Disappearing gammas

The CMS data on the Higgs in the gamma-gamma channel has been released this morning, see slides from a talk at Moriond. Basically the excess over the SM prediction seen in this channel in earlier data is gone, with CMS reporting ratios to the SM predicted value of .78 +/- .27 using one sort of analysis, 1.11 +/- .31 using another, so, naively averaging, say .95. ATLAS sees 1.65, so a naive combination would give 1.3, only about one sigma high, very consistent with the SM.

Amusingly, the better than 4 sigma signal CMS was advertising last summer in this channel that was part of the case for the discovery announcement has largely vanished in the new 8 TeV data. With one analysis method, they see only a 2 sigma signal in the 8 TeV data. If they had been working with this new, larger and better, data set instead of the older, smaller 7 TeV data set, the Higgs discovery claims might not have been possible last summer. Of course, the CMS + ATLAS combined gamma-gamma results are very strong evidence for a Higgs signal, and the ZZ results are overwhelming, so the existence of a new particle is not in doubt. This is actually what you expect if a SM Higgs is there: you should get reversion to the mean and disappearance of the earlier too large observed excesses.

CERN has a press release out today which is getting a log of attention, headlined
New results indicate that particle discovered at CERN is a Higgs boson. This emphasizes results about the spin, but the new gamma-gamma results are what is significant, as they remove the one anomaly that was getting a lot of attention from theorists hoping for some kind of violation of SM behavior.

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16 Responses to Disappearing gammas

  1. behghk says:

    CERN does not call it a Brout-Englert-Higgs-Guralnik-Hagen-Kibble-pleaseaddmynametothelist-(Anderson hey what about me?) boson?

  2. King Ray says:

    Success has a thousand fathers but failure is an orphan.

  3. dark says:

    To anyone -
    what are the scientific ramifications of finding a *single* higgs boson (and no SUSY @ LHC) with SM only properties @125-6 GEV to the likelihood of SUSY, MSSM, GUT SUSY-GUT? I was of the understanding that they predicted multiple higgs bosons., and therefore, finding 1 and only 1 decreases the likelihood of SUSY or GUT.

  4. Eric says:

    Dark,

    The additional Higgs bosons predicted in the MSSM can have large masses such that they would not have been observed at the LHC. This is also true of all other scalars in the MSSM.

  5. dark says:

    eric ok thanks,

    but in those class of models are those “too large for LHC energies” masses “natural” and “well-motivated” or simply epicycles?

    I thought natural well motivated MSSM prefer a very light Higgs 110GEV?

  6. jinb says:

    Scalars are more naturally heavy than they are light, the only expectation for them to be light being the hierarchy problem, but otherwise if you relax that assumption it’s not arbitrary. Quite the opposite, it would be arbitrary to have them light, which is the guiding principle behind nima’s split susy model. Just abandon TeV scale hierarchy problem and see what’s the most natural thing for susy to do.

    SUSY does prefer a light Higgs relative to the Z mass, and 125 GeV certainly is light.

  7. paddy says:

    And just what is the “most natural” unnatural thing for susy to do? kinda like a word game eh?

  8. Thomas Larsson says:

    That the Higgs mass seems to sit exactly at the border of SM consistency is interesting, and reminds me of a similar phenomenon in another part of physics. In the 1940s Lars Onsager proved some inequalities that critical exponents must obey for consistency. Twenty years later people found that these inequalities were in fact identities, i.e. critical exponents are on the border of being inconsistent. The underlying reason for this is scale symmetry.

    Extrapolating this observation to the SM, the fact that Higgs seems to be borderline inconsistent could indicate that some symmetry principle is at work. There is of course no secret what I believe that this symmetry principle might be.

  9. A says:

    “but in those class of models are those “too large for LHC energies” masses “natural” and “well-motivated” or simply epicycles?”

    I wouldn’t call them epicycles because you don’t have to add anything to the model to obtain them, but the higher you raise the remaining SUSY masses, the more finely tuned is the smallness of the electroweak scale relative to those SUSY masses.

