Revealed: The Best Higgs Plots.

In the previous post I explained that the CMS Higgs plots shown at Lepton-Photon were not as good as they could have been because the MVA analysis for the WW channel was not ready. In fact the earlier MVA based analysis for WW shown at Europhys is better in theory than the Cut-based analysis shown at LP. The best combination plot should use all the best data from each channel over all the experiments and that means using the MVA WW channel from EPS for CMS. So here is the best possible plot (in theory) using all the best LHC data and the latest Tevatron data. I have even added in the LEP result for the first time .

This is a pretty nice result. Everything is excluded at 95% confidence in the mass range from 145 GeV to 460 GeV, but there are small excesses over the range from 115 GeV to 145 GeV. A good thing to notice about this plot is that the expected CLs line is below the 95% confidence limit all the way up to 500 GeV. If there were no Higgs boson in that range they would expect to have excluded it, but they haven’t.

At this point I think that signal plots are more informative than the exclusion plots so here is how the signal changed between EPS and LP.

Remember that in these plots a level at zero indicates the absence of a Higgs Boson and a level at one indicates the presence of a Higgs boson. So the signal in the 115 GeV to 145 GeV is roughly the right strength for the Standard Model Higgs but it has dropped in the 140GeV area with the latest data as the error bands have tightened (though not as much as we previously thought). Now we should just wait for more data to resolve the low mass range, or should we?

I want to make the case that there is a big problem with these plots. Our expectation is that as more data comes in a sharp peak (or two) will emerge somewhere in the low mass region to reveal where the Higgs is. However, the plot is dominated by the WW channel over most of this range and the WW channel has low resolution. This is because it uses missing energy observations to construct the underlying mass of the events. The W’s decay into neutrinos which can never be detected directly. The result is that the Higgs appears as a broad excess in the WW channel and you can’t locate it well. The WW channel is great for excluding large ranges of the mass spectrum, but it is not good for pinpointing a low mass Higgs that has a narrow width.

Furthermore, the situation will not improve as more data is added. The WW channel will always remain low resolution and it will always dominate the combination plot. Sadly the Tevatron data has the same problem. It is dominated by WW and bb channels with neutrinos in each case. In fact the detectors themselves have poorer resolution and even the digamma and ZZ channels are only ever plotted at 5 GeV intervals for the Tevatron. So what should we do? if some data could be making the plot worse the best thing is to remove it and see what we get. So here are the signal plots without WW channels and without Tevatron data.

These plots use mostly the digamma and ZZ channels from the LHC. The LEP data is also retained because it is high-resolution too. How many Higgs bosons do you see now? Above 160 GeV the Higgs is strongly excluded by WW data in the earlier plots. Without WW, the ZZ channel dominates but the background is high above 155 GeV which accounts for the large error bands. So the bump centred on 165 GeV can be safely ignored.

What is particularly interesting now is the bump at 140 GeV. Some people said that this excess came mostly from the WW channel, yet when the WW channel is removed the bump is still there with nearly 2-sigma significance. The two bumps peaking at 118 GeV and 128 GeV are also the right size for a Higgs signal but error bands are still too big. Any of these bumps could be statistical fluctuations but it is very unlikely that they all are.

With current data available in the high-resolution channels it is not yet possible to draw robust conclusions, but I think I have demonstrated that this will be the best way to find the Higgs with future data. I hope the experimenters will take note and produce similar plots from the official data.

Updated results with 2.5/fb could appear within weeks and we will see where the three candidate bumps are heading. With 5/fb or more by the end of the year these plots will be showing strong signals and with 10/fb or more by the end of 2012 the Higgs discovery should be conclusive from these plots, unless it isn’t there.

39 Responses to Revealed: The Best Higgs Plots.

  1. Dilaton says:

    I like looking at these plots :-)

    If some experimenters are not happy about them or disagree with the methods Phil uses to combine the data or with the analyses he applies they are free to do it better and show plots with the “officieal” data themselves … ;-P ;-)

    Cheers

  2. JollyJoker says:

    It just struck me that in addition to exclusion areas, “There can’t be an SM Higgs here” above 145 GeV, we now have the opposite, “There can’t be no Higgs here” around the same 145 GeV.

    • Philip Gibbs says:

      Yes the signal plot is nice and symmetric between Higgs and no Higgs. The only thing to bare in mind is that the standard required for acceptance (5 sigma) is much higher than the standard normally required for exclusion (2 sigma)

      • JollyJoker says:

        I assume the look elsewhere effect is zero for exclusion. It would be interesting to know what the required sigma to get the same adjusted confidence for an “inclusion area” is.

