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Thursday, September 4, 2008

Large hadron Collider and its soul

Located on the outskirts of Geneva and in sight of the Alps, Meyrin is likely the only town in the world that decorates its traffic circles with inactive, high-powered superconducting magnets.
Such decorations are only logical when buried beneath this bucolic Swiss canton and extending well into France is the biggest traffic circle of them all: the 27-kilometer-long Large Hadron Collider (LHC), the most powerful particle accelerator ever built, set to come online Sept. 10. The launch of the multibillion-euro machine is expected to receive much fanfare, including live coverage on Eurovision.
Rather than avoiding collisions, the LHC exists for one reason: to smash subatomic particles together as fast as we can and as hard as we can, to see what happens next. With enough energy, the fundamental forces that shape the world could be laid bare, overthrowing — or reinforcing — scientists’ understanding of the universe.
“This is the biggest scientific instrument ever constructed,” says Jiří Niederle, a physicist at the Czech Academy of Sciences who coordinates the country’s scientific contributions to the LHC.
“We hope we’re reaching a new era, where many questions will be answered,” he said, and “that some essential progress can be reached.”
For the past few decades, physics has existed in a relative stasis, ever since the finishing touches were put to the Standard Model, which describes the building blocks of matter, so-called elemental particles, as well as the forces that control how these particles interact. Each new high-energy experiment has verified the model, without revealing anything yet unknown.
Physicists hope the LHC will change all that. The atom smasher is operated by the European Organization for Nuclear Research (CERN), a lab jointly run by 20 European countries, including the Czech Republic, which contributed just under 1 percent of CERN’s budget last year.
Far more important than the country’s financial commitments are the contributions of Czech scientists and researchers, some of whom have labored on projects associated with the LHC for more than a decade.
Long shut out from the lab — Warsaw Pact countries had their own facility, located in the Russian town of Dubna — the LHC and its experiments are the first large-scale CERN project that has seen Czech involvement on every level, from assembling tiny silicon detectors to track the aftermath of collisions, to designing the web of computers needed to break down the massive amounts of data spitting out of the LHC’s experiments.
With no major efforts under way to develop a similar particle accelerator anywhere else in the world, the LHC has become the defining physics experiment of at least a generation, and the hopes and fears of a multitude of Czech, European and international scientists rest in the spiraling paths of invisible particles that will shoot out from the atom smasher’s collisions.
Go ask Alice
Soft-spoken with a bushy beard and withdrawn eyes, Karel Šafařík stands in front of a 16-meter-high underground steel chamber, painted rust red, which is called Alice.
Alice, short for “A Large Ion Collider Experiment,” is one of several gigantic experiments arrayed along the length of the LHC’s track, each poised to study the billions of collisions occurring each second when the accelerator’s two beams, streaming in opposite directions at velocities near the speed of light, are crossed. The energy from these impacts will spit out minute bits of short-lived matter that will be captured on Alice’s array of sensors before winking, once again, out of existence.
More than 1,000 scientists have contributed to Alice, with Šafařík a leading light in the process: He oversees the experiment’s physics, and has worked on the project for some 15 years. Born in Czechoslovakia, Šafařík worked at Dubna until 1989, when he was then courted by several Western physics labs. He joined CERN in 1993.
Alice is contained in a massive iron “warm” magnet, so called because it operates at room temperature, not at the cryogenically cooled levels necessary for the superconducting magnets that move particles around the LHC. Alice weighs approximately 8,000 tons; its doors alone weigh 1,000 tons and take one day to close.
Šafařík points at a blue chamber inside Alice, which during a visit in the late spring was still open. This part of the experiment is called the “time-projection chamber,” he said, which is not as science-fiction-seeming as it sounds. “The detector has a fantastic ability to really trace particles in three dimensions,” he said. “This one is the largest in the world.”
Unlike several other large experiments located at the LHC — notably Atlas and CMS — Alice is designed to study what happens when heavier atoms are collided; in Alice’s case, electrically charged lead nuclei. For part of the year, these lead ions will be piped into the collider, accelerated along its loop by radio waves.
