Mystery particle spotted? Discovery would require physics so weird that nobody has even thought of it

Mystery particle spotted? Discovery would require physics so weird that nobody has even thought of it
CMS detector. Credit: Laura Gilchrist/Flickr, CC BY-ND

There was a huge amount of excitement when the Higgs boson was first spotted back in 2012 – a discovery that bagged the Nobel Prize for Physics in 2013. The particle completed the so-called standard model, our current best theory of understanding nature at the level of particles.

Now scientists at the Large Hadron Collider (LHC) at Cern think they may have seen another particle, detected as a peak at a certain energy in the data, although the finding is yet to be confirmed. Again there's a lot of excitement among , but this time it is mixed with a sense of anxiety. Unlike the Higgs particle, which confirmed our understanding of physical reality, this new particle seems to threaten it.

The new result – consisting of a mysterious bump in the data at 28 GeV (a unit of energy) – has been published as a preprint on ArXiv. It is not yet in a peer-reviewed journal – but that's not a big issue. The LHC collaborations have very tight internal review procedures, and we can be confident that the authors have done the sums correctly when they report a "4.2 standard deviation significance". That means that the probability of getting a peak this big by chance – created by random noise in the data rather than a real particle – is only 0.0013%. That's tiny – 13 in a million. So it seems like it must a real event rather than random noise – but nobody's opening the champagne yet.

What the data says

Many LHC experiments, which smash beams of protons ( in the atomic nucleus) together, find evidence for new and exotic particles by looking for an unusual build up of known particles, such as photons (particles of light) or electrons. That's because heavy and "invisible" particles such as the Higgs are often unstable and tend to fall apart (decay) into lighter particles that are easier to detect. We can therefore look for these particles in experimental data to work out whether they are the result of a heavier particle decay. The LHC has found many new particles by such techniques, and they have all fitted into the standard model.

Mystery particle spotted? Discovery would require physics so weird that nobody has even thought of it
New data. Credit: CMS Collaboration

The new finding comes from an experiment involving the CMS detector, which recorded a number of pairs of muons – well known and easily identified particles that are similar to electrons, but heavier. It analysed their energies and directions and asked: if this pair came from the decay of a single parent particle, what would the mass of that parent be?

In most cases, pairs of muons come from different sources – originating from two different events rather than the decay of one particle. If you try to calculate a parent mass in such cases it would therefore spread out over a wide range of energies rather than creating a narrow peak specifically at 28GeV (or some other energy) in the data. But in this case it certainly looks like there's a peak. Perhaps. You can look at the figure and you can judge for yourself.

Is this a real peak or is it just a statistical fluctuation due to the random scatter of the points about the background (the dashed curve)? If it's real that means that a few of these muon pairs did indeed come from just a large parent particle that decayed by emitting muons – and no such 28 GeV particle has ever been seen before.

So it is all looking rather intriguing, but, history has taught us caution. Effects this significant have appeared in the past, only to vanish when more data is taken. The Digamma(750) anomaly is a recent example from a long succession of false alarms – spurious "discoveries" due to equipment glitches, over-enthusiastic analysis or just bad luck.

This is partly due to something called the "look elsewhere effect": although the probability of random noise producing a peak if you look specifically at a value of 28 GeV may be 13 in a million, such noise could give a peak somewhere else in the plot, maybe at 29GeV or 16GeV. The probabilities of these being due to chance are also tiny when considered respectively, but the sum of these tiny probabilities is not so tiny (though still pretty small). That means it is not impossible for a peak to be created by .

Mystery particle spotted? Discovery would require physics so weird that nobody has even thought of it
CMS model of a Higgs boson decaying into two jets of hadrons and two electrons. Credit: Lucas Taylor/CERN, CC BY-SA

And there are some puzzling aspects. For example, the bump appeared in one LHC run but not in another, when the energy was doubled. One would expect any new phenomena to get bigger when the energy is higher. It may be that there are reasons for this, but at the moment it's an uncomfortable fact.

New physical reality?