  3. 1111 says:

    I think choosing EPS MVA result as the CMS WW input is not fair. You can argue MVA is by design more sensitive than cut based analysis but CMS LP result has more data which deliver more important information.

    Using LP dataset to perform a MVA analysis will give CMS a better WW result than their current version but that doesn’t justify the choice of EPS MVA result.

    • Philip Gibbs says:

      You can certainly take that point of view. Of course it is a moot point if we agree that the plots with no WW channel data are a better way to locate the Higgs.

  4. Luboš Motl says:

    Fun plots, agreed about the resolution of WW etc. All the results still look too noisy…

  5. I am just wondering if the CERN/SLAC bets for a light Higgs boson are being hidden with these nice plots :D.

    Just thinking the odds from the theoretical and “popular” side:

    1)SUSY phenomenologists usually prefer 114-128, mainly centered about 120 ( GeV).

    2)Non minimal model supporters, I think, should prefer 128-140 GeV, or some heavier interval not yet excluded by data.

    3) No Higgs fan club is waiting for no Higgs signal plot 114-1 TeV, and waiting for “something stranger there”…

    Am I simplifying too much?

    I would say that no Higgs odds, or invisible Higgs fans, are lesser than those who prefer Higgs, excepting the fact that their interval is bigger. So, do you think is it a 2/3 vs. 1/3 bet? I presume that the most of physicists prefer Higgs to no Higgs.

    Daisy Higgs flower: Higgs, no Higgs, Higgs, no Higgs, Higgs,no Higgs,…LOL

    • Philip Gibbs says:

      The probabilities for each of the three bumps being a Higgs from the last plot above are about 90% at 118 GeV, 70% at 128 GeV and 95% at 140 GeV. So the chance of no Higgs is 0.1*0.3*0.05. I make that a 99.85% chance of a Higgs. You may wish to apply a trial error to reduce it a little if you think you might have looked elsewhere.

      However, I don’t take bets.

      • How do you calculate that probabilities from the bumps?
        I would like to know how to calculate it.

        I also dislike bets! But as people get nervous from the absence of a clear signal, scepticism grows. The vaccum can not be unstable so, something must happen in the LHC scale but likely, the signal can not easly be separated from the background ( the LHC engineers had told that long ago).

        I remember that some conservative estimation of SM Higgs “time observation” based upon LHC luminosity and the Higgs SM cross-section in the diphoton channel ( without SUSY or extra stuff) predicted that 2 years would be necessary of data collecting would be necessary in order to see a SM Higgs. We are almost “on schedule”. 2009-2010-2011

      • Bruce Blackshaw says:

        Phil, I take it your probabilities are based on the assumption that there could be multiple Higgs bosons?

      • Philip Gibbs says:

        Yes there are lots of models with multiple Higgs bosons such as SUSY so it is a fair to allow for that. However I don’t think there are many models that put three so close together! If it is not possible to have that then I agree that the probability would not be so good

        These probabilities should not be taken too seriously because you can’t calculate real probabilities without taking into account prior probabilities of various models and they are not meaningful quantities (and for other reasons). This is just a rough indication that a Higgs boson looks very likely in the data at this point.

  6. [...] entradas en su blog, Gibbs publica hoy una nueva combinación “corregida” en “Revealed: The Best Higgs Plots.” viXra log, september 1, 2011. Podemos analizar esta combinación suponiendo que es [...]

  7. In healthy science, one tries to be as objective as humanly possible.

    One does not tell nature how it should be.

    Rather one studies and learns from nature.

    One does not make excuses for, or rationalize away, negative results.

    One does not add epicycles to a failing paradigm.

    Rather one goes back and looks at the inadequately tested assumptions for possible sources of error.

  8. Jin He says:

    http://blogs.scientificamerican.com/guest-blog/2011/08/23/a-higgs-setback-did-stephen-hawking-just-win-the-most-outrageous-bet-in-physics-history/

    ………. They state that, with a 95% probability, the Higgs does not exist within the range of energies the LHC has so far explored, between 145 and 466 billion electron volts. The probability of nonexistence is not overwhelming—there is still a 5% chance that the Higgs is hiding somewhere within this energy range. And, more importantly, the lower energy range from 114 to just under 145 billion electron volts, a region of energy that Fermilab has determined, through earlier experiments, may harbor the Higgs, has not been ruled out. But the Higgs is quickly running out of places to hide. Lower energy levels have been accessible to smaller accelerators, such as the Tevatron at Fermilab and the LEP—the LHC’s predecessor at CERN—and neither collider had found it. Perhaps the Higgs does not exist at all……….

