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#5136729 · 23 Mar 2007, 18:30 · · პროფილი · პირადი მიმოწერა · ჩატი
აგერ ცინცხალი ამბები ცერნის შესახებ საიენს მაგაზინიდან...
Science 23 March 2007:
Vol. 315. no. 5819, pp. 1654 - 1655
DOI: 10.1126/science.315.5819.1654
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LARGE HADRON COLLIDER:
Stability, International Character Honed CERN's Competitive Edge
Adrian Cho
The qualities that helped the lab make the LHC a reality could put it a step ahead in the race for the next great particle smasher
Cosmopolitan. CERN (foreground) hosts scientists of 111 different nationalities.
CREDIT: CERN
In the 1980s, physicists hammered out plans for a gargantuan particle smasher that would reveal the key bit of matter that would complete their theory of the known particles. The behemoth would also blast out scads of new particles and open new vistas of inner space. It would be the hub about which the world of particle physics would turn for decades.
Meanwhile, a few researchers at the European lab, CERN, near Geneva, Switzerland, mused of building a smaller machine on the cheap. They called it the Large Hadron Collider (LHC).
Two decades later, the LHC is about to chase the discoveries never made by that other machine, the infamous Superconducting Super Collider (SSC). Designed to reach energies three times higher than those of the LHC, the SSC died uncompleted in 1993 when its budget ballooned from $4.6 billion to more than $8.3 billion and the U.S. Congress killed it.
Why did the SSC fail and the LHC succeed? Physicists can point to many stumbling blocks that tripped up the SSC (Science, 3 October 2003, p. 38). Instead of building at an existing lab, officials chose a remote site in Waxahachie, Texas; researchers made a small but expensive design change; the United States tried to go it alone and sought international partners only belatedly. The LHC succeeded for reasons equally concrete--and those factors could give CERN the edge in the competition for the next gigantic collider, the proposed 31-kilometer-long straight-shot International Linear Collider (ILC).
All agree that CERN's rock-steady budget was a key to its success in building the LHC. In keeping with the treaty that created the lab in 1954, each of CERN's now 20 member nations supports the lab in proportion to its gross domestic product. "The treaty creates stability because the member countries recognize that this isn't something you vote up or down every year," says CERN Director General Robert Aymar. The arrangement sets the lab budget 5 years in advance and even allows officials to borrow against future income, as they did in 2002 when they found that the LHC was running 20% over budget. In contrast, the SSC was far more vulnerable. In the United States, Congress funds the national labs year by year, which means lab budgets fluctuate and projects such as the SSC face the ax repeatedly.
When building the LHC, CERN also benefited from moving continuously from one collider to the next. CERN researchers began designing the LHC even as they built another machine, the Large Electron-Positron Collider (LEP), which ran from 1989 to 2000. By using LEP's tunnel to house the LHC and existing accelerators to feed it, CERN officials saved billions of Swiss francs and built the LHC without an increase in the lab's budget.
Continuity has also helped the lab accrue talented personnel. "The most important thing to making a project like this work is the quality of the people working under you," says CERN's Lyndon Evans, who leads LHC construction. "One of our advantages [in maintaining staff] is that we came off another project, LEP, which wasn't so long ago."
Even before the LHC is up and running, physicists around the world are looking toward the next big accelerator and are trying to draw some lessons from the contrasting fates of the LHC and the SSC. They say they will need the ILC to study in detail the new particles the LHC should spot (Science, 21 February 2003, p. 1171). Researchers in the United States, Japan, and Europe all want to build the machine close to home, and "the U.S. and Japan had better look up and humbly learn from CERN's history and experience," says Nobu Toge of the Japanese accelerator laboratory KEK in Tsukuba. Still, Toge adds, "everyone has a long way to go to learn how to make the ILC a successful global project before jumping over each other to see who is to host it."
That hasn't stopped early jockeying, however. Europeans point to CERN's success with the LHC and its explicitly international character as big plusses. "Very probably, CERN has an advantage over any other place to host an even-more-international effort than already exists," says CERN's Aymar.
CREDIT: CERN
But Japanese and American physicists say they have advantages of their own. For example, CERN's unwavering budget could actually be a liability in the competition for the ILC. Although CERN's funding doesn't dip unpredictably, it also doesn't climb quickly, as all 20 member nations must agree on any increase. In contrast, the U.S. government can rapidly ramp up funding for projects. "The U.S. system is more dynamic and can react to things more quickly," says Pier Oddone, director of Fermi National Accelerator Laboratory in Batavia, Illinois. That may be important for the ILC, which will probably cost between $10 billion and $15 billion, with the host picking up half the tab.
