UF physicist leads team that discovers protons and neutron relatives

Published: October 23 2006

Category:Research, Sciences

GAINESVILLE, Fla. — A scientific collaboration led by a University of Florida physicist announced today the discovery of two rare types of particles, exotic relatives of the much more common proton and neutron.

The scientists, part of the Collider Detector at Fermilab, or CDF, collaboration at the Fermi National Accelerator Laboratory in Batavia, Ill., discovered two types of so-called Sigma-sub-b particles, each one about six times heavier than a proton.

“These particles are like rare jewels that we mined in our data,” said Jacobo Konigsberg, a physicist at the University of Florida and spokesman for the collaboration. “Piece by piece, we are developing a better picture of how matter is put together. We learn more about the subatomic forces that hold quarks together and tear them apart. Our discovery fills another couple of holes in the ‘periodic table’ of baryons.”

Baryons are particles that contain three quarks, the most fundamental building blocks of matter. There are six types of quarks: up, down, strange, charm, bottom and top. Protons contain two up quarks and one down quark, signified as “u-u-d”, while neutrons have two down and one up, signified as “d-d-u”. The two newly discovered baryons are made of two up quarks and one bottom quark. The new particles are extremely short-lived, decaying within a tiny fraction of a second.

Konigsberg leads the scientific and managerial team at CDF. His duties include monitoring scientific results and ensuring the smooth running of the technology underpinning the experiments. As spokesperson, his other roles include overseeing all other high-level management positions, setting the lab’s priorities and ensuring the CDF gets the support it needs to meet its mandate.
Utilizing Fermilab’s Tevatron collider, the world’s most powerful particle accelerator, physicists can recreate the conditions present in the early formation of the universe, reproducing the exotic matter that was abundant in the moments after the big bang. While the matter around us is comprised of only up and down quarks, exotic matter contains other quarks as well.

The Tevatron collider at Fermilab accelerates protons and antiprotons close to the speed of light and makes them collide. In the collisions, energy transforms into mass, according to Einstein’s famous equation E=mc^2. To beat the low odds of producing bottom quarks — which in turn transform into the Sigma-sub-b according to the laws of quantum physics — scientists take advantage of the billions of collisions produced by the Tevatron each second.

“It’s amazing that scientists can build a particle accelerator that produces this many collisions, and equally amazing that the CDF collaboration was able to develop a particle detector that can measure them all,” said CDF co-spokesman Rob Roser, of Fermilab. “We are confident that our data hold the secret to even more discoveries that we will find with time.”

The CDF experiment identified 103 u-u-b particles, positively charged Sigma-sub-b particles and 134 d-d-b particles, negatively charged Sigma-sub-b particles. In order to find this number of particles, scientists culled through more than 100 trillion high-energy proton-antiproton collisions produced by the Tevatron over the last five years.

In a scientific presentation Friday, CDF physicist Petar Maksimovic, professor at Johns Hopkins University, presented the discovery to the particle physics community at Fermilab. He explained that the two types of Sigma-sub-b particles are produced in two different spin combinations, J=1/2 and J=3/2, representing a ground state and an excited state, as predicted by theory.

Quark theory predicts six types of baryons with one bottom quark and spin J=3/2. The CDF experiment now accounts for two of these baryons.

CDF is an international experiment of 700 physicists from 61 institutions and 13 countries. It is supported by the Department of Energy, the National Science Foundation, and a number of international funding agencies. (The full list can be found at http://www-cdf.fnal.gov/collaboration/Funding_Agencies.html.) Using the Tevatron, the CDF and DZero collaborations at Fermilab discovered the top quark, the final and most massive quark, in 1995.

Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operated under contract by Universities Research Association Inc.


Jacobo Konigsberg, Konigsberg@phys.ufl.edu, 630-840-3623

Category:Research, Sciences