Little bump causes big excitement in high-energy physics

On April 6, UI physics postdoctoral research associate Viviana Cavaliere presented, on behalf of the CDF collaboration at Fermilab, tantalizing new indications that a previously undiscovered particle, 150 times the mass of the proton, could be lurking in collisions that produce a W boson accompanied by two hadronic jets.

The results presented Wednesday were based on Cavaliere's PhD thesis research, which was completed at the University of Siena (Italy) in December 2010. 

In his article, which appeard in the online edition of the Chronicle of Higher Education (April 7, 2011), Paul Basken noted that "...the finding originated about a year ago with Viviana Cavaliere, a graduate student from the University of Siena, in Italy. She began poring over data from the Tevatron—which smashes protons and antiprotons together two million times a second, 24 hours a day, seven days a week—to classify the frequencies at which some known basic particles, such as bosons and quarks, are produced.

"Ms. Cavaliere and three Italian colleagues were surprised to find an unexpected spike in their chart depicting the sizes and frequencies of the particles produced in each collision. The spike represented about 250 cases out of about 10,000 in which the collisions appeared to be producing an unknown and unexpected particle about 150 times bigger than a proton.

"While that's a low number of cases, the clarity of the spike suggests less than a 0.01 percent chance that the data will turn out to be some kind of aberration, Ms. Cavaliere and her team reported. Subsequent checks of the findings will include exhaustive reviews of recorded data from years of past collisions, and attempts to replicate the results.

"If upheld, the finding could mean an overhaul of a century of theoretical consensus on the basic forces and particles that comprise the universe. Or it could help provide the evidence necessary to affirm the theory, known as the standard model, and answer some of its unresolved mysteries. Either way, it would be a very big deal.

"Earlier this year, Fermilab researchers found evidence of unexpected variations in the rate at which top quarks and their corresponding antiparticles are produced in collisions. That discovery, and the one by Ms. Cavaliere, were given odds of certainty greater than "three sigma," a statistical measurement of significance, meaning less than a half-percent chance of not being upheld."

Cavaliere joined the CDF and ATLAS groups at Illinois in January 2011, where she is working with Physics Professor Mark Neubauer.

At Illinois, Cavaliere and her collaborators refined the initial analysis into its present form, which has been submitted to Physical Review Letters. A preprint of the paper was posted on arXiv on April 4.

A video of Cavaliere's April 6 presentation of the results at Fermilab is available.
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Contact: Mark Neubauer, Department of Physics, 217/244-3913.

Writer: Celia M. Elliott, Department of Physics, 217/244-7725.

Article includes excerpt from an article by Paul Basken, "As Lawmakers Battle Over Cuts, Physicists Try to Beat the Odds.", Chronicle of Higher Education (April 7, 2011) .Cavaliere Photo courtesy of Fermilab.

If you have any questions about the College of Engineering, or other story ideas, contact Rick Kubetz, editor, Engineering Communications Office, University of Illinois at Urbana-Champaign, 217/244-7716.