Physicists in North America and Asia also note that, although CERN is an international laboratory, it does not embrace all countries equally. CERN's 20 member nations enjoy a special status compared to "guest" nations such as Japan and the United States, and many question whether the treaty structure is flexible enough to accommodate a truly global project.
Timing may be key. CERN will be paying off the LHC until 2011, and after that, the lab plans to upgrade the machine to produce even more collisions. So CERN will have its hands full until the middle of the next decade. In contrast, the United States will have no colliders for particle physcis in operation after 2009. Japan has a smaller collider that it may upgrade and will soon be finishing a large proton accelerator complex. "If we plan to build the ILC in the 2020s, CERN is a good candidate," says KEK's Mitsuaki Nozaki. "However, if we wish to start construction soon after the first physics results come out of the LHC around 2010, then the U.S. and Japan are the only realistic candidates."
Of course, whether the ILC gets built at all depends on whether the LHC discovers anything worthy of further study.
მეორე სტატია
Science 23 March 2007:
Vol. 315. no. 5819, pp. 1652 - 1656
DOI: 10.1126/science.315.5819.1652
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LARGE HADRON COLLIDER:
Having a Blast, Wish You Were Here
Adrian Cho
The Large Hadron Collider at CERN will smash particles at unprecedented energy and may open new realms of discovery. It will secure Europe's ascendancy in particle physics for years to come
Broad shoulders. Protons will collide in the centers of titanic ATLAS and three other detectors.
CREDIT: MAXIMILIEN BRICE/CERN
NEAR GENEVA, SWITZERLAND--Measuring 15 meters across and weighing 13,010 metric tons, the enormous disk of machinery dangles from bundles of cables like a gigantic yo-yo. Sectioned like an orange and festooned with electrical cables, the contraption could be mistaken for a flying saucer hoisted on edge. In fact, it's part of a huge barrel-shaped particle detector, the Compact Muon Solenoid (CMS), that will soon snare bits of matter from the new highest-energy particle smasher, the Large Hadron Collider (LHC) here at the European particle physics laboratory, CERN.
The colossus hovers a few centimeters above the concrete floor of a cavernous subterranean hall. All day, workers have lowered it down a shaft barely wide enough to take it. The 100-meter journey strains the nerves, says Hubert Gerwig, an engineer at CERN.
Now that it's almost over, Gerwig can relax a little. "Want to see it move?" he asks Archana Sharma, a physicist at CERN. Gerwig pushes the wall of metal. "If you get a feel for the resonant frequency, you can excite it" to oscillate, he says. Sure enough, the giant stirs. "Okay, okay, it's moving!" shouts Sharma, as millions of dollars' worth of delicate equipment sways ever so slightly across the grain of the concrete.
Gerwig isn't the only one here who is a little giddy with nervous excitement. In a few months, CERN researchers will have completed the 27-kilometer-long LHC, and in November, they hope to put the largest and most complex experimental device ever built through its warm-up laps. Smashing particles at energies seven times higher than the previous record, the LHC should blast out the one bit of matter missing from physicists' theory of the known particles. It could also spit out a slew of other particles and open a new era of discovery. The LHC will make CERN the world's center for particle physics.
Considering its size and technological complexity, the LHC "is the modern equivalent of the pyramids," says Peter Limon of Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, who is working on the machine. But the LHC is more than a technological marvel. It embodies a broader movement in particle physics. For decades, the United States paced the field. Now, as the LHC eclipses Fermilab's Tevatron collider, Europe takes the lead. "It is certainly true that the center of gravity of physics has moved to CERN," says Hans-Ake Gustafsson, an experimenter from Lund University in Sweden. "And the U.S. recognizes that because it's investing a lot of money in the experiments here."
No one knows what the LHC will find. But this much is clear: The LHC has already created a revolution in particle physics.
LHC or -EST
It is difficult to describe the LHC without resorting to superlatives. Not only will the LHC smash particles at the highest energies, but it will also feed the largest and most complex particle detectors ever built for a collider. They will pump out the greatest torrent of data; in a year, each could fill a stack of DVDs 25 kilometers high. The LHC will consume a record 120 megawatts of power, enough to sustain every household in the canton of Geneva. At a cost of 4.7 billion Swiss francs ($3.8 billion), it's the most expensive collider ever built. The United States is chipping in $531 million, mostly for detectors.