  9. alejandro rivero says:

    Tony Smith had some scans of old journals, during the catch of the W particle or the top quark, I can not remember, where some information was recovered by people from outside experiments -old seniors- and used to claim a signal. I guess that some old timers in the CERN will be afraid of history repeating itself, now here online.

    • alejandro rivero says:

      I mean, recovered just as Philip is doing, from published data and plots.

    • Philip Gibbs says:

      Even if someone like me found something they missed I am sure that 99.99% credit for the discovery has to go to experimenters who worked for years to set up the detectors, set the triggers, write the software etc.

      In any case, by showing everyone what I intend to look for I am blowing any chance of a surprise scoop. Someone else might do it though.

  10. Janko Kokosar says:

    “Everything is excluded at 95% confidence in the mass range from 145 GeV to 460 GeV, but there are small excesses over the range from 115 GeV to 145 GeV.”
    Maybe measurements at lower energies need more measurements, to be excluded at 95% confidence, because of different principle of measurements?

  11. Tony Smith says:

    Alejandro, it was Carlo Rubbia (who did much admirable work and in my opinion deserved his Nobel Prize) who prematurely announced around 1984 that CERN had found the Tquark at around 40 GeV, and then later realized that the Tquark was a misinterpretation so CERN had to “undiscover” it, which was not totally possible because of things like a 12 July 1984 Nature article a copy of which is on my web site at
    tony5m17h.net/CERN84Tquark.gif

    There are some old folks (like me) who remember that,
    and nobody wants to repeat such a thing,
    so CERN is right to be careful in Higgs announcements.

    Note that it was NOT “people from outside experiments” who made the wrong claim – it was Carlo Rubbia himself (the ultimate insider).

    Tony

    PS – There was another controversy some years later when Dalitz, Goldstein, and Sliwa analyzed some Fermilab data that indicated to them that the Tquark might be around 120 GeV.
    Dalitz, Goldstein, and Sliwa had thought that the data was public, but some at Fermilab thought otherwise, and a very unpleasant controversy ensued, fueled by a misleading article in the New Scientist and concern at Fermilab about funding for an upgrade.
    (An analogy here might be worry that finding the Higgs (and no clear supersymmetric stuff) could lead to funding cuts on future LHC or new collider operations.)

  12. Tony Smith says:

    Phil, thanks very much for plots that emphasize
    the gamma gamma data and ZZ data which are cleaner
    even though you get not so many events and may have to wait a bit longer to get clear results.
    It is fun to see the race between 118 and 128 and 140.

    Maybe at Halloween the Great Pumpkin will tell us who wins.

    If it is my favorite (140), there are at least two possibilities:
    1 – 140 is the only Higgs state and that is that;
    2 – 140 is only one of several (in my view 3) Higgs states.

    1 would require that the 140 peak be high enough in a Best fit plot (see Tommaso Dorigo’s 22 August 2011 blog entry “New CMS Limits on Higgs Mass”) to account for 100 per cent of the Standard Model Higgs strength
    while
    2 would require that the 140 peak be lower (maybe 50 or 60 per cent) of the SM Higgs strength, with the rest of the SM Higgs strength spread among the other Higgs states (that might exist around 200 or 240 GeV or so).

    Since I am also interested in the 200 to 240 GeV range,
    can you show
    a high-resolution Higgs plot for the range higher than 200 GeV?

    Tony

    • Philip Gibbs says:

      I’ve emailed you the extended plot. It wont look very different from the low-res plot above 200 GeV.

      Arguably, the only high-res channel above 200 GeV in ZZ-4l

  13. wl59 says:

    The peaks around 139 and 118 diminuished to 60% between EPS and LP. That’s nothing different than what happened with the total amount of data, including WW and Tevatron too. The only what seems to be ‘stable’ is the 128 peak. One should check if at that mass are really more obtained data, or continuously few or no data at all (as it seems on an earlier EPS plot where these data’s uncertainty was 100%) . According to your blue plots, it’s mean error would have diminuished slightly, what could mean that there were slightly more data contributing to it — however only if the mean error in your picture is that determined from the amount and weight of the real observations and obtained data, not from the predictions.