The theory is even more incongruous. Just as experimental particle physicists spend their time looking for new particles, theorists spend their time thinking of new particles that it would make sense to look for: particles that would fill in the missing pieces of the standard model, or explain dark matter (a type of invisible matter), or both. But no one has suggested anything like this.

For example, theorists suggest we could find a lighter version of the Higgs particle. But anything of that ilk would not decay to muons. A light Z boson or a heavy photon have also been talked about, but they would interact with electrons. That means we should have probably discovered them already as electrons are easy to detect. The potential does not match the properties of any of those proposed.

If this particle really exists, then it is not just outside the standard model but outside it in a way that nobody anticipated. Just as Newtonian gravity gave way to Einstein's general relativity, the standard model will be superseded. But the replacement will not be any of the favoured candidates that has already been proposed to extend : including supersymmetry, extra dimensions and grand unification theories. These all propose new particles, but none with properties like the one we might have just seen. It will have to be something so weird that nobody has suggested it yet.

Luckily the other big LHC experiment, ATLAS, has similar data from their experiments The team is still analysing it, and will report in due course. Cynical experience says that they will report a null signal, and this result will join the gallery of statistical fluctuations. But maybe – just maybe – they will see something. And then life for experimentalists and theorists will suddenly get very busy and very interesting.


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Journal information: arXiv

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User comments

Nov 07, 2018
A threshold gammaray will split into a positron and negatron when acted upon by an external force. if such a force does not exist, then whatever process that has increased the photon energy up to threshold will continue, and external fields could cause these higher-than-threshold gammarays, or mesons to split into muons.

Nov 07, 2018
What's a "negatron?" Meanwhile, gamma rays are not mesons.

Back to reality, this is probably a statistical fluctuation. But you have to follow every one of those up; historically, a percentage of them have turned out to be something truly new.

Nov 07, 2018
What if somebody has thought of this mystery particle spotted at 28 Gev! that discovery would require physics so weird that nobody has even thought of It.

Nov 07, 2018
What's a "negatron?"
"The term was coined by Carl D. Anderson, who had discovered the positron. He suggested it be used for the negatively charged particle only, with electron being used for either the negatron or positron. "

-You find such things on a thing called wiki.

This is what happens when you get the erroneous opinion that youre smarter than the people youre conversing with.

Nov 07, 2018
negatron . . . noun . . . an obsolete word for electron


https://www.dicti...negatron

Otto, how's that inferiority complex of yours going? Did correcting a much smarter person on some obscure and obsolete term make you feel better?

Otto's Internal Dialog:

Otto not dumb, Otto prove Otto not dumb. Otto look up word. Make Otto look smart. Otto just as smart as Da Schneib. Otto click on first link on Google search. Now Otto know more about negatron than Da Schneib. Otto spend all day proving Otto just as smart as Da Schneib. Otto feel better.

Nov 07, 2018
LOL, only ever used in science fiction. In Amazing Stories.

Nov 09, 2018
Mark. Did you read the rest of the thread? Da scheide was implying that the poster made up a word, and was so sure of his knowledge of EVERYTHING that he didnt bother to check before doing so.

You can support this kind of infantile hubris if you want but it makes you look silly as well.

Nov 09, 2018
Da scheide was implying that the poster made up a word


Are you sure? Maybe he was simply reacting to the use of an archaic term.

Nov 09, 2018
Da scheide was implying that the poster made up a word


Are you sure? Maybe he was simply reacting to the use of an archaic term.
Like I said, if you had read the thread before commenting you would have seen that he didnt know what it meant.

Why you trollin me dude?

Nov 09, 2018
Otto, was your comment designed to add to the conversation (no or a pathetic attempt) or attack Da Schneib to make yourself feel better about being Otto (looks like a winner)?


Nov 09, 2018
I enjoy illuminating sloppy, lazy ignorance especially from asses who claim they rarely meet people who are as smart as they are.

You may wish to admire me for it but I really dont care either way.

We sit here on the internet but people like der scheide (and yourself) seem to think they can make up any sort of deplorable bullshit they want, and not get called on it, like they have done for most of their pre-internet lives.

