June 15, 2010

Elusive God Particle May Come In Several Varieties

According to a new study, there may be multiple versions of the elusive "God particle," or Higgs boson.

The Higgs boson particle is the primary goal for the $10 billion Large Hadron Collider (LHC) experiment near Geneva.

However, recent studies from the LHC's U.S. rival suggest physicists could be hunting for five particles, not one.

The data points to new laws of physics beyond the current accepted theory, known as the Standard Model.

The Higgs boson is the sub-atomic particles that explains why all other particles have mass.

However, no one has detected it for decades.

Results gathered by the DZero experiment at the Tevatron particle accelerator, pirated by Fermilab in Illinois, have helped support the idea of multiple Higgs bosons.

DZero is designed to shed light on why the world around is composed of normal matter and not anti-matter.

Researchers working on the experiment have observed collisions of protons and anti-protons in the Tevatron.

The collisions produced pairs of matter particles slightly more often than they yielded during anti-matter particle experiments.  Anti-matter is the opposite of matter.

Physicists had already seen such differences, but these effects were small compared to those seen by the DZero experiment.

The DZero results showed much more significant "asymmetry" of matter and anti-matter.

Bogdan Dobrescu, Adam Martin and Patrick J Fox from Fermilab say this large asymmetry effect can be accounted for because of the existence of multiple Higgs bosons.

They say the data points to five Higgs Bosons with similar masses, but different electric charges.

Three of the charges would be neutral and one would have a negative and positive electric charge.  This is known as the two-Higgs doublet model.

Martin told BBC News that the two-Higgs doublet could explain the DZero team's results while keeping much of the Standard Model intact.

He said, "In models with an extra Higgs doublet, it's easy to have large new physics effects like this DZero result."

"What's difficult is to have those large effects without damaging anything else that we have already measured."

Martin explained that there were other possible interpretations for the DZero result.

But, he added, "The Standard Model fits just about every test we've thrown at it. To fit in a new effect in one particular place is not easy."

The Standard Model incorporated all that was then known about the interactions of sub-atomic particles.

However, many physicists regard it as incomplete, a mere stepping-stone to something else.

The Standard Model has only one Higgs "doublet."  Martin said that although we tend to think of the Higgs boson as one particle, it actually comes in a package of four.

"In the Standard Model, you only see one of them because the other three are absorbed into [other parts of the scheme] such as the W and the Z bosons. There's only one left," he told BBC News.

"So if you want to add another Higgs doublet - you actually have to add four more particles."

The two-Higgs doublet model also ties in with a theory in particle physics known as supersymmetry.

Supersymmetry represents an extension to the Standard Model, which says that each particle in the scheme has a more massive "shadow" partner particle.

However, physics have lacked experimental evidence for the existence of these more massive particles so far.

Evidence for the "God particle" and for supersymmetry could be uncovered by the LHC.

The researchers have published the latest study on the pre-print server arXiv.org (see link below).  Three researchers are based at Fermilab but are not DZero team members.


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