[HN Gopher] The physics anomaly no one talks about: What's up wi...
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The physics anomaly no one talks about: What's up with those
neutrinos?
Author : nsoonhui
Score : 149 points
Date : 2021-09-19 08:51 UTC (14 hours ago)
(HTM) web link (backreaction.blogspot.com)
(TXT) w3m dump (backreaction.blogspot.com)
| [deleted]
| mrfusion wrote:
| It's weird I submitted this yesterday. I wonder why it let the
| same submission in. Different urls somehow?
| Tomte wrote:
| Several hours later is usually treated as a new submission. You
| can submit yourself again the next day (or later the same day).
| mrfusion wrote:
| It seems like that's normally the case but I've had certain
| articles I can resubmit for 10 days or more.
| mrfusion wrote:
| Thanks. And to the other commenter. That's probably what
| happened. No biggy.
| _Microft wrote:
| The URL you submitted has a trailing parameter while this one
| does not. Maybe this is why it did not get automatically
| merged.
| SubiculumCode wrote:
| No one talking about? Except for all these papers?
| https://scholar.google.com/scholar?start=0&q=MiniBooNE&hl=en...
| frumiousirc wrote:
| I'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.11...
|
| The 4th figure is the money shot.
| lvs wrote:
| She really doesn't explain the basic research problems well,
| and I'm still mystified as to why she gets so much traction
| here.
| topynate wrote:
| She has a very empirical way of looking at things which is
| somewhat uncommon in theoretical physicists and appeals to
| interested outsiders who haven't been "inducted" into string
| theory or what have you. E.g. we might be able to do without
| dark energy, so why put so much emphasis on dark energy? We
| don't even see one superparticle at LHC, but grad students
| are still being pushed into stringy shit - why not cut our
| losses? Or on the flip side, here's a 6 sigma result!!! - why
| don't her peers seem to care?
|
| The other side would be someone like Lubos Motl, who used to
| be quite popular too. His main point is that the mathematical
| completeness and coherence of string theory means it's the
| only game in town. Which, that might be a fair point, for all
| I know, but I'm a maths grad and I can only vaguely
| appreciate what he's going on about most of the time. It just
| needs a lot of study to get to grips with these theories well
| enough to judge them in the absence of confirmatory empirical
| evidence.
| ncmncm wrote:
| It is rare to see two-sigma results like this reported in
| physics. Or did I misunderstand?
| tsimionescu wrote:
| There 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 wrote:
| The paper I asked about reports a 2 s result.
|
| That is distinct from the _other_ 4.7 s and 3.8 s 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 s result merit
| publication?
| maxnoe wrote:
| Because outcomes of (in this case even large, complex,
| expensive) experiments should be published independent of
| outcome?
| civilized wrote:
| Unpaywalled
| 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?
| bazzargh wrote:
| They do mention it, it's at the end of their conclusions:
|
| "The results explicitly show the strong tension between null
| results from disappearance searches and appearance-based
| indications for the existence of light sterile neutrinos." p7
|
| So yes they are saying there is tension between disappearance
| and appearance experiments, which is which?
|
| "In this analysis, the measurement of muon (anti)neutrino
| disappearance by the MINOS experiment is combined with
| electron antineutrino disappearance measurements from the
| Daya Bay and Bugey-3 [16] experiments using the signal confi-
| dence level (CLs) method [17, 18]. The combined results are
| analyzed in light of the muon (anti)neutrino to electron
| (anti)neutrino appearance indications from the LSND [8] and
| MiniBooNE [9] experiments." p3
|
| So yes they are saying there is tension between MiniBooNE
| results and MINOS, Bugey-3. I've no insight into the results
| either but GP's characterization of this paper was accurate.
| [deleted]
| SiempreViernes wrote:
| uh,they do say "Regions of parameter space to the right of
| the red contour are excluded." you can see for yourself where
| mosto of the miniBoone resylts lie. By the way, why not link
| the preprint? https://arxiv.org/abs/1607.01177
|
| The existence of a contradiction with other experiments was
| also something that was reported at the time:
|
| > Despite the affirmation of LSND's 20-year-old results,
| physicists have not concluded that there is a fourth neutrino
| species. The findings directly contradict those by a diverse
| set of experiments, including the Main Injector Neutrino
| Oscillation Search, the Daya Bay Reactor Neutrino Experiment,
| and the IceCube Neutrino Observatory
|
| https://physicstoday.scitation.org/do/10.1063/PT.6.1.2018061.
| ..
| wintercarver wrote:
| Tangential, 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
| hprotagonist wrote:
| The 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 wrote:
| But, 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 wrote:
| I 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 wrote:
| we 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 wrote:
| Coming 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 wrote:
| > 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 wrote:
| Again: 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 wrote:
| There 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.
| [deleted]
| [deleted]
| rpz wrote:
| Why 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?
| z5h wrote:
| We don't. E.g.
| https://en.m.wikipedia.org/wiki/Sudbury_Neutrino_Observatory.