What Alice hopes to recreate are the conditions that existed a few millionths of a second after the Big Bang, when matter is theorized to have existed in a far different state, called quark-gluon plasma. Under this extreme temperature and pressure, the force that ties together quarks, the particles that compose protons and neutrons, would not yet have established itself. The universe instead would have been one primordial soup of quarks and other particles.
Beyond Alice, Czech scientists are also working on two of the LHC’s other experiments, Atlas and Totem, Niederle says. Atlas is the largest experiment at CERN, with almost 2,000 contributors from 35 countries, and it will be searching for the Higgs boson, supersymmetry and extra dimensions. (See story, below) Totem is a much smaller experiment, measuring the strength of the LHC’s beams using detectors called Roman pots, which were made in the Czech Republic.
These experiments will be engaged in a friendly competition, each with the potential to make the same discoveries — or verify each others’ results. What all have in common is a dependence on the LHC and its collisions.
Zoo of machines
Alice will have to wait for lead collisions, as the first particles to be pumped in the LHC will be single protons, which make up the nucleus of the simplest atom, hydrogen. The protons’ path starts with a small bottle of hydrogen, says Paul Collier, standing at a diagram of CERN adjacent to the facility’s brand-new control center, which he oversees.
The physics lab has developed into “quite a zoo of machines,” he said. From that bottle, the protons are fed into consecutive smaller, older particle accelerators, each of which brings the “bunches” of protons to a higher energy level until they reach the LHC. Within 20 seconds, the beam will have traveled some 6 million kilometers.
This year the LHC will not operate at its maximum energy level, or “design luminosity,” as it will shut down again over the winter during CERN’s traditional break, timed for when electricity comes into demand to heat homes in Switzerland and France. Once it is fully broken in, the LHC will collide protons at a combined energy of 14 trillion electron volts (TeV). The world’s previous record holder, the Tevatron, located in Batavia, Illinois, peaks at 2 TeV.
The beam is mainly controlled by two types of powerful magnets, quadropoles and dipoles, both of which are superconducting, meaning they must be brought close to absolute zero to operate, some minus 271 degrees centigrade — lower than the temperature of outer space. The LHC’s 1,232 dipole magnets are responsible for bending the beam, and represent the upper limits of magnetic strength that can be achieved today, allowing the LHC to reach such high energies.
Not only must the protons be put on a curved path, but the beams must be narrowed, by the quadropoles, to an incredibly thin route for collision, Niederle says.
“For instance,” he said, “if you take Prague tunnel in Letná, you’d have to have the same precision as putting two needles at either end and making sure they collide in the middle. … At CERN, everything is in smaller dimensions, but the precision is the same.”
With such concentrated energy, the beam is dangerous. After a normal operating cycle, which lasts 10 hours, the beam will have lost 40 percent of its protons, mostly due to collisions. At that point, the beam will be “kicked out” of the ring and eventually dumped “physically onto a huge block to absorb the energy,” Collier said. “The thermal shock involved in this is quite high.”
Beyond the beam, CERN is essentially an industrial site and many of its greatest dangers are electrical, or gases. “For example, the LHC has 130 tons of helium in it,” Collier said. “That’s a hell of a lot of helium.” The lab’s safety systems are rigorous and foolproof, he adds.
What about the risk of miniature black holes, which catapulted the LHC to some more dubious notoriety earlier this year when a lawsuit was filed, in Hawaii, of all places, to delay its start? While it is possible such black holes could be created, they represent no danger, largely due to their minute size, according to an independently reviewed report issued by CERN in June.
The world’s computer
With so many collisions projected to occur every second at the LHC, CERN realized that it would not be able to provide all the computing power needed to analyze the information streaming from the collider’s five experiments, with their combined 150 million sensors delivering data 40 million times per second. What was needed, instead, was a whole new way of processing.
