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Should the Tevatron see the Higgs boson? What-if LHC does not observe it?

  1. Sep 21, 2006 #1
    Should the Tevatron see the Higgs boson? Given that it can collide at the TEV scale, shouldn't this be enough to see the HIGGS BOSON?

    What-if LHC does not observe the Higgs boson? Obviously this is bad for the standard model. Would this disconfirm string theory? Can the standard model accommodate a higless state?
     
  2. jcsd
  3. Sep 21, 2006 #2

    selfAdjoint

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    Tevatron, although it has TEV center of mass collision energy, can only deliver something like 200 MEV max to create a particle, depending on the experimental setup. But because theories are so interconnected, it can detect things that give reliable inferences about particles which it is unable to see, and it is hoped to greatly constrain the Higgs mass by work at Fermilab this year and next before LHC really gets going. They may be able to rule out the MSSM too, if not knock supersymmetry on the head for sure, which would of course kill superstrings. But the string community is already working on alternatives for just this contingency.

    As for getting mass without a Higgs, people are working on that, too, but no winners just yet. May you (theoretical physicist) live in exciting times!
     
  4. Sep 22, 2006 #3
    The Tevatron also has a luminosity issue. Producing a Higgs boson is quite rare - you don't just need enough energy - you have to wait for it to happen. The Tevatron beam is quite 'dim' compared to the LHC, so even once they have the energy they will not produce many Higgs bosons.

    They claim that they should be able to find a 120GeV Higgs boson by about 2009, which is not far from the LHC estimate. This could cause some interesting rivalry...

    BTW, selfAdjoint: I presume you meant 200GeV max? (200MeV wouldn't even be enough to create a proton!) Even then they can actually get a bit more than that.
     
  5. Sep 22, 2006 #4

    selfAdjoint

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    You're absolutely correct. It was a typo.
     
  6. Sep 22, 2006 #5
    Hello,
    I thought 200mev would be enough to create the higgs boson.
    How could TEV (or LHC for that matter) rule out MSSM? Ruling out either or both MSSM or the higgs boson would kill strings for sure. Proton non-decay also is problematic.

    Should the Higgs boson have been seen by TEV?
     
  7. Sep 23, 2006 #6
    The MSSM is ruled out if there is no Higgs lighter than 130GeV (since that is the upper bound on the Higgs mass in the MSSM). However, this doesn't rule out supersymmetry. It is not too difficult to push the upper bound up to about 170GeV by adding more particles. But that wouldn't be the MSSM of course.

    Also, string theory only needs supersymmetry at the Planck scale. Since we know supersymmetry is broken if it exists, there is no problem with breaking it at the Planck scale. Then you would never see supersymmetry in a low energy collider.

    So seeing supersymmerty would be a nice boost for string theory, but not seeing supersymmetry is not even slightly damaging to string theory.

    As for the last question, the biggest reason we need a Higgs boson is to cure the potential violation of unitarity in WW scattering. If it doesn't do that then the Higgs mechanism doesn't make sense and there is really no Higgs boson. To cure this, the Higgs boson needs to be lighter than 700GeV or so. So to answer your question, we WILL find the Higgs boson by 1TeV OR we find something else (hopefully something exciting and not thought of!).
     
  8. Sep 24, 2006 #7

    Haelfix

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    Its an interesting question actually. I *think* string theory gets a huge blow if there is nothing that resembles a scalar higgs like particle, as its fairly generic in their constructions, as it cures several vacuum instability problems they have. Ive asked a few string theorists about this several times, and they think for awhile and tend to find no way around it. Its probably possible as there is a lot of fudge room, but it becomes highly nongeneric and problematic (actually the electroweak sector by itself more or less demands something to be there, if nothing is observed, more or less everyone becomes very confused).

    Supersymmetry is an enormous parameter space, nondetection of superpartners < 1 tev makes the enterprise ugly (and highly nonminimal). It wouldn't rule anything out, but it becomes a lot harder to convince theorists that we're on the right track. Things like Split supersymmetry become favored, and well thats horrendous.

    The other nightmare scenario is the discovery of a single higgs scalar and absolutely nothing else. A disaster, it means we face the full brunt of the hierarchy problem with almost no logical way around it.

    Almost everyone I know hopes for a lot of exotics.. And something unexpected.
     
    Last edited: Sep 24, 2006
  9. Sep 26, 2006 #8
    What's the alternatives for just this contingency?
     
  10. Sep 26, 2006 #9

    selfAdjoint

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    I'll see if I can find some links. The basic idea is to enhance non-supersymmetric bosonic string theory to handle fermions.

    I should also add that the superstring partisans have already responded to the line of argument I cited with this: "Since supersymmetry is known to be broken at SOME scale above our present observations, it won't invalidate supersymmetry to find that it is broken at the weak scale". By broken at some scale they mean we don't observe any superpartner particles. THEY interpret this as "The theory is true at the Planck scale, but broken somewhere south of that." I don't know if they caught this attitude from the string theorists or if the influence went the other way.
     
    Last edited: Sep 26, 2006
  11. Sep 26, 2006 #10

    selfAdjoint

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    I'll see if I can find some links. The basic idea is to enhance non-supersymmetric bosonic string theory to handle fermions.

    I should also add the the superstring partisans have already responded to the line of argument I cited with this: "Since supersymmetry is known to be broken at SOME scale above our present observations, it won't invalidate supersymmetry to find that it is broken at the weak scale". By broken at some scale they mean we don't observe any superpartner particles. THEY interpret this as "The symmetry is true at the Planck scale, but broken somewhere south of that." I don't know if they caught this attitude from the string theorists or if the influence went the other way.
     
  12. Sep 26, 2006 #11
    Is 26 degrees of freedom worse than 10?
     
  13. Sep 26, 2006 #12
    Are you refering to me? I have never been called a 'superstring partisan' before, since I am not much of a fan of superstrings, but it is definitely true that superstrings only need supersymmetry at the Planck scale to survive. Ruling out low energy supersymmetry would not hurt string theory (except on a propaganda level). (I presume you meant 'Planck scale' in the last part of the bit I quoted.)

    I also don't think you would rule out supersymmetry by not finding a Higgs boson. There is no reason why you couldn't break electroweak symmetry in some other way (eg. extra dimensions) but still have susy at a slightly higher scale, say 10TeV. You would have lost one of the prime motivations for susy but you would not have ruled it out.
     
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