| zbendefy wrote:
| Results can be better controlled this way
| _Microft wrote:
| There are lots of experiments that do not require particle
| accelerators but if you want to observe neutrinos after they
| have travelled only a few dozen meters, you need a source at
| that distance.
| ars wrote:
| How do they know they are only detecting neutrinos from the
| designated source, and not also other neutrinos mixed in?
| _Microft wrote:
| I am not an expert on this, so take it with a grain of
| salt:
|
| Neutrinos are not directly detected. What happens is that
| they interact with matter in a medium and produce muons or
| electrons that are moving faster than the speed of light in
| that medium. That's only possible because the speed of
| light in said medium is less than the speed of light in
| vaccuum by the way. These fast-moving, charged particles
| lead to the generation of a cone of cherenkov radiation,
| not unlike a supersonic object is producing a mach cone.
| From that cone, the direction of the particle motion can be
| inferred.
|
| One could also keep the detector running while switching
| the source on and off to establish a baseline and calculate
| the excess of detected particles while the source was
| switched on.
|
| https://en.wikipedia.org/wiki/Cherenkov_radiation
| misnome wrote:
| This is somewhat correct, but talking about only one
| class of experiment (Cherenkov detectors).
|
| Indeed it's the child-particles of the interactions that
| are observed, so, electrons muons and Tau particles.
| Depending how you are measuring, (many approaches) these
| interactions are generally separable - and usually you
| can get some directionality out of your measured event -
| so you know the direction it came from.
|
| Combining the direction with timing - with an accelerator
| you know exactly when the pulse of neutrinos were
| produced - this means you can exclude a very large amount
| of background.
|
| Some background does get through, but you can measure it
| with e.g. the source turned off as you suggest, or the
| times when you know the source isn't otherwise producing
| (like in between pulses) to get a background rate. You
| then generate enough data from the source to effectively
| "drown out" the background.
|
| Much the same can be done with reactor sources - very
| often when building an experiment with a reactor as a
| source, there will be some government-level agreement to
| allow knowledge of what power the reactor is being run
| at, as well as shutdowns.
|
| Along with Cherenkov, there are and have been
| scintillator, chemical-energy-deposition, Photographic
| film and even ocean-audio based methods of detection.
| Probably some more exotic ones I am forgetting also.
|
| (I did a PHD in neutrino physics, although been out of
| the field a few years)
| _Microft wrote:
| Thanks for the reply, it is very much appreciated!
|
| I did not know that "ocean-audio based methods of
| detection" for neutrinos are even possible and will
| certainly look that up later.
| misnome wrote:
| I don't know if any of them ever ended up getting off the
| ground, but the theory was that you could pick up the
| step-function shockwave from underwater interactions with
| a giant array of microphones. There were some test arrays
| in the Mediterranean IIRC, but cursory searches seem to
| imply that optical underwater arrays seem to have been
| pursued instead.
|
| It always seemed a neat idea, that you could instrument
| absolutely gigantic volumes with.
| _Microft wrote:
| I guess the sound might be very characteristic because
| variations in the process of generation might be limited
| (amount of energy delivered / type of particle created?)
| and I would expect it to sound a lot like a sharp "ping"
| if I had to take a guess. Temperature, salinity and
| currents would affect propagation and dispersion but deep
| enough in the sea there might be a stable enough
| environment to be able account for that. A very
| interesting idea at least!
| drclau wrote:
| > if you want to observe neutrinos after they have travelled
| only a few dozen meters
|
| Genuinely curious here, why is the travelled distance
| important?
| icegreentea2 wrote:
| If you want to measure neutrinos transforming, then knowing
| the distance to source lets to calculate rate of
| transformation.
| frutiger wrote:
| Why can't you sample at one point on the earth's surface
| and sample again at that point's antipode? You would know
| the distance that was travelled, and have measurements at
| both points.
| user-the-name wrote:
| Neutrinos mainly come from the sun, and the sun is
| massively larger than the earth. You can't draw any
| conclusions from measurements at two points at a distance
| that is much smaller than the size of the source itself.
| misnome wrote:
| How would you know the two different neutrinos
| interactions came from the same source/distance without
| producing them yourself?
| frutiger wrote:
| I wouldn't need to. By sampling hundreds of thousands of
| events, I would know the odds of getting a particular
| neutrino from a particular source is the same.
| qrybam wrote:
| That's part of the problem, they had 500 detection
| "events" over 15 years of operation.
| candiodari wrote:
| Well that's not the problem. The problem is natural
| sources are too big. The distance difference between you
| and the top of the sun and the middle is like 100x the
| length of the equator. Neutrino sources in the sun have
| very irregular shapes, so that too changes the distance.
| And you have zero control over it all. All you'd ever see
| is the equivalent of a soft shadow, you'd never get a
| point source.
|
| The second thing you might want to do: "filter" neutrinos
| ... well that just doesn't work at all. Nothing stops (a
| decent amount of) neutrinos. So you can't filter them and
| create a known point with, say, only electron neutrinos
| like you can with light. There are also no known
| astronomical objects that filter neutrinos. They fly
| right through a star, so that's no good either.
