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”
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.
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.
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.
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
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“
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
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.)