A proton-proton collision event in the CMS experiment producing two high-energy photons (red towers). This is what we would expect to see from the decay of a Higgs boson but it is also consistent with background Standard Model physics processes. © CERN 2012
You might have seen the New York Times Headline on July 4th “Physicists Find Elusive Particle Seen as Key to Universe”
“I think we have it”
said Rolf-Dieter Heuer, the director general of CERN.
While CERN’s spokespeople were reasonably tentative in their description (they called it “Higgs-like”), they did not exhibit as much caution as the OPERA folks did when announcing the evidence for potentially faster than light Neutrinos. This time CERN went to a lot of skillful effort to make it a media circus – and succeeded.
But did they find a Higgs particle?
Short answer – No.
At the very least – not yet.
CERN did find two different weak signals indicating a *New Particle* weighing in at around 125 GeV. Now that is cool, very cool !
They seem to have found a new heavy particle. It weighs more than half of the heaviest particle known.
Signal of likely New Particle. Credit: CMS Team
Uncertainty overview: Its a lot “easier” to find a particle than to find its properties.
So far, the experimenters are not fully confident they’ve found a new particle. Both the Atlas and CMS teams called their results “Preliminary.”
The “5-sigma” (global significance was actually only something like 4.9 sigma) is only a statistical probability, a tiny bump on a graph (actually 4 graphs) and it still could evaporate (remember Faster-than-light Neutrinos had even stronger “6-sigma” data).
However the probability of a new particle is growing with more data, multiple experiments (which are strong positive signs, but you might appreciate this article “Why we shouldn’t combine Higgs searches across experiments“),
Although Banks still won’t let you cash a check on it – the signal alone is good enough to open up some champagne !
Contrary to what many media reported and implied, there is no similar “5-sigma” argument that the signal is a Higgs.
“We don’t know if its a Higgs boson.” – Joe Incandela, CERN CMS Experiment Leader
Now that the particle find is somewhat established there will be a search for Higgs properties with more focused experiments.
However, there’s another problem or two that I didn’t identify before the announcement.
The two different experiments (Atlas and CMS -Compact Muon Solenoid) each show a signal – but at two different masses.
Hmmmm . . .
Before you get annoyed that I’m throwing cold water in the face of an exciting moment, reflect on two things. I’m not the one who arranged the media circus and most importantly — how science is supposed to work. (Here’s a nice refresher by Gordon Bonnet: The Higgs boson, uncertainty, and the scientific method)
To resume, the masses are close (and even overlap in their error bars): 125.3 GeV (+/- 0.6 GeV) and 126.5 GeV, but the peaks admittedly do not match.
The problems identified earlier remain:
All we have is statistics on indirect events — there is no direct “picture” evidence, no “glimpse,” of the new particle. Let me use an analogy.
We never get to see the cue billiard ball (the new particle), only the secondary balls it hits. Then we measure what those secondary balls are (photons, taus or quarks etc.), and do.
So far there is zero evidence this signal has any Higgs properties. Period.
We do not know if it has spin (a Higgs particle should have Zero spin) or chirality, or most importantly if it has any purported effect related to giving mass to other particles. All we know is its mass / weight. (That’s not wholly true. We do know the rate it seems to be showing up – under differing experimental circumstances, and it is appearing twice as often as theorized.)
Nevertheless, let me use another analogy.
If I had a scale behind a fence (so I can’t see it) and the scale told me something on it weighed 125 pounds – can I conclude it is my missing refrigerator? or a Panda? or a garbage can filled with Horseradish? Of course not.
This means this new particle could be “just” another Boson or Quark or something else interesting (though symmetry says it should be a boson because only a boson should decay into exactly two other photons). There’s absolutely nothing particularly special about this signal yet. A Top Quark is heavier, as is a Top Anti-Quark.
The Atlas data shows a clear “bump” at a mass of 126.5 GeV (that’s good), but the bump size is twice what is hypothesized by the Standard Model (this “double what was theorized” is not yet a serious problem, just an interesting note though it does weaken the “Higgs-iness” arguments).
There are five different kinds of decays predicted by the Standard Particle Model which CERN is looking for:
1) Two photons (Gamma rays actually. These gave the best data yet in both experiments),
2) a Tau and an anti-Tau (there is a complete lack of Tau – anti-Tau decays which is odd, but not a deal killer, though it does conflict with the Standard Model),
3) a Bottom quark and an antiBottom quark (seen by Fermilab’s Tevatron at 3 sigma, but not at all by CERN’s experiments,
4) W and W (This decay produces one positive and one negative charged W boson. Though when I add up two 80 GeV W particles they exceed 125 GeV by a huge amount . . . – how can a 126 GeV mass decay into 160 GeV? (2 x 80 Gev W particles) — See explanation by Aidan Randle-Conde in a comment below, and
No ZZ Top Decay – They Only Get Better
5) ZZ decay (Second best data. Like Neutrons, Z bosons have no electromagnetic charge. Here again, two Zs times 91 GeV = 182 GeV – way more than the new particle at 125 GeV.)