  10. Allan Rosenberg says:

    According to the Washington Post, the conclusion “helps solve one of the most fundamental riddles of the universe: how the Big Bang created something out of nothing 13.7 billion years ago.” http://www.washingtonpost.com/world/europe/physicists-say-they-are-now-confident-they-have-discovered-the-long-sought-higgs-boson/2013/03/14/0ffa6562-8c90-11e2-adca-74ab31da3399_story.html Let all of the people who say HEP experimentation is a waste of resources chew on that!

  11. bang says:

    It does help, in its own way. Take away the Higgs, the quarks and leptons, the (nonabelian) gauge bosons, the photons … and what do you have? No photons, ergo no blackbody radiation, ergo no CMB, ergo … how will you even be able to say the Universe came from a Big Bang?

  12. emile says:

    I’ve found recently that many people (even a few in HEP) confuse the Higgs boson of the SM with the particle predicted by Higgs. Back then, there was no SM, and no weak neutral boson. The prediction involved a scalar field that coupled to W bosons to give them their mass. I’m glad that CERN is now making the point that this is a Higgs boson: there is a particle beyond a reasonable doubt, it couples to weak bosons, and spin measurements are compatible with a spin 0+ particle and the alternatives are disfavoured (at ~95% CL or greater).

    @bang: could you expand a bit on cosmology without EWSB? so we would have no photon but we would have four massless bosons, including the “B”. So what would replace the CMB? matter-anti-matter particles would annihilate to what? There would be a background radiation of Bs? I had not thought of this before…

  13. Michael Brown says:

    @emile Recently read this physics stackexchange question on the standard model without EWSB. I found Ron Maimon’s answer in that thread to be interesting and well worth reading.

    Note that QCD still gives a mass to the weak gauge bosons (though much smaller than their actual masses due to the Higgs), and nuclear physics is very different. I’d love to know if anyone has any scholarly references about this.

  14. Alex says:

    “I’d love to know if anyone has any scholarly references about this.”

    Yes, for example Robert Shrock and Chris Quigg made quite an effort exploring this scenario explicitely here:

    http://arxiv.org/pdf/0901.3958

  15. bang says:

    @emile: Back up a step and set aside EWSB. Go back much further, to the days before QM and Relativity. Go back to the 19th century. Scientists in the 19th century (geologists etc) had come to realize that the Solar System was at least hundreds of millions of years old. Scientists also knew enough physics to realize that the Sun was a ball of mainly hydrogen gas, and its approximate size and its radiated power. They also knew from chemistry that chemical hydrogen burning to water could not provide eneough energy to sustain the Sun’s radiated power for such a long time. So the source of the Sun’s energy was a puzzle which 19th century physicists knew they could not explain with the physics of the day.

    My point is they knew that they did not know. They knew that there was new physics `out there.’

    And they were correct. We know today that thermonuclear fusion is the source of the Sun’s energy. It is a form of energy unknown in the 19th century. It required both QM and Relativity to answer the puzzle of the source of the Sun’s energy.

    So, my point is that the Higgs, etc. do help to increase our understanding of fundamental processes, the interaction of matter and radiation, and this does help, in its own way, to understand the physical processes of the Big Bang. Don’t jump ahead so quickly to EWSB.

  16. Flakmeister says:

    With regards to the the earlier modest excess over the SM in the di-photon channel one needs to appeal to the old adage “discoveries are always made on an upward fluctuation”….

    I do have to admit that “No-lose theorem” for a TeV scale collider is starting to look like the lowest possible payoff was in the offing… Too bad, even though I was never a fan of low energy SUSY, but, discovering would have enabled a return to the Golden Age of Particle Physics, i.e. when everyone with pulse could find something new, but unlike the 60s, one could actually calculate quantities….

    Given the slim prospects and likely timeline for the next collider, perhaps it is just as well that it was a SM higgs and that was “all she wrote”….

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