Sunday, January 6, 2013

CERN's LHC To Shut Down For Repair & Upgrades

The necessary data for determining whether there truly is a Higgs Boson or not is already there

Actually that is not quite correct. To really determine whether we have a Standard Model Higgs boson we need to see its decays into things called fermions (particles that make up matter) and so far we have only see it decay into bosons (particles that create forces). The problem is that the heaviest fermions the "Higgs" can create, b-quarks, are also created by different physics that is ~a billion times more likely than a Higgs decay so it's like try to find a piece of straw in a haystack (a needle is easy if you have a big enough magnet!). The next heaviest fermions, tau leptons - a very heavy cousin of the electron - decay in a way which makes them look very much like quarks and so, to a large degree, suffer the same problem (identifying taus in the trigger is something I actually work on).

So to be able to see these decays we need a lot of data and it is not entirely clear whether we will have enough in the current dataset to see these decays - my best guess is that we might hit 3 sigma "evidence" but without some very clever analysis I think a 5 sigma "discovery" is unlikely. In addition we also need to measure the spin of the Higgs to confirm that it is a scalar, spin-0, particle. This again requires large statistics and again I don't know that we have enough data yet - time will tell.

The big reason for the shutdown is for the energy upgrade. If this new particle really is the Higgs then we can expect new physics out there to explain why the Higgs is so much lighter than the planck scale - the energy where gravity becomes important (the reasons behind this are complex!). This new physics may also explain what Dark Matter is so there is a great deal of hope that getting the energy up to ~13TeV (which is what is expected after the upgrade) may give us access to this new physics.

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/wLdHOdxlxCo/story01.htm

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