Stay tuned, because just like the Faster than Light Neutrinos – this Higgs story is a long way from over.
So even if the signal later turns out not to be a Higgs particle, for the meantime – lets celebrate Physics being the headline on the New York Times.
1) ATLAS did not release any of their new data on other searches. This could be good news as well as otherwise. Lets hope ATLAS found yet another signal.
For more info:
July 4, 2012: CERN LHC “Seminar” / Press Conference “Update in the search for the Higgs boson“
Higgs FAQ 2.0 by Matt Strassler
An excellent in depth (yet understandable) article on the science details of the Higgs search and recent observation of a new particle “Understanding the Higgs search” by Aidan Randle-Conde
Matt Strassler’s Post-Seminar Summaries
Sean Carrol’s “blow-by-blow” coverage of the Seminar
God particle or goddamn particle?
Science Journalism: Not Buying The Higgs Hype
A New Particle – But is it Higgs?
Faster Than The Speed Of Light (BBC Video)
PS Oh, with all the celebration you might have missed the announcement “Higgs boson discovery leads to FDA-approved ‘mass reduction’ weight loss therapy.” (and yes, its a spoof.)
English
The decay rates of the unknown particle are also compared to what you would expect from the Standard Model for a Higgs boson. That is why you know it’s a Higgs boson.
Thank you for your thought Marcel.
Please let me suggest that we don’t “know” it’s a Higgs boson, as even the experimenters carefully will not say that. (Though the media certainly have).
The decay rates (I’ve updated some of that information since you posted your note) seem to have a few discrepancies with Standard model predictions. One decay rate is twice what was theorized.
“So far, none of the experimenters is 100 percent certain they’ve found a particle.”
Yeah, they’re only 5-sigma certain, which is vastly more certain than when pretty much anyone else says they’re “not 100 percent certain”. Which is, scientifically speaking, a tautology. Nothing is 100% certain. So why point out that they aren’t 100% as if to downplay their certainty, rather than talking about how certain they actually are?
Thank you for your response.
You’re right. I shouldn’t have used the idea 100 percent certain.
While I meant the experimenter’s personal sentiments about certainty they indicated at the press Conference, my phrase could also be construed to indicate the percent probability that they found a Higgs particle. Thanks to your concern, I’ve removed the phrase.
Science has a lot of degrees of evidence from possibility to probability to certainty.
Don’t you think the term “Certainty” should be reserved from phenomena that have more than a few data points?
Don’t you think there’s a gigantic difference in the amount and quality of data supporting the concepts of gravity and electromagnetism – than CERN’s data indicating a new particle ?
There’s also potential system error which was apparently the cause of the Faster than Light Neutrinos. If you recall, that experiment has 6-sigma data – higher than claimed for the new particle.
These are reasonable concerns that might reasonably lead one to be skeptical.
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Hi David.
Just replying to the point about the massive vector boson (WW and ZZ final states.)
A particle can decay to two other particles of a higher combined mass only if one of them is a virtual particle, so that its mass is smaller than its nominal mass. In that case the particle at 126GeV can decay to a Z with mass 91GeV and and a virtual Z, with a mass less than 35GeV, or a W with a mass of 80GeV and a virtual W with a mass less than 46GeV.
This leads to a suppression of the branching fraction to these final states, but otherwise it’s quantum mechanically allowed.
Thank you Aidan – for an explanation of how a particle can decay into two particles with more total mass than the original particle.
Nevertheless, I remain skeptical about Virtual particles, in this case Zs and Ws, primarily because Virtual particles either cannot be observed by definition, or have the self-contradictory “property” that if they are observed – they cease to exist.
(I feel like it is far easier and more credible to describe the phenomena often explained as virtual particles – as fields – analogous to magnetic fields.)
In this case I’m a bit surprised and disappointed to learn that the WW decay isn’t really a WW decay. They really mean the detection of a W (a real live W boson with mass and charge) and a Virtual W boson – something that can’t be detected. Same thing for the ZZ decay.
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I’m following another blog written by the son of Comay, a retired physicist who claims that the W,Z and the new particle are top quark mesons. I have two questions:
1. He explains here why the top mesons must appear: http://nohiggs.wordpress.com/2012/10/09/why-top-quark-mesons-must-exist/
2. He also published recently an article which claims that W equation cannot be equations of elementary particle.
What is your opinion about the two issues? What is the author’s mistake?
Thanks!
Hello
I see that my previous comment is still waiting and you probably do not allow comments with links to other sites.
Is it possible that you will send an answer to my email address? If you do – please let me know:
– can I put your answer as a comment in Comay’s blog?
– can I say that this is a reply that I received from you?
If you answer – I will act exactly as you instructed. You can see in his blog that 2 professors replied to his ideas and he answered them.
Thank you very much for your time.
Hello Valery,
As you see we do allow links in comments.
I appreciate your asking, but as much as I’d like to drop everything read the article — I am up to my ears in deadlines and just can’t get to the article you suggest for the near future. I will put it on my “To read list.”