STRANGE matter may not be the strangest of all. Researchers at a particle
accelerator near New York have created “doubly strange” atomic nuclei. These
contain rare “strange” quarks and are supposed to be the first step towards
strange matter—thought to exist only in superdense neutron stars. But the
next step failed to materialise.
Protons and neutrons in everyday matter are made of “up” and “down”
quarks—just two of the six types of quark. But neutron stars, the dense
cores of dead stars, may contain a soup of strange quarks with exotic
properties. Persuade two strange quarks to get together in the same nucleus, and
physicists reckon their mutual attraction might just create a precursor of
strange matter.
To test this prediction, a team at Brookhaven National Laboratory smashed a
beam of negative kaons into a beryllium target. A negative kaon is a strange
quark paired with an anti-up quark. In the debris, they spotted more than 40
doubly strange nuclei. Each nucleus contained a proton and neutron plus two
lambda particles, each composed of an up, a down and a strange quark.
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The researchers expected the strange quarks’ attraction to then collapse each
nucleus into a droplet of quark soup known as an H particle. Instead, the
strange quarks stayed bound up in their lambda particles. Robert Chrien of the
Brookhaven team says, “Even in a neutron star I don’t think a quark soup could
澱.”
Despite the disappointment over strange matter, strange quarks will still
affect the shell structure and shape of the nuclei, which could influence
whether dying stars simply collapse, or explode in a supernova. “Even without
quark matter, it is possible for strangeness to play a role in stars,” says Ben
Gibson, a strange-quark expert at Los Alamos National Laboratory in New Mexcio.