In a circular tunnel beneath the border of France and Switzerland, scientists will this Wednesday just after 6pm begin one of the most ambitious scientific projects ever undertaken. Half a world away, researchers in Melbourne and Sydney who have played a crucial part in the enormous collaborative effort will be watching in great anticipation.
The Large Hadron Collider, the world’s largest particle accelerator complex, will smash together sub-atomic particles that have been accelerated to dramatic speeds, with the aim of understanding the basic forces of nature that have shaped our universe since the beginning of time.
“It really is very exciting,” says Professor Geoffrey Taylor from the University of Melbourne, who has been working on the project since its beginnings in the early 1990s. “We know we’re on the cusp of something significant.”
The Large Hadron Collider (LHC) will recreate, on a miniscule scale, conditions very similar to those that existed soon after the Big Bang. Its main purpose is to explore the validity and limitations of the Standard Model, the current theoretical framework for how physics operates at the most fundamental level.
The LHC was built by the European Organization for Nuclear Research, but has been funded, designed and constructed in collaboration with scientists from around the world. At last count, the project has involved more than eight thousand physicists from universities and laboratories in 85 countries.
It has also been more than twenty years in the making, says Professor Taylor. The idea of the LHC first arose in the early 1980s and the CERN Council first approved the project in December 1994.
After a long process of planning, design and construction, the first attempt to circulate a beam of protons through the entire LHC is scheduled for 10 September 2008. The first high-energy collisions are expected to happen not long after, on 21 October 2008.
Deep beneath the Earth
The collider is housed in a circular tunnel 27 kilometres long, at a depth of between 50 and 175 metres below the ground. The tunnel, 3.8 metres in diameter and lined in concrete, was actually built in the mid-1980sto house an earlier collider. It straddles the border between Switzerland and France, although most of it is in France.
“The big thing about the LHC is that it collides the protons at much higher energy than other colliders,” says Dr Kevin Varvell from the University of Sydney, another LHC collaborator. “It gives us much more reach really, and brings us a little bit closer to the Big Bang. We hope that it will fill in some missing gaps in our understanding of subatomic physics.”
The LHC’s collider tunnel contains two adjacent pipes, each of which contains a beam of protons (a proton is one type of hadron). The beams travel in opposite directions around the ring, kept on path by more than 1600 superconducting magnets, most of which weigh more than 27 tonnes.
Once or twice a day, the protons will be accelerated to an energy of 7 tera electron volts (TeV), giving a total collision energy of 14 TeV. At that point, the protons will be travelling so quickly that it will take each one less than 90 microseconds (that’s ninety thousandths of a second) to travel around the ring.
As the particles smash together they will “break apart” into smaller, more fundamental components, giving physicists a fleeting chance to observe those particles, some of which will never have been seen before.
“We know we are likely to find something very important, something scientifically quite profound,” Professor Taylor says.
One of the most highly anticipated products of the collider might be the elusive Higgs boson, which could explain how other elementary particles acquire properties such as mass. If scientists can verifiy the existence of the Higgs boson, it would be a significant step in the search for a Grand Unified Theory, which aims to bring together three of the four known fundamental forces: electromagnetism, the strong nuclear force and the weak nuclear force, leaving out only gravity.
In addition to this, scientists hope the LHC could reveal supersymmetric particles, micro black holes or even extra dimensions.
The ATLAS detector: Australia’s role
Scientists from the University of Melbourne and the University of Sydney have jointly contributed to one of the six detectors at the LHC. Their contributions include designing detectors and shielding, developing software to model the behaviour of the detector, and software that triggers the collection of information.
Around the ring of the LHC are positioned 6 detectors, which have been designed to search for the new discoveries revealed as the protons collide. Australia’s physicists have been most closely involved in the development of one of these detectors, known as the ATLAS experiment.
ATLAS, itself the product of a worldwide collaboration, is roughly 45 meters long, more than 25 meters high, and weighs about 7,000 tons, making it about half as big as Notre Dame Cathedral in Paris.
“Bigger is not necessarily better, but in this case it’s the only way we can do this kind of science because of the instruments we need,” says Dr Varvell.
The sophisticated technology incorporated into this device is designed to detect “anything new within reason, and to allow us to be fairly sure we will see what we expect,” he says.
If all the data from ATLAS was recorded, it would fill 100,000 CDs per second, the project scientists say, which is enough to create a stack of CDs 450 feet high every second, reaching to the moon and back twice each year.
Fortunately, not all the data is collected, and ATLAS will actually only record data that might show signs of new physics—“only” 27 CDs-worth per minute.
Australia’s scientists were particularly involved on the radiation resistance of silicon detectors in the centre of ATLAS. Challenges included designing technology that would function at the extreme conditions generated in the LHC. “The biggest issue was the intensity of the machine, which is more than 1,000 times higher than current machines,” said Professor Taylor.
“The speed of the read-out will also be 10,000-15,000 times higher. We had to do a lot to make the detectors viable.”
Australian companies were also involved in constructing copper shields that form part of the machine, and in 2003 Professor Taylor’s team supervised the despatch of 14 pieces of shielding to LHC, weighing some 35 tonnes.
Do we need it, and is it safe?
The discoveries that will be made by scientists working at the LHC will rewrite our understanding of how the universe began and the way it operates at the most fundamental level, says Dr Cathy Foley, President of the Australian Institute of Physics.
“It wasn’t that long ago that we didn’t even know that atoms existed,” she says.
“That discovery allowed us to do all manner of things that people couldn’t have dreamed possible before. If thanks to the work at the LHC we’re able to understand subatomic particles, it will surely lead us to new technologies or ways of understanding the world around us. We will look back in 100 or 200 years and marvel at how antiquated are the things we can do today.”
Taking part in such an enormous collaborative project is an important opportunity for Australian physicists to take their place in a global scientific endeavour, Dr Foley said.
“Also, from a political point of view, being part of such a big project says we want to collaborate with colleagues around the world in a way that can break down political barriers. That’s extraordinarily powerful.”
She also dismisses the fears drummed up by some media outlets that the LHC will create a black hole that will somehow swallow up the earth. “Scientists think the kinds of collisions that the LHC will be generating happen all the time in nature,” she says.
Although the particles will be smashed together at speeds that generate large amounts of energy in sub-atomic terms, when you compare it to more everyday events they are less impressive, she notes.
“We’re talking about something that has got less energy than a flying mosquito,” she says. “It’s like a rice-bubble pop.”
Feature written by Stephen Pincock for the Australian Institute of Physics and Science in Public.