X(5568): New particle 'tetraquark' sheds light on Big Bang and early universe

A new particle has been discovered; and it is unlike anything ever seen before. The particle, known as X(5568), is made up of four different types of quark – a tetraquark.

This discovery will help scientists understand the beginnings of the universe, and will shed light on how these quarks "stick" together.

A single quark is a building-block of subatomic particles. Therefore, each of these particles are made up from a combination of different quarks, giving them different characteristics (including electrical charge and mass).

For example, protons are made up of three quarks, just like neutrons. The difference is, they consist of different types of quark, which is what makes them different.

Scientists are aware of six different types of quark currently: known as up, down, strange, bottom, charm and top. These are known as the quark flavours.

Researchers have identified particles made up of two or three quarks over the past 60 years, but a particle made from four quark flavours has been elusive. New research, published in Physics Review Letters, claims to have identified the first four-flavoured tetraquark.

"For most of the history of quarks, it's seemed that all particles were made of either a quark and an antiquark, or three quarks; this new particle is unique – a strange, charged beauty," said Daria Zieminska, lead researcher of the investigation. "It's the birth of a new paradigm. Particles made of four quarks – specifically, two quarks and two antiquarks – is a big change in our view of elementary particles."

Discovering X(5568)

The discovery was made by the DZero collaboration at the US Department of Energy's Fermilab. They noticed the first hints of a tetraquark in July 2015, but did not believe they were on the cusp of its discovery.

"At first, we didn't believe it was a new particle," Dmitri Denisov, spokesperson for DZero, told Symmetry Magazine. "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."

This new particle was made up of four different flavours of quark; similar to a four-cheese pizza. Each cheese is exactly that – cheese – but they all have slightly different flavours and textures which makes the pizza unique.

The particle was named X(5568), after its mass of 5568 Megaelectronvolts – around 5.5 times heavier than a proton. The four flavours of quark which made up this particle were up, down, bottom, and strange.

The researchers say this discovery will improve physicists understanding of quark matter – particles that would have existed moments after the Big Bang. These particles, made up of quarks and gluons, only exist by themselves at extremely high temperatures – billions of times higher than can be produced in the lab.

In February 2016, CERN's Large Hadron Collider managed to recreate the beginning of the universe, and therefore observe quarks and gluons in the brief moments following the Big Bang. They found that these particles behaved more like a liquid than a gas, even though they were existing in unbelievably high temperatures.

The discovery of this particle comes after an experiment in CERN's Large Hadron Collider discovered a pentaquark, in July 2015.

Researchers plan to keep investigating quarks; especially the glue that bounds them together.