That's just wrong.

Facts are facts are facts. Why do YOU seek to defend people who dont respect them?

Nov 09, 2018
Otto, was your comment designed to add to the conversation
-And what is the conversation worth if the participants are liars and fabricators? The subject line immediately changes at that point.

Nov 09, 2018
Da scheide was implying that the poster made up a word


Are you sure? Maybe he was simply reacting to the use of an archaic term.
Just to be clear, "negatron" is an archaic word only ever used in science fiction written for pulps in the 1930s. Next The GOO is going to bring Bergenholms. (Imaginary anti-inertia space drives from the Lensman series, which is amusing though not very technically sophisticated.)

Nov 09, 2018
Just a dumb old artist, here...
I didn't know what a negatron was, either. I just figured Tim meant electron, anyway...
I think Otto assumed DS was being snide and patronizing and not just asking out of curiosity.
Smart is the ability to quantify, and subsequently qualify observed data.
In the meantime, no one commented that the statement that gamma rays are not mesons, was a correct one...
And they're not muons, either...

BTW, DS. Am I as smart as you?
Or just not as well as informed?

Nov 09, 2018
@Whyde, probably not but you have compensating talents. They don't register on IQ tests, most likely, but I do not dismiss them. I am quite socially inept. That's because I was taught science when I was young instead of social graces or art; I rebelled to the extent of insisting on playing music, but never quite made up the ground in politics.

Don't think I am beating my chest crying "Mea culpea, mea maxima culpea," because I did extraordinarily well in technology. But don't think that makes anything you did of less value. I'd actually like to see some of your art. You can observe mine on the Internets.

Nov 09, 2018
@Whyde, probably not but you have compensating talents. They don't register on IQ tests, most likely, but I do not dismiss them. I am quite socially inept. That's because I was taught science when I was young instead of social graces or art; I rebelled to the extent of insisting on playing music, but never quite made up the ground in politics.

Don't think I am beating my chest crying "Mea culpea, mea maxima culpea," because I did extraordinarily well in technology. But don't think that makes anything you did of less value. I'd actually like to see some of your art. You can observe mine on the Internets.

I did pretty well in the technology sector as well. But I burned out...
My "art" is on the internet as well. Just look up The New Homestead SIlverware Artistry.

Nov 09, 2018
I did. Thanks.

Nov 10, 2018
Good luck with your business enterprise, Whyde. Why isn't your Catalogue page working?

Nov 10, 2018
OK It's working now.

Nov 10, 2018
Protons and Electrons versus Negatron's and Positrons
Da Schneib> What's a "negatron?" Meanwhile, gamma rays are not mesons.

My Twopence worth
A Negatron is simply a negative-proton or that's my take on the issue

Nov 10, 2018
I think Otto assumed DS was being snide and patronizing and not just asking out of curiosity
That's right.
I am quite socially inept. That's because I was taught science when I was young instead of social graces or art; I rebelled to the extent of insisting on playing music, but never quite made up the ground in politics
So where and how did you learn to be a pompous ass? A dichotomy.

And how did you learn that youre smarter than most anyone youve met? Maybe you have only met 2 people and they were both progressives?

But you've lucked out. You can post here and find out how smart you're not.

Nov 10, 2018
My Twopence worth
A Negatron is simply a negative-proton or that's my take on the issue
And so youre WRONG because you didnt freeking LOOK it UP.

Another dumbass.

Nov 10, 2018
Protons and Electrons versus Negatron's and Positrons
Da Schneib> What's a "negatron?" Meanwhile, gamma rays are not mesons.

My Twopence worth
A Negatron is simply a negative-proton or that's my take on the issue

Actually, I think the original poster meant the opposite of a positron... Which would be an electron (since they are created in pairs)

Nov 10, 2018
@Whyde it's like referring to a goal as "that netumungus thingie."

Nov 11, 2018
@Whyde it's like referring to a goal as "that netumungus thingie."

Well.... there ARE a few "nuts" among us... :-)

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