Numbers alone cannot convey the immensity of the project, however. Step into the hall housing the ATLAS detector, and you find yourself face to face with a machine eight stories tall and half as long as a soccer field. The thing could fill the nave of a cathedral, but instead of the Holy Spirit, it's packed with particle trackers, light-emitting crystals, and enough other gizmos to fill 100 million data channels. And it's as precise as it is big, says CERN's Peter Jenni, spokesperson for the 1800-member ATLAS collaboration. It can measure the curving path of a particle called a muon to within 40 micrometers, half the width of a human hair.
Circling below the French countryside between Lake Geneva to the east and the Jura Mountains to the west, the accelerator itself looks a bit like a glorified sewer pipe. Visitors to the LHC's otherworldly tunnel must carry oxygen packs in case the machine's cryogenic system leaks suffocating helium; workers on bikes sneak up on the inattentive. The LHC lies along one side of the gently curving tunnel, an endless line of big blue cylinders connected end to end like sausages. These are the revolutionary magnets that steer the beams around the ring. Twice as strong as those at Fermilab's Tevatron, they in fact house two accelerators carrying protons in opposite directions.
The brawny collider aims foremost to discover one thing: a long-sought particle called the Higgs boson. The Higgs would complete the so-called standard model of the known particles, says Jonathan Ellis, a theorist at CERN. "You could consider the Higgs boson the period on the end of the standard-model sentence," he says. But physicists hope the standard model is not the final word and that LHC will blast out other particles and surprises (see p. 1657). "We had Stephen Hawking here, and he told us that he wasn't so sure we'd find the Higgs boson and that he was more interested in mini-black holes," Jenni says. "People have different ideas."
Mighty ATLAS and CMS will race for those breakthroughs at the energy frontier. "It's going to come down to who is better prepared and whose detector is more complete" when the LHC starts running, says Tejinder Virdee of Imperial College London, spokesperson for the 2359-member CMS collaboration. "They can confirm [our discoveries], that's allowed." The LHC could discover the particles predicted by a concept called supersymmetry after running for just a year, Virdee says. But the LHC will also feed two specialized detectors to stake claims to leadership in other areas as well.
CREDIT: CERN
A detector called LHCb will study the asymmetries between particles containing elementary bits of matter called bottom quarks and their antimatter foils. Physicists at specialized colliders in the United States and Japan have studied the subtle differences as the bottoms decay to other "flavors" of quark, in hopes of finding hints of new particles (Science, 13 October 2006, p. 248). Even if ATLAS and CMS see those particles directly, "you want to study how things couple to these new particles," says CERN's Tatsuya Nakada. "And that's what you can do with flavor physics.
Seven kilometers away, a detector named ALICE will study a soup of particles called a quark-gluon plasma. The ultrahot plasma filled the infant universe, and physicists at Brookhaven National Laboratory in Upton, New York, have recreated it by smashing gold nuclei with their Relativistic Heavy Ion Collider (RHIC). For a few weeks a year, the LHC will smash lead nuclei at energies 28 times higher, letting ALICE peer deeper into the fleeting plasma, says CERN's Jürgen Schukraft. "The things you can look at here you can't look at with RHIC even if you run it for 50 years," he says.
Two decades in the making
But first, researchers must complete the collider. After a decade of construction, they are on schedule to finish this year, says CERN's Lyndon Evans, who leads the effort. (Researchers expect to lower the last magnet into the tunnel in mid-April.) A Welshman with a sonorous voice and silver hair, Evans has the phlegmatic demeanor of one who has dealt with crises large and small. On his computer he pulls up graph after graph of progress on the LHC's myriad subsystems. On each a rising red "just in time" line stands out. "It has some magical properties," Evans says. "Things tend to bounce off it" to stay on schedule.
In spite of the dash to the finish, the push for the LHC has been a marathon. Physicists dreamt the collider up more than 20 years ago even as CERN built another machine, the Large Electron-Positron Collider (LEP), which ran from 1989 to 2000. In fact, they planned to reuse LEP's tunnel and feed the LHC with existing accelerators. "Without that, it would have been impossible to build the machine on a constant [lab] budget," says CERN Director General Robert Aymar. At the time, physicists in the United States were planning the 87-kilometer-long Superconducting Super Collider (SSC). The LHC couldn't match the SSC's energy, but it could smash more particles, says CERN chief scientist Jos Engelen. In 1993, the U.S. Congress killed the uncompleted SSC, leaving the field open for CERN, which gave the LHC the green light the following year.
