Not Even Wrong

I’m trying to get over my Higgs obsession, and move on to other topics, but one last posting about this for now…

The first thing to say is that this is the biggest thing to happen in fundamental physics in about 30 years (i.e. since the discovery of the W and Z). It’s a remarkable event and huge success for high energy physics, vindicating at the same time the colossal efforts that have gone into making the LHC and its detectors work, as well as the theoretical framework of the electroweak part of the Standard Model. Today’s New York Times has a front-page story by Dennis Overbye, above the fold, which is very well done. In general the press reports that I’ve seen have been quite good, with minimal speculative nonsense thrown in. According to Overbye, CERN DG Heuer made the right decision to go ahead and simply claim discovery only on Tuesday afternoon. All in all, CERN has done an excellent job of communicating this story to the public (except perhaps for the “don’t believe the bloggers” business, but what else could they do…).

Attention will turn now to who gets rewarded for all this, in particular, who gets a Nobel Prize? Personally I think the experimentalists are first in line, and with no obvious figureheads, a prize for three groups: ATLAS, CMS and the CERN accelerator engineers and physicists would be highly appropriate. If it’s not too late in their process, maybe this could even be done in time for this year’s prize, announced October 9.

As far as theorists go, Frank Close has posted something about this here. With the restriction to three people, he argues for Englert, Higgs, Kibble. Personally I think Anderson deserves a piece of it, see here. There’s also a good argument to be made that what has just been validated is not the older work on the Higgs mechanism, but the Weinberg-Salam model of 1967 (extended to quarks), and that has already been rewarded with a Nobel.

I’ve been trying to get accurate numbers for the signal sizes seen by CMS and ATLAS in the various channels, but the only information out there now is the slides from the two talks. Resonaances includes the crucial plot from each experiment giving the signal sizes normalized to the SM, and eyeballing these and averaging, one gets 1.0 in the ZZ channel, 1.75 in gamma-gamma channel, about .75 in the WW channel (only CMS reports 2012 data). In the bb and tau-tau channels, no significant signal is seen, but the expected signal size there is very small. The errors per experiment are something like +/- .4, which you can make your own judgement about how to reduce for the combination. The bottom line is that, within errors, everything is consistent with the SM predictions. The gamma-gamma channel is the one to watch, it is about 2 sigma high.

The DG also announced a new LHC schedule, extending this year’s proton-proton run by two months, to mid-December. This will hopefully allow the experiments to each accumulate another 20 inverse fb of data, finishing this run and going into a two year shutdown with a total of 30 inverse fb to analyze and use to improve the results on the Higgs.

While this announcement is a great triumph for physics, unfortunately it significantly increases the probability of what has become known as the “Nightmare Scenario”: a SM Higgs discovery and nothing else at LHC energies. Before the LHC results started to come in, this scenario and its consequences was easy to ignore, but we may be getting closer to the point where it needs to be taken very seriously.

Update: For a rather complete analysis of the data about the different Higgs decay channels, see this new preprint.

I hear reports that mobs of possibly violent physics live-bloggers have massed outside the CERN auditorium where the Higgs results will be discussed tomorrow morning. I’m going to sleep through this, then wake up late tomorrow (it’s a vacation day here…), have a leisurely breakfast and check to see where the numbers ended up, then try out Philip Gibbs’s applet.

I don’t know exactly what numbers the experiments will be reporting, but basically both CMS and ATLAS should each have 4 sigma-ish or better evidence for the Higgs in two separate channels, gamma-gamma and ZZ. So, that’s four independent measurements of a narrow resonance, any one of which would be strong evidence for the Higgs. Best bet for one of these coming in at over 5 sigma is probably the ATLAS gamma-gamma result. Or, just combine any two out of four of these results using Philip’s software.

Things to look for if you’re following the talks and press conference:

• The “D” word. Will it be used? Kind of a silly question though. July 4, 2012 will go down in history as the date of the announcement of the discovery of the Higgs, no matter what people say tomorrow.
• What are the signal sizes in the two channels? You should be able to use Philip’s applet to combine the CMS and ATLAS numbers, and get a combined gamma-gamma number and ZZ number. Are these consistent with the SM prediction? Already tonight, hep-ph is starting to overflow with phenomenology papers describing models where gamma-gamma is enhanced with respect to the SM. I guess that indicates that tomorrow’s numbers will be higher than the SM prediction.

I hope there will be plenty of champagne involved!

Update: Today so far I’ve been mostly on vacation, celebrating Higgs/Independence Day by sleeping late, doing a short piece on TV for Al Jazeera, going out for an excellent lunch, and lying around in the air conditioning checking out the news from other sources (it’s brutally hot out there…). Later maybe a movie, dinner and fireworks.