Luckily for CERN — which is famous as the birthplace of the World Wide Web — the explosive growth of the Internet has provided the perfect solution. Rather than trying to process data solely at its farm of 4,000 computer processors, CERN will instead tap the resources of the many scientific institutions collaborating and funding the LHC, using a method called grid computing.
Leading CERN’s efforts in this is Zdeněk Sekera, who was born in Czechoslovakia and worked, like Šafařík, at Dubna. Sekera left for the United States in 1969, after the Prague Spring, and spent 25 years at U.S. high-tech firms before rejoining CERN six years ago.
Each year, the LHC will produce the equivalent of 20 million CDs of data — stacked on top of each other, these CDs would be 20 kilometers high, more than twice the height of Mount Everest, Sekera says. CERN’s IT building already draws 4.5 megawatts of power for its computers, and expanding much further would be infeasible. “Where do you get the power?” he asks.
Instead, the grid lashes together computers all across the world into one massive mainframe, dedicated to breaking down “events” from the LHC that have been flagged as possible signs of undiscovered particles. Like an electricity grid, computing power and storage space can flow in from anywhere into one common pool.
“The idea is that the whole grid … looks to anybody like one computer,” Sekera says. “The whole world is a computer for you,” he adds.
CERN did not invent the grid, but it is now the leading pioneer in developing the technology: More than 140 computing centers now contribute to its grid, including facilities in the United States and Japan, both of which are significant partners in the LHC. The Czech Republic is a smaller partner, with 300 CPUs in Prague hooked up to the grid.
Beyond analyzing LHC events, CERN’s grid has a wide potential for other scientific uses. Most famously, it has already been used in efforts to find a drug to counter the H5N1 bird flu, with researchers last year analyzing 500,000 druglike molecules, searching for which have the most potential in fighting the flu. Great potential exists for its use in weather simulations and bioinformatics, as well.
One experiment, one life
The scale and complexity of the LHC can only be rivaled by some of the greatest scientific efforts ever made, such as the race to the moon or the development of the atomic bomb. More so than those efforts, the LHC is truly international, which is made clear on a visit to its outdoor cafeteria, where, in the shadow of Mont Blanc, a multitude of languages can be heard.
The duration of the experiment — about two decades on, it is only about to begin, and it could likely operate for 20 years — means that some physicists will spend their whole careers devoted solely to the LHC. This concerns Michal Tomášek, a Czech physicist who works on Atlas.
“Back when I was a student,” he says, “there were 20 to 40 experiments that lasted five to six years, and you had an opportunity to go from one to another. … [Now] it’s really one experiment for one life.
“I’m slightly afraid that fewer and fewer people will want to devote their whole life to one experiment. This may be a problem.”
Nevertheless, the whole field of particle physics, which has largely labored in purely theoretical limbo for decades, could be reinvigorated by discovering something, anything beyond the Standard Model, be it evidence of string theory (a dominant but unproven field within physics), extra dimensions or, most tantalizing, particles that are completely unpredicted.
“Physics, even if it was first created in a theoretical mind, has always been checked by experiment to see if it’s correct or not,” Niederle said. “But we are now reaching such demands for energy levels that make it nearly impossible to check theories. … We hope [with the LHC] to reach an energy region where we can at least see the first symptoms hinting at confirmation of our theories.”
The preamble of 15 years of unrequited experimental pressure will not likely be released this year, but, once the LHC is operating at full strength in 2009, it likely won’t be long for discoveries to emerge — if they do.
“If you look at the history of human beings,” Niederle added, “there were several times that people thought they knew almost everything and nothing new can be observed.” Then X-rays were discovered, for example, and the scientific world was thrown into upheaval.
The billion-euro question for Nierderle, Šafařík and the thousands of other physicists who have devoted their lives to the LHC is this: Is now one of those times?
Paul Voosen can be reached at


Scientists hope to find ‘God particle’  : The theory behind the Large Hadron Collider

A divide has existed in physics for the past half-century between two pillars that, together, describe the universe. One, general relativity, proposed by Albert Einstein, shows how gravity, space and time interact on a cosmic scale, allowing scientists to calculate the movements of heavenly bodies with unerring accuracy.

