Has a Hungarian physics lab found a new force of nature?
nature.com
nature.com
The original paper is https://arxiv.org/abs/1504.01527 The important graph is figure 4 in page 4. I made a colored version: http://imgur.com/Mya66KZ
The black circles are the experimental data. That's what they really saw. (Actually, these measures are very indirect and noisy, so this is the data after a lot of processing, but let's assume that this is standard incontrovertible processing.)
Each measurement has an experimental error, that is marked by the + cross in each circle. So imagine that each circle is a bigger fuzzy ellipse that is 7 times wider and 3 times taller than the circles.
If they assume that there is no new particle, in their simulation they would get the dashed curve, that is always decreasing. It's dashed in the original graph and painted in gray in the "improved" version.
The problem is that the experimental data in the ellipses are too far from the theoretical curve of the simulation without a new particle, so something strange is happening. (A new particle, experimental error, other ...)
They assume that the difference is caused by a new unknown particle, with some properties. In particular, they have to guess the mass of the particle.
If they guess that the particle is very heavy, for example 17.6MeV, they get a curve that looks like an "U", it's dot-dashed in the original and painted in blue in the "improved" graph. It coincides with the "no particle" curve when the angle is less than 130°, but then it starts increasing. The new curve doesn't look like the experimental ellipses at all, so they have to keep trying.
If they guess that the particle is very light, for example 15.6MeV, they get a curve that is also decreasing, it's dotted in the original graph and painted in yellow in the "improved" graph. It coincides with the "no particle" curve when the angle is less than 110°, but then it is bigger. But comparing it with the experimental data, it is too big for 110°-130° and too small for 130°-160°. The new curve also doesn't look like the experimental ellipses at all, so they have to keep trying.
If they guess that the mass of the particle is 16.6MeV, they get a curve with a bump, it's solid in the original graph and painted in red in the "improved" graph. It coincides with the "no particle" curve when the angle is less than 110°, it's slighter bigger at 120° and has an interesting maximum near 140°. The new curve pass through all but the last ellipse, so it looks like a good fit. So the conclusion is that they probably have a new unknown particle with a mass of 16.6MeV!!!
Actually, they (obviously) tried with more possible masses, not only this three values. And compare the simulation with the data using statistics, not the drawings. The details are in figure 5. With 16.6MeV they got the better agreement with the experimental data.
The particles have other properties besides mass. Some of them can be calculated with theoretically, for example the charge. Others, like spin, have to be tested using simulations, because using other values produces different looking curves.
Obviously, the complete paper has more details, but I hope this is a good starting point to start reading it.
EDIT: Fixed "GeV" -> "MeV"
The only yellow I see is in the mess of colors prior to 110°. It looks like the referenced line is actually the line that you painted green?
1. They see a bump (aka "resonance") which can generically be modeled as a new particle/state (whether it's a dark force particle, or a nuclear state or atomic state or whatever).
2. (Small correction to the above post: the mass of the resonance is 16.6 MeV not GeV) Atomic physics operates at the eV scale, and the mass of a Be nucleus is roughly 10 GeV (10^9 eV). So, given that this bump fits the 16.6 MeV (10^7 eV) scale which between the other two scales, this might either be some detailed nuclear physics (eg: some Berellium resonance) or an honest-to-god new particle.
3. Since the angular separation is roughly 135 degrees, it seems reasonable that the intermediate state is moving fast ("boosted") [1]. That means that it cannot be as heavy as a whole nucleus -- therefore, if this was a Berellium resonance then the angle between the electron-positron pair would leave back-to-back (180 degree separation). That is what pushes the interpretation towards a new particle/force.
[1]: https://en.wikipedia.org/wiki/Particle_decay#From_two_differ...
(I agree with your other points.)
From what I understood the angle would imply that this force interacts with a given range but not outside of this range (so it might be strong nuclear? hidden dimensions? new forces?)
My take on this, it is probably a parametrization of something we do not understand in terms of a particle. This something may be a experimental effect or a theoretical lack of understanding or insufficient methods for calculation, or a new particle. The energy range is sort of interesting since it is close to the energy range of hadron spectroscopy, a field which is littered with 2-sigma 'tantalizing hints' of new physics. To end this, I believe it is a temptation to speculate (read I will claim I resisted the temptation until "told you so" is an appropriate response), that a heavy charged particle, cough di-photon excess, could be involved in creating the different couplings to u and d quarks.
Honestly, this gives a very hep-th impression: "An anomaly! we solve it by adding an X-particle with properties that magically explain the anomaly. Hurray!"