The news was pretty much as expected: a strong signal from both experiments in two channels, very close to a 5 sigma level when combined. CERN did the right thing by simply claiming discovery, avoiding the situation suggested by the early AP story, where they seemed to be trying to say that they weren’t quite at the discovery level. For details, the slides are here, and the usual suspects (Philip Gibbs, Tommaso Dorigo, Resonaances, Matt Strassler) all did an excellent job of providing details in real time as they came available. Probably also other bloggers I haven’t had time to look at.

I’m still trying to get together combined numbers for the signal size in the various channels. It looks though that in the ZZ channel the size is close to the SM prediction, 2-3 sigma too high in gamma-gamma (nearly twice the expected size). So, still compatible with the SM, but the gamma-gamma excess is intriguing. Theorists with even better information than me have already started yesterday flooding hep-ph with papers supposedly explaining it.

Now, back to vacation….

A commenter here reports that a CERN video announcing that “We have observed a new particle” was released early, and is available here. Note that the language used refers to “observation” NOT “discovery”, indicating that CERN has decided on a version of the 5 sigma discovery criterion that has not yet been met. “Observation” generally means a lower standard of evidence such as 3 sigma. However, it appears that they are sensibly playing this down, with nothing in the video mentioning the word “discovery” or their decision not to use that word. Most physicists likely will however use “discovery” to describe these results, since the combined CMS/ATLAS results should be way beyond 5 sigma (look to Philip Gibbs tomorrow for exact numbers).

In the video, there is reference to “very very strong evidence” for a narrow peak in gamma-gamma (presumably above 4 sigma, close to 5 sigma in each experiment), as well as “also evidence” for ZZ (4 sigma?) and “less conclusive” evidence in other channels.

Immediate Update: The word here is that CERN is claiming that this is just one of multiple videos made to cover all eventualities. Maybe tomorrow’s version will substitute “discovery” for “observation”…

Update: As commenter Tim points out, this is a CMS video, not a CERN one, so it just refers to CMS results. Evidently CMS is not claiming “discovery”, but that doesn’t mean ATLAS doesn’t have slightly better results and will make a discovery claim. Also, it doesn’t show what CERN will say about the joint results of the two experiments.

Besides the Daily Mail, the AP is now reporting Proof of “God Particle” Found. They include the caveat:

But after decades of work and billions of dollars spent, researchers at the European Organization for Nuclear Research, or CERN, aren’t quite ready to say they’ve “discovered” the particle…

Senior CERN scientists say that the two independent teams of physicists who plan to present their work at CERN’s vast complex on the Swiss-French border on July 4 are about as close as you can get to a discovery without actually calling it one…

Rob Roser, who leads the search for the Higgs boson at the Fermilab in Chicago, said: “Particle physicists have a very high standard for what it takes to be a discovery,” and he thinks it is a hair’s breadth away.

which suggests that neither CMS nor ATLAS have quite managed to reach the 5 sigma threshold, and CERN remains dedicated to not discussing the obvious result of combining the data.

The AP report also has:

CERN spokesman James Gillies said Monday, however, that he would be “very cautious” about unofficial combinations of ATLAS and CMS data. “Combining the data from two experiments is a complex task, which is why it takes time, and why no combination will be presented on Wednesday,” he told AP.

From everything I’ve heard, my impression is that the reason no official combination is being produced is not because it would be technically impossible to do so on a time-scale of days, but because the decision not to do such a combination for ICHEP was made for reasons described here. The problem with this is that it may lead to a lot of confusing explanations like this in the AP report, which muddles how particle physics experiments are done and the obscure issue of 5 sigma/experiment or in combination:

experts familiar with the research at CERN’s vast complex on the Swiss-French border say that the massive data they have obtained will essentially show the footprint of the key particle known as the Higgs boson — all but proving it exists — but doesn’t allow them to say it has actually been glimpsed…

Roser compared the results that scientists are preparing to announce Wednesday to finding the fossilized imprint of a dinosaur: “You see the footprints and the shadow of the object, but you don’t actually see it.”

Better for CERN to just announce discovery and break open the champagne…

Update: Weird. The AP seems to have changed their title from “Proof” to “Evidence”. This may be the first time in history that a media headline about particle physics is incorrectly pessimistic (“Evidence” usually means a 3-sigma signal, which existed last December, “Proof” would be a better way to describe a 5+ sigma signal, if that’s what the combined CMS/ATLAS data shows).

Update: Curiouser and curiouser. I’m hearing that per-experiment combinations are around 5 sigma or above. Very unclear why the AP report is indicating no completely conclusive discovery announcement. Maybe the CERN administration is playing a game with us, downplaying expectations…

Update: As pointed out in a comment, Matthew Chalmers at Nature has

The ATLAS and CMS experiments are each seeing signals between 4.5 and 5 sigma, just a whisker away from a solid discovery claim.

