The CMS detector will trace sub-atomic debris created when particles travelling almost at the speed of light collide
MARK HENDERSON, SCIENCE EDITOR
It is the most ambitious and expensive civilian science experiment in history, based on the biggest machine that humanity has yet built. It has sparked alarmist fears that it might create a black hole that will tear the Earth apart, and it has triggered two last-minute legal attempts to stop it
And next Wednesday, after almost two decades of planning and construction, the project in question will finally get under way.
Beneath the foothills of the Jura mountains, in a network of tunnels that bring to mind the lair of a crazed Bond villain, scientists will fire a first beam of particles around a ring as long as the Circle Line on the London Underground. This colossal circuit, 17 miles (27km) in circumference, is the world’s most powerful atom-smasher, the £3.5 billion Large Hadron Collider (LHC), created at CERN, the European particle physics laboratory near Geneva. Some 10,000 scientists and engineers from 85 countries have been involved. In the years ahead it will recreate the high-energy conditions that existed one trillionth of a second after the big bang. In doing so, it should solve many of the most enduring mysteries of the Universe.
This extraordinary feat of engineering will accelerate two streams of protons to within 99.9999991 per cent of the speed of light, so that they complete 11,245 17-mile laps in a single second.
The two streams will collide, at four points, with the energy of two aircraft carriers sailing into each other at 11 knots, inside detectors so vast that one is housed in a cavern that could enclose the nave of Westminster Abbey. The detectors will trace the sub-atomic debris that is thrown off by the collisions, to reveal new particles and effects that may never have existed on Earth before. The mountains of data produced will shed light on some of the toughest questions in physics.
The origin of mass, the workings of gravity, the existence of extra dimensions and the nature of the 95 per cent of the Universe that cannot be seen will all be examined. Perhaps the biggest prize of all is the “God particle” – the Higgs boson. This was first proposed in 1964 by Peter Higgs, of Edinburgh University, as an explanation for why matter has mass, and can thus coalesce to form stars, planets and people. Previous atom-smashers, however, have failed to find it, but because the LHC is so much more powerful, scientists are confident that it will succeed. Even a failure, however, would be exciting, because that would pose new questions about the laws of nature.
“What we find honestly depends on what’s there,” said Brian Cox, of the University of Manchester, an investigator on one of the four detectors, named Atlas. “I don’t believe there’s ever been a machine like this, that’s guaranteed to deliver. We know it will discover exciting things. We just don’t know what they are yet.” The guarantee applies, however, only if the hardware works as it should, and the LHC’s first big test comes on Wednesday, when the first beam of particles is injected into the accelerator. That is a huge technical challenge. “The beam is 2mm in diameter and has to be threaded into a vacuum pipe the size of a 50p piece around a 27km loop,” said Lyn Evans, the LHC’s project manager, who will oversee the insertion. “It is not going to be trivial.”
Engineers will use magnets to bend the beam around the LHC’s eight sectors, until it finally begins to circulate. “That’ll be the first sight of relief, that there are no obstacles in the vacuum chamber,” Dr Evans said. “There could be a Kleenex in the chamber – we’ve had that before. Only when we get the beam around will we be able to tell it’s clear.” Once the first beam is in – probably the one running clockwise, though that has yet to be decided – the team will insert the second, anticlockwise stream of particles. The first collisions, to test the detectors, should follow by the end of next week.
The next step will be to “capture” the beams so they fire in short pulses, 2,800 times a second. These will then be accelerated to an energy of 5 tera-electronvolts (TeV), generating collisions of 10TeV.The detectors should be calibrated by the end of the year and the collisions will then be ramped up to their maximum energy of 14TeV, generating the conditions that prevailed fractions of a second after the Big Bang.
One of the first scientific discoveries is likely to concern a theory called supersymmetry. Tejinder Virdee, of Imperial College, London, who leads the Compact Muon Solenoid (CMS) detector team, said: “What supersymmetry predicts is that, for every particle you have a partner, so it doubles up the spectrum.
You have a whole new zoology of particles, if you like.” Theory suggests that if supersymmetry is real, evidence to confirm it should emerge quickly from the LHC, possibly as soon as next year. “If it pops up it’ll be quite easy to see,” Professor Cox said.
