On September 10th, CERN will switch on the Large Hadron Collider (LHC)and in the process begin arguably the most ambitious science experiment ever undertaken.
Professor Brian Cox answers questions sent in by the audience about CERN's new Large Hadron Collider and the major experiment which is planned to be launched on the 10 september 2008. Do you have a question? Ask expert Brian Cox anything about the project and read his responses to other questions.
Three decades after its conception, half as long in construction, and several years behind schedule, the switch will finally be flicked on the Large Hadron Collider (LHC) at CERN in Geneva, on 10 September.
Once up and running, the $10 billion machine will be world's most powerful particle collider, smashing protons into each other at an energy seven times higher than that of the Tevatron collider in the US. Physicists will then be in uncharted territory, hunting for new particles that could overturn their theories about nature's most fundamental laws.
The main reason for announcing the start-up date almost five weeks in advance is to give the thousands of physicists working on the LHC's four giant particle detectors time to prepare. "This will focus the minds of all concerned to respect the date announced," LHC project leader Lyn Evans told New Scientist.
It has taken six months and hundreds of tonnes of scarce liquid helium just to cool the superconducting magnets that will bend the protons around the 27-kilometre-ring to their operating temperature. Once all 1600 are sitting comfortably at -271 °Celsius, in the next week or two, around 1400 electrical tests will be carried out to make sure that everything is wired up correctly.
This weekend, the operations team will test the injection of protons into one of the LHC ring's eight sectors. This involves using a pulsed magnet to "kick" bunches of protons out of a smaller accelerator called SPS and down a 'transfer line' into the LHC. The procedure is tricky because the pulses and bunches must coincide to within a fraction of a millisecond.
Come 10 September, when the warren of caverns and tunnels has been checked out and sealed off – using high-security, iris-scanning locks, the first protons will be whipped up to nearly the speed of light through a chain of smaller accelerators on the CERN site. Then they will be injected into one of the LHC's two adjacent beam-pipes at an energy of 0.45 trillion electron volts (TeV).
The protons might get just a few tens of metres into their 27-km circuit before veering off course and being lost, so the operations team will adjust the magnets and try again with a fresh beam until they have systematically threaded the protons around the entire machine. That could take from a few hours to a few days with a crew working around the clock. Then, the team will have to do the same for the beam in the other direction.
The next challenge will be to get the beams in a stable orbit for several hours at a time. Only then can CERN contemplate ramping up the energy to 5 TeV and finally bringing the counter-rotating beams head on at a collision energy of 10 TeV.
If luck is on their side, that should take place around the time of the official LHC inauguration on 21 October. In early 2009, the protons are set to collide at the full energy of 14 TeV.
Discoveries will come much later still. Although some exotic new particles, if they exist, could reveal their presence when the beams collide this year, it will likely take a year for researchers on the LHC's four experiments to understand their cathedral-scale detectors well enough to make a discovery.
Finding the Higgs boson, which would solve the mystery of where mass comes from, could take two to three years.
The LHC schedule has suffered several setbacks, including a delay in fitting the cryogenic plumbing for the liquid helium and a shorter interruption last March due to faulty magnets.
But CERN is now on the home stretch. "It's been a long haul," says Evans. "We're finishing a marathon with a sprint."
Quantum World - Learn more about a weird world in our comprehensive special report.
| Skeptoid #109 | |||||||
As you may have heard by now, some people have voiced concerns that particle collisions from the LHC will create tiny black holes. Black holes have such intense gravity that they consume everything around them, even light. And so,
within a fraction of a second, this tiny black hole will consume the collider itself, France, Switzerland, and then the entire Earth, presumably followed shortly thereafter by our whole solar system.Clearly not a fear to be taken lightly.
The best known opposition to the Large Hadron Collider comes in the form of a much publicized lawsuit, filed in Hawaii by two individuals, science writer Luis Sancho and retired nuclear safety officer Walter L. Wagner, against the US Department of Energy, Fermilab, CERN, the National Science Foundation and Does 1-100.
The lawsuit presents affidavits from the plaintiffs and five other individuals, stating their opinion that dangerous black holes could be formed and seeking to block operation of the collider until these fears can be adequately studied.It seems a reasonable precaution, given how incredibly gigantic and powerful the LHC is, and how Biblical the scale of the destruction it might wreak.