Update: The Atlantic covers the best blogs you should be reading to follow the Higgs story. They miss Resonaances and a few others. About me, they have:

If the Higgs boson was a dead celebrity, Woit would be your TMZ — first to the scene, first to break it, and have it be right.

The Higgs discovery announcement will be at 9am next Wednesday. This is close enough that I can’t reasonably be accused of “subverting the scientific process” and ruining the LHC Higgs analyses by reporting the results here. Unfortunately, no source has provided me with these results yet, so that won’t happen anyway, at least not right now. However, I have learned the following, which may be of interest:

• On Monday at 9am Fermilab will try and steal a little bit of the LHC’s thunder by announcing some new evidence for the Higgs from the Tevatron data. This uses the channel of a Higgs produced with a W or Z, the Higgs then decaying to pairs of b-quarks. This is a channel where the Tevatron is sensitive to a Higgs signal, but the LHC isn’t (at the higher LHC energies backgrounds are too large).
• ATLAS and CMS each collected about 6 inverse femtobarns of data before the technical stop on June 18th, and they are rushing to get as much of it analyzed as possible. They are concentrating on the two most sensitive channels: H->gamma+gamma and H->ZZ->4l and are likely to have over 5 inverse femtobarns of 2012 8 TeV data analyzed in these two channels to present at ICHEP.
• There may not be any 2012 Higgs data from other channels presented at ICHEP. ATLAS will have a H->WW->lvlv analysis, but likely not ready for public release.
• To get the statistical significance necessary to claim a Higgs discovery, the experiments will be producing a combination of their best analysis of the 2011 data in all channels and the 2012 data in the H->gamma+gamma and H->ZZ->4l channels.
• There will be no CERN combination of ATLAS and CMS results publicly released. This is not because such a thing is hard to do (and I believe it is actually being done, just not released), but because of political reasons. I don’t much understand these, but this blog entry gives some of the kind of reasoning being used.
• With no CERN combination, attention will focus on Philip Gibbs at viXra log who in the past has produced reliable unofficial combinations of data, and is likely to do so again.
• With the discovery a done deal, the attention of physicists will focus on the question of whether the signal being seen is compatible with SM predictions, or whether this new particle has unexpected properties. Here the main two numbers to look for are the ATLAS + CMS signal size in each of the two most sensitive channels. To get these, you can do your own combination of the separate ATLAS and CMS numbers, or wait for Philip. The signal size is a product of the Higgs production cross-section and the branching ratio for the channel. I’ve seen estimates of the reliability of the SM prediction of the cross-section varying from 15% to 25% (see more here). The branching ratios are much more accurately known.
• Probably nothing new about SUSY at ICHEP. New SUSY analyses are being targeted for the SUSY2012 conference in August.

Update: Resonaances has more here, including the news that CMS will report 2012 data about the H->WW->lvlv channel (about the significance of this, see the June 29 posting at viXra log), and possibly others. Whether the 5 sigma significance level will be reached by a single experiment remains unclear…

Update: Finally confirmation from a reliable media outlet… The Daily Mail reports God particle is ‘found’. One evidence for this is that supposedly “Five leading theoretical physicists have been invited to the event on Wednesday”. This may mean Englert, Higgs, Guralnik, Kibble and Hagen, with Anderson getting dissed as usual.

Update: Tommaso Dorigo is providing background to the imminent Tevatron announcement here, and I assume will be discussing the actual results immediately upon release. The papers with the results will be released here this morning.

Update: The interesting bottom line from the Tevatron is that they see an excess in the bb channel that the LHC is not sensitive to, of size 2 +/- .7 times that predicted by the SM for a Higgs of mass 125 GeV. So, a marginally significant signal, of size consistent with the SM. The LHC should soon report the sizes of such signals in 3 other channels. In a couple of days we’ll have excesses in four channels, of sizes enough to claim discovery of a Higgs (or something very much like it, depending on how consistent the signal sizes are with the SM).

Update: The Tevatron paper on the Higgs combination is here. Most important number is the fit for the signal size for H->bb, for a 125 GeV Higgs. It’s 1.97 +.74/-.68 (where the SM prediction is 1).

I learned via Physics World that CERN will hold a press conference on Wednesday July 4 to give an “Update on the search for the Higgs Boson”. More information has just appeared (including a press release here), showing that there will be a 2 hour seminar on the results starting at 9am Geneva time, followed by a press conference at 11am.

Reports from the experiments indicate that at least one of them, if not both, will reach the 5 sigma level of significance for the Higgs signal, when they combine 2011 and 2012 data and the most sensitive channels. So, this will definitely be the long-awaited Higgs discovery announcement, and party-time for HEP physicists.

One could note that the last major announcement of the discovery of a new elementary particle at CERN was also made on a Wednesday, July 4, back in 1984. That one didn’t work out so well, but things are very different now, with results from two independent experiments and a high standard of evidence.