Blogging ICHEP 2010

A collective forum about the 35th edition of
the International Conference on High Energy Physics (Paris, July 2010)

Monday, July 26, 2010

Higgs still at large

Finally came the moment we all waited for at this conference:
Tevatron now excludes the standard model Higgs for masses between 156 and 175 GeV. The exclusion window widened considerably since the last combination. Together with the input from direct Higgs searches at LEP and from electroweak precision observables it means that Higgs is most likely hiding somewhere between 115 and 155 GeV (assuming Higgs exists and has standard model properties). We'll get you bastard, sooner or later.

One interesting detail: Tevatron can now exclude a very light standard model Higgs, below 110 GeV. Just in LEP people missed it ;-) Hopefully, Tevatron will soon start tightening the window from the low mass side.

Another potentially interesting detail: there is some excess of events in the $b \bar b$ channel where a light Higgs could possibly show up. The distribution of the s/b likelihood variable (which is some inexplicably complicated function that mortals cannot interpret) has 5 events in one of the higher s/b bins, whereas only 0.8 expected. This cannot be readily interpreted as the standard model Higgs signal, as then one would also expect events at higher s/b where there is none. Most likely the excess is a fluke, or maybe some problem with background modeling. But it could also be an indication that something weird is going on that does not fit the standard model Higgs paradigm. Maybe upcoming Tevatron publications will provide more information.


  1. Dear Jester,

    a nice text but the inexplicably complicated s/b variable that cannot be understood by mortals - only by motls :-) - is just an acronym for "signal over background" and this self-explanatory quantity is drawn on the log scale as the x-axis. ;-)

    The excessive events occur at places where the signal is much bigger than the background. For you personally, the right interpretation is that you should increase your activity in saving those $10,000 that you will owe me one year after you lose our SUSY bet.

    More information about the Kilminster talk:

  2. Gee, Lubos, do you think every event in the detector shows up with a little tag attached that says "Hi! I'm 10 times more likely to be signal than background!"? The quantity "signal/background" is computed by some likelihood which is some big code that takes a huge number of inputs, presumably including Monte Carlo simulations of varying degrees of reliability, and spits out one number. These things tend to be something of a black box, at least to the people who didn't write the code, and hence, unable to be understood by mo(r)t(a)ls. Certainly without many more details, neither you nor I can claim to understand exactly what this variable means.

  3. Gee, do any of you guys actually believe in fairy fields anymore?

  4. OK, I'll bite: what do you think unitarizes WW scattering, Kea?

  5. Dear Anonymous, I just kindly pointed out that it's not true that "mortals cannot interpret" the s/b function. They surely can - it is interpreted the signal-over-background ratio.

    You may claim that such an interpretation is wrong; or it is not an interpretation; or that the interpretation of the ratio is not accessible to the humans. But all these statements are easily shown to be incorrect so your suggestion that there was anything imperfect about my proposition is just a vicious emission of fog.

    Events don't come with tags and passports but indeed, the purpose of the "esoteric" function is de facto to provide the events - or at least their ensembles - with exactly such tags. After all, the events come with their almost full description of the final state (which particles or jets and which momenta) and for each final state, one can calculate the cross section from the Higgsless background as well as the contribution of the signals. So it's just being calculated and plotted. The calculation is not a one-line calculation because it depends on the laws of physics - on dynamics - but it doesn't mean that it has to be impenetrable to humans. In fact, I am confident that most physics PhDs, at least after reading my text, will feel that they know what it meant.

    I think it's pretty clear that Jester just didn't have an idea what s/b meant which is why he - incorrectly and somewhat maliciously - wrote that it followed that almost no one else had the idea, either. It surely doesn't follow.


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