The other pillar, quantum theory, describes the particles and forces that form the subatomic world: quarks, which combine to make protons and neutrons; electrons; other particles, like muons and neutrinos; electromagnetism; and the strong and weak forces that bind atoms together. Mostly finished by the 1970s, these descriptions, which have been almost entirely experimentally verified, are called the Standard Model.
The one unproven element of the Standard Model involves the origin of mass and reasons particles have different weights. A theoretical explanation, named after the Scottish physicist Peter Higgs, says particles acquire weight by interacting with a “Higgs field.” If this is true, scientists using the Large Hadron Collider (LHC) should discover a particle called the Higgs boson, which is also nicknamed the “God particle” — a handle that has launched 1,000 newspaper headlines.
While the Higgs boson is the LHC’s most likely discovery, what scientists are hoping for is a way to rectify their two pillars, gravity and quantum mechanics. Physicists love an orderly world, and, from Einstein on, it has been a matter of agitation that these two standards go haywire when jointly applied to parts of the universe that are incredibly tiny and dense, such as black holes, or the Big Bang.
Many physicists feel they now have a theory that resolves this conflict: superstring theory, or string theory for short. Since the 1970s, in several waves, physicists have proposed that quarks are not tiny points but rather strings of material, the vibrations of which determine what type of particle or force arises from them.
It is a theory that by its sheer elegance alone has won over a large percentage of physicists. Unfortunately, it exists without any experimental verification, and the energies needed to find strings — and the technology to see them — are far beyond the limits of human ability, even at the LHC.
Rather than seeing strings, then, scientists hope the LHC will give evidence of elements essential to string theory, such as the existence of extra dimensions and supersymmetry.
Supersymmetry is now an integral part of string theory that says each particle in the Standard Model has a “superpartner,” a symmetrical particle that helps counter some of the “frenzy” (as the physicist Brian Greene puts it) at the quantum level.
None of these superpartners has yet been detected, but scientists believe the energy levels reached at the LHC could give rise to these particles. Such a discovery, which would likely reap a Nobel Prize or other honors, would be “a compelling, if circumstantial, piece of evidence for string theory,” according to Greene.
Also important to string theory is the existence of six (or seven) extra spatial dimensions, beyond the three to which we are accustomed. How could we possibly have missed these extra dimensions? Well, they just may be too small to see, according to Jiří Niederle of the Czech Academy of Sciences.
“It’s like if you take a garden hose and look at it from a great distance,” Niederle says. “You will not see it as a tube, but rather like a [two-dimensional] curve. These [dimensions] are so small that you can’t distinguish that they have special structure.”
Only certain particles may be able to move through these dimensions, like gravitons, which are supposed to transmit gravitational force but have not yet been verified. (They are another element of string theory.) If one of these particles is created during a collision at the LHC and moves to another dimension, Niederle says, evidence should exist of its missing energy.
Beyond these subatomic concerns, astrophysics has opened several large questions during the past decade by showing that visible matter accounts for merely 4 percent of the universe. It’s theorized that the rest of the universe is made up of dark energy and dark matter, with the former making up 73 percent, and the latter 23 percent.
Dark matter’s existence has been proved by much indirect evidence, such as the rotational speed of galaxies. It does not interact with electromagnetism, and therefore light, making it unobservable — and therefore unmeasurable by direct means, at least so far.
Dark energy is even more mysterious. It is associated with outer space and is the most popular explanation as to why the universe’s expansion is accelerating, rather than slowing, as would be expected if only gravity were considered.
Should the LHC shed light on any of these theories beyond the Higgs boson, it would be considered a rousing success; if only the Higgs is found, physicists may be at a loss where to look for experimental proof next.
And there remains one other tantalizing possibility: If nothing is discovered, then a completely new explanation of the physical world may be demanded.

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