New tetraquark particle discovered

A new particle comprised of all-differing quark content been found from data collected using the Tevatron collider at the FermiLab in Illinois.

The particle - a tetraquark known as X(5568) - composed of a bottom, strange, up and down quark could clarify the rules governing quarks. This is because no tetraquark found before has been made of four different flavours. X(5568) decays into two mesons, before decaying further into other daughter particles.

Dmitri Denisov, co-spokesperson for the DZero experiments that occurred at the FermiLab, said at first the scientists didn’t believe they’d found a new particle. “Only after we performed multiple cross-checks did we start to believe that the signal we saw could not be explained by backgrounds or known processes, but was evidence of a new particle,” he said.

The first evidence of a tetraquark was reported in 2003 by the Belle experiment in Japan, with others announced in following years. The tetraquarks that have been previously discovered had two quarks that were the same flavour.

[caption id="attachment_52667" align="alignnone" width="540"] Scientists are now trying to work out how the quarks are arranged. Credit: Fermilab[/caption]

Last year, scientists at the Large Hadron Collider in Switzerland detected a pentaquark. Usually, quarks are more likely to be found as pairs – mesons – or in threes as baryons (which are neutrons or protons).

Paul Grannis, DZero co-spokesperson, said: “The next question will be to understand how the four quarks are put together. They could all be scrunched together in one tight ball, or they might be one pair of tightly bound quarks that revolves at some distance from the other pair.”

More than 70 institutions from almost 20 countries were involved in the DZero project, which finished operating in 2011, but is having its collected data analysed by scientists.

The findings were published in Physical Review Letters.