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Tevatron Experiment Could Send Particle Physicists Back to the Drawing Board

By Richard Adhikari
Apr 7, 2011 3:13 PM PT

Experiments conducted at the Tevatron particle accelerator at the Fermi National Accelerator Laboratory in Illinois seem to indicate that a new particle has been found.

Tevatron Experiment Could Send Particle Physicists Back to the Drawing Board

A paper posted on the laboratory's website Monday brought out this point.

Stripped of the scientific terminology ("the invariant mass distribution of jet pairs produced in association with a W boson using data collected with the CDF detector which correspond to an integrated luminosity of 4.3 fb....), it says there's a bump in mass.

That could point to a new particle, possibly a non-standard boson.

If a new particle has indeed been discovered, it would mean that most of our ideas about what is beyond the standard model of elementary particle physics are wrong, Lawrence M. Krauss, foundation professor at Arizona State University's School of Earth and Space Exploration, told TechNewsWorld.

The discovery "would be a very fundamental discovery in particle physics," said John Ellison, professor and vice chair of the department of physics and astronomy at the University of California Riverside.

Fermi Labs did not respond to TechNewsWorld's request for comment by press time.

Things That Go Bump in the Tevatron

The experiment consisted of banging together a proton and an anti-proton at about 2 TeV of energy, according to a blog post by Flip Tanedo on the USLHC website. USLHC consists of U.S. scientists participating in the CERN Large Hadron Collider experiment.

One TeV is the amount of kinetic energy a flying mosquito produces, so we're looking at the Small Bang here.

The collision gave off energy particles and excess mass. Apparently, the excess mass is not described by current theoretical predictions within the statistical and systematic uncertainties, according to the paper posted on Fermi Labs' website.

After plotting the data, a second bump was found that peaks around 150 GeV, Tanedo wrote.

One GeV is a billion electron volts. In physics, an electron volt is the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt. The electron volt is not an SI unit, and its value must be obtained experimentally. It's commonly used with SI prefixes such as "G" for giga.

Deviations and Inferences Therefrom

The second bump has a statistical significance of 3.2 standard deviations, which means the probability that it's from a standard background process is very small, UC Riverside's Ellison told TechNewsWorld.

In statistics, there's a rule stating that for a normal distribution, nearly all values lie within three standard deviations of the mean. Just over 68 percent of the values lie within one standard deviation of the mean; about 95.4 percent lie within two standard deviations; and about 99.73 percent lie within three standard deviations.

This is called the "68-95-99 rule," the "three-sigma rule," or the "empirical rule."

However, that's not enough to certify that the bump is a new particle.

"To claim discovery of a new particle, five standard deviations is usually required," Ellison explained.

This certification could come "very soon," as the D0 Experiment, a worldwide collaboration of scientists conducting research on the fundamental nature of matter, can look for the same effect, Ellison suggested.

Ellison is a member of the D0 (D-Zero) Collaboration and also a member of the CMS (Compact Muon Solenoid) experiment at the CERN Large Hadron Collider.

Getting More Data

The CERN LHC will provide definitive data about this bump in the coming year or so, Arizona State's Krauss said.

"There is not enough data now to claim a definitive discovery," Krauss added. "The claimed bump doesn't fall into the category of any predicted particles, so it cannot be easily classified."

One possibility, if the discovery is confirmed as a new particle, is that it could be a new boson like the Z-boson but heavier, UC Riverside's Ellison suggested.

If the discovery is indeed confirmed, this would be the first particle that does not fit into the standard model of particle physics, Ellison pointed out.

The standard model of particle physics is a theory of three of the four known fundamental interactions and the elementary particles that take part in these interactions. These particles -- quarks, leptons and gauge bosons -- make up all visible matter in the universe.

What Is a Tevatron?

The Tevatron is the second highest energy particle collider in the world after the CERN HLC.

It accelerates protons and antiprotons in a ring 3.9 miles long.

The Tevatron will be shut down in September, as it has been made obsolete by the CERN HLC, although some U.S. scientists are opposed to this.


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