Sunday Night Higgs?

Lepton-Photon 2011 begins Monday morning, the schedule is here. It should start off with a bang, with the latest Higgs search results from ATLAS and CMS presented starting at 11:20am local time, the middle of Sunday night here. There will be a press conference on Wednesday.

If the hints of a Higgs signal seen in the data presented last month at EPS-HEP 2011 are real, they should be more pronounced in the new data (the experiments have now collected about twice as much data as that used in the analyses presented at EPS-HEP 2011). The Higgs Combination Group should by now have produced a combined analysis using last month’s data from the ATLAS + CMS and presumably that will also be released on Monday or soon thereafter. They have just today released a new document giving the details of how the combination is done: Procedure for the LHC Higgs boson search combination in summer 2011. Still holding out on us though in terms of the real data, that document just shows toy data…

Update: The latest rumor I’m hearing is that the only analyses updated with new data (nearly twice as much) since EPS-HEP that will be available Monday will be from individual channels. Analyses combining the different channels won’t be ready for another 2 to 3 weeks. I still think though that we should see the CMS+ATLAS combination of the old data shown at EPS-HEP. So, if the Higgs is there, a definitive signal may still not quite yet be available. These people do need to take a vacation sometime in the summer…

Update: The news is that CMS and ATLAS have produced new combinations (although the combination of older ATLAS + CMS data has not been released, and I’d love to know why…). The bottom line is that the hints of a Higgs around 140 GeV have weakened with the addition of more data. A simplified summary of the current situation would be:

  • No Higgs above 145 GeV
  • In the region 135-145 GeV, both experiments are seeing somewhat more events than expected from background, but less than expected if there really was a Higgs there.
  • Not enough data to say anything about 115-135 GeV, the Higgs could still be hiding there. If so, a malicious deity has carefully chosen the Higgs mass to make it as hard as possible for physicists to study it.
  • More details available on the conference slides that should be available here. Tommaso Dorigo and Matt Strassler have commentary.

    Update: Still no word on why no CMS+ATLAS combination has appeared. Philip Gibbs has hacked together an unofficial version (see here and here). Comparing the EPS data to the latest, one sees clearly that a marginally significant signal consistent with a Higgs has weakened quite a bit with the new data (and thus, there was little to no evidence for such a Higgs in the new data). Also worth reading, commentary from Jester here.

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    45 Responses to Sunday Night Higgs?

    1. M says:

      The rumor is different

    2. Charles says:

      What is the rumor this round?

    3. Peter Woit says:

      Charles,

      If I had heard any believable rumors, I’d post them here. Maybe M can share more details with us. Or, anonymous posting by the well-informed is encouraged…

    4. null says:

      Would there be any reason for “Lepton-Photon 2011″ and “Higgs Combination Group” to announce a null result (if there is one)? So if they do plan an announcement, presumably they found some evidence for a higgs?

      How many fb-1 have been collected to date?

    5. SA says:

      Over 2/fb

    6. bonk says:

      There’s no point in keeping announcing null results. BUT, since many people have nothing better to do other than wait for Higgs results, suddenly there is a point.

    7. Peter Woit says:

      null, bonk,

      With this amount of data, the result (even a null result) is guaranteed to be interesting. If you really don’t see anything, you can rule out the possible existence of a Higgs on more and more of the allowable mass range. If this can be done all the way to the LEP limit (this is still a ways away), you’ve shown there is no SM Higgs and shown there is something dramatically wrong with our understanding of the SM. If you do see a signal, that’s of course big news and the beginning of a research program to understand exactly how the Higgs behaves.

      The least interesting thing is a signal of marginal statistical significance, but as data accumulates this starts to become impossible. Either you see the thing or you show that it isn’t there.

    8. Emile says:

      Bonk: since there is no point in announcing null results, the two experiments will not tell the rest of the world in what mass range the Higgs has been excluded. And, they won’t bother to tell the world if/when the whole mass range has been excluded either.
      CDF and DO would also like to apologize for releasing null results.

    9. Hi,

      I think “bonk” must be joking. ;) CMS and ALTAS are testing a wide range of possible Higgs masses and any statement that there is no evidence for a standard model Higgs boson within that range is an important scientific result. There is an hypothesis, and then there is the experimental test. This is not really grounds for cynicism, right? ;)

      About 2 fb-1 has been collected by each experiment, but you can expect some fraction, say 20%, not to ready yet for analysis. Since the increase in the data samples is rapid, the need to combine ATLAS and CMS results is not so strong. I’m sure each experiment will show updated combined results, but I would not necessarily expect to see an ATLAS+CMS combination.

      bye

    10. Peter Woit says:

      Hi Michael,

      I’m hearing from other sources the opposite: that individual ATLAS and CMS combinations of new data aren’t yet ready (although some individual channels are). Also, the LHC Higgs Combination Group was supposed to have an ATLAS+CMS combination based on analyses released at EPS-HEP ready a week or two ago for release at Lepton-Photon. Is there any reason that won’t happen?