The Large Hadron Collider (LHC) is a gigantic scientific instrument near Geneva, where it spans the border between Switzerland and France about 100 m underground.
It is a particle accelerator used by physicists to study the smallest known particles – the fundamental building blocks of all things. It will revolutionise our understanding, from the miniscule world deep within atoms to the vastness of the Universe.
Two beams of subatomic particles called 'hadrons' – either protons or lead ions – will travel in opposite directions inside the circular accelerator, gaining energy with every lap. Physicists will use the LHC to recreate the conditions just after the Big Bang, by colliding the two beams head-on at very high energy. Teams of physicists from around the world will analyse the particles created in the collisions using special detectors in a number of experiments dedicated to the LHC.
There are many theories as to what will result from these collisions, but what's for sure is that a brave new world of physics will emerge from the new accelerator, as knowledge in particle physics goes on to describe the workings of the Universe. For decades, the Standard Model of particle physics has served physicists well as a means of understanding the fundamental laws of Nature, but it does not tell the whole story.
Only experimental data using the higher energies reached by the LHC can push knowledge forward, challenging those who seek confirmation of established knowledge, and those who dare to dream beyond the paradigm.When in operation, about seven thousand scientists from eighty countries will have access to the LHC, the largest national contingent of seven hundred being from the United States. Physicists hope to use the collider to test various grand unified theories and enhance their ability to answer the following questions:
The Standard Model (reference) is a theory devised to explain how sub-atomic particles interact with each otherThere are 16 particles that make up this model (12 matter particles and 4 force carrier particles). But they would have no mass if considered aloneThe Higgs boson explains why these particles have mass. Particles acquire their mass through interactions with an all-pervading field, called the Higgs field, which is carried by the Higgs boson.
| By Paul Rincon Science reporter, BBC News |
A vast physics experiment built in a tunnel below the French-Swiss border is fast becoming one of the coolest places in the Universe.
The Large Hadron Collider is entering the final stages of being lowered to a temperature of 1.9 Kelvin (-271C; -456F) - colder than deep space.
The LHC has thousands of magnets which will be maintained in this frigid condition using liquid helium.
The magnets are arranged in a ring that runs for 27km through the giant tunnel.
Once the LHC is operational, two particle beams - usually consisting of protons accelerated to high energies - will be fired down pipes running through the magnets.
These beams will then travel in opposite directions around the main ring at close to the speed of light.
At allotted points along the tunnel, the beams will cross paths, smashing into one another with cataclysmic force. Scientists hope to see new particles in the debris of these collisions, revealing fundamental new insights into the nature of the cosmos and how it came into being.
The most powerful physics experiment ever built, the LHC will re-create the conditions just after the Big Bang.
Currently, six out of the LHC's eight sectors are between 4.5 and 1.9 Kelvin, though all sectors of the machine have been down to 1.9 Kelvin at some stage over the last few months.
By comparison, the temperature in remote regions of outer space is about 2.7 Kelvin (-270C; -454F).
Roberto Saban, the LHC's head of hardware commissioning, said that in order to obtain high magnetic fields without consuming too much power, the magnets were required to be "superconducting".
This is the property, exhibited by some materials at very low temperatures, to channel electrical current with zero resistance and very little power loss.
Helium exhibits spectacular properties at 2.2 Kelvin - becoming "superfluid". This allows it to conduct heat very rapidly, making it an extremely efficient refrigerant.
No particle physics facility on this scale has ever operated at such low temperatures. But, so far, the hardware was performing as predicted, Roberto Saban explained.
"We have a very systematic process for the commissioning of this machine, based on very carefully designed procedures prepared with experience we have gathered on prototypes."
He added: "Our motto is: no short cuts? exchanging a single component which today is cold, is like bringing it back from the Moon. It takes about three to four weeks to warm it up. Then it takes one or two weeks to exchange. Then it needs three to six weeks to cool down again.
"So, you see, it is three months if we make a mistake."
Two sectors of the LHC are currently not cold enough for testing to proceed. Electronics that control the cryogenic systems in these sectors are being moved to an area where they will be better shielded against particles that shoot out of the machine during collisions.
Closing the circle
One sector of the ring is being run as if the LHC was operational and carrying a beam. This is so that crews can de-bug software and hardware and gain experience of running operating cycles.
