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Fermilab physicists discover "doubly strange" particle:
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Six quarks--up, down, strange, charm, bottom and top--are the building blocks of matter. Protons and neutrons are made of up and down quarks, held together by the strong nuclear force. The DZero experiment has discovered the Omega-sub-b particle, which contains two strange quarks (s) and one bottom quark (b).



Once produced, the decay of the Omega-sub-b (Ωb) proceeds like fireworks. The particle travels about a millimeter before it disintegrates into two intermediate particles called J/Psi (J/ψ) and Omega-minus (Ω-). The J/Psi then promptly decays into a pair of muons. The Omega-minus baryon, on the other hand, can travel several centimeters before decaying into yet another unstable particle called a Lambda (Λ) baryon along with a long-lived particle called kaon (K). The Lambda baryon, which has no electric charge, also can travel several centimeters prior to decaying into a proton (p) and a pion (π). (Credit: DZero collaboration.)



Baryons are particles made of three quarks. The quark model predicts the combinations that exist with either spin J=1/2 (this graphic) or spin J=3/2. The graphic shows the various three-quark combinations with J=1/2 that are possible using the three lightest quarks--up, down and strange--and the bottom quark. The DZero collaboration discovered the Omega-sub-b, highlighted in the graphic. There exist additional baryons involving the charm quark, which are not shown. The top quark, discovered at Fermilab in 1995, is too short-lived to become part of a baryon. (Credit: DZero collaboration.)



The DZero collaboration identified 18 events that have the distinctive signature of the expected decay products of the Omega-sub-b. The mass of the particle is 6.165 0.016 GeV/c2. (Credit: DZero collaboration.)



The Fermilab accelerator complex accelerates protons and antiprotons close to the speed of light. Converting energy into mass, the Tevatron collider can produce particles that are heavier than the protons and antiprotons that are colliding. The Tevatron produces millions of proton-antiproton collisions per second, maximizing the chance for discovery. Two experiments, CDF and DZero, search for new types of particles emerging from the collisions.



The DZero detector is about the size of a 3-story house. The detector surrounds the collision point and records the path, energy and charge of short-lived particles emerging from the collisions. Its subsystems record the "debris" emerging from high-energy proton-antiproton collisions, unveiling the forces governing the subatomic world. Tracing the particle tracks back to the center of the collision, scientists discover what processes take place at the core of proton-antiproton collisions.



Some of the 600 scientists of the DZero collaboration in front of the DZero detector shortly before it began taking data in 2001.



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Last modified: 04/28/2009 |