Such a discovery might also help to explain dark matter, which is thought to account for much of the missing mass of the Universe. Only about 4 per cent of matter – galaxies and the like – is visible to our telescopes. “In this new zoology, the lightest super-symmetric particle is a prime candidate for explaining dark matter,” Professor Virdee said.
The search for the Higgs could take longer, though it depends on the particle’s mass and thus the energy of the collisions in which it might be found. If it is at the heavier end of the possible range, the discovery could take as little as 12 months. A lighter Higgs would take longer to find, as the particles into which it would decay would also be lighter and harder to track.
Other potential discoveries include evidence for the existence of extra dimensions beyond the familiar three of space and one of time, and the creation of miniature (and harmless) black holes, though these are less probable. “Most of us think we’d be very lucky to find these things,” Professor Cox said.
There are two more detectors. The LHCb will investigate why there is any matter in the Universe at all, while Alice aims to study a mixture known as quark-gluon plasma, which last existed in the first millionth of a second after the big bang.
From gluons to sparticles
Particle
In physics, this term refers to sub-atomic particles – entities that are smaller than atoms. Some, such as protons and electrons, are the constituents of atoms. Others, such as quarks, are the constituents of other particles. Still others, such as photons and neutrinos, are generated by the Sun. And yet more, such as the Higgs boson, are theoretical: predicted but still undiscovered
Hadron
This is more than an excuse for a geeky physics joke – “Is that your hadron, or are you just pleased to see me?” Hadrons are particles with mass, made up of quarks that have been bound together
Protons, neutrons, quarks and gluons
Protons and neutrons are the best-known types of hadron. Each is composed of three smaller units, called quarks, and gluons that stick the quarks together. Protons have a positive charge, while neutrons have a neutral charge
Higgs boson
A theoretical particle, which is thought to give matter its mass. First proposed by Peter Higgs, of the University of Edinburgh, in 1964, it is sometimes nicknamed the “God particle”. The Large Hadron Collider (LHC) should confirm whether it exists. The theory suggests that other particles travel through and interact with a field of Higgs bosons, which slows the particles down and gives rise to their mass. The process is often likened to moving through treacle. In the early 1990s Lord Waldegrave of North Hill, then the Science Minister, staged a competition for the best explanation. The winning analogy was of Margaret Thatcher – a massive particle – wandering through a Tory cocktail party and gathering hangers-on as she went
Standard model
The orthodox theory of modern physics. It is based on two other theories – general relativity and quantum mechanics – and its main weakness is that it cannot yet fully describe gravity or mass
Quantum mechanics
The main principle of the standard model, which describes how particles and forces behave at atomic and sub-atomic scales
General relativity
Einstein’s theory describing gravity. It is exceptionally well attested, but not fully compatible with quantum mechanics
Supersymmetry
The hypothesis that all particles have an accompanying partner known as a “superparticle” or “sparticle”. There is good theoretical evidence for it, but it has not yet been confirmed by experiment
Dark matter
Only about 4 per cent of the Universe is made up of visible matter. Another 25 per cent is “dark matter” – which can be inferred from its gravity, but cannot be seen. The remaining 71 per cent is still more mysterious “dark energy”. The LHC could shed light on what dark matter is, possibly through discoveries about supersymmetry
Extra dimensions
We are all familiar with four dimensions – three of space and one of time. But some theoretical physicists suggest that there could be as many as 26. Most physicists find these every bit as hard to visualise as normal people, but they make mathematical sense
The Independent Sep 05, 2008
The Big Question: Is our understanding of the Universe about to be transformed?
By Steve Connor, Science Editor
Friday, 5 September 2008
Independent Graphics
Why are we asking this now?
Next Wednesday the biggest machine and international scientific experiment ever built will be switched on. Called the Large Hadron Collider (LHC), it is a giant $10bn "atom smasher" that has been constructed at the European centre for nuclear research (Cern) in Geneva.
It consists of an underground circular tunnel 27 kilometres in circumference, which is about the size of the Circle Line on the London Underground. At various points along the tunnel, four massive instruments have been positioned to act as sub-atomic microscopes for analysing the extremely high-energy collisions that will occur between two opposing beams of protons, the atomic nuclei of hydrogen atoms. The aim of the experiment is to understand the fundamental forces of nature and the sub-atomic particles that compose all matter in the Universe.
