CERN sets new high-energy collision record

One of the very first collisions recorded between two lead ions at the LHC’s top energy(Credit: CERN)

The Large Hadron Collider (LHC) recently set a new record, as CERN announced that the world's most powerful accelerator had achieved the highest-energy collisions of heavy atomic nuclei. The Geneva-based laboratory says that on Wednesday at 11:15 am CET, the 27 km (17 mi)-long supercollider fired two counter-circulating beams of lead nuclei at one another and the results were recorded by the ALICE heavy-ion detector.

The LHC recently completed a major upgrade, and since its restart earlier this year it's been colliding protons at record high energy. Now it's moving on to large lead nuclei containing 208 neutrons and protons. The purpose is to learn more about how the Universe formed a few billionths of a second after the Big Bang, by studying how strongly interacting systems at high densities behave.

According to the University of Copenhagen, which is participating in the CERN study, the Universe at this point was in a state known as the quark-gluon-plasma (QGP) that was made up of a hot, dense mix of quarks and gluons. About a millionth of a second after the Big Bang, this mix was fused into the protons and the neutrons of atomic nuclei, by the strong nuclear force that bind quarks together.

What CERN is trying to accomplish is to recreate the high temperature, liquid-like state of matter made of quarks and gluons similar to that at the start of the Universe by smashing together heavy atomic nuclei. By converting the kinetic energy from the collision into matter for an instant, the scientists are able to produce a small volume of quarks and antiquarks at a temperature of over 4,000 billion degrees.

"The collision energy between two nuclei reaches 1,000 TeV (tera-electron volts). This energy is that of a bumblebee hitting us on the cheek on a summer day," says Jens Jørgen Gaardhøje, professor at the Niels Bohr Institute at the University of Copenhagen. "But the energy is concentrated in a volume that is approximately 1027 (a billion-billion-billion) times smaller. The energy concentration is therefore tremendous and has never been realized before under terrestrial conditions."

The scientists hope that by studying such extreme energy events, they will be able to gain a better understanding and create new models of quark-gluon-plasma and of the strong interaction that will provide new insights into the first billionth of a second of the Universe.

"While it is still too early for a full analysis to have been carried out, the first collisions already tell us that more than 30,000 particles can be created in every central collision between two lead ions," says Gaardhøje. "This corresponds to an unprecedented energy density of around 20 GeV/fm3. This is more than 40 times the energy density of a proton."

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