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What do they expect from the Large Hadron Collider ?

  1. Apr 20, 2005 #1
    I've read here
    about the LHC buing under construction at CERN and they say that it will collide protons and other ions at very high speeds , but they don't say what new particles are expected to appear ,or what theories do they expect to be proved or disproved,so please tell me.
  2. jcsd
  3. Apr 20, 2005 #2
    Finding the Higgs boson is one of the purposes I think.
  4. Apr 20, 2005 #3
    Finding the Higgs boson, provided that it exist ! More importantly, just explore the physics at a higher energy, including finding the Higgs boson if the minimal scheme of the standard model applies, or testing which extension is best suited if this minimal scheme fails. Also, maybe providing the first experimental tests of string theory by measuring the rate of mini black-hole production and evaporation.
  5. Apr 20, 2005 #4


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    What they really hope for, is to find 1 or 2 different Higgs particles, a Kaluza Klein cascade, and the lightest superpartner.
  6. Apr 20, 2005 #5
    Do they expect to find the superpartner of one of the Higgs bosons ? I didn't know there has to be more than one - are you talking about the boson and its anti-particle ,and they want to find the lightest superpartner between the superpartner of the Higgs boson and the superpartner of the anti-Higgs-boson ?
    And what is a Kaluza-Klein cascade ?

    Last edited: Apr 20, 2005
  7. Apr 20, 2005 #6


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    If they see the lightest superpartner (and hopefully maybe the 2nd lightest) we then know Susy is valid and we have a few parameters that are nailed down in the MSSM.

    If we see a single Scalar Higgs, its rather boring and dull and we dont really learn much. Otoh if we see several Higgs at different energies we can start figuring out the Higgs sector, there are many different models. We might even see the little Higgs.

    KK modes are for large extra dimensions and potentially Stringy stuff.

    We might see other things too, like technicolor. Basically we hope to see a lot of different particles (hopefully ones we haven't even guessed at yet). All those things will in principle go a long way to solving the problems with the standard model and astrophysics bounds.
  8. Apr 20, 2005 #7


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    Haelfix, my take is if they DON'T see evidence for supersymmetry, and in fact see evidence against it, THAT would be exciting. Supersymmetry has been oversold as the one solution for the standard model, and it would be nice to see the physics comunity turned onto something else.
  9. Apr 20, 2005 #8
    There are many, many answers to this question. In some sense, the LHC isn't so much an experiment as an entire laboratory, and different people will try to use the data it produces in different ways. Here's the most interesting from my point of view:

    The Standard Model is based on a symmetry that connects the electromagnetic and weak forces, called (oddly enough) Electroweak symmetry. Now, if you go through the math and figure out what this symmetry implies, you find that if the symmetry is exact then no fundamental particles can have a non-zero mass. We know that the symmetry is not exact, just from the fact that the electromagnetic and weak forces behave very differently at low energies. This leads to an interesting possibility: whatever it is that broke the electroweak symmetry also generated the mass of all fundamental particles. So in some sense understanding the dynamics of electroweak symmetry breaking is equivalent to understanding the origin of mass. That would be very cool. However, there is a very important unanswered question:

    What breaks electroweak symmetry?

    One of the main motivations for building the LHC (the main motivation) is to answer this question. The Standard Model proposes that a scalar field, the Higgs, aquires a non-zero vacuum expectation value, and that works mathematically, but we have no direct evidence for such a particle. (We have some indirect evidence, but it's far from a firm conclusion). There are also theoretical reasons to believe that the Standard Model picture is far from complete (search for "The hierarchy problem" or "The gauge hierarchy problem"). For this reason people have proposed many extensions of the Standard Model, including (but not limited to, not by a long shot :eek:): Supersymmetry, Technicolor, Large extra dimensions, Warped extra dimensions, Little Higgs, Fat Higgs, Higgsless, ....

    The good news is that there is reason to believe that, whatever the mechanism is, the LHC has a good chance of finding it.
  10. Apr 20, 2005 #9


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    SUSY helps solve a lot of nagging problems in the standard model, and falsification would leave a lot of unanswered problems lingering with potentially no good solution.

    Basically the more exotics the LHC sees the better we are in terms of explanatory power.
  11. Apr 24, 2005 #10
    The mechanisms for breaking EW symmetry and generating fermion masses don't actually have to be related at all- it's just a nice feature of the (SM) Higgs that they can be.

    The LHC *has* to find something related to EW breaking- unless there is new physics at 1TeV, the theory doesn't work. That's not to say it'll be the Higgs particle, of course.

    Even if SUSY isn't found at the LHC, the theoretical motivations are so nice it'll still knock around as a theory- all the sparticle masses will just be predicted to be an order of magnitude higher, just out of experimental range!
  12. Apr 24, 2005 #11
    The hierarchy problem is if you believe the uncertainty principle of quantum mechanics allows for pairs of short-lived virtual particles to appear from the vacuum and then disappear again. These virtual particles can affect the mass of the Higgs, and when arbitrarily large energies are allowed in quantum mechanics it makes the Higgs mass arbirarily large which is in contradiction with the requirement that the Higgs be lighter than a few hundred GeV - less than the top quark.

    I would keep a skeptical mind about the exsistence of Higgs particles or Higgs Field being the "medium" through which all fundemental particles interact. If this Higgs field is only present within the realm of an atom, what contains these particles and what lies outsite an atom? Isnt is more consistent to say that medium outside an atom is the same medium within an atom? Thereby if the medium outside an atom is a Higgs particle field the Photon would have considerable interaction with such and yet it does not aquire mass.

    I have no idea what I just said. haha

    Anyway Heres a good article http://physicsweb.org/articles/world/15/11/3
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