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Experimenters at Fermilab discover exotic relatives of protons and neutrons

Fermilab Press Release, Interactions News Wire #86-06
October 23, 2006

Batavia, Illinois — Scientists of the CDF collaboration at the Department of Energy's Fermi National Accelerator Laboratory announced today (October 23, 2006) the discovery of two rare types of particles, exotic relatives of the much more common proton and neutron.

"These particles, named Sigma-sub-b [Σb], are like rare jewels that we mined out of our data," said Jacobo Konigsberg, University of Florida, a spokesperson for the CDF collaboration. "Piece by piece, we are developing a better picture of how matter is built out of quarks. We learn more about the subatomic forces that hold quarks together and tear them apart. Our discovery helps complete the 'periodic table of baryons.'"

Baryons (derived from the Greek word "barys", meaning "heavy") are particles that contain three quarks, the most fundamental building blocks of matter. The CDF collaboration discovered two types of Sigma-sub-b particles, each one about six times heavier than a proton.

There are six different types of quarks: up, down, strange, charm, bottom and top (u, d, s, c, b and t). The two types of baryons discovered by the CDF experiment are made of two up quarks and one bottom quark (u-u-b), and two down quarks and a bottom quark (d-d-b). For comparison, protons are u-u-d combinations, while neutrons are d-d-u. The new particles are extremely short-lived and decay within a tiny fraction of a second.

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=mc2. 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 cospokesperson 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 (Σ+b), and 134 d-d-b particles, negatively charged Sigma-sub-b particles (Σ-b). 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 on Friday, October 20, 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 different types of baryons with one bottom quark and spin J=3/2 (see graphic). 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.

InterAction Collaboration media contacts (www.interactions.org):

CDF institutions:

  1. Academia Sinica, Taipei, Taiwan
  2. Argonne National Laboratory, Argonne, Illinois
  3. Institut de Fisica d'Altes Energies (IFAE-Barcelona), Spain
  4. Baylor University, Waco, Texas
  5. Brandeis University, Waltham, Massachusetts
  6. University of California at Davis, Davis, CA
  7. University of California at Los Angeles, Los Angeles, CA
  8. University of California at San Diego, San Diego, CA
  9. University of California at Santa Barbara, Santa Barbara, CA
  10. Instituto de Fisica de Cantabria, CSIC-University of Cantabria, Santander, Spain
  11. Carnegie Mellon University, Pittsburgh, PA
  12. University of Chicago, Chicago, Illinois
  13. Joint Institute for Nuclear Research, Dubna, Russia
  14. Duke University, Durham, North Carolina
  15. Fermi National Accelerator Laboratory (FNAL), Batavia, Illinois
  16. University of Florida, Gainesville, Florida
  17. University of Geneva, Switzerland
  18. Glasgow University, United Kingdom
  19. Harvard University, Cambridge, Massachusetts
  20. University of Helsinki, Finland
  21. University of Illinois, Urbana, Illinois
  22. INFN, University of Bologna, Italy
  23. INFN, Laboratori Nazionali di Frascati, Italy
  24. INFN Sezione di Padova, Universita di Padova, Italy
  25. INFN, University and Scuola Normale Superiore of Pisa, Italy
  26. INFN, University di Roma I, Italy
  27. INFN, Trieste, Italy, and Universita di Udine, Italy
  28. IPP, Institute of Particle Physics, McGill University, Montréal, Canada
  29. University of Toronto, Canada
  30. ITEP, Institute for Theoretical and Experimental Physics, Moscow, Russia
  31. The Johns Hopkins University, Baltimore, Maryland
  32. Universitaet Karlsruhe, Germany
  33. National Laboratory for High Energy Physics (KEK), Tsukuba, Japan
  34. The Center for High Energy Physics(CHEP) Kyungpook National University, Seoul National University, and SungKyunKwan University, Korea
  35. Lawrence Berkeley National Laboratory (LBNL) Berkeley, California
  36. University of Liverpool, United Kingdom
  37. University College London, United Kingdom
  38. CIEMAT, Madrid, Spain
  39. Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts
  40. Michigan State University, East Lansing, Michigan
  41. University of Michigan, Ann Arbor, Michigan
  42. University of New Mexico, Albuquerque, New Mexico
  43. Northwestern University, Evanston, Illinois
  44. The Ohio State University, Columbus, Ohio
  45. Osaka City University, Japan
  46. Okayama University, Japan
  47. University of Oxford, United Kingdom
  48. CNRS-IN2P3, LPNHE, Paris, France
  49. University of Pennsylvania, Philadelphia, Pennsylvania
  50. University of Pittsburgh, Pittsburgh, Pennsylvania
  51. Purdue University, West Lafayette, Indiana
  52. University of Rochester, Rochester, New York
  53. Rockefeller University, New York, New York
  54. Rutgers University, Piscataway, New Jersey
  55. Texas A&M University, College Station, Texas
  56. Tufts University, Medford, Massachusetts
  57. University of Tsukuba, Tsukuba, Japan
  58. Waseda University Tokyo, Japan
  59. Wayne State University, Detroit, Michigan
  60. University of Wisconsin, Madison, Wisconsin
  61. Yale University, New Haven, Connecticut