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    Zooming In On The Higgs
    By Tommaso Dorigo | February 24th 2012 02:00 AM | 12 comments | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

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    Thanks to Sven Heinemeyer and his colleagues, we can give a peek today at the status of the agreement of top and W boson masses with Standard Model predictions for the Higgs boson mass, and with SUSY predictions as well. The figure below is just one of the many versions he has produced.



    Maybe I should not say "SUSY predictions", as it is clear, by inspecting the figure above, that the green band is quite wide, a result of the many free parameters whose value have an impact in determining the mass of the lightest Higgs scalar.

    In any case, the graph represents an impressive picture of self-consistency of the Standard Model with the experimentally allowed values of the Higgs boson (the blue band).

    We used to talk of an existing "tension" between radiative correction fits and existing bounds for the Higgs (which have remained those of LEP II for almost a decade before the first Tevatron exclusions and then the LHC exclusions pitched in), but it is clear that much of that tension has faded away: everything is consistent with a Higgs boson of mass in the 125 GeV ballpark.

    So, will it be a SUSY or a SM Higgs ? You know what I believe, but you are allowed to dream on - SUSY allows you an infinite set of different dreams, in a over-100-dimensional parameter space. But if you are a pragmatic dreamer you might want to wait and check the new CMS and ATLAS results on SUSY bounds - they are going to appear in a couple of weeks, right in time for the last winter conferences. So stay tuned!

    UPDATE: in the comments thread below, Sven correctly points to a better version of the figure, see below.


    Comments

    lumidek
    In any case, the graph represents an impressive picture of self-consistency of the Standard Model with the experimentally allowed values of the Higgs boson (the blue band). 
    Given the fact that the blue circle sits in the green band, what you really meant is the following (thank me for the correction, you're welcome):
    In any case, the graph represents an impressive picture of self-consistency of the Minimal Supersymmetric Standard Model with the experimentally allowed values of the Higgs boson (the blue band). 
    This is again a funny "Sheldon-comment" which makes me LOL ;-)

    Any comment on the paper saying that CDF sees nothing in diphoton Higgs channel?

    http://www-cdf.fnal.gov/physics/new/hdg/Results_files/results/hgamgam_de...

    What needs to be said? Their sensitivity is at 10x the standard model in the interesting region.

    I don't understand what your comment about sensitivity is supposed to mean.

    As to what needs to be said, some commentary would be nice, it seems strange to me that when authors see bumps the papers are trumpeted everywhere, but when here is one which doesn't see it seemingly contradicting the others, it is ignored. So I wonder if there is a legitimate reason for ignoring it or if it is some sort of bias.

    lumidek
    Dear Paul, there is no contradiction here. The claim that "sensitivity is 10 times the Standard Model" means that only if there were new physical phenomena that would make these diphoton final states 10 times more frequent than predicted by the Standard Model, then the Tevatron could see some signal.
    Right now, it only sees the noise and this is exactly what is predicted by the Standard Model for the diphoton channel for 10/fb at the Tevatron.



    Thanks to Lubos for clarifying what I meant.

    Paul: I apologize for the hit-and-run comment, let me elaborate on that (very nice) CDF analysis:

    First, looking at table 1, the number of stndard model Higgs to diphoton events expected in that dataset is 27ish. Then in the appendix, you can see that their combined detector acceptance, trigger efficiency and reconstruction efficiency is less than or around 10% (depending on the details of how the Higgs is produced). So on average, you'd expect the tevatron to see 2 events in the dataset (here "on average is in the frequentist sense of "suppose we repeated the tevatron experiment many times...").

    Now, you can see in the diphoton mass plots that there are hundreds of events in each bin, something like 200 or 300 around the interesting region (125 GeV). The natural bin by bin fluctuations would be expected to be sqrt(300)=17. The natural statistical noise is 8-9 times larger than the signal, so CDF doesn't expect to be sensitive to the standard model.

    If, on the other hand, things conspired outside of the standard model to boost the number of signal events by a factor of ten, then the signal size is at least comparable to the background, so in this hypothetical scenario you might expect to see something. The exact factor is not quite ten, but is calculated from the background distribution. The sensitivity is the answer to the question "compared to the standard model, how large would the signal production have to be so that we only have a 5% chance of a null result like we got." then, reversing this question, you can say that you are 95% sure that Higgs production and decays to diphoton happen less frequently than this sensitivity. For this analysis, that limit is way up at 10x the standard model prediction.

    I hope that's enough detail to clear things up! If you're a more regular reader of this blog (so that you can make sense of Higgs limit plots), the usual green and yellow band plot is fig5 in your linked PDF.

    Cheers!
    Brian

    Ok, I get it now, thanks a lot for clarification.

    Looks even nicer if
    a) the latest (preliminary) world average for MW is used
    b) the SM and MSSM regions are restricted to be consistent with a Higgs mass between 123..127 GeV
    as can be seen here:

    I would call it consistency, but not "excellent". What is excellent is the CDF measurement.
    Anyway the plot easily fools you: the higgs mass band is very narrow (ATLAS and CSM limits taken too seriously)
    and this makes one superficially think that the consistency is not so great.
    It is funny that it looks like we know the higgs mass range much better than the error band on the Top and on the W...
    Overall, we are closing in and hopefully this year we will know something new, finally!

    dorigo
    Well, it is not only funny - it is true: if you assume the SM is valid, then our knowledge of the Higgs boson mass is not too different from our knowledge of the top. The top is known to 0.9 GeV accuracy, the Higgs is known to 2-GeVish one.

    Cheers,
    T.
    I was talking about being fooled by the plot scales and I got fooled too ;)
    Thanks.