Happy Higgs Day

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….

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24 Responses to Happy Higgs Day

  1. Q. I says:

    Peter, you don’t seem to be happy about the announcement.

  2. Peter Woit says:

    Q. I,

    Not at all. It’s a fantastic achievement, and amazing after all these years to finally be exploring experimentally the Higgs phenomenon. I’m looking forward to seeing what the numbers say, whether they agree with the SM or not. Either way though, it’s an important day and a time for the field of HEP to celebrate (experimental) progress.

  3. fred says:

    although this is great work by the experimentalists, lets also remember the great work of theorists predicting this phenomena about 40 years ago, back when it was impossible to directly probe anywhere near this kind of energy scale! A great triumph to the power of theory, logic, extrapolation, etc. All things that are currently used by theorists today to look ahead to the new challenges

  4. Chris Oakley says:

    It is curious that they should choose July 4 as the date to make the announcement. Maybe it was to give Americans something more meaningful to celebrate than disloyalty to the British crown.

  5. Pingback: Live-Blog zu den Higgs-igen Enthüllungen im Juli « Skyweek Zwei Punkt Null

  6. Yuval Sanders says:

    I was watching the announcement today and I wanted to comment here, since your blog is how I obtain a lot of particle physics news. CMS announced a 4.9 sigma confidence of the existence of a new boson that has decay channels identical to what would be expected of a scalar Higgs. ATLAS announced 5.0 sigma. They are careful not to claim discovery of a scalar Higgs, but they are announcing the discovery of a new boson.

  7. jg says:

    Both teams are being ultra cautious, but at the end of the ATLAS presentation of the 5.0 sigma result CERN Director General Rolf Heuer says “I think we got it, you agree?” and the audience go wild! (Well, Peter Higgs was a bit more restrained, but he did finally applaud too)

  8. A. says:

    Both Incandela and Gianotti gave nice talks, even if they did try to cram too many details in. Clearly excited by the results.

    Heurer’s “I think we got it, do you agree?” fell rather flat. Clearly scripted to be the “one small step” moment of the conference, did anyone else notice the awkward pause before the applause started, during which the audience realised they couldn’t really do anything but agree?

  9. csa says:


    In addition to the whole “comic sans” discussion.

  10. csvargas says:

    Sorry, I’m not a physicist but as I understand, “what gives mass to the Higgs boson” is the Higgs field. In fact, the field would be the really important discovery and the boson would be just its proof.

    Am I getting the picture right?

  11. TB says:

    Thanks for blogging, I’ve lurked for a long time, and I appreciate the clarity you bring.

    A lot of talk about whether this is a standard Higgs or not. This non-physicist isn’t sure what that means and what it’s implications are. Seems people invested in multiverse theory are very excited about that, but I could be misunderstanding?

  12. MomentCaptor says:

    I am such a huge fan of this weblog; however, when are you going to respond? It’s July Fourth in America already!!! I’ve been anxiously awaiting to hear your response now that the talks are over and the champagne has be popped. Let’s have it!

  13. SpearMarktheSecond says:

    The bump at 125 GeV in gamma gamma definitely persisted in the new data, and in 2 experiments. It is impossible that the bump is a statistical fluctuation.

    Didn’t stay up for the talks, but the slides don’t invest much effort in, `What else could this be?’. But the S/B is so low their aren’t a whole lot of useful plots (like distribution of the events in time, space, etc) that could help. If it is a systematic problem, only clever graduate students and postdocs in the huge collaborations could know.

    I think CMS’s shifting of bin widths and final plot weighted by S/B are very odd, a bit of unwarranted massaging. Thought Atlas seemed more consistent.

    The 4lepton signals seem fairly convincing too, and are quite convincing evidence that the gamma gamma peak is not a systematic effect. Liked CMS analysis better… used kinematics better.

    All the rest is smush, except, maybe, the Tevatron.

  14. anonomous says:

    I should have gone to sleep but I couldn’t help it and stayed up to watch the live webcast. What a great presentation – the excitement of watching it live was well worth it (especially the applause when Peter Higgs entered the room!). This has to be the biggest day in physics in the last 100 years!

  15. neo says:

    What are the implications of a *single* higgs @125-126GEV to SUSY extensions of SM? If the SUSY exists, should the LHC have detected multiple Higgs and not just one?

  16. Fred D. says:

    What is the actual probability that the discovered boson is something other than the Higgs? I would think that probability is very small.

  17. Casey Leedom says:

    So now that we “know” that there’s “something” at 125GeV, would it be possible to construct a specific experiment/set of equipment to specifically look at this mass range in order to get more details more quickly?

  18. Sciency Sciencer says:

    Maybe they chose independence day because the US stopped funding their collider project and left it to a collaborative international effort?

  19. Peter Woit says:


    Whatever they are seeing, its properties are close to those of the SM Higgs. From now on, attention will focus on measuring “how close”. Quite possibly the result will end up being “it behaves exactly like the SM Higgs is supposed to, to within the accuracy we can measure”. Much more interesting would be: “it behaves like the SM Higgs, except it does X differently”, which would be an exciting clue about how to do better than the Standard Model.


    There has been talk of muon-antimuon or photon-photon collider “Higg Factories”, and now we know the energy they would have to be designed for. The problem with muons is their short life-time, but people are working on the concept. I don’t know much about photon-photon colliders, but such a thing might be possible to build for less than the cost of the ILC.

  20. Obs says:

    As for the date, there’s no need for conspiracy theories here — the annual International Conference for High Energy Physics (ICHEP) opened today in Melbourne, and the CERN seminar was synced with the opening reception (and not just the seminar — the LHC run schedule for 2012 was intentionally designed to produce as much data as possible before the conference.)

  21. Tony Smith says:

    Peter, as to muon colliders,
    it is not the “… problem with muons is their short life-time …”
    because relativistic time dilation takes care of that nicely.

    The most serious problem is neutrino radiation.
    See hep-ex/0005006 by Bruce King of BNL for details.

    At first thought, neutrino radiation looks not harmful,
    but in a muon collider the neutrino flux is so great that it irradiates
    a lot of the surrounding land making it radioactive,
    which secondary radioactivity is really serious.

    If it were not for the neutrino radiation, it would be a no-brainer
    to build a muon collider on the Fermilab site,
    but the radiation would seriously endanger Chicago.

    Maybe the Chinese Western Desert would be a good place to build it,
    but a lot of development work could be done at Fermilab.


  22. Callum says:

    I have been looking for a comment on the difference between the CMS and ATLAS results – 1 GEV sounds a lot to me. Is this a result of experimental or analytical differences?
    (sorry if this has been covered before…)

  23. piscator says:

    Callum: 1 Gev is not so big compared to 125 GeV. The error on the quoted results is about +- 0.6GeV for so a 1GeV difference is within 2 standard deviations so nothing to get excited about. If it persists as the error decreases then the experiments would need to look for systematic differences.

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