ANN ARBOR, Mich.–University of Michigan physicists have made significant contributions to the discovery of a new particle called the Cascade b () baryon while working on the D0 (D-zero) experiment at Fermi National Accelerator Laboratory (Fermilab) located in Illinois. This discovery serves as a road sign on our long journey to answer the question "What is the world made of?"

"My colleagues and I are delighted to have been involved with this discovery and to further confirm the extant model of particle physics in a domain where different generations of quarks combine to form a fundamental particle," said UM Physics Professor Homer A. Neal.

The world is made from a few fundamental building blocks. These and the forces holding them together are elegantly summarized by a theory called the Standard Model of particle physics. In this theory, the building blocks consist of three generations of quarks and leptons. Physicists study these building blocks through high-energy collisions at particle accelerators.

At Fermilab, protons and anti-protons collide at the world’s highest laboratory energies in the Tevatron collider. These violent collisions occasionally produce heavy particles thanks in part to Einstein’s famous equation, as matter and energy are convertible. Most of these heavy particles are short-lived and often decay, either directly or through other intermediate unstable particles, into lighter and long-lived particles. These stable particles are then detected using large sensitive instruments enclosing the interaction point.

The observation of thebaryon by the D0 experiment represents the first observation of a particle formed of quarks from all three known generations. Thebaryon is made of a down, a strange, and a beauty (nickname for bottom) quark. It is the heaviest baryon discovered to date that decays through the weak interaction, a force responsible for most radioactive decays.

Sifting through over a billion collisions recorded over the last five years, physicists from Michigan, the University of Oklahoma and other colleagues found 19 events consistent with the decay of a new particle having approximately 6 times the proton mass. The odds of the observed signal due to background fluctuation are less than.

Three Michigan physicists were centrally involved in this effort. Professor Jianming Qian, the current leader of the University of Michigan D0 Group, and the recent coordinator of overall D0 physics, was the major coordinator of, and a contributor to, the ensuing analysis. Dr. Eduard de la Cruz Burelo, a Postdoctoral Research Associate at UM first observed the signal in related data that he was processing at the request of his advisor, Professor Homer A. Neal who founded the Michigan D0 group. Through analysis of this larger sample, evidence was found by Dr. Burelo for the newparticle.

After the original observation, the ensuing analysis was followed by the entire Michigan D0 Group. A paper titled "Direct observation of the strange b baryon Xb" has been submitted to the journal Physical Review Letters. This discovery fills a missing piece in the Standard Model and solidifies our understanding of what makes up the world.

D0 is an international experiment of approximately 600 physicists from 82 institutions of 19 countries. It is supported by the Department of Energy, National Science Foundation, and a number of international funding agencies. Fermilab is a national laboratory funded by the Office of Science of the U.S. Department of Energy, operating under contract by Fermi Research Alliance, LLC. The Michigan D0 group consists of Professors Homer A. Neal, Jianming Qian and Bing Zhou, research fellows Eduard de la Cruz Burelo, Alan Magerkurth, and Jonas Strandberg, graduate students Jim Degenhardt and Chun Xu.



Contact: Carol Rabuck

Phone: (734) 763-2588

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