Its actually in hep-ph though, which I guess shows that I'm out of touch : / Anyway, exploit hunters have there uses too I guess.
Some thoughts from the thick of things:
1. It's important to remember that nuclear physics backgrounds for such an experiment are hard to model (so that one can subtract them out). The field is littered with "anomalies" coming from systematics and backgrounds. This is why physicists are very cautious with this claim. The authors of the theoretical model claim that it should be easily testable (interesting signals in several different experiments) over the next 2-3 years, so that's one reason to be optimistic about knowing where this stands.
2. This model goes against the grain of most of our theories for how the baryonic matter (essentially nuclei of all kinds) could be created in the universe! If you believe in this newly proposed model as truly another force of nature, then one might need a new paradigm for generating all the matter we see.
There are some theoretically intriguing aspects of the model, so I'm looking out for the follow-up paper by the authors (sometime in the next few weeks?) dealing with several of these aspects.
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Edited to add a link to the slides and elaborating on point #2 below
For more advanced readers (along with the caveat that I don't fully understand the details of their model): We understand very well the production of nuclei soon after the big-bang [3] and there's no room to modify that theory. So, any more fundamental model will have to produce baryons before that era of the universe. The Sakharov conditions [4] for producing baryons require a breaking of Baryon number (you can't have a net excess of baryons over anti-baryons unless you break the symmetry between the two). Usual models produce baryon number by using the fact that U(1) baryon number is anomalous in the presence of electroweak sphalerons [5]. However, in the newly proposed theory U(1) B-L [6] is gauged and hence cannot be anomalous (thereby invalidating the conventional paradigm for generating baryons). Maybe a spontaneous breaking of that symmetry happens early enough in the universe to not mess with the theory of nucleosynthesis but I'm not aware of work along such a paradigm.
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[2]: https://indico.cern.ch/event/518614/contributions/1198831/at...
[3]: https://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
[4]: https://en.wikipedia.org/wiki/Baryogenesis#Sakharov_conditio...
[5]: https://en.wikipedia.org/wiki/Sphaleron#Sphalerons_and_baryo...
It's honestly a bit jarring.
This may not be the right thread to ask this in but it's right enough I suppose.
edit: good example discussion
http://www.scientificamerican.com/article/dark-matter-modifi...
No, the standard model is just three forces (electromagnetic, weak, and strong) plus gravity. A fifth force would be beyond the standard model.
I loosely associate forces with bosonic fields -- photons for EM, gluons for strong, and something confusing for weak. But then no one seems to want to call the Higgs field a "force".
Here's one incomplete answer:
> Q: Why isn't Higgs coupling considered a fifth fundamental force?
> A: The Higgs exchange between matter particles can certainly be called a force. Whether it can be viewed a fundamental force, is a matter of taste. But there is one important distinction between the force due to the Higgs exchange and the usual fundamental interactions. The strong and electroweak interactions are described as gauge interactions. It means that they are not put by hand but arise automatically when you require that the matter fields be invariant under local certain internal transformations (phase rotations, color transformations, etc.). In contrast to that, the "Higgs force" is put into the model by hand, as its presence is not driven by any symmetry consideration. You can equally nicely consider a model with zero Yukawa coupling.
http://physics.stackexchange.com/questions/1080/why-isnt-hig...
If they are not fundamental, does that mean physicists suspect they are complex interactions of other, fundamental forces?
And yes, the non-fundamental forces (like friction) are complex interactions of fundamental forces. For friction it's the sum of electric forces between atoms. The important point is that an atomistic model of friction gives you an essentially unsolvable problem, while the effective macroscopic model of friction is high school stuff.
But the effective formula that the magnitude of the friction force equals a material constant times the magnitude of the normal force from the plane onto the brick gives you a very simple model (solvable with pen and paper).
Is it a new force? It looks like the type of particle that would explain it hasn't been entirely ruled out from all the global data we have. If other planned experiments that will be sensitive to the same properties of the proposed particle and aren't dependent on nuclear decays do see it, then there you go. If they don't then they don't.
A false sillogism, indeed, but that's how you make headlines. And btw doesn't make the discovery any less exciting.
One interpretation I've seen is that there are 4 Higgs bosons, three of which are "swallowed" by 3 of the the weak-force bosons which and become the W+ W- and Z. The remaining 4th Higgs boson (the 4th degree of freedom of the Higgs field) is what we can see, together with the 4th weak-force boson, the photon, which remains massless.
So I think it's reasonable to consider that the Higgs boson belongs to the weak force.
