Monday, July 02, 2012

Tevatron: DØ has made a lot of Higgs progress

Papers: , CDF
There was a 90-minute-long webcast at the Tevatron today. This is how their combined searched looked a few months ago:

The excesses were over 2 sigma. The peak is fuzzy largely because of the energy uncertainty in events with a W-boson decaying to neutrinos, among other particles.

Especially the DØ collaboration has made some progress in recent months – they worked on the finer details, were improving systematic uncertainties, Monte Carlo etc.

The result is that the statistical significance has been improved. The local excesses are as high as 3.2 sigma; with the look-elsewhere punishment included, the global significance is 2.5 sigma. However, the energy resolution is poor and the strongest excess is near 135 GeV or so.

The shape of the curve isn't quite new – its change in recent 2 years was very slow – but only now, the signal got stronger than the Standard Model including the Higgs.

The retired American collider still reports a significant excess of bottom-quark Higgs-like decays for a Higgs mass 125 GeV in particular – even relatively to the Standard Model with the Higgs boson predictions – which would favor a larger tan(beta) in supersymmetric models – something that may be true or untrue independently of supersymmetry. You see that the full black curve in the picture above (a log likelihood ratio distribution) is actually even below the dashed red curve – which indicates a signal stronger than even the Higgsful Standard Model prediction. The LHC doesn't seem to share this observation, however.

Watch at

The Independhiggs Day Seminar at CERN is 1 day and 16 hours away right now. Are we close to the Higgs discovery? John Ellis – who has 60,000+ citations in particle physics – said the following 4 days ago:
If you're jealous about Ellis' Standard Model Lagrangian T-shirt, you should at least buy the Higgs boson T-shirt from – see the icon next to the previous paragraph. :-) And if you think that Ellis can only say those things in English but not in French, then jump to 15:37 once the video gets black and seemingly over at the beginning. :-) My French isn't perfect but around 17:00, the interview becomes characteristically French as the French media babes try to study every thread in Ellis' T-shirt.


  1. Does this mean the mass of the Higgs is most likely to be 135 GeV? I remember reading that it was thought the mass would be closer to 125 GeV .

  2. No, it doesn't mean that the Higgs mass is likely to be 135 GeV.

    The Higgs mass is quite certainly at 125 ± 2 GeV. This follows from the LHC that has a much stronger signal, with a better energy resolution. If you have such a superior signal, you obviously shouldn't pay attention to any details coming from a less powerful analysis.

    The difference between the Tevatron's preference for a 135 GeV and 125 GeV Higgs is statistically insignificant so giving any importance to the fact that the maximum is actually at a wrong mass - where the significance is just a little bit higher than it is for the correct mass - would be completely stupid. The Tevatron says "I don't know" which mass is right. It surely doesn't have the capacity to pick 135 over 125 GeV.

  3. Wait, never mind. My understanding of the data must have been incorrect. I just saw the "exclusions" slide so apparently 135 GeV has been ruled out. How would different values of the mass effect Supersymmetry? Could we narrow down "the landscape" with an accurate mass measurement of the Higgs?

  4. Dear Chris, 135 GeV has been usually quoted as the maximum Higgs mass one may get in the minimal supersymmetric standard model for justifiable values of the parameters. However, it would put some tension to the model building. Even 125 GeV is arguably too high relatively to the expectations that SUSY phenomenologists had.

    135 GeV would be "kind of fully" consistent with the Standard Model without SUSY. However, the correct mass 125 GeV isn't consistent with the Standard Model valid up to the Planck scale because the Higgs potential becomes unstable at an energy below the Planck scale. If the Higgs were 125 GeV and the Standard Model were right, it would mean that the Higgs behaves like some kind of "tachyon" if you study its properties at very short distances, an inconsistency.

    135 GeV has been ruled out in the SM by the LHC, of course, but that doesn't prevent one from seeing 2-sigma excesses and even higher excesses at some points, especially if the energy resolution is poor.

    Again, concerning your last comment, I want to emphasize that it's stupid to pay attention to statistically insignificant "preferences" of some values of a quantity - the Higgs mass in this case - over another if the difference is really small relatively to the noise because such a mode of reasoning means that one is being distracted by - or deliberately overselling - noise.

    This may be normal in climate "science" where people would be eager to claim that the man-made effects are "most likely" based on similarly sloppy arguments, but it is totally unacceptable in genuine science. When we simplify the situation, the LHC data are superior in almost all respects so if we have the LHC data, the Tevatron data can't tell us almost anything new. Paying a comparable attention to wiggles in the Tevatron graphs relatively to the sharp LHC graphs would be like identifying a murderer from his fuzzy footprints in the sand if you also have a high-resolution photograph of himself during the murder. The comparison is a bit exaggerated but it's qualitatively right.

  5. "the LHC doesn't SEEM to share this observation"... (= appear, assume, give the impression, look like, pretend...). Sigh, ok I'm just trying to give more space to a positive outcome ;)

  6. Thanks for the clarification!

    I don't understand enough about string theory yet to thoroughly read any papers on model-building but i'd like to start reading current papers to understand more about what's going on in the field. I'd assume that the difficultly you alluded to in regards to a 125 GeV Higgs implies that different masses of the Higgs require somewhat qualitatively different models (not just quantitatively different). Is this true?

  7. What John Ellis said; I expect that both CMS and Atlas will be confirming the 2011 results with a sigma declaring discovery of a resonance at 125 , but the Higgs signature will take time to establish, because we will be still looking at statistics combined from more channels, and branching ratios will not be measured to an accuracy to establish it as a Higgs .

  8. So the more we are approaching the Higgs the more it becomes elusive. It's like if we were trying to travel at the speed of light : the faster we are the longer it takes to reach it. :-/

  9. Maybe there is no THE (SM) higgs but only a (125 GeV) higgs, which is esear to approach ... ;-) ?

    BTW I am absolutely not jalous about Ellis' SM Lagrangean T-shirt; I have it in blue and a second one showing a nice collision in ATLAS :-P
    But in the "Universe of Particles" exhibition at CERN, one of the Spheres containe the SM Lagrangean and below another equation with really corresponding really FAT diagrams ... :-D

    These I want to have on a T-shirt .... !!! :-)

  10. This impression is due to the wide spreading of information due to the internet. In 1983, when they were looking for the Z and the W, at the point of research we are now the information was not in the media and the world all over. It circulated among physicists at coffee table discussions and appeared at conferences in due time, and finally a press release came out which informed interested on lookers.

    Now the audience is enormous and demanding a preview, and this demand created the composite plots, which did not exist in 1983, and which will give a sureness that a resonance is there, but , as Ellis said, there is a long way, statistics wise and analysis wise, to go , until the behavior of this resonances in its branching ratios and angular distributions is nailed down with similar statistical accuracy to its existence. It is only then that one can decide if it is the SM Higgs, a SS Higgs or something entirely different ( I have acquaintances with money on composite models).

    There is nothing elusive about it. It is the standard way all particles have been discovered up to now. The audience is different and its expectations are like a child waiting for birthday presents.

  11. I only have a T-shirt "Talk nerdy to me"... it was a present :-(