The particle collisions at CERN create cascades of particles which are tracked by detectors like ALICE (above). By tracking the path of the particles back, scientists can extrapolate what happened during the collision. Image Credit: ALICE
New experiments at CERN’s Large Hadron Collider (LHC) show the early Universe may have behaved like a fluid.
The tests emulated the conditions just after the Big Bang, when temperatures were high enough to break apart protons and neutrons.
Normally, protons and neutrons are made of particles called quarks which are bound together by particles known as gluons.
However, just after the Big Bang, those quarks and gluons were free from each other, creating what is known as a quark-gluon plasma.
This plasma acts like a fluid.
To gain a better understanding of the properties of the primordial ‘fluid’ that used to comprise the Universe, a team of scientists from the Neils Bohr Institute used the LHC to smash together heavy ions.
These collisions create a similar level of energy to that found just after the Big Bang.
The collisions also create a shower of particles which the LHC’s detectors pick up, allowing scientists to back track their distribution to work out:
· The positions and orientation of the initial particles.
· The conditions inside the initial particle.
· The shear viscosity of particles – how resistant they are to flowing.
Shear viscosity is the main attribute that these experiments tried to pin down.
“It is one of the most important parameters to define the properties of the quark-gluon plasma because it tells us how strongly the gluons bind the quarks together,” says You Zhou from the Niels Bohr Institute.
These collisions have been done with iron ions in the past, but this time the team used heavier xenon ions, which will help to pin down the value of the shear viscosity even more precisely.
“No matter the initial conditions, lead or xenon, the theory must be able to describe them simultaneously.
If certain properties of the viscosity of the quark gluon plasma are claimed, the model has to describe both sets of data at the same time,” says You Zhou.
The team hopes to collide different types of ions in the future to pin down these properties even further.