Wednesday, February 1, 2012

Physics & Math - Lazy photon among the missing in exotic LHC roll call

Leptoquarks are still missing at the LHC (<i>Image: Fermilab</i>) 
Leptoquarks are still missing at the LHC (Image: Fermilab)

Lazy photons, leptoquarks and string balls were just some of the exotic no-shows at the world's largest particle smasher. It was the most comprehensive particle roll call to date.
The Large Hadron Collider at CERN, near Geneva, Switzerland, has become synonymous with the search for the Higgs boson, which has been predicted by the standard model of physics. But physicists are also hoping that the LHC will throw up rare particles from theories that go way beyond the standard model, such as string theory.
To that end, Eva Halkiadakis and colleagues from the CMS experiment, an LHC detector, sifted through the debris from 400 trillion proton smashes. They didn't find any exotica, Halkiadakis told a seminar at CERN on 31 January.
Among the no-shows were: microscopic black holes; string balls, the tangled lengths of string predicted by string theory; colorons, novel particles that interact via the strong nuclear force; leptoquarks, a Frankenstein's monster of a particle created when a quark and lepton break the standard-model rules and bind together; and so-called "lazy photons", neutral particles that hang around in the detector for a while before decaying.

Bound quarks

No tell-tale signs of extra dimensions - beyond the three of space and one of time that we experience - were spotted either. "These are needle-in-the-haystack searches," Halkiadakis said.
Bagging something entirely outside the standard model would be an even greater prize for some than discovering the Higgs boson, the standard model's prescription for giving the most fundamental building blocks of matter their masses.
Thankfully for lovers of this subatomic stuff, it's still early days. More complete searches will be presented at the annual Moriond meeting in La Thuile, Italy, in March. The LHC is expected to restart in early March after a winter break.
Meanwhile, the LHC has already found one previously unseen particle. In December, researchers working on the other major LHC detector, ATLAS, reported finding a bottom quark and bottom antiquark bound together in a new excited state. It goes by the unwieldy name of χb (3P) - pronounced kai-bee three pee - and is entirely within the realms of the standard model.

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