Higgs Update

The announcement of new Higgs results from the LHC is now scheduled for about a month and a half from now, July 7th, 9:30 and 10am Melbourne time, at ICHEP2012. The LHC is performing well, with nearly 2.5 fb-1 of integrated luminosity/experiment. With only 2-3 weeks more of data collection before the cutoff for what can be analyzed in time to be made public July 7, one can expect the July announcements to be based on perhaps 4-5 fb-1 per experiment. Rough estimates show that, combining last year’s 5 fb-1 at 7 TeV and this year’s expected data, if the SM Higgs really is there at 125 GeV, each experiment should see a signal of 4 sigma significance. This is not quite the 5 sigma significance traditionally set for a discovery claim, but very close.

It thus looks possible that a discovery claim will require combining the results from CMS and ATLAS. The LHC Higgs Combination Group has been hard at work for the last couple years, developing methods for combining results from the two experiments. This time, they will be ready to quickly combine all the data from the two experiments, and maybe this will be what gives the 5 sigma needed for CERN to claim discovery. I don’t know what the plan is for when they will be provided with the CMS/ATLAS data, or when they plan to announce a result.

The LHC-HCG is competing with Philip Gibbs, who today released a Higgs Combination Java Applet which allows anyone to produce their own data combinations. If the LHC-HCG can’t produce a combination by 10:30am July 7, CERN should perhaps consider getting Philip’s applet properly set up and having DG Heuer publicly press the right button, allowing CERN to claim the Higgs discovery before Philip does.

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15 Responses to Higgs Update

  1. Rob R. says:

    This is not quite the 5 sigma significance traditionally set for a discovery claim, but very close.

    [re: “very close”]Forgive the noob question, but, I thought, statistically speaking, there was a big difference between 4 and 5. As a layman, I thought it was akin to the (logarithmic) Richter scale (i.e., while 5 sigma is a somewhat arbitrary cut-off it was still much larger than a 4 sigma.) Is a 4 sigma really a big deal? Dumb question? Not Even Wrong, even?

  2. Peter Woit says:

    Rob R.,

    My “very close” maybe is overly optimistic, but Not Even Wrong, since I haven’t specified the metric. To give some more numbers to justify it though, the same calculation I’ve seen that has an expected significance of 4 sigma at 125 GeV gives an expected significance of 5 sigma at 130 GeV. Also, this is just the expected significance: if they get lucky and get a statistical fluctuation of more events than expected, say of size 1 sigma (where the sigma now is a different one…), they would get to 5 sigma.

  3. HHG says:

    There will be no official combination until each experiment will have reached 5 sigma alone – for “political” reasons.

  4. Peter Woit says:

    HHG,

    Thanks! But if CERN in early July is looking at CMS and ATLAS 4 sigma announcements, do they have a plan for dealing with the “political” problem of the Higgs discovery being announced not by them, but on viXra log?

  5. Bernhard says:

    HHG,

    that´s a bit strange statement. Two experiments getting 4 sigma, would be more than enough to claim a discovery. Not so time ago one the the spokespersons of one experiment was actually claiming that ATLAS and CMS getting a bit more than 3 sigma would allow them to claim. 5-sigma alone EACH is overkill.

  6. Peter Woit says:

    Bernhard,

    Maybe CERN would just go ahead and announce “discovery”, on the grounds that it really doesn’t matter how you do the combination, the conventional standard has clearly been met. Pretty odd though if the only quantitative combination result available is that from Philip.

  7. Anonyrat says:

    Since CERN has no competition, in my opinion, there is no need to hurry up the claim of discovery of the Higgs. Whether two months or six months from now, it will be the CERN collaborations that discovered the Higgs. So let them do it as carefully and properly as they can.

  8. emile says:

    I think it could be a mistake for CERN and the experiments not to combine their results. **IF** the two experiments had over 4 sigma each at ICHEP, everyone would consider the Higgs discovered, and unofficial combinations would provide the “discovery threshold” of 5 sigmas. When CERN did eventually release results of one or both experiments with more than 5 sigmas, the cat would already be out of the bag, and the level of interest will just not be there: people will say that they have not announced anything they did not already know. They (CERN) should be prepared to go public with an official combination **IF** the two experiments together meet the discovery threshold or they will lose control of the PR game. This kind of event happens very, very rarely. You have to milk this for all it’s worth. You can’t mess things up because of “political reasons”.

  9. BJM says:

    It seems to me that announcing discovery while both experiments are at 4 sigma alone but together reach 5 sigma is ideal from the standpoint of equal sharing of credit. If the announcement awaits both experiments to reach 5 sigma, one will inevitably reach it first and claim (and perhaps be due) sole credit. Is that desirable?

  10. strong field physicist says:

    BJM,

    In my opinion not. Scientifically, its good to have two independent experiments which may eventually confirm a discovery. But there is no valid reason why official combinations would detract from experimental independence. This political rubbish, though perhaps inevitable, is not justified. I dont think any particular experiment should see this as “their” discovery. Since funding is in a vast part from the public purse, its more correct to see it as *humanity’s* discovery.

    I’m all for Phil’s efforts (and his applet). It plays an important part in bringing science to the people – so to speak. Its just a bit sad that we are reduced to digitising data from webpages

  11. Nex says:

    I played with the applet and it looks to me that there is only a distinctive bump in the gamma gamma channel at ATLAS and CMS, while other experiments and channels are also above expectations there they are very flat and very broad and look to me like an underestimation of the background in the 110 – 140 GeV/c2 region.

    Isn’t the fact that the bump is only in one channel a reason for skepticism?

    Personally I doubt the Higgs boson is real and the data as presented by the applet doesn’t look convincing at all. The most likely explanation of the data IMHO is the underestimation of background in the 110-140 range combined with 3 upward fluctuations (CMS actually sees 2 similar bumps one at 125 and one at 135) in the gamma gamma channels, two of which happened to overlap.

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  13. Bernhard says:

    Nex,

    you have to remember that the Tevatron results (2.2 sigma) are also consistent with the interpretation of a signal there. I agree one should be careful and has the right to be skeptical, but things are looking more and more in the direction of a signal rather than a statistical fluctuation.

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  15. David Derbes says:

    There is one sort of political reason for announcing the discovery in July (if they have the data from both ATLAS and CMS that, responsibly combined, give 5 sigma): the age of the theorists involved. There are a lot of individuals whose work contributed to this; the Sakurai Prize was split six ways. But it was done circa 1964, nearly fifty years ago. Robert Brout has died. Peter Higgs whose health, as far as I know is fine, is 82. I don’t know how the Nobel committee will assign credit, but you can’t win it posthumously. It would not in my opinion reflect well on anyone if Englert or Higgs or any of the other four survivors died between, say, July and late September, when the evidence will presumably be more definitive. (Disclaimer: Peter Higgs was my thesis supervisor, and I admit to wanting to see him win. Who else additionally wins is fine by me. :-))

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