The elusive top quark

22 April 1998

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On 22 April 1994, the 440 members of the CDF experiment at Fermilab, in Illinois, submitted a paper to The Physical Review* describing their first evidence for the production of top quarks in collisions between protons and antiprotons at the laboratory's Tevatron accelerator. The top quark was the long-sought sixth and heaviest member of the family of quarks - the building blocks of protons, neutrons and many other less familiar particles. This week's image shows a particularly good example of the particle tracks that reveal the "signature" of top quarks in the CDF detector. The proton and antiproton have collided at the centre of the image to produce a top quark and a top antiquark, which decay almost instantly (within 10-24 s) to other particles. The top quark has decayed to a lighter b quark, a positron (antielectron) and a neutrino. The positron leaves the track towards bottom left (e+), the b quark materialises as the jet of particles that shoot off towards the bottom right (jet #4), while the neutrino is undetected. (This decay is directly analogous to neutron beta decay.) The top antiquark has decayed to three lighter quarks which create the other jets of particles (#1, #2 and #3).

*( see F. Abe et al., The Physical Review D50 2966 (1994) )

Credit: Fermi National Accelerator Laboratory

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