Proton has a strange cousin: Fermilab finds new particle predicted by standard model.

Physicists have found a new heavy cousin of the proton hiding in a pile of data at the Fermi National Accelerator Laboratory in Batavia, Ill.

The new particle, long predicted to exist, is made of a bottom quark--the second-heaviest of all quarks--with two, much lighter strange quarks essentially orbiting around it, says Fermilab physicist Dmitri Denisov. The laboratory announced the discovery on September 3 and submitted a paper for publication to Physical Review Letters.

The particle, known as omega-b-minus, is one of many possible combinations of quarks predicted by the standard model of particle physics. The 1964 discovery of a particle made of three strange quarks was the landmark that established the mathematical basis for what would become the theory of quarks, says physicist Michael Peskin of the Stanford Linear Accelerator Center in Menlo Park, Calif. "This much later discovery is just another feather in the cap of this excellent theory," he says.

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Researchers at Fermilab's DZero detector, which smashes together protons and antiprotons circling almost at light speed in the Tevatron accelerator, took about a year to sift through data gathered between 2002 and 2006. The data described the debris from the collisions, in which the particles' huge energy creates hundreds of new quarks and other particles.

"We needed 100 trillion events to select events which can be interpreted as an omega-b-minus," and just a handful fit the bill, says Denisov, a DZero spokesperson. In each case, the researchers did not observe the new particle itself because it decayed almost immediately. Instead, the DZero detector picked up a signature combination of five particles left over by omega-b-minus decay. The physicists calculated the new particle's mass at 6.2 billion electronvolts, about six times that of a proton and very close to theorists' predictions.