Physicists at U.S. Department of Energy's Fermi National Accelerator Laboratory have discovered a new particle made of three quarks, the Omega b baryon, the lab's leading scientist Qian Jianming told Xinhua Wednesday.
The particle contains two strange quarks and a bottom quark. It is an exotic relative of the much more common proton and weighs about six times the proton mass.
Qian, originally graduated from University of Science and Technology of China and now a professor at University of Michigan, played a leading role in the discovery of this new particle. It was detected for the first time in a particle accelerator at Fermilab in Illinois.
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 Qian.
Qian is among 600 physicists from 90 institutions involved in DZero, the international experiment at Fermilab that produced these results.
Qian said detecting the Omega b baryon was like finding a needle in a haystack. They 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 1 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.
The discovery of the doubly strange particle brings scientists a step closer to understanding exactly how quarks form matter and to completing the "periodic table of baryons."
(Xinhua News Agency September 11, 2008)