Higgs Escapes Part of Exclusion Region

This past winter a combined analysis of data from the two Tevatron experiments showed at 95% confidence level that the Higgs mass could not be in the range 160-170 GeV. This was a better result than expected: statistically the experiments should not have been able to exclude any of the mass range, but were helped by a downward statistical fluctuation.

Today a new and improved combined analysis was released using more data, and the new result is that there has been a reversion to the mean, no more help from statistical fluctuation downwards. Statistically, this time they should have been able to exclude 159-168 GeV, but now the fluctuation is a bit upwards, so the actual exclusion region is 163-166 GeV. In essence, better data has shown that the likelihood of a 160-163 or 166-170 GeV Higgs, something that was previously assigned a probability of a bit less than 5%, now has a probability a bit more than 5%. So, any putative Higgs particle in those mass regions has now escaped being tarred with the unfair label of “excluded”.

If the Higgs is actually there at a certain mass, as one gets closer and closer to having sufficient data to exclude its existence, one should find oneself doing nowhere near as well as expected as far as excluding that mass. A thoroughly irresponsible person might see some significance in the fact that, unlike the analysis from earlier this year, the new improved analysis with more data does a worse job of exclusion than expected over much of the low mass range, peaking at 1.5 sigma or so for the mass range around 135 GeV.

Update: More detail and rank speculation about this from Tommaso Dorigo here.

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5 Responses to Higgs Escapes Part of Exclusion Region

  1. Peter Lee says:

    Just wondering if this means that Alain Connes’ Non-Commutative Geometry theory predicting a Higgs mass of around 170 GeV might still work out?
    I enclose a copy of his posting in August 2008 when an earlier result excluding a Higgs mass of 170 GeV came out.


    In a rather ironical manner the first Higgs mass that is now excluded by the Tevatron latest results is precisely 170 GeV, namely the one that was favored in the NCG interpretation of the Standard Model, from the unification of the quartic Higgs self-coupling with the other gauge couplings and making the “big desert” hypothesis, which assumes that there is no new physics (besides the neutrino mixing) up to the unification scale. My first reaction is of course a profound discouragement, mixed with an enhanced curiosity about what new physics will be discovered at the LHC.
    I’ll end with these verses of Lucretius:
    Suave, mari magno turbantibus aequora ventis,
    e terra magnum alterius spectare laborem;
    non quia vexari quemquamst jucunda voluptas,
    sed quibus ipse malis careas quia cernere suave est.
    [Pleasant it is, when over a great sea the winds trouble the waters, to gaze from shore upon another’s tribulation: not because any man’s troubles are a delectable joy, but because to perceive from what ills you are free yourself is pleasant.]
    Posted by AC at 3:57 PM 20 comments

    Monday, August 4, 2008

  2. piscator says:

    maybe the thoroughly irresponsible person would see 1.5 sigma worth of significance? 😉

  3. Martin says:

    Hi Peter,

    I have heard of particles with a signal at the 5 sigma significance level disappearing into noise.
    How often in your experience does it happen that a particle is found in its (e.g. 2 sigma) exclusion zone?


  4. Peter Woit says:

    Peter Lee,

    This just improves the bad odds a bit for the 170 GeV prediction of Connes from 5% to something a bit bigger.


    There aren’t many examples I know of of this kind, so hard to say. In principle, one time in 20 this should happen. There’s also the phenomenon to keep in mind that when experimentalists err, it generally is on the side of thinking their results are more accurate than they really are…

  5. Hi Peter,
    thanks for the irresponsible link 😉
    I think that the 1.5 sigma at 115 GeV are a way more interesting thing than the narrow exclusion, because of the electroweak fits and because of the LEP II excess.
    Also, a 160 gev Higgs will be seen or wiped off the board in a few months by LHC, so the 115-140 gev region retains less ephemeral value.

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