Undergraduate Helps Discover Beautiful Quark Combinations

For his work, Field received the Department of Physics and Astronomy Stoddard Prize for the best thesis of 2006. His supervisor, department chair Arie Bodek, won the 2004 American Physical Society's Panofsky Prize for measuring the distribution of quarks inside protons and neutrons. Bodek's doctoral thesis provided the evidence of the quark's existence and was the basis for the 1990 Nobel Prize in physics.

There are six types of quarks: up, down, strange, charm, bottom/beauty, and top/truth. Particles with three quarks are called baryons, the most common of which are protons and neutrons. A proton has an up-up-down combination, while a neutron consists of down-down-up.

Scientists have observed many baryons, but combinations including the heavy bottom quark have remained elusive because they are difficult to produce: a lot of energy is required to create these heavier particles. In fact, until the evidence announced today by the Collider Detector at Fermilab (CDF) group, scientists had observed only one type of baryon with a bottom quark. CDF physicists now have evidence of two more types of baryons, one with an up-up-bottom combination, the other with down-down-bottom. These can be thought of as a proton and neutron with the third quark replaced by a bottom quark.

Fermilab's Tevatron collider hurls protons and antiprotons through a four-mile circular accelerator close to the speed of light. Billions of particles smash together, releasing an enormous amount of energy, which creates other particles such as the two newly discovered baryons.

Analyzing the Tevatron data, physicists observed approximately seventy up-up-bottom particles and seventy down-down-bottom particles. As predicted by theory, the new particles decay within a tiny fraction of a second and have a mass of about six times that of a regular proton.

Rochester faculty who are members of the CDF group include professors Bodek and Kevin McFarland, and senior scientists Willis Sakumoto, Howard Budd, and Pawel de Barbaro. Field started his research with the Rochester CDF group by spending a summer as an REU (Research Experience for Undergraduates) student at Fermilab and continued his work during the academic year.

As professor Bodek says, “The discovery fills another open spot in the periodic table of baryons and verifies the power of the standard model of particles and forces. The University of Rochester is very proud of Scott Field's contribution.”

For additional information about the discovery, see the Fermilab press release at http://www.fnal.gov/pub/presspass/press_releases/sigma-b-baryon.html.