The LHC's magnets must also undergo electrical testing. Each sector of the machine contains about 200 electrical circuits. Each circuit may consist of as many as 154 magnets or as few as one.
They are being tested for their ability to handle very high currents - up to 12,000 Amps .
"We power each circuit, making sure it goes to its design current. But above all, we are verifying that all the protection systems around it - which are there to detect an eventual quench - are operating as expected," said Roberto Saban.
A quench occurs when some part of the magnet starts to heat up, becoming resistant to electrical current. Engineers have built in a recovery system to detect these quenches before they affect the magnetic field bending particles around the ring and shut off the circulating beams.
The machine's cool-down should take another two weeks to complete, provided no serious problems are found. Electrical testing of the magnets may take another couple of weeks.
Before the LHC is "switched on" for the first time, the proton beams have to be boosted to high energies in a chain of particle accelerators called the injectors.
Once the machine is cold, operators will inject beams into the main ring, threading them through each independent sector of the LHC until they close the circle.
A timing, or synchronisation, system is used to ensure each of these sectors behaves as if they were a single machine.
When the LHC is switched on it will operate at an energy of five trillion electron-volts. It will then be shut down for the winter, so that the magnets can be "trained" to handle a beam run at seven trillion electron-volts.
| Brief Description of the LHC. Energising the quest for 'big theory' By Paul Rincon BBC News science reporter, Geneva |
Cern's Atlas detector will search for the elusive "God particle" (Image: Cern/Maximilien Brice)
"We are at a point where experiments must guide us, we cannot make progress without them," explains Jim Virdee, a particle physicist at Imperial College London.
"We must wait for the data to speak."
Over a coffee in the lobby of building 40 at Cern, the sprawling experimental facility situated on the Swiss-French border, Professor Virdee says physics has reached a critical juncture.
In the 1970s, the theory known as the Standard Model was considered a triumph of theoretical physics, incorporating all that was then known about the interactions of sub-atomic particles.
Today it is regarded as incomplete, a mere stepping stone to something else.
The Standard Model cannot explain the best known of the so-called four fundamental forces: gravity; and it describes only ordinary matter, which makes up but a small part of the total Universe.
The Large Hadron Collider (LHC) at Cern (The European Centre for Nuclear Research) is costing some 3bn Swiss francs (1.9bn euros; £1.3bn), which is paid for by contributions from Cern's member countries (including the UK) with support from international partners such as the US, Japan, China and India.
It should reinvigorate physics' biggest endeavour: a grand theory to describe all physical phenomena in nature.
The Large Hadron Collider takes shape
About 100m below us, in a tunnel that runs in a ring for 27km (17 miles), the LHC is being assembled
from its constituent parts like a vast, impossibly complex Meccano set.
When it is switched on for a pilot run in summer 2007, this huge physics experiment will collide two beams of particles head-on at super-fast speeds, recreating the conditions in the Universe moments after the Big Bang.
The beam collisions should create showers of new particles, revealing new physics beyond the Standard Model. In order for that to happen, the LHC needs to reach much higher energies than previous colliders.
Sealed vacuum
The particle beams, composed of either protons or lead ions, will be created in Cern's existing chain of particle accelerators and then injected into the LHC. Here they will receive an additional electrical impulse to boost them up to their final energy; the equivalent of seven trillion volts.
Some 1,232 "dipole magnets" will carry these high energy beams through their interior and bend them around the LHC.
Each one undergoes a rigorous quality test before it can be lowered into the tunnel. At the Cern site known as SM18, Dr Mike Lamont, from Cern's beam operations group, shows us round the hangar-like facility where the magnets are put through their paces, 12 at a time.
The tests are run at 1.9 Kelvin (-271C), the eventual operating temperature of the LHC. This is just a shade above "absolute zero" and colder than the vacuum of outer space. The magnets are cooled to this ultra-low temperature by bathing them in liquid helium.
The magnets undergo thorough testing before they are lowered into the tunnel
When helium is cooled to 2.17 Kelvin, it exhibits remarkable properties. In this "superfluid" state, it flows with almost zero viscosity and an unusually high thermal conductivity. This makes it ideal for cooling and stabilising a large superconducting system like the one at the LHC.
In 2007, Mike Lamont will be one of the machine co-ordinators "driving" the LHC: "It's a huge challenge," he says. "The magnets are one thing, but then you've got 27km of instrumentation and controls. Everything's got to be synchronised incredibly well."