|
| Third you could filter observations. But again you hit
| the filter problem. You _can_ focus neutrinos
| measurements (even if you can 't focus the neutrinos
| themselves), but that lowers the amount of neutrinos you
| measure further. And you're only measuring like maybe 50
| per cubic meter of water, so you don't have much to work
| with.
|
| I guess you could wait for things to get especially good
| for your measurement but you'll be waiting a long time.
| bryan0 wrote:
| From TFA:
|
| > the three types of neutrino-flavors mix into each other.
| That means, if you start with, say, only electron-
| neutrinos, they'll convert into muon-neutrinos as they
| travel. And then they'll convert back into electron
| neutrinos. So, depending on what distance from a source you
| make a measurement, you'll get more electron neutrinos or
| more muon neutrinos.
| misnome wrote:
| Energy ranges, knowing exactly how far you are from the source
| of the neutrinos, and background exclusion.
|
| If you are too far from the source, the mixing you might be
| measuring might have happened already happened. You can build a
| detector right next to the source, and also far away, and
| correlate the differences.
|
| External interference can be excluded on energy range,
| direction, and "timing" - you know exactly when the pulse
| happened in the source and can exclude things outside that
| window (as the neutrinos all travel at the speed of light to
| within measurement error).
|
| Things like neutrinos from the sun can and have been measured,
| but for many things you want to measure you need more careful
| control.
| bryan0 wrote:
| From TFA:
|
| > we have three flavors of neutrinos and these mix into each
| other as they travel....There are natural sources like the sun,
| and neutrinos that are created in the upper atmosphere when
| cosmic rays hit. And then there are neutrinos from manmade
| sources, particle accelerators and nuclear power plants. In all
| of these cases, you know how many neutrinos are created of
| which type at what energy. And then after some distance you
| measure them and see what you get.
| akira2501 wrote:
| > given their apparent abundance?
|
| That's part of the problem. Which Neutrinos are you measuring?
| The ones from your experiment, the ones from the Sun, the ones
| from the environment? They're exceptionally light particles, so
| effective shielding is difficult.
|
| It's why a lot of these experiments are deep underground. The
| one I visited was in northern Minnesota in an old abandoned
| Mine placed half a mile under the surface and positioned in
| such a way to receive a neutrino beam all the way from Fermilab
| in Chicago.
|
| The smaller and lighter the phenomenon, the larger your
| laboratory needs to be come.
|
| https://en.wikipedia.org/wiki/MINOS
| kurthr wrote:
| If everything was as expected, we don't, but the issue is that
| there appears to be something different about the particles
| coming from the accelerator (sterile neutrinos? or simply
| shorter distance?) since these results haven't been seen in
| other experiments. Of course the fact that the results could be
| separately replicated (and combined to give the 6sigma
| confidence) is another useful aspect.
|
| If there are sterile neutrinos... they are a possible dark
| matter particle.
| gumby wrote:
| She mentions this in her transcript. First of all they aren't
| as common on earth as other particles (she says "10-15 have
| passed through you while listening to this paragraph". How many
| photons hit you in that period of time? If you can make a bunch
| at once (as a side effect of another high energy interaction)
| you can look at them in a known place at a known time.
|
| Secondly, she mentions LSND which was a big tub of liquid that
| would interact with neutrinos that passed through it. Flashes
| from those interactions would be picked up by photo detectors
| (hence "scintillation"). The most famous such setup in a mine
| in Japan, but there are several such "neutrino telescopes".
| solidgol wrote:
| She said 10 to the 15. 10^15
| dnautics wrote:
| To be fair I also heard 10-15 on the first pass and then
| had to think about it for a second.
| _tom_ wrote:
| That's because she actually said "ten to the fifteen" not
| "ten to the fifteenth", so you have to decide if you
| autocorrect by removing the "the" -> "ten to fifteen" or
| by adding the "th" -> "ten to the fifteenth".
|
| Easy to get confused.
| mkl wrote:
| "Ten to the fifteen" is also correct, and in my
| experience more common. It's short for "ten to the power
| of fifteen", whereas "ten to the fifteenth" is short for
| "ten to the fifteenth power".
| _tom_ wrote:
| Not "ten to fifteen", but "ten to the fifteenth"
|
| A bit larger. :-)
| [deleted]
| ISL wrote:
| That'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.
| fuzzfactor wrote:
| >Maybe people just don't like neutrinos?
|
| My sentiment exactly.
| tim333 wrote:
| There's a poem about that
| https://www.symmetrymagazine.org/article/february-2011/decon...
| fuzzfactor wrote:
| I appreciate that.
|
| It was truly as uplifting as it could be.
| neurtrinosfake wrote:
| Neutrons ain't real therefore neutrinos ain't real
|
| https://www.youtube.com/watch?v=gYHGdBqI7z4
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(page generated 2021-09-19 23:01 UTC)