A NEW recruit has joined the weird and wonderful band of particles that physicists make in their accelerators. It鈥檚 called a doubly charmed baryon, and physicists believe it hasn鈥檛 existed in nature since the earliest minutes after the big bang.
Back in the 1960s, theoretical physicist Murray Gell-Mann developed a classification scheme for the elementary particles such as protons and neutrons that exist in atomic nuclei. The scheme assumes that these particles, known as baryons, are each made up of three smaller components called quarks, which come in any of six imaginatively named 鈥渇lavours鈥�: top, bottom, up, down, charm, and strange.
Gell-Mann鈥檚 scheme predicts the existence of flavour combinations that have never been seen, and physicists look for telltale signs of the missing baryons in data from collisions in particle accelerators. Now a team at the Fermilab National Accelerator in Illinois has presented the first evidence for the existence of particles, baryons that contain two charmed quarks.
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Mark Mattson and Jim Russ from Carnegie Mellon University analysed data from particle collisions gathered by the international SELEX collaboration at Fermilab. They saw signals from one baryon containing two charmed quarks and a down quark and from two baryons containing two charmed quarks and an up quark.
But the find isn鈥檛 quite what they expected. Like protons and neutrons, the two new particles differ in just one respect: one has an up quark and the other a down quark. But the difference between the two particles鈥� masses is 60 times the difference between the masses of a proton and a neutron. 鈥淓ither they are doing something funny and we don鈥檛 quite understand why, or we haven鈥檛 got their energy states labelled right,鈥� says Peter Cooper of Fermilab. The analysis also suggests that doubly charmed baryons are ten times as common as expected.