Searching for the God particle
Geneva, (OBSERVER NEWS SERVICE)
By Robin McKie
Line and engineered to one-billionth of a metre accuracy, the $6bn, 27km circular proton accelerator deep beneath the Swiss-French border is the world's largest machine. And it's been built to uncover the smallest fragments of the cosmos. Robin McKie travels to Geneva to meet the scientists determined to prove the existence of the God particle
Physicist David Evans has an unusual take on the $6bn underground particle accelerator he is helping to complete on the Swiss-French border outside Geneva. 'If it works, we will have built the most complex machine in history,' says the Birmingham University researcher. 'If it doesn't, we will have assembled the world's most expensive piece of modern art.' These sentiments suggest a certain nervousness among Europe's scientific elite as their great project reaches fruition - though most researchers say they are confident of success. They insist that when Europe's Large Hadron Collider (LHC) is switched on in November, it will hum into life as expected. Beams of protons, one of the key constituents of an atom's nucleus, will be hurtled at colossal velocities around the machine's 27km circular tunnel and made to smash into each other. Subterranean vaults of electronic detectors will track the sub-atomic rubble erupting from these collisions. Huge refrigerators, filled with liquid helium, will cool key parts of the collider to -270C, colder than outer space, while above ground, a bank of 5,000 computers will analyse the detectors' vast output - equivalent to the release of a DVD's worth of electronic data every second - and so help physicists uncover the secrets of the universe's structure.
This is science on a gargantuan scale: a device the size of London Underground's Circle Line, engineered to one-billionth of a metre accuracy, which will probe the universe's tiniest constituents and study the Big Bang birth of the cosmos 13bn years ago. To this end, thousands of physicists and engineers - most seconded from national research centres across the continent - have laboured for a decade to set up the most expensive, most complicated scientific experiment ever attempted.
Clearly, a lot is expected of this machine, so perhaps it is not surprising that there is an air of concern in the corridors and offices of the LHC's home at Cern, Europe's particle physics laboratory. Such worries are focused less on the possible failure, however, and more on the issue of timing. Physicists know it will take months to tune their hadron collider (hadrons are a class of particle that includes the proton) to a perfect pitch so it churns out the data that they need to find new particles. And that gap could be awkward, for delays just might allow a bunch of upstart Americans, using a rival, older and less powerful device, to beat Europe to the draw. For the past few months, scientists at the Fermilab laboratory in Illinois have hinted that their ageing accelerator, the Tevatron, may be on the threshold of uncovering the Holy Grail of modern physics: the Higgs boson, or the God particle, as it is sometimes known.
The existence of the Higgs boson was first proposed by the Edinburgh University physicist Peter Higgs in 1964 to explain why objects - including people - in our universe have mass. The Higgs interacts with other particles, thus making them heavy, by clinging to them like treacle, he argued. After initial suspicion, the idea caught on and has become the cornerstone of modern physics. However, no matter how hard scientists have tried, they have failed to get a single glimpse of a Higgs. Such an omission is embarrassing, and scientists badly want to put it right. Proof of the particle's existence would, if nothing else, confirm that their theories about the universe are broadly right. 'It's probably the closest to God that we'll get,' admits Jos Engelen, Cern's chief scientist.
Getting close to God and finding the Higgs was a prime reason for constructing the LHC. Its tunnels, super-conducting magnets, experiment halls and banks of computers have been put together with this very much in mind. For almost a decade, Cern has concentrated on this project, at the expense of virtually all other research. But now, at the last minute, the Yanks are threatening to steal Europe's thunder: a galling prospect - though European scientists insist they are not downhearted. If the Americans want a battle, they can have one. 'We have spent most of the last decade building this machine,' says Professor Jim Virdee, of Imperial College London. 'Now we are almost there. There is a real buzz about the place. The race is on.'
For its part, Cern also insists that even if it loses out in the race to the Higgs, its great machine will still go on to make discoveries of even greater importance in the more distant future. These include the prospect of finding extra dimensions in space and of uncovering particles that could account for 'dark matter', which is believed to permeate the universe and account for most of its mass. Nevertheless, discovering the Higgs is a task that has acquired immense symbolic importance for Cern.
But how do you find one? Not easily, is the answer. You have to recreate the conditions of the first moments of the universe's explosive birth, when the cosmos seethed with strange, exotic, highly energetic particles. Do that, and Higgs particles will start to pop into existence, scientists predict. The only issue is, of course, the rather tricky business of reproducing the early universe. That task requires the construction of a device of extraordinary proportions: the Large Hadron Collider.
For a start, the machine will soak up 10 times more energy than any other particle accelerator on earth, consuming 120 megawatts of electrical power - enough for an entire Swiss canton - to accelerate bunches of protons, kept in two beams, each less than a hair's-breadth in diameter, to speeds that will come 'within a gnat's whisker of the speed of light', according to Steve Myers, head of Cern's beam mechanisms. One beam will circulate clockwise, the other anti-clockwise. Then, at four points along the collider's tunnel, the beams will cross over. Bunches of protons - each containing 100bn particles - will slam into other oncoming bunches, triggering collisions that will fling barrages of sub-atomic detritus in all directions. These explosive interactions will form the core of the great collider's operations and will generate new types of particle, including the Higgs, that will pop fleetingly into existence before disintegrating into a trail of other sub-atomic entities.