Even recycling as much as they could, researchers had to push the limits of technology, Evans says: "Society is willing to pay a certain amount and no more, and to make the LHC possible, we had to be innovative." Researchers have designed the strongest magnets by far for an accelerator, crammed two accelerators into one set of magnets, used wires of high-temperature superconductor to distribute power, and pioneered a type of radiation-hard electronics for their detectors. They even chill the liquid helium that cools the magnets to an extra-frigid 1.9 kelvin to make it a free-flowing superfluid, which is also an outstanding heat conductor.
To be sure, the LHC has hit some potholes along the way. In 2001, a review showed that the project was running behind schedule and 20% over budget, forcing the lab to scale back other projects and refinance the LHC (Science, 28 June 2002, p. 2317). In 2004, problems emerged with the cryogenic lines that transport the liquid helium to the magnets. Workers had to rip out, repair, and reinstall 3 kilometers of line, creating an enormous backup of the magnets they'd been installing as soon as they arrived. "I'd imagined storage for 50 magnets, and in the end I had to find room for 1000," says Evans, who scattered them all over the lab.
Now, about 2 years behind their original schedule, researchers see the light--or, more correctly, the other end of the accelerator--at the end of the tunnel. Soon workers will put down their wrenches and welding torches, and researchers will begin to bring the machine to life. "We are very excited," Engelen says, "and a bit worried because now we have to deliver."
See you in Switzerland
Already, physicists are flocking to CERN in anticipation. Some 7500 of 111 different nationalities have registered to work on the site, as the LHC lures talent away from other experiments, such as CDF and D0 at Fermilab. "When I was hired, I started to work on D0," says Adam Yurkewicz, a postdoc at Stony Brook University in New York. "But I told them I wanted to switch to ATLAS because it's the forefront; it's the place for discovery."
In fact, CERN feels a bit like a resort for the nerdy set. Motley buildings nestle along streets named for Einstein, Feynman, and other famous physicists. Here and there lies equipment awaiting assembly. In the evenings, friends meet in the cafeteria to chat over a beer, a Danish Carlsberg or Czech Budweiser. "There is a different atmosphere than in the U.S.," says David Silvermyr, a Swede from Oak Ridge National Laboratory in Tennessee. "If you go to lunch here, people are talking about, 'We're excited about this,'or 'We're going to build that.' In the U.S., people talk about budgets."
But if the LHC is changing the map of particle physics, it also marks a leap in the field's evolution toward ever-bigger projects. Since the 1960s, experimental collaborations have grown to include dozens, then hundreds, and now thousands of scientists. That explosive expansion has led some particle physicists to seek more intimate environs in other fields (Science, 5 January, p. 56). But it doesn't faze those who have chosen to work at the LHC. "I'd still have a sense of satisfaction no matter what was discovered and how big a role I had in it," Yurkewicz says. "I'd know that I contributed."
Bargain basement. CERN saved billions by building the LHC in a tunnel drilled for an earlier accelerator.
CREDIT: CERN
Nevertheless, researchers recognize the challenge of rising from such a crowd to a position of leadership. "It is a very competitive environment," says Rosy Nikolaidou of CEA Saclay, France, who works on ATLAS. "Each day, you have to prove that you are the best and that you deserve your chance." Nektarios Benekos, an ATLAS member from the Max Planck Institute for Physics in Munich, Germany, says young researchers must think strategically to avoid, for example, being pigeonholed. "For sure, you must not stick too much to a particular subsystem, because you lose touch with the entire detector," he says.
Those who cannot move to Europe face the challenge of keeping contact with experiments thousands of kilometers away. That's a big problem for American physicists, who make up 20% of the ATLAS team and 30% of the CMS team. To address it, physicists are relying in part on a high-capacity computing network called the Grid to transmit data to key labs in other countries. Those "analysis support centers" will serve as gathering places that bring the LHC a little closer to home, says Michael Tuts of Columbia University, who manages the U.S.'s ATLAS research program. "They're places where you can go and get the water-cooler conversation," he says.
In fact, even as CERN draws people, the Grid should help extend the reach of particle physics across the globe, says Harvey Newman of the California Institute of Technology in Pasadena, who chairs the board that oversees the U.S.'s CMS team. "There are countries that weren't in the field in a serious way, and now they are there," he says. For example, physicists in Pakistan, India, and Brazil will have access to the LHC data in their home countries.