Except for the Higgs boson, the usual picture is that matter particles are fermions and force mediators are bosons:
https://upload.wikimedia.org/wikipedia/commons/thumb/0/00/St...
Is this correct? And if so, does this fact matter in deciding whether to say Higgs == fundamental force?
If it were the same at all space time points it would be a constant, and rather boring (more like a cosmological constant).
EDIT: btw, you got the scalar/vector definition wrong.
A scalar field is one where each point in space can be labeled by a single scalar (not the same vale for all points), for example a temperature reading at different locations.
A vector field assign a distinct vector (i.e. magnitude and direction) to each point in space, for example if you take a compass around the globe you can assign to each location the direction the compass arrow is pointing.
A tensor field is of course assign a tensor to every point in space. I only have rough understanding of what a tensor is, as a first approximation it can be understood as a matrix with special properties.
There's smarter people than me working on dark matter, but one thing to consider is that dark matter may well be simply that -- matter that we're unable to see for inane reasons such as being on a plane of vision that we're unable to see, similar to the unified model of an active galactic nucleus: http://web.physics.ucsb.edu/~ski/skipicture-1.html.
Again, exciting, but too soon to really say anything. Everyone should be suspect of the claims, it's just par for the course in physics.
For systems using radioactive decay as seed, this should have very little effect, as the involved previously-unknown effects are extremely small and the properties influenced by them are unlikely to be used as a source of randomness anyway.
It's like if I said:
"What if zebras are green and red, but we see them as black and white because we don't drink enough water?".
It kind of sounds like an actual logical argument, but it's not even wrong.
Why did you jump to the conclusion that the well understood thing should be replaced by the new and unknown thing?
Perhaps you mean that radioactive decay may have a causal mechanism involving dark matter? Possibly. For such a model to be taken seriously, it would need to agree with our (presumably very numerous and precise) existing observations, as well as either predict the outcome of some new, falsifiable experiment; and/or simplify/unify some disparate existing results into a common framework.
Even if such a model manages to overcome all of those filters, radioactive decay would still be a very real phenomenon. For example, discovering that light is an electromagnetic wave doesn't at all imply that "there's no such thing as light"; discovering that gravity is curvature of spacetime doesn't mean "there's no such thing as gravity"; etc. Like radioactive decay, those are phenomena which we have very direct evidence for, and which theories and models must try to explain.
In comparison, some theories/models postulate the existence of entities which we have no direct evidence for, such as phlogiston, luminiferous aether, dark matter, etc. The only evidence for these is the success of the model that predicts them; that evidence may be undermined if a better model is discovered which doesn't require these entities (e.g. the kinetic theory of gases for phlogiston and special relativity for luminiferous aether).
Hence, if we discover a better model for predicting flat galactic rotation curves, gravitational lensing in excess of the visible matter, etc. which doesn't require an exotic form of matter, then we might claim "there's no such thing as dark matter".
However, even if that were to happen, we certainly couldn't claim that "there's no such thing as flat galactic rotation curves", "there's no such thing as gravitational lensing in excess of the visible matter", etc. since, like radioactive decay, those are phenomena we have observed.
If a theory disagrees with observed phenomena, or claims "there's no such thing" as the observed phenomena, then the theory is wrong. That's precisely what empirical falsification is about. We've observed the phenomena, so that theory cannot describe the world we live in.
[1] https://en.wikipedia.org/wiki/Faster-than-light_neutrino_ano...
http://nautil.us/issue/24/error/the-data-that-threatened-to-...
http://news.discovery.com/space/opera-leaders-resign-after-n...
https://en.wikipedia.org/wiki/Betteridge%27s_law_of_headline...
I'll wager a pint (or suitable non-alcoholic equivalent) on it :) Win-win, since if I 'lose' I buy you a pint but something truly wonderful will have been discovered :)
Just because your post is obvious doesn't mean it's not also the right response to this article.
1.)The given audience in any form is always changing. He might have given new information to someone who hasn't seen it before(young,new english speaker, ect)
2.)We are talking about SCIENCE and whats great about SCIENCE is that to do it well requires SKEPTICISM. The article itself even says that the results haven't been confirmed by a different specialized lab. I would be floored if we discovered another fundamental force but like all things we should ANALYZE all points of a subject.
I think you're being too generous with regard to the OP's comment. That comment appeared to be mostly a throw-away attempt to reference Bettridge's law, rather than offering any substantiate thoughts on the potential discovery or its likelihood of being a spurious result.
Yes there are bad titles out there, though this article's is light years from the worst. That is no reason to bog HN threads down with predictable gunk. Anything predictable is boring.
"Who will win the US presidential election?"
"No."