The operators of CERN’s Large Hadron Collider have restarted that particle accelerator after taking a winter break, and they are gradually getting it up to their target energy. In it, protons go in opposite directions at speeds very close to light in a vacuum, giving them kinetic energies enormously greater than their rest masses. When they collide, they produce a spew of other particles, thanks to E = mc^2, and among these particles are those that particle physicists are especially interested in.
Late last year, the LHC reached the record of the Fermilab Tevatron, accelerating protons up to 1 TeV, and this year, they hope to go up to 3.5 TeV. Its operators plan to shut it down next year and upgrade it to make 7-TeV energies. A TeV is over a thousand times the rest-mass energy of a proton; one could make a thousand protons with that energy.
The LHC’s operators hope to produce a variety of particles, including a missing piece of the Standard Model and several of them predicted by various extensions of it. If they fail, they should get much-improved lower limits on their masses and upper limits on their interactions.
That missing piece of the Standard Model is the Higgs particle, which has the odd property that its ground-state field strength is nonzero. Other particles interact with it, and this continually-present Higgs field makes them massive.
Among the various extensions of the Standard Model are supersymmetric versions of it. Supersymmetry relates particles with different spins, and that makes it very attractive for Grand Unified Theories and Theories of Everything. However, no particle is known which is a supersymmetry partner of another known particle.
Higgs particles and supersymmetry partners are expected to have masses a little above the limits found with the likes of the Fermilab Tevatron. So if they exist, the LHC should be able to produce them.
Such discoveries will provide additional clues for physics at Grand Unified Theory energies, which are over a trillion times greater than even the LHC’s maximum energy. Do various interaction strengths converge onto a few values at GUT energies? We will get a better idea from what we see with the LHC.
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