Waking the giant
The full torrent of terabytes may be a while in coming, however. Researchers plan to send protons around the ring in November and begin taking data next spring. Even then they will start at low energy--less than half the Tevatron's--and with low beam intensity, or "luminosity." "If we can get up to a tenth of design [luminosity at full energy] after the first year, I think that would be miraculous," says Michael Lamont, an accelerator physicist at CERN. "And I think the experimenters would be quite happy with that."
Researchers must go slow because the LHC is the first collider powerful enough to destroy itself. Each of the LHC's beams packs a staggering 362 megajoules of energy, the equivalent of 90 kilograms of TNT and enough to melt 500 kilograms of copper. Should the machine accidentally steer a beam into its own innards, the protons could drill a hole tens of meters long, potentially taking the LHC out of action for months.
To prevent such a calamity, accelerator physicists have gone to extremes to protect the LHC from itself. More than 4000 super-fast beam-loss monitors will sense protons spraying out of the beam. Independently, beam-current monitors will infer losses by measuring the amount of circulating charge. And beam-position monitors will sense when the beams stray from their proper course. These systems can trigger magnets that can safely kick the beams out of the machine in the few hundred microseconds it takes to make two or three revolutions, less time than it takes a wobbly beam to veer off course entirely. "For the LHC, we've tried from the start to cover all the different possible failure scenarios so that we don't have an accident," says CERN's Rüdiger Schmidt.
Even if nothing goes wrong, physicists must take extraordinary steps just to make the LHC run. The collider is designed to pack 1014 protons into each beam, and if just one 10-millionth of them flew into a magnet, they would heat it enough to temporarily kill its superconductivity, triggering a beam dump. To avoid such "quenches," researchers have installed hundreds of adjustable constrictions called collimators that will catch the inevitable wayward particles. "Out of every 1000 particles [headed toward the collimators], not more than one should escape to reach the magnets downstream," says CERN's Ralph Assmann. "Without this system, the LHC cannot run."
Those are just the technical challenges. When the time finally arrives to power up the machine, the main challenge will be managing the people, Lamont says. "There's going to be a lot of people standing in the control room, maybe not twiddling the knobs but looking over your shoulder, and that's as it should be; this is as exciting as it gets," Lamont says. "But what you really want is four guys sitting behind closed doors quietly figuring out how to make it work." Those four will have to cope with the crowd. Who could blame anyone for wanting to be there when the LHC ushers in a new era in particle physics?
მესამე სტატია
Science 23 March 2007:
Vol. 315. no. 5819, pp. 1657 - 1658
DOI: 10.1126/science.315.5819.1657
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LARGE HADRON COLLIDER:
Physicists' Nightmare Scenario: The Higgs and Nothing Else
Adrian Cho
Many fear the LHC will cough up only the one particle they've sought for decades. Some would rather see nothing new at all
Suppose you are a particle physicist. A score of nations has given you several billion Swiss francs to build a machine that will probe the origins of mass, that ineffable something that keeps an object in steady motion unless shoved by a force. Your proposed explanation of mass requires a new particle, cryptically dubbed the Higgs boson, that your machine aims to espy. When, after 2 decades of preparation, you get ready to switch on your rig, you would fear nothing more than the possibility that you were wrong and the particle doesn't exist, right? Not exactly.
Many particle physicists say their greatest fear is that their grand new machine--the Large Hadron Collider (LHC) under construction at the European particle physics laboratory, CERN, near Geneva, Switzerland--will spot the Higgs boson and nothing else. If so, particle physics could grind to halt, they say. In fact, if the LHC doesn't reveal a plethora of new particles in addition to the Higgs, many say they would rather it see nothing new at all.
With a bang. Spotting just the Higgs boson, shown in this simulation, could bring collider physics to an end.
CREDIT: CERN
That may seem perverse, but put yourself again in the shoes of a particle physicist. In the 1960s and 1970s, researchers hammered out a theory called the standard model that, in spite of leaving out gravity and suffering from other shortcomings, has explained everything seen in collider experiments ever since and left physicists with few clues to a deeper theory. At the energies the LHC will reach, the standard model goes haywire, spitting out negative probabilities and other nonsense. So the collider has to cough up something new, researchers say. If it spits out only the Higgs, however, the new golden age of discovery could end as soon as it begins.
