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The LHC

  1. Feb 18, 2010 #1
    when is the LHC find out if higgs boson excist?
     
  2. jcsd
  3. Feb 18, 2010 #2

    ZapperZ

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    When they get convincing experimental data.

    Zz.
     
  4. Feb 18, 2010 #3
    ya but they have collided particles already shouldnt they know now? have they found any rvidence at all from the LHC?
     
  5. Feb 18, 2010 #4
    In fundamental physics, we claim discovery when we have checked our results beyond doubt on statistical fluctuations. When you search for the Higgs boson, you make spectra with a certain number of background events (continuous background) and a certain number of signal events (peak above the background). That means the LHC analysis must gather more events in the peak than what is expected from solely the background. Unfortunately, the backgrounds for Higgs boson are rather large and tricky to keep under control. It will therefore take quite some data (and time) before a discovery can be claimed : of the order of months, more likely a couple of years, of good data.
     
  6. Feb 18, 2010 #5
    yes that makes sense, but what im asking is if they have found ANY data at all to there possible existence.
     
  7. Feb 18, 2010 #6
    It's possible that they already have, but nobody can tell you a likelihood right now. We will be able to compute the likelihood that they have already produced a Higgs once we know if the Higgs boson exist, and if so what its mass is. What you must realize is that even then (once we would supposedly know the Higgs boson and its mas), we will not be able to tell, event by event, whether the Higgs boson was produced. By definition, signal and background are impossible to distinguish on an event by event basis. Same initial state, same final state, only a large sample with statistical analysis can help you distinguish signal from background.
     
  8. Feb 18, 2010 #7
    ok so do you have any approximite idea when they should know?
     
  9. Feb 18, 2010 #8
    If the Higgs boson exists, how long they will need to gather statistics depends on its mass . It seems the Higgs boson is more likely to be light (from Tevatron) so it's the difficult case, and you will have to wait at least a couple of years.
     
  10. Feb 18, 2010 #9
    dang iv been rather excited to find out but patience is vertue
     
  11. Feb 20, 2010 #10

    jtbell

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    I've been waiting for over thirty years to find out if the Higgs exists. I can wait another year or two. :smile:
     
  12. Feb 20, 2010 #11
  13. Feb 20, 2010 #12

    blechman

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    it's going to be quite a while before the LHC experiments formally announce that they have seen the Higgs. Even if they find it relatively quickly (say, in the first year or two), this is such an important discovery, that the scientists are going to want to double-triple-quadruple-check that the analysis is right. Then, they'll want to check it again!

    The top quark was "discovered" in the early 1990's, but the actual announcement of its discovery was not until 1995. We're just going to have to wait for it. Better safe and sure, than being the laughing stock of the scientific community when they have to withdrawal the paper due to an error...
     
  14. Feb 21, 2010 #13
    The most likely three-sigma discovery target, assuming it's there at all and assuming no further engineering delays, is (as far as I know) two to three years from the time the collider is launched at full luminosity. There is a possibility that we'll find something other than Higgs before than and it'll make the search for Higgs irrelevant.
     
  15. Feb 21, 2010 #14
    Is that for full luminosity at the full 14 TeV center-of-mass energy? Since they've decided to run for the first 2 years at only 7 TeV, my impression is that even after the end of those 2 years they still may only have data more or less comparable to the Tevatron (with respect to detecting a standard model Higgs). Then they're going to shut down to replace all the interconnects. It seems like you probably shouldn't start holding your breath just yet. It may take a number of years (possibly 5 or more, especially if it's in lower part of the mass range).

    There's certainly the possibility of finding something else first, but I'm not sure what they could find that would make the Higgs search irrelevant.

    I'm not affiliated with any of these experiments, though, so my impression may not be correct.
     
  16. Feb 21, 2010 #15

    Vanadium 50

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    That's not my recollection - and I was there. (Along with 900 other people, of course)

    Tevatron "Run I" began in 1992. The 1992-1993 run led to the 1994 CDF paper http://arxiv.org/PS_cache/hep-ex/pdf/9405/9405005v1.pdf" [Broken]. CDF was in a difficult position - there were not enough top candidate events for a discovery, but there were too many for an improved limit compared to their last paper - which had only 20% of the data. Hence a paper that didn't really answer the question "do you see it or not"?

    In 1995, midway through the second half of Run I (50 pb-1 for D0 and 67 pb-1 for CDF), both experiments wrote "Observation" papers.
     
    Last edited by a moderator: May 4, 2017
  17. Feb 21, 2010 #16

    blechman

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    I was only in High School back then, so I have to bow to your hands-on knowledge! :wink:

    I was only trying to make the point that even though there was evidence earlier than 1995, CDF and D0 were careful not to publish their discovery papers until they were prepared to stand by the result, which is always good practice for science! I think of the famous scene where everyone just started clapping in the auditorium after running out of ideas for why the result might be wrong.

    The top quark had been "discovered" previously in the 1980s at 40 GeV, and then at 120 GeV, so there was plenty of reason to want to be careful! All I meant to say was that even when the Higgs is "discovered," which may or may not happen early in the Run, I think ATLAS and CMS will be cautious before announcing their results publicly. At least, I hope they will be.
     
    Last edited by a moderator: May 4, 2017
  18. Feb 21, 2010 #17
    quarkballs (glueballs), teknimesòns, leptoquarks?
     
  19. Feb 21, 2010 #18
    What do you call quarkballs ? You mean exotic mesons ? I do not think the LHC is a well-suited place to search for QCD exotics.
     
  20. Feb 21, 2010 #19
    Even if the Higgs is found once, it should take about two years until they officially anounce it.
     
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