The crucial point is that the greater the energy generated by a collider, the bigger the particles it can create. Matter and energy are interchangeable, so if you release vast amounts of energy you will create new, very large particles in your beam collisions. And most predictions suggest the Higgs is relatively big, hence scientists' past failure to produce them - their machines have simply not been powerful enough. The LHC should put that right.
Making God particles is one thing, of course. Spotting them and confirming their existence is another. To do that, four great experiment halls - known as Alice, Atlas, CMS and LHCb - have been constructed round the collider's collision points and into these vaults, 90m below ground. Scientists and engineers have fitted thousands of tonnes of detectors and magnets to track the pathways of escaping particles. These chambers are vast - the nave of Notre Dame would fit inside Atlas, for example - and the instruments inside are breathtakingly complex: arrays of detectors and magnets are piled up around each other like layers of a great metallic onion. Particles created by proton collisions will whizz out through these layers, decay into other particles while in flight, and leave telltale signs of their passage. Billions of interactions will take place every second, though the vast majority will be automatically rejected by the collider's computers, which will be programmed to recognise only interesting, unusual particle flight patterns.
In the case of the Higgs, theorists predict the collider will be lucky to make more than one or two of these particles a day. 'The problem is that we will need to create several hundred and study their behaviour before we can be sure we have the Higgs,' says Jim Virdee. It will therefore take several months, with the LHC working flat out, before European physicists can be sure they have got their baby. Most expect that success will come in late 2008.
The Americans have already been battering beams of particles together to try to create the Higgs. However, the US machine strains to reach the colossal energies needed for such a task, and despite hints, US scientists have yet to produce the goods. 'You never know, they might just do it - but I doubt it,' adds Virdee. 'They will need a lot of luck to beat us.' The Higgs is just the start. Many other strange new particles will emerge from its proton collisions and help solve a host of other scientific puzzles. Consider the example of dark matter. Physicists and astronomers have shown that the particles which make up stars, planets and humans account for only a tiny fraction of the universe's mass. Something else is out there, an invisible form of matter - hence the title 'dark matter' - that is generating gravitational ripples throughout the cosmos. Sub-atomic entities called super-symmetrical particles are a favourite candidate, and researchers believe there is a strong chance the Large Hadron Collider will produce them. It is even possible that these particles will reveal the existence of at least another six new dimensions of space - a fairly boggling prospect, to say the least.
But then Cern is a mind-boggling place: a town of 2,500 permanent staff and a constant influx of around 7,500 visiting experts, each dedicated to the uncovering of the universe's mysteries. Apart from the Nobel prizes that have already been won here, Cern has also generated some of the planet's slickest engineering work. Tim Berners-Lee created the world wide web in 1991 while working at Cern. Other spin-offs include the development of brain scanners and the use of isotopes in medical research.
You can get a real feel for the talent, creativity and eccentricity of the place in its large, ramshackle, neon-lit cafeteria which, day and night, is filled with shifts of technicians, secretaries, researchers, theoreticians and policy-makers. Perched on plywood seats at long Formica tables, earnest young researchers swig beer and argue over the minutiae of particle physics; some fiddle with their laptops; others scribble on notepads. As the LHC reaches readiness, the air of anticipation is palpable.
'In a way we are in a perfect situation,' says Dr Jo Cole of Britain's Rutherford Appleton Laboratory, and a key worker in the CMS experiment hall. 'Either we prove the theoreticians are right and help in the garnering of Nobel prizes. Alternatively, we will show they were wrong. We will have found something else that is new and exciting, and will have overturned accepted science.'
The intriguing point is that most scientists here, if given the choice, would probably plump for the latter scenario. Yes, it would be great to beat the Americans to the Higgs, but it would be even better if Cern found that Higgs did not exist at all, or that it came with a whole new class of sister particles that had never been predicted by theorists. Far better to rock the boat than have it continue to sail on calm waters. 'It is uncertainty that we really relish,' adds David Evans. 'We don't like things that are all neatly sewn up.' And that is a crucial point. The public may think that scientists are control freaks who want to order the universe in safe compartments. In fact, the reverse is true: constant revolution is what they really desire.
And never before have scientists been better equipped to bring about that revolution. They have built the world's biggest machine committed to uncovering the universe's smallest fragments, which, in reality, is a vast device dedicated to seeking out uncertainty and undermining scientific convictions. Even if the Higgs turns up more or less on cue, it won't take the LHC much longer to start producing all sorts of strange results that will perplex and confuse the theorists. That is its real purpose. 'I will happily bet a month's salary, which admittedly is not very much, that we will have thrown up whole new fields of physics within two years of switching on the LHC,' says Evans. 'And really, that is why this is going to be such a great place to work in over the next decade.'
Sci. & Tech.