Why is it causing such excitement?
Although we have built "atom smashers" before, this one is different in terms of how much energy will be involved. Two beams of protons will be spun in opposite directions within the underground tunnel and will attain speeds just a fraction shy of the speed of light, meaning that they will make about 11,000 laps of the circuit every second.
When they are accelerated in this way to collide head-on with each other, the resulting impact between the two proton beams will generate about seven times the energy of the LHC's nearest rival machine, the Tevatron atom smasher in Batavia, Illinois. The LHC scientists hope to get up to energy levels of 14 teraelectron volts (TeV) and so in the process create conditions that last occurred less than a billionth of a second after the Big Bang, when the Universe was created some 13.7 billion years ago.
What's the point of all this?
In order to understand what things are made of, and the forces that hold them together, it is necessary to break apart the sub-atomic constituents of matter. It is only by breaking apart a proton that scientists are able to see what is going on within this infinitesimally small unit of matter. The answer comes down to even smaller particles, some of which are so small or elusive that they have so far escaped detection. So far we know of 12 subatomic particles and 4 forces, but this is just the start. More importantly, scientists hope to resolve some of the biggest problems in physics. They hope for instance to one day unify all the disparate forces of nature, from the small-scale nuclear forces within an atomic nucleus to the force of gravity, which acts between planets and galaxies. They call this the "theory of everything" and there is hope that the LHC will make important contributions to our wider understanding of the biggest questions concerning creation, time and the nature of matter.
Isn't it risky to mess around with high-energy collisions?
There are some theorists who believe that the collisions may create "mini" black holes. But even if they do result from the experiment, they will be sub-microscopic in size and disappear within a fraction of second of coming into existence.
Few if any sensible scientists believe that these minuscule black holes pose any threat, for instance by merging into a bigger black hole that could swallow up Geneva. Some Russian scientists have also suggested that it may be possible for the LHC to create the conditions that could in theory allow time travel. They have rather fancifully painted a scenario where future time travellers come back to visit us through the LHC, but, as other theorists have pointed out, such time travellers would have to be atom-sized to pass through the tiny "worm holes" through time and space that the LHC may or may not create.
What exactly will happen when the experiment gets under way?
For the first time, scientists will attempt to put a beam of protons into the tunnel and to accelerate it around the entire circuit. Then, possibly later that day, or certainly in the days to follow, a second beam will be put into the tunnel and accelerated around the same tunnel but in the opposite direction. It is just possible, although unlikely, that the two beams might collide, which will cause the instruments to start registering readings. However, it is only when all the finer adjustments have been made that the two beams will reach the highest energy levels that could result in some very interesting discoveries.
What important findings might emerge?
The most interesting things are almost certainly going to be those that are least expected -- or even totally unpredicted. However, there is one sub-atomic particle that theorists have already predicted to exist.
Formally called the Higgs boson, but nicknamed the "God Particle", it could explain why matter has mass and hence lead to a greater understanding of the force of gravity. At the energy levels of the LHC, it is very likely that the first Higgs boson will be registered. Indeed, Prof Peter Higgs of Edinburgh University is 90 per cent confident that the particle named after him will be discovered by the LHC. How quickly the Higgs is found – assuming it exists – depends on how heavy it is, with a lighter Higgs being harder to detect than a heavier one. But this is just one of many possible discoveries that the LHC could make. Physicists hope that the machine will also find the mysterious supersymmetry particles that are thought to have been created at the beginning of the Universe. The theory of supersymmetry says that all known particle have a heavier partner, but none has ever been detected.
If the LHC finds evidence of supersymmetrical particles, it may have also found the reason why 90 per cent of the mass of the Universe exists as invisible "dark matter".
How difficult was it to build the LHC and its machines?
Very. The 27-km tunnel is aligned to better than a tenth of a millimetre and underground rivers had to be temporarily frozen to permit its construction. The giant magnets used to accelerate the proton beams have to be held together with a force that can resist 500 tons per square metre -– equivalent to one jumbo jet per square metre.
They are supercooled to 1.8 degrees above absolute zero (-273C), making the LHC the coldest place in the known universe, with enough freezing capacity to keep 140,000 domestic fridges at a temperature of -271.2C. The civil and mechanical engineering involved was almost as momentous as the science, which could account for why next week's switch on was originally scheduled for three years ago.
Is such a huge experiment worth it?
Yes...
* We need to know how the Universe is put together to understand our place in it
* The cost is trivial compared with that of not expanding on our existing knowledge
* There have been huge spin-offs from similar experiments, notably the internet
No...
* The science is too distant and abstruse for enough worthwhile benefits to humanity
* Particle physics is less important than, say, medicine and biology
* If scientists have misunderstood the physics there's a risk of creating a black hole
The Daily Telegraph Sep 05, 2008
Scientists get death threats
over Large Hadron Collider
By Roger Highfield, Science Editor
Last Updated: 12:01am BST 05/09/2008
Scientists working on the world's biggest machine are being besieged by phone calls and emails from people who fear the world will end next Wednesday, when the gigantic atom smasher starts up.
• Rap about Large Hadron Collider becomes YouTube hit
• The Big Bang: atom-smashing could uncover truth
• Time travellers from the future 'could be here in weeks'
The Large Hadron Collider near Geneva, where particles will begin to circulate around its 17 mile circumference tunnel next week, will recreate energies not seen since the universe was very young, when particles smash together at near the speed of light.
Hadron Collider: The final pieces slot into place
Such is the angst that the American Nobel prize winning physicist Frank Wilczek of the Massachusetts Institute of Technology has even had death threats, said Prof Brian Cox of Manchester University, adding: "Anyone who thinks the LHC will destroy the world is a t---."
The head of public relations, James Gillies, says he gets tearful phone calls, pleading for the £4.5 billion machine to stop.
"They phone me and say: "I am seriously worried. Please tell me that my children are safe," said Gillies. Emails also arrive every day that beg for reassurance that the world will not end, he explained. Others are more aggressive. "There are a number who say: "You are evil and dangerous and you are going to destroy the world." "I find myself getting slightly angry, not because people are getting in touch but the fact they have been driven to do that by what is nonsense. What we are doing is enriching humanity, not putting it at risk."
There have also been legal attempts to halt the start up. The remarkable outpouring of concern about turning on the experiment, the most ambitious in history, comes as a new report concludes that it poses no threat to mankind.
Since 1994, when the collider was first mooted by the multi-national European nuclear research organisation (CERN), dogged doomsayers have claimed that there would be a small but real risk that an unstoppable cataclysm would take place. Many of the emails received by Gillies cite a gloomy book - Our Final Century?: Will the Human Race Survive the Twenty-first Century? - written by Lord Rees, astronomer royal and president of the Royal Society.
"My book has been misquoted in one or two places," Lord Rees said yesterday. "I would refer you to the up-to-date safety study." The new report published today provides the most comprehensive evidence available to confirm that nature's own cosmic rays regularly produce more powerful particle collisions than those planned within the LHC. The LHC Safety Assessment Group has reviewed and updated a study first completed in 2003, which dispels fears of universe-gobbling black holes and of other possibly dangerous new forms of matter, and confirms that the switch-on will be safe.
The report, 'Review of the Safety of LHC Collisions', published in the Journal of Physics G: Nuclear and Particle Physics, proves that if particle collisions at the LHC had the power to destroy the Earth, we would never have been given the chance to worry about the LHC, because regular interactions with more energetic cosmic rays would already have destroyed the Earth.
The Safety Assessment Group writes, "Nature has already conducted the equivalent of about a hundred thousand LHC experimental programmes on Earth - and the planet still exists." The Group compares the rates of cosmic rays that bombard Earth to show that hypothetical black holes or strangelets, that have raised fears in some, will pose no threat.
As the Group writes, "Each collision of a pair of protons in the LHC will release an amount of energy comparable to that of two colliding mosquitoes, so any black hole produced would be much smaller than those known to astrophysicists." They also say that such microscopic black holes could not grow dangerously. As for the equally hypothetical strangelets, the review uses recent experimental measurements at the Brookhaven National Laboratory's Relativistic Heavy-Ion Collider, New York, to prove that they will not be produced in the LHC.
The collider is designed to seek out new particles including the long-awaited Higgs boson responsible for making things weigh what they do, the possible source of gravity called dark matter, as well as probe the differences between matter and antimatter.
No comments:
Post a Comment