The successful collision of proton beams in Cern's Large Hadron Collider means research can now accelerate, writes DICK AHLSTROM
CHAMPAGNE BOTTLES popped and the Irish celebrated on Monday when the world’s largest particle accelerator began delivering data. Three PhD students from UCD are involved in one of the experiments and were on hand to witness the drama as it unfolded.
“There was great excitement – it was a massive day,” says Dermot Moran, who along with James Keaveney and Stephen Farey, is working towards a degree at Cern, the European Organisation for Nuclear Research, based in Geneva.
They were there as Cern’s massive Large Hadron Collider (LHC), built at a cost of
€4 billion, began circulating two beams of protons and then allowed them to collide. This was the first real data to come from the LHC, with four of the experiments positioned along its 27km-long ring recording the results of proton-proton collisions.
The collider was first switched on in September 2008, but a major system failure forced its shutdown. Repairs costing €40 million were required to put it right, and late last week its operators began sending beams intermittently through the ring.
With the first collisions finally accomplished, this means that the LHC has now advanced beyond where it was after the 2008 start-up.
“It is super. The first collisions are a milestone for us,” says Dr Ronan McNulty, who heads UCD’s high energy experimental physics group. “We are ahead. We never got collisions last year.”
The LHC is built into a tunnel under the French-Swiss border near Geneva. It is designed to send proton beams around the ring at close to the speed of light and then collide them to release enormous amounts of energy.
These experiments help recreate conditions as they existed billionths of a second after the Big Bang, which formed the universe and space-time. The protons in turn break down into smaller constituent parts and enable physicists to study the fundamental nature of matter.
The energy of a particle accelerator is measured in standard units known as electron volts. The current energy record of 1 teraelectron volts (1TeV, a million million electron volts) is held by the Tevetron accelerator at Fermilab in the US. The LHC is meant to operate at 14 TeV, seven TeV per beam, giving it the energy to find things that no other accelerator can.
Chief among these sought-after discoveries is the Higgs boson, sometimes referred to as the “God particle”. First theorised by Prof Peter Higgs, of the University of Edinburgh, it remains the final particle still missing from the so called “Standard Model”, which attempts to describe the fundamental structure of matter.
It is thought that only the LHC has the energy levels required to find the Higgs.
There is still a very long way to go, however, before the LHC begins operating at its higher design energies, says Dr Tara Shears, of the University of Liverpool, which leads the group responsible for an LHC experiment called the LHCb, a group that includes the UCD team.
Shears explains that beams were crossed to deliver collisions adjacent to each of the four main experiments, allowing research teams to test their equipment. These beams were injected into the ring at just 0.45 TeV, well below the designed seven TeV. According to Shears, the first collisions were “quite unexpected”, given that they weren’t scheduled to happen before December.
The next step will be to begin accelerating the beams, speeding them up so that collision energies can reach 1.2 TeV per beam, according to Cern. This should happen before Christmas and set a new world record for collision energies of a combined 2.4 TeV.