If the lone Higgs has just the right mass--about 190 times the mass of a proton--it would tie up the standard model's loose ends and leave physicists even more thoroughly stymied than before, says Jonathan Ellis, a theorist at CERN. "This would be the real five-star disaster," he says, "because that would mean there wouldn't need to be any new physics all the way up to the Planck scale," the mind-bogglingly high energy at which gravity pulls as hard as the other forces of nature. The Higgs alone could essentially mark a dissatisfying end to the ages-long quest into the essence of matter.
If, on the other hand, the LHC sees no new particles at all, then the very rules of quantum mechanics and even Einstein's special theory of relativity must be wrong. "It would mean that everything we thought we knew about everything falls apart," says Harvey Newman, an experimenter at the California Institute of Technology in Pasadena. That would thrill many but is so unlikely that it would be "essentially impossible" for the LHC to see nothing new, Newman says. Others agree.
Physicists have no similar guarantee that the LHC will reveal not only the Higgs but also exotic new particles that would point to new physics and open a new era of discovery. So the LHC is a gamble, and many are pulling for the more exciting long shots.
Quack like a Higgs
Easily the most famous particle not yet discovered, the Higgs has even been crowned the "God particle" by one Nobel laureate. In reality, however, it is merely an ad hoc solution to an abstruse problem in the standard model: how to give particles mass.
The particular challenge is to give mass to particles called the W and Z bosons, which convey the weak nuclear force. According to the standard model, the weak force that causes a type of radioactive decay and the electromagnetic force that powers lightning and laptop computers are two facets of the same single thing. The two forces aren't precisely interchangeable: Electromagnetic forces can stretch between the stars, whereas the weak force doesn't even reach across the atomic nucleus. That range difference arises because photons, the quantum particles that make up an electromagnetic field, have no mass. In contrast, the particles that make up the weak force field, the W and Z bosons, are about 86 and 97 times as massive as the proton.
Unfortunately, the persnickety standard model falls apart if theorists simply assign masses to the W, Z, and other particles. So the masses must somehow arise from interactions of the otherwise massless particles themselves. In the 1960s, Peter Higgs, a theorist at Edinburgh University in the U.K., realized that empty space might be filled with a field, a bit like an electric field, that could drag on particles to give them inertia, the essence of mass. The field would consist of a new particle, the Higgs boson, lurking "virtually" in the vacuum.
Nature appears to follow this scheme. Using it, theorists predicted the masses of the W and Z. And at CERN in 1983, the two particles weighed in just as expected, in collisions energetic enough to pop them out of the vacuum.
Now, mounds of data point to the Higgs. For example, the lifetime and other properties of the Z depend on the cloud of virtual particles flitting around it like flies swarming a rotten ham sandwich. Precise studies of the Z suggest that a Higgs at most 200 times as hefty as the proton lurks in that cloud. Comparing the masses of the W and a particle called the top quark shows a similar thing, says Gordon Kane, a theorist at the University of Michigan, Ann Arbor. "These are two completely independent pieces of evidence that there is something that walks and talks and quacks like a Higgs," Kane says. "The existence of the Higgs in the LHC range is essentially certain."
Discovering the Higgs would complete the standard model. But finding only the Higgs would give physicists little to go on in their quest to answer deeper questions, such as whether the four forces of nature are somehow different aspects of the same thing, says Aldo Deandrea, a theorist at the University of Lyon I in France. "If you have just a Higgs that is consistent with the standard model, then you probably don't know what to do next," he says. "What then?"
CREDIT: CERN
Good taste and extra dimensions
Most researchers say they'll never face that question because the LHC will discover plenty of other things. Many expect it to blast out particles predicted by a concept called supersymmetry (SUSY), which posits a heavier "superpartner" for every known particle. That may seem unduly complicated, but SUSY solves problems within the standard model, points toward a deeper theory, and may even explain the mysterious dark matter whose gravity holds the galaxies together. "SUSY is unique in that it does all these things automatically," CERN's Ellis says.
Most concretely, SUSY solves a technical problem caused by the Higgs boson itself. The Higgs, too, must be shrouded in virtual particles, and they ought to send its mass skyrocketing. SUSY would explain why the Higgs is as light as it appears to be, because mathematically the effects of partner and superpartner on the Higgs mass tend to cancel each other. SUSY would also help explain the origin of the Higgs, which is just tacked onto the standard model but emerges naturally from the structure of SUSY.
SUSY could also help unify the four forces. The standard model accounts for three of them: the electromagnetic force, the weak force, and the strong nuclear force that binds particles called quarks into protons, neutrons, and other particles. The strengths of the three increase with the energy of collisions, and if the