Today's posting will be the eighth and final entry in my series on the Large Hadron Collider (LHC). I wanted to end with a brief discussion of possible new things that may be found at the LHC, beyond the Higgs boson and supersymmetric particles, which I've already covered.
At this moment, however, Peter Woit's "Not Even Wrong" blog is reporting rumors that technical difficulties may delay the start of physics data collection at the LHC until 2009. Thus, we may end up waiting longer than expected to find out if the various proposed types of new particles are discovered.
One development that some researchers are looking toward is the possible appearance of evidence for extra spatial dimensions beyond the three we're familiar with. String theory, among other ideas, posits the existence of extra dimensions.
The December 2005-January 2006 issue of Symmetry magazine included an article entitled "The Search for Extra Dimensions," which suggests what kinds of signs could be suggestive of extra dimensions. The article focuses on research at Fermilab's Tevatron collider, but also mentions the LHC. A key step in the search would be finding evidence for the graviton, an as-yet-undiscovered particle that's posited to communicate the gravitational force. According to the article:
One way Fermilab experimentalists... hope to detect extra dimensions is to catch a graviton in the act of disappearing into another dimension. Collisions create a symmetrical ball of energy and, like fireworks, particles should spray in all directions. A tell-tale sign of extra dimensions would be a collision in which visible particles sprayed only in one direction, suggesting that an invisible particle traveled in the other direction. This particle could be the key to extra dimensions—a graviton, leaving our visible universe and disappearing into a fourth spatial dimension. Unfortunately, gravitons are not the only invisible particles. Lightweight particles called neutrinos, which very rarely interact with matter, can also travel right through a detector without a trace.
The ability to search for extra dimensions hinges on a researcher's ability to track neutrinos. "If you don't know your neutrinos, you don't know anything about extra dimensions," says [Joe] Lykken. By calculating the probability of creating a neutrino and comparing that to the number of asymmetrical events observed in the Tevatron, Fermilab researchers hope to discover an excess of events unaccounted for by neutrinos. Such a discrepancy could be the first experimental evidence of gravitons disappearing into extra dimensions.
The article concludes thusly:
But even if the Tevatron fails to find evidence of extra dimensions, CERN's LHC will continue the search in 2007. With significantly more energy, the LHC will be able to probe ever smaller radii.
"If we haven't found extra dimensions with the Tevatron by then, the LHC may still do it," says Lykken. "This is the type of discovery we should be able to make in the next five years."
I'll leave you with this Seed magazine piece from July 2006, in which several prominent scientists discuss their visions for discoveries at the LHC.