Smash! The search for ‘sparticles’

Dark matter and strings
If supersymmetry truly exists, it could help solve a few nagging problems in physics.

For one thing, the theory may offer an explanation for dark matter — the mysterious stuff in the universe that astronomers can detect gravitationally, but not see.

"The most popular supersymmetric theories predict the existence of a stable supersymmetric particle, the neutralino," said Enrico Lunghi, a theoretical physicist at the Fermi National Accelerator Laboratory in Chicago. "This is an excellent candidate for dark matter. The problem is that we haven't seen any. It's another good reason for hoping to find supersymmetry at the LHC."

Neutralinos may be the lightest sparticles, so they might be able to exist in nature without decaying immediately.

Supersymmetry also helps resolve the fundamental problems between physics at the very small scale of particles (quantum physics) and physics at the very large scale, where Einstein's general relativity takes over.

"It's a necessary step in solving the discrepancy between the standard model [of particle physics] and gravity," Lunghi said. "It can be a very important ingredient in eventually having a theory of everything."

Additionally, if supersymmetry is proven correct, it could offer a boost to string theory, which includes the concept of supersymmetry. However, supersymmetry could still exist even if string theory is wrong.

"Supersymmetry can exist with or without string theory," Nath said, "but it would be very encouraging for string theory if sparticles are observed. If they don't find any sparticles then it's not good news for supersymmetry or string theory."

Unproven
Some scientists are skeptical about whether supersymmetry exists and whether LHC will be able to prove it.

"Supersymmetry is a very beautiful idea," said Alvaro de Rujula, a theoretical physicist at CERN, "but it's hard for me to believe that it is not only true in nature but exists at this energy. It may be true but inaccessible to this machine."

Even if the LHC produced sparticles, de Rujula said, it would only create a few of them and the signatures could be difficult to identify.

"People will jump to conclusions, but it won't be so easy to tell if they are really supersymmetric," he said. "It may take some luck to have a convincing case for supersymmetry at the LHC."

For many physicists, the possibility of not finding what they are looking for is exciting, too.

"It's better when we are wrong than when we are right," de Rujula said. "Things are really interesting when we don't understand them. That's a good position for a scientist."

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