, the reason is because for this type of experiment, the researchers were studying short-baseline oscillations. A curious property of neutrinos is that they oscillate -- we interact with them through their "flavor", but they propagate through space in a mixture of flavor eigenstates, so a neutrino that is created as an electron-type neutrino can interact later as a muon-type (or tau-type) neutrino. LSND and MiniBooNE study short-baseline oscillations, where L/E (the distance travelled divided by the particle energy) is very small, a few meters on a ~1MeV neutrino. By comparison, almost all the (vast number!) neutrinos that pass through each of us each second come from much farther away. Most of them come from the Sun, so their origin is distributed over a sphere 100x the diameter of the Earth (and, to make matters worse, something called the MSW-effect scrambles things further). So, people who study these effects either build an accelerator or snuggle up next to a reactor. In principle, one could use the existing neutrinos from the Sun to do this sort of experiment, but one would need a material capable of blocking all of, say, the electron-type neutrinos from the Sun. If such a thing existed, we could place a detector a few meters away from that filter and watch for electron-type neutrinos to reappear. Alas, the only known material perhaps capable of achieving such a task exists for a fraction of a second inside core-collapse supernovae -- the extremely dense infalling matter is so dense that it can actually trap some of the outgoing neutrinos.... until the neutrino pressure blows it apart. 2) In this specific case, the experiments were originally done with muon anti-neutrinos. The easiest way to get those is with a particle accelerator. 3) One can also attempt to get at this sort of thing (though the approach has different sensitivity/systematics) through reactor-neutrino experiments, as one of the downvoted posts below suggests. For the shortest baselines, though, there's probably really nothing like a beam-experiment. 4) (an aside) One thing that Hossenfelder doesn't really address in the article: There are still systematic-uncertainty questions around LSND and Mini/MicroBooNE. The modern experiment has addressed many of them, but not all. The experiments are difficult and the anomalies have their quirks. Yes, the combined result reaches a statistical power of ~6-sigma, but I don't think you'll have to look too far to find credible experimentalists who have concerns about the result. This is in contrast to something like the Higgs, where the discovery was fairly clean and simultaneously confirmed by two groups. LSND was huge news back in the day, but the difficulty/expense of replication and the substantial experimental challenges mean that the situation remains fairly murky.
- wintercarver 5y agoTangential, but for those interested in large-scale neutrino physics projects check out the successor to Japan’s Super-Kamiokande experiment, Hyper-Kamiomande: https://en.wikipedia.org/wiki/Hyper-Kamiokande https://en.wikipedia.org/wiki/Hyper-Kamiokande
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- SubiculumCode 5y agoNo one talking about? Except for all these papers? https://scholar.google.com/scholar?start=0&q=MiniBooNE&hl=en&as_sdt=0,5&as_ylo=2017 https://scholar.google.com/scholar?start=0&q=MiniBooNE&hl=en...
- GOONIMMUNE 5y ago> Now, to be fair, neutrino-mixing in and by itself isn’t all that weird. Indeed, quarks also do this mixing, it’s just that they don’t mix as much. That *neutrinos mix is weird because neutrinos can only mix if they have masses. But we don’t know how they get masses. Could someone explain to a layman why "neutrinos can only mix if they have masses"? Perhaps I don't understand what it means to "mix"
- LatteLazy 5y agoI believe... Particles without mass are required to travel at the speed of light. Particles traveling at the speed of light don't experience time in their own frame of reference. For instance a photon is emitted and absorbed at the same instance from its point of view. So they have no time to do anything like change properties.