Monday 23 October 2017

Large Hadron Collider signal 'may show big bang conditions'

Tom Chivers

A never-before-seen signal in a collision at the Large Hadron Collider has raised hopes that the giant particle accelerator is on the verge of serious breakthroughs.

A series of high-energy proton-proton collisions observed at the Compact Muon Solenoid (CMS) detector led to 100 or more charged particles being produced. These so-called "high multiplicity" collisions were unusual in that the resulting particles are "correlated" - associated with each other at the moment of their creation.

One interpretation of the results is that the protons are being forced together at such high energies that the quarks that form them are released, becoming a free-flowing fluid of quarks and gluons like that which existed immediately after the big bang.

Similar results were seen when colliding copper ions at the Relativistic Heavy Ion Collider (RHIC) in the USA. However, the much higher beam power of the LHC means that similar energy collisions can be achieved even with a single proton, just 1/63rd of the weight of a copper ion.

Scientists at RHIC have interpreted their results to mean that they have reproduced the super-hot, super-dense conditions of the universe's first moments. If they are right, and if the LHC's results can be recreated, then the LHC is on course for real achievements.

In November physicists intend to start smashing together lead ions, with an atomic weight of 207, three times the size of copper. If the simple proton-proton collisions have been as successful as some are saying, then the possibilities for what will be unveiled in the lead collisions are huge.

James Gillies, the head of communication at CERN, is cautiously optimistic. "What's exciting is that the LHC is starting to deliver new physics," he says.

However, he is keen to emphasise that the "big bang" state is just one of many interpretations of the data. "The other possibilities are much less exciting", he stresses.

Guido Tonelli, a spokesman for the CMS, said: "[This phenomenon] has never been seen before in proton-proton collisions... This observation demonstrates the power and versatility of the CMS detector, as well as of the physicists exploiting it. We are now on our way to exploring, inch by inch, the new territory made accessible by the LHC."

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