    • Philip Gibbs says:

      The peaks may have diminished but the signals got nearer the green line which is where they should be for a positive signal.

      • wl59 says:

        But probably we have to extrapolate this, that these signals will continue to diminuish towards zero, because it are any false signals, or signals of something else than Higgs

      • Philip Gibbs says:

        It is not valid to extrapolate. Levels could go up or down next time. The movements up or down will eventually diminish and it will stop moving.

  14. Simplicity says:

    First I have to thank Gibbs for this wonderfull physics blog ! I read it every day.

    I am not a physicist myself. But I am curious about the following:

    Is the higgs-boson, they hunt for at LHC and now may have found, A PART OF THE CONTENTS INSIDE THE ELEMENTARY-PARTICLES ?

    I hope you are competent to give a exact answer on this question :-)

    • Philip Gibbs says:

      It is not a meaningful question

    • steve says:

      Until about 1927, it worked to imagine the world as built from a hierarchy of marble-like objects, in which you find that most of the marbles actually are composed from smaller, more point-like marbles that exist ‘inside’. It is natural to imagine that you can keep looking inside, looking for ‘even more elementary’ particles. But it seems the world is not so ordinarily intuitive, and that a better imagining is that these particles are like energetic twists in a moving rubber band. The harder you hit, the more knots you get. If you hit an electron with enough energy, a hydrogen atom might pop out! That rubber band is constantly twisting, and the closer you look, the more twists and knots you see being created and annihilated — very dynamic! A description combines the ephemeral particulate-ness of quantum mechanics with the indefinitely-divisibleness of fields, and that is why we call it ‘quantum field theory’. In this analogy, there are many types of rubber, and they interact, and the Higgs is an expression of the interaction. So Yes, you would find a Higgs inside an elementary particle if you whack hard enough — because it will be created by the whacking! But, this intuitive explanation is now worse than the marbles, so I will now untwist myself and vanish ….

    • Philip Gibbs says:

      There is a great deal of information on the web about the Higgs at all levels so it would be silly to try to start explaining it here. Do a google search for videos about Higgs if you want an easy watch, or try the very good Higgs FAQ at http://profmattstrassler.com/articles-and-posts/the-higgs-particle/360-2/ by Matt Strassler.

  15. chris says:

    Phil, you should be given te title of master Higgs hunter :-)

    thanks a lot for the plots, they are really great. so a 140GeV Higgs is not yet off the table? This is good news for SM lovers like myself.

  16. wl59 says:

    I suppose that the lack of a Higgs will not invalidate the SM completely. Correct may be these parts, which reduce several effects to more basical ones. However, at one place this have to stop, otherwhise one would get a TOE of one formula: 0 = 0 . The limits are, where we reach the real basical interactions. These should correspond to the number of irreduceable dimensions. Although there exist similarities between dimensions, equations of motion between their co-ordinates of an object, and conservation laws for certain quantities, different dimensions are not ‘essentially the same’, one substituable by others, nor this are fundamental actions. An unification is possible only between secundary effects or interactions, which only contain redundances because they are superpositions of primary interactions. I think, inertia and gravitation are such primary interactions, so that they can be unified. To my opinion, the primary dimensions are: Events/WorldPoints ; Time; kinetic Extension (resulting together with time in one space direction); TangentialPlane/Curvature (2 geometrical space directions); in the following dimensions matter isn’t localizeable so that they are irrelevant for us (but they are neither time-like nor space-like but something else). There may be affinities between them, but they are essentially different, none of them can be substituted by another (perhaps approximately in the sense of very similar coefficients of equations of motion of objects, but not essentially). And each of them corresponds to a primary natural force. Higgs would mean, that the inertia can be represented and full substituted by something else, and a Graviton would mean that the gravitation can be represented by something more simple. Thus, the SM may be correct in these parts where it reduces secondary forces / effects to more basical or primary ones, but not where it tries to eliminate the primary forces also.

  17. Is a “graviton” related to a leprechaun?

    “Gravitons” come up in many physics discussions, but I would like to ask the speakers an impertinent question.

    In the entire history of the Earth has any person actually observed a “graviton”, or is it more like a deity (i.e., ya gotta have faith, man!)?

    • Philip Gibbs says:

      We are open to broad discussions on this blog but comments like this full of rhetoric and sarcasm serve no purpose other than to antagonise and are likely to be deleted. I will leave this one just as an example of the kind of thing not to be posted.

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