After yesterday’s post concerning the media reporting on the Higgs search, a lot of people have been asking me this: “Given that the Standard Model Higgs particle (the simplest possible Higgs particle) will be found or ruled out in the coming few months, why will it take as long as ten years to be sure nature sports no Higgs particle or particles of any type?” Well, this deserves a long explanation, which I promise to provide soon, but for starters I recommend my September article on Implications of Current Higgs Searches, which will give you an idea of just how complicated the situation could be. If it’s too long for you, just look at the figure at the end of the article! It doesn’t capture the full story, but it may give you a sense for why CERN’s presentations on December 13th cannot possibly mean the end of the Higgs discussion.
Another thing I could recommend, especially to those who are willing to sit through a certain amount of technical mumbo-jumbo enclosed within a largely non-technical discussion, is the first 8 (or even 20.5) minutes of a lecture I gave in 2010 to graduate students who were not Large Hadron Collider [LHC] experts. (If it loads too slowly you can download it from this page; it is my June 18th lecture.) Even a layperson with some prior knowledge of the LHC and the Higgs particle should be able to get a sense for the main point: how easily nature, with the tiniest twist on the Standard Model Higgs particle, could make the search for the Higgs particle(s) much more difficult and require much more LHC data than we currently have. This is not to say that the search for an exotic type of Higgs is guaranteed to be much more difficult; some exotic Higgs particles are not that hard to detect. But you can’t say you’ve ruled out all the possibilities until you’ve gone exhaustively through the many difficult cases.
As an example: as was pointed out at least as far back as 1983, an exotic form of Higgs particle might decay to undetectable new particles over 90% of the time, delaying all standard search strategies for years, and requiring also a very difficult (but possible) search for an undetected Higgs particle recoiling against two observed jets. Hard as this is, it is not the most challenging case, by a long shot.
I should add that when I say “ten years” that is of course my best guesstimate. The precise time frame will depend on how well the LHC runs and at what energies and collision rates, and on how clever theoretical and experimental particle physicists are in getting the best out of the data. I don’t think it will take fifteen years; I am sure it will take much more than five, because we won’t have enough data by then for the toughest cases.