Smash! The search for ‘sparticles’

By Clara Moskowitz

updated 1:34 p.m. ET Jan. 28, 2008

Squarks, photinos, selectrons, neutralinos. These are just a few types of supersymmetric particles, a special brand of particle that may be created when the world's most powerful atom smasher goes online this spring.

The Large Hadron Collider, under construction at the French-Swiss border at a particle physics lab called the European Organization for Nuclear Research (which is better known by its French acronym, CERN), will very likely change our understanding of the universe forever. The 17-mile-long underground particle accelerator will send protons flying around its circular track until they smash into each other going faster than 99 percent of the speed of light. When the particles impact, they will unleash energies similar to those in the universe shortly after the big bang, the theoretical beginning of time.

Scientists don't know exactly what to expect from the LHC, but they anticipate its energetic collisions will create exotic particles that physicists have so far only dreamed of.

Many researchers are hoping to see supersymmetric particles, called sparticles for short. Sparticles are predicted by supersymmetry theory, which posits that for every particle we know of, there is a sister particle that we have not yet discovered. For example, the superpartner to the electron is the selectron, the partner to the quark is the squark and the partner to the photon is the photino.

Closing in
Recently, researchers at Northeastern University have clarified what kind of sparticles the LHC might find. There are about 10,000 possibilities for the pattern of the first four lightest sparticles that might be created, said Pran Nath, a Northeastern theoretical physicist who is working on producing sparticles at the LHC. But after studying experimental astrophysical data, and the predictions of certain theoretical models, Nath and his collaborators, Daniel Feldman and Zuowei Liu, reduced the number of possible patterns down to 16.

"If these assumptions are correct, we can say in what order these sparticles will be created," Nath told SPACE.com. "So we tried to look for the signatures of these sparticles."

If the LHC produces sparticles, researchers will not be able to observe them first-hand because they will decay too quickly. The scientists can only hope to identify the signatures of supersymmetric particles by studying the jets of regular particles produced when sparticles disintegrate.

"It is important to know how the sparticles will be ordered in mass because different theories lead to different patterns," Nath said. "So this means that if we see those patterns, we may be able to extrapolate back to a theory."

The LHC will begin testing in April. It will produce the first preliminary data later this year.

Where have they gone?
When sparticles were first imagined, scientists wondered why we don't observe them in the universe now. The explanation, they think, is that sparticles are much heavier than their normal sister particles, so they have all disintegrated.

"The heavier an unstable particle is, the shorter its lifetime," Nath said. "So as soon as it is produced it begins to decay."

Creating sparticles requires an extreme amount of energy — the likes of which only existed shortly after the Big Bang, and perhaps in the LHC.

Physicists are not sure why sparticles don't have the same mass as particles, but they speculate that the symmetry could have been broken in some hidden sector of the universe that we cannot see or touch, but could only feel gravitationally.

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