Two experiments running simultaneously at the fermi national accelerator laboratory in
batavia, ill., have observed a new particle called the cascade baryon. it is one of the most massive
examples yet of a baryon—a class of particles made of three quarks held together by the strong
nuclear force—and the first to contain one quark from each of the three known families, or
generations, of these elementary particles.
protons and neutrons are made of up and down quarks, the two first-generation quarks. strange
and charm quarks constitute the second generation, while the top and bottom varieties make up
the third. physicists had long conjectured that a down quark could combine with a strange and a
bottom quark to form the three-generation cascade baryon.
on june 13, the scientists running dzero, one of two detectors at fermilab’s tevatron
accelerator, announced that they had detected characteristic showers of particles from the decay of
cascade baryons. the baryons formed in proton-antiproton collisions and lived no more than a
trillionth of a second. a week later, physicists at cdf, the tevatron’s other detector, reported their
own sighting of the
source: d. c., “pas de deux for a three-scoop particle,” science news, vol. 172, july 7, 2007

which combination of three quarks will produce a neutron?