September 12, 2008
New Particle Discovered
University of Michigan physicists played a leading role in the discovery of a new particle, the Omega b baryon, which is an exotic relative of the proton. It was detected for the first time in a particle accelerator at Fermi National Accelerator Laboratory (Fermilab) in Illinois, Fermilab has announced.
The heavy particle is scarce today, but scientists believe it was abundant soon after the Big Bang.
"This discovery helps us understand how matter was formed in the universe. It shows the critical success of the quark model and gives us new insight into the strong force, which binds quarks together to form larger particles," said Jianming Qian, a professor in the Department of Physics.
This discovery is largely attributed to the work done by Qian, physics postdoctoral fellow Eduard de la Cruz Burelo and physics professor Homer Neal. They are among 600 physicists from 90 institutions involved in DZero, the international experiment at Fermilab that produced these results.
"The contributions from these three team members from the University of Michigan were extremely important to this discovery," said Fermilab's DZero spokesman Dmitri Denisov.
The Michigan scientists pressed to re-examine previously gathered data for evidence of this particle, rather than wait for new data. "Their persistence paid off," said Denisov, who pointed out that these three Michigan scientists were also instrumental in DZero's discovery of a particle called the cascade b baryon last year.
Qian said detecting the Omega b baryon was like finding a needle in a haystack. The U-M team developed algorithms that allowed them to analyze almost 100 trillion particle collisions to find 18 events with the distinctive characteristics expected from the decay of the Omega b baryon.
In the collisions in the experiment, protons and anti-protons traveling near the speed of light hit head on, occasionally producing exotic heavy particles such as the Omega b baryon. The baryon travels about one millimeter before it decays into other particles.
Baryons are particles that make up the visible matter in the universe today. Protons and neutrons are the lightest baryons. All baryons are made of different combinations of three quarks. Quarks are smaller particles that come in six "flavors:" up, down, charm, strange, top and bottom. Scientists organize these flavors into three families.
Protons and neutrons are made of the quarks in the first family: up and down quarks. This new particle is the first baryon ever detected that is made only of quarks from the other two families. The Omega b baryon has two strange quarks and one bottom quark.
DZero is supported by the U.S. Department of Energy, the National Science Foundation and several international funding agencies.
Burelo, Neal, and Qian are among the co-authors of a paper on the finding that has been submitted to Physical Review Letters. The paper is called "Observation of the doubly strange Omega b baryon."
Image Caption: Aerial view of the Fermilab site. The ring in the foreground is the Main Injector and the ring in the background is the Tevatron. The circular ponds dissipate waste heat.
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