    11. M says:

      The rumor is that the combinations of different channels within single experiments will be shown at 1.5 fb-1 (but no ATLAS + CMS combinations) and that unfortunately the hint at 140 GeV XXXXXXXXXXXX, partly because the background XXXXXXXXXX.

    12. Anonymous says:

      Do you personally believe that they’re going to find the SM Higgs boson, Peter?

    13. Peter Woit says:

      Anonymous,

      I have no idea whether there’s an SM Higgs, or something more interesting is causing electroweak symmetry breaking. I’ve been wanting to know this for more than 30 years, so very much looking forward to finding out….

    14. bonk says:

      In the Tuesday talk “BSM results from LHC”, we will also get an update on SUSY with over 1.5 fb^-1. Is that right?

    15. bonk says:

      Just watched ATLAS and CMS talks. Moderate enlargement of last month’s exclusion regions. They expressed disinterest in combining data, because data are being produced faster than can be combined. Also, last month’s excess has decreased in significance.

    16. Thomas Larsson says:

      Does decreased significance mean probably no Higgs? If the signal were real, we would expect significance to increase with more statistics, right?

    17. Fred says:

      There is no Higgs and probably no new physics. Wow.
      Sorry Higgs, Guralnik, Hagen, Kibble, Brout, Englert, Anderson, Weinberg, and Salam, but you were wrong all along. Good effort though.

    18. DB says:

      The UK’s guardian newspaper is reporting from the Lepton-Photon conference in Mumbai that there’s nothing to see here, the signals have all but vanished.

      http://www.guardian.co.uk/science/2011/aug/22/higgs-boson-signals-fade

    19. jon-student says:

      Suppose there’s no Higgs. From wikipedia, there appears to be several proposed Higgless models: are some of them testable with LHC data accumulated so far? If not, how much more data would be needed: end of 2012? or the 7 Tev run after 2013? or even more? Thanks, exciting times!

    20. Thomas Larsson says:

      Don’t Higgsless models also require something like a Higgs at the LHC, even if it is composite. E.g. a bound state of technifermions?

    21. m says:

      Wow, some people are fast at concluding there’s no Higgs! The limits do not cover the whole mass range; the Higgs could still be light and compatible with SM predictions if it exists!

    22. Peter Woit says:

      jon-student,

      The search for the SM Higgs is very straightforward in the sense that you have a very precise model to test, with everything completely determined except the value of one parameter. In terms of testability/predictivity, it almost never gets any better than that.

      If there is no Higgs, and something else is responsible for electroweak symmetry breaking, there are lots of possibilities that have been suggested, but none that are really compelling. These have lots of undetermined parameters. In many cases evidence should be visible at the LHC if you do the right analysis, but you can also come up with models that would not have effects visible at the LHC. For now I suspect the experiments will remain focused on looking for the Higgs, but if that gets ruled out, attention will move to other possibilities, and in some sense the subject will get a lot more interesting…

    23. Alex says:

      Slow down, what are you people talking about? Looking at the ATLAS/CMS exclusion plots, they are still pretty much what one would expect to see right now if there was a Higgs at above 140 GeV for example. Any data points that go beyond the sigma/sigma_SM =1 line are bound to become smaller if it is a SM like Higgs. Large peaks beyond that line are not expected to prevail if the SM Higgs is realized in nature.

      @Thomas Larsson,

      The family of so-called Warped Higgsless Models which became famous around 2003, do not have to have any fundamental scalar resonances, in their range of perturbative validity, which extends up to about 5 TeV. (apart maybe from the radion which represents fluctuations of the size of the extra dimension).
      This is in contrast with so-called composite-Higgs models. It is conceivable that if the radion is light, it might get some effective nonrenormalizable somewhat higgs-like couplings, but not necessarily comparable to what a Higgs would do.

    24. Alex says:

      In my last comment it was supposed to read

      “The family of so-called Warped Higgsless Models which became famous around 2003, do not have to have any —————- scalar resonances, in their range of perturbative validity, which extends up to about 5 TeV.”

    25. felix says:

      95% CL exclusion:
      ATLAS
      146~232, 256~282, 296~466
      CMS
      145~216, 226~288, 310~400
      Tevatron
      100~109, 156~177
      I don’t understand why people take this as a sign that the Higgs might not exist. Since precision electroweak constraints favor a light Higgs, ruling out larger Higgs masses only makes us more confident in the SM.

    26. Charles says:

      The “Higgs” also could be composite – consistent with the general proof of some of the theorists back in 1964.

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    28. Out of curiosity, do there happen to be any theoretical models which predict that the Higgs should be exactly where it is most difficult to find?

    29. chris says:

      Harry Johnston,

      yes, in fact one extremely compelling one. if there is the SM Higgs in the region of 130~160 GeV then unitarity of the SM is guaranteed up to beyond the Planck scale. so if you think the SM is all there is up to gravity and if you disregard all naturalness-based arguments, the Higgs is ‘expected’ to lie in that region.

      if it will turn out to be a 130GeV SM Higgs – well then very probably goodbye to all accelerator-based signals of BSM physics for probably the rest of our and our grandchildrens lifes (although one has to be careful with this sort of statements).

    30. chris says:

      the SUSY summary was just given: no signal again.

    31. Eric says:

      “Not enough data to say anything about 115-135 GeV, the Higgs could still be hiding there. If so, a malicious deity has carefully chosen the Higgs mass to make it as hard as possible for physicists to study it.”

      Isn’t this precisely the Higgs mass range expected in the MSSM (< 130 GeV)? Apparently, the malicious deity goes by the name, Susy.

    32. Peter Woit says:

      Eric,

      Minimal susy (as well as precision electroweak fits) most naturally leads to lower values of the Higgs mass. It’s the LEP bound that gives you the 115 GeV. Already a malicious deity seems to have been at work, pushing the Higgs mass just above where LEP could see it.

      Maybe the LHC will find no superpartners, just the Higgs of the MSSM. Hard to see how that would work, but I’m sure susy modelers can find a way…

    33. Eric says:

      Peter,

      You need to be careful about what you mean by “natural”. Natural is whatever nature does, not what you think it should be based on your personal judgment. In the case of minimal supersymmetry, the Higgs mass can be as great as 130 GeV. In fact, taking into account all current constraints, the “most likely” Higgs mass is around 118 GeV. If this is the case, then no Higgs signal should have shown up yet, but it should show up by the end of 2012.

      In the case of the observation superpartners, you are essentially looking at the situation with a very naive and uninformed point of view. As has been pointed out to you by other commenters, the current contraints are based on simplified models which make certain assumptions. The main assumption of these models is that squarks and gluinos decay directly to the lightest neutralino, and thus produce large missing energy signatures. This definitely does not have to be the case, which would cause the signals of the superpartners to be much more difficult to see. Similar considerations apply if R-parity is violated. Besides these considerations, the squarks and gauginos easily be as heavy as 2 TeV, meaning that it would not be possible to see them until the second higher energy LHC run after the year-long shutdown/upgrade.

    34. Pingback: LHC lässt dem Higgs immer weniger Verstecke « Skyweek Zwei Punkt Null

    35. Tom says:

      The CMS speaker himself said it would be worthless to present a combination plot at this point as it would be outdated by the time it appears since the data has been coming in so quickly. Since pp data taking ceases at the end of Oct. it is reasonable to expect a combination to appear before the end of the year holidays.

    36. Peter Woit says:

      Tom,

      From what I hear, while there was some concern about the value of a combined CMS+ATLAS result when the individual experiments already had more data and better results, a deciding fact was that at the last minute a mistake was found in one of the input channels to the combined result. So, an excellent reason not to release it publicly at the conference…

    37. Pingback: Higgs Boson – Imaginary Particle Remains Science Fiction | Cosmology Science Blog © 2011 David Dilworth

    38. Peter Woit says:

      Thanks drl,

      Looks like Tommaso’s prediction was pretty good. By the time all Tevatron data is analyzed next year, their limits may be about what he was expecting. The LHC schedule however, didn’t work out as expected….

    39. Funes the Memorious says:

      Another quote from that same thread, showing not-so-accurate predictions:

      My personal preferred guess (30%) is that the Higgs is at the 115 GeV level, and it’s one of the light Higgs scenarios that are natural in SUSY.

      But the discovery of Higgs will be a few-day celebration only. It’s a trivial thing. We know that something like the Higgs must be there to make the WW WW scattering unitary, and the fundamental scalar is simply preferred by precision measurements.

      The real question to answer is SUSY below TeV, and other potential new physics.

      Ah! Those were the days when “SUSY below TeV” seemed to be just within reach…

    40. steve newman says:

      “Not enough data to say anything about 115-135 GeV, the Higgs could still be hiding there. If so, a malicious deity has carefully chosen the Higgs mass to make it as hard as possible for physicists to study it.”

      .
      Could someone explain what makes one energy range easier or harder than another for Higgs detection.
      thanks.

    41. Bill K says:

      What makes the Higgs boson easier or harder to detect is which decay channels are available, what their branching ratios are, and how easily they can be distinguished from the QCD background. See for example http://www.hep.lu.se/atlas/thesis/egede/thesis-node14.html. At low mass the leading decay is H -> b-bbar, very hard to identify. But the H -> WW is easy, and note how rapidly its branching ratio rises with increasing Higgs mass.

    42. Allan Rosenberg says:

      I used to think Lederman called the Higgs the God particle just to sell books. I didn’t give him enough credit. Now I realize that he called it the God particle as a sly prediction that it doesn’t exist.

    43. Chris Oakley says:

      Lederman has covered the possibility of the Higgs being composite, too, since God, assuming he exists, is also composite, comprising the Father, Son and Holy Spirit.

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