Sub-atomic boffins glimpse four-pack tetraquark

The X(5568) particle - two mesons in exotic marriage

Sub-atomic boffins believe they've found evidence for the existence of a new "tetraquark" particle comprised, as the name suggests, of four quarks.

Scientists working on the DZero Experiment, using data collected between 2002 and 2011 by Fermilab's Tevatron collider, sniffed for a postulated particle containing two mesons (each with a quark and anti-quark).

Diagram showing X(5568) decay into two mesons

X(5568) decay into Bs and pi mesons

Fermilab elaborates: "DZero searched for new exotic states decaying into a Bs meson and a pi meson.

"Both of these are well-known mesons, which travel finite distances before decaying via the weak nuclear interaction.

"The Bs meson is composed of a quark and an antiquark of bottom and strange types, and the pi meson has an up and down quark and antiquark."

According to scientists, the Tevatron data confirms the tetraquark exotic state - dubbed the X(5568) particle - by providing evidence of its decay into the aforementioned Bs and pi mesons.

What scientists don't yet know is how the the quarks are configured in the X(5568) particle.

They might be packed together in a square "tetraquark" layout, or "configured as two pairs in a so-called molecular state, similar to a molecule of hydrogen, in which the two hydrogen atoms circle each other".

The two possible configurations of the four quarks

Take your pick: The two possible four-quark configurations.

The tetraquark agreeably fills the numerical gap between three-quark baryons, such as protons and neutrons, and the pentaquark. Back in 2005, research at the experiments at Thomas Jefferson National Accelerator Facility in Virginia suggested the latter didn't exist, although last year physicists at CERN's Large Hadron Collider declared they'd nailed the little blighter. ®

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