At four points around the LHC ring, the two beams cross each other, causing some of the particles to collide head-on. Near each of the crossing points will sit a detector, an experiment the size of a mansion, to capture and measure new particles produced in the collisions.
A simulation shows what a Higgs signature might look like The LHC's four detectors are named LHCb, Alice, Atlas and the Compact Muon Solenoid (CMS). Each is worked on by a dedicated team of physicists.
While LHCb and Alice are designed to investigate specific physical phenomena, Atlas and CMS are designated "general purpose" detectors.
They will both aim to identify the elusive Higgs boson (known as the "God particle" because of its importance to the Standard Model), look for so-called supersymmetric particles and seek out the existence of extra dimensions.
As such, the scientists working on Atlas will to some extent be competing with those on CMS. Both teams aim to be first to find the Higgs, leaving the other to "verify" their discovery
(a scientific euphemism, one suspects, for "eat humble pie").
Mass giver
The Higgs boson explains why all other particles have mass. According to the theory, particles acquire their mass through interactions with an all-pervading field, called the Higgs field, which is carried by the Higgs boson.
At Point One in Switzerland, we don hard hats, squeeze into a lift with the construction workers and descend into the enormous cavern that will house Atlas, the bigger of the two general purpose detectors.
The modules that make up this giant experiment have been built separately in laboratories around the world and transported to Cern for assembly.
"The same happens with big aircraft such as the Airbus A380," observes Dr Alan Barr, a physicist at University College London and Atlas team member. "They make all the bits separately, bring them together and it all fits.
"The thing is, we only ever build one," comments Cern scientist and Atlas team member Dr Pippa Wells. "We don't make one Atlas, then another, and find out we know what we're doing by the fifth."
"We've got one shot, it's got to work first time," says Alan Barr.
Testing time
Over the border at Cessy in France, the CMS team will soon begin testing individual "slices" of its experiment to see whether each can detect cosmic rays from space.
Much of the assembly of the CMS is taking place above ground. Large elements will then be lowered by crane into the underground cavern built to house it. This process will take about six months.
A wrangle over the supply of crystals lining the detector's electromagnetic calorimeter (which measures the energies of particles produced in collisions) has now been resolved. But part of this component won't be ready for installation in CMS by the LHC's pilot run in 2007. 
Individual slices of the CMS will be tested above ground
However, says team member Jim Virdee, the calorimeter will be complete and installed in the CMS by April 2008, ready for the start of the LHC's main science run. The delay won't put the CMS at a disadvantage in the race to find the Higgs, he adds, since over a year's worth of data will be needed to announce a discovery.
Cern's chief theorist Professor John Ellis even thinks finding the Higgs could shed light on another great mystery in physics: dark energy.
Dark discovery
In 1998, two teams studying supernovae showed that this dark energy is accelerating the expansion of the Universe. Subsequent work revealed that dark energy may make up about 70% of the Universe, but the best theories could not explain it.
According to John Ellis, however, the Higgs field is the perfect candidate for the source of dark energy.
"The Higgs mechanism fills all of space with a field. Unlike the gravitational field, which is strong around the Sun and the centre of the galaxy, the Higgs field would have essentially the same value everywhere,"
he explains.
"It would give you dark energy, in the sense that dark energy is energy density in empty space a long way away from any matter."
There's just a small problem with the idea, says John Ellis: it gives 120 orders of magnitude too much dark energy.
"If we find the Higgs, it would corroborate this whole theory that there's this Higgs field sitting throughout the Universe providing dark energy. Then we can get on to the next question which is why it has the value it does."
Such a breakthrough would energise debate on a "unified theory" to describe all natural phenomena. Discoveries such as supersymmetry may also bridge gaps between experimental evidence and string theory, one attempt at building a grand scheme.
The LHC might even reveal something completely unexpected about the workings of our Universe. And that, say physicists, might be even more satisfying.
The Standard Model is a theory devised to explain how sub-atomic particles interact with each other There are 16 particles that make up this model (12 matter particles and 4 force carrier particles). But they would have no mass if considered alone The Higgs boson explains why these particles have mass. Particles acquire their mass through interactions with an all-pervading field, called the Higgs field, which is carried by the Higgs boson.
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