Higgs Non-News

The two main LHC experiments have now recorded just about 5 inverse femtobarns each of data this year (CMS here, ATLAS here). This is the last week of the proton run, so that number will be near the total available for analysis until next spring when the next proton run gets started.

For some idea of what this means for the Higgs search, see for example Tommaso Dorigo’s discussion here of last year’s ATLAS projections about this. 5 inverse femtobarns was at the high end of what was expected, and the ATLAS projection was that this would be just barely enough to expect to be able to rule out a Higgs at 95% confidence level, all the way down to the LEP limit at 114 GeV. Of course, this expectation is statistical. If the Higgs is not there, and one is lucky (downward statistical fluctuation in number of events), then one can exclude at better than 95%. If one is unlucky (upward fluctuation), or the Higgs is really there, the 95% exclusion will not be achievable.

The LHC Higgs Combination Group has now combined the ATLAS + CMS Higgs results released at the summer conferences, and plans to release this in time for the HCP 2011 conference next month. Because of the efforts of Phil Gibbs, about all that needs to be said about the LHC-HCG plot is that it looks an awful lot like his, which is available here. An SM Higgs is excluded at 95% for masses below about 480 GeV, down to a lower limit of around 135 GeV (the data is actually very flat and close to the right value to exclude the SM from 135 GeV to 145 GeV).

The huge question of course is now whether there is a Higgs with mass between 135 GeV and the LEP limit (114 GeV). The current LHC data shows no definite sign of the Higgs, but the statistics is still too low to really say anything, especially for the lower part of the region. The crucial thing to watch now is the Higgs to gamma-gamma channel, which is the only one sensitive enough to hope to rule out or see a Higgs in the 115-125 GeV region, for the current amount of data collected. I don’t know when the experiments expect to release new data in this channel, just that their goal has been to each have some sort of result in December. Perhaps they’ll release something at HCP 2011, more likely not. The only rumor I’ve heard is from someone who has seen a recent plot of the ATLAS data for this channel, and he tells me he doesn’t see any bump in this region. But work on this data is on-going, and I have no idea what CMS is seeing or not seeing (my efforts to get Tommaso Dorigo drunk in Antwerp last month didn’t yield much).

At last month’s CERN Council meeting, there was a report submitted to the Council on “The scientific significance of the possible exclusion of the SM Higgs boson in the mass range 114-600 GeV and how it should be best communicated.” The report is based on the summer 2011 data, and it emphasizes excluding the Higgs at not just 95% (2 sigma), but at 5 sigma, something that will require (if the Higgs is not there) combining the 10 inverse femtobarns of data from each of the two Tevatron experiments and a similar amount from each of the two LHC experiments, something that won’t be possible until sometime after mid 2012.

Update: One more related item. At Berkeley starting today, ATLAS is holding an Analysis Jamboree on Higgs Searches. First two days is the good stuff, open only to ATLAS members, but the last day there will be an open session with theorists allowed.

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15 Responses to Higgs Non-News

  1. Anon says:

    Your link to Tommaso Dorigo’s post starts http://http//.

  2. dir says:

    to fix the higgs mass, zz*–>4l and h–>2gamma channels are important. it seems to me that philip gibbs’s combination of these channels does hint a 140 gev higgs, see
    http://blog.vixra.org/2011/09/18/higgs-days-at-santander/

  3. Peter Woit says:

    Anon,

    Thanks, fixed.

    dir,

    I guess the kind of question raised by Phil Gibbs in that posting explains why CERN is looking for better than 95% exclusion in the combined channels, just to make sure.

  4. chris says:

    where are all the spies if one needs them :-)

  5. Paolo Valtancoli says:

    If the Higgs is not found, phenomenologists are ready with their fancy higgless models…

  6. Bernhard says:

    Paolo,

    the discussion is about the SM Higgs for the moment. It will take a huge amount of data to discard just any Higgs.

  7. Tony Smith says:

    As to the Higgs to gamma-gamma Channel,
    Eilam Gross in Slide 57 of his 29 August 2011 presentation
    “Higgs Searches at the LHC”
    described CMS results at around 1.7/fb saying:

    “… A local moderate (yet genuine) 2.3 sigma excess
    is seen in CMS around 120 … LEE washes out the excess

    There is 2.8 sigma [around 140] with Higgs to gamma-gamma
    which is reduced to 1.7 sigma with the LEE …”.

    So, whether or not use of LEE (the Look Elsewhere Effect) is
    a decision with significant consequences
    that needs to be taken carefully in analyzing the 5/fb Halloween data.

    Tony Smith

    PS – His slide 22 shows the connection between
    the 140 peak on the CMS Brazil Band plot
    and
    the same 140 peak as a bump on the CMS data histogram.

  8. Peter Woit says:

    Tony,

    The released gamma-gamma data from this summer is just not enough to have any realistic hope of seeing a SM Higgs signal, at 120 or 140 GeV. To get an idea of the significance of any excess you see anywhere in it, you definitely need to include the look elsewhere effect, since you are looking for an excess anywhere in a large region. Statistically, you’re sure to find some excess somewhere.

    By now CMS and ATLAS should have much more data analyzed, approaching the amount needed to actually see something. Whether they have enough to say something definitive will be very interesting to see. Maybe we’ll find out in December…

  9. null says:

    Has the Tevatron collected enough fb-1 to decide the issue in the interesting region 114-135GEV?

  10. ohwilleke says:

    IIRC, the issue with the 135-145 GeV range was that given the power of LHC to see a signal there, there possible signal was much weaker than one would expect from a SM Higgs even if it had some statistical signficance – we should have see twice as many sigmas of significance as we did at last publication. In contrast, at 115-125 GeV where there was also some hint of a signal, the power of the LHC to see anything in that mass range was weak enough to not be inconsistent with a SM Higgs.

  11. Shantanu says:

    Peter, curious about your comments on the discussion about eternal inflation on cosmicvariance between Tom Banks and Sean Carroll.

  12. younghun park says:

    Peter
    As null said, many people including me want to know about the analytic result of Tevatron. Do you know something on Tevatron? If you have heard, I hope to get good information from you.
    Cheers

  13. Peter Woit says:

    null, yonghun park,

    For the details of the Higgs story at the Tevatron, see here:

    http://indico.cern.ch/getFile.py/access?contribId=60&sessionId=0&resId=1&materialId=slides&confId=141983

    They have reported results this past summer based on up to 8.6 inverse femtobarns (per experiment), now have about 10 inverse femtobarns. Speculation is that they might report results at Moriond (March), but definitely by next summer’s conferences. They should be competitive with this year’s LHC results at the low end of the interesting mass range (just above 114 GeV), less so as the mass gets larger. In any case though, they should be able to just barely see or exclude a Higgs in the interesting region. Whatever their result is, if it’s consistent with the LHC results (either an exclusion or positive evidence) that would provide confirmation (or the LHC would provide confirmation to them depending on how you look at it…).

    So far though, they’re not seeing anything in the interesting mass range, but so far with statistics too low to claim exclusion. But they’re almost there…

  14. Peter Woit says:

    Shantanu,

    I haven’t followed the details of their discussion, but from what I did read and what I’ve heard from Banks in the past, I tend to agree with his argument that effective field theory arguments being used in this area are dubious, so there’s no particular reason to believe in eternal inflation. But I’m equally dubious that he has any believable alternative. This is an area where physics has gotten too close to metaphysics for my taste. There’s neither experimental observation nor solid theoretical argument available to decide the issues they are discussing, so this kind of discussion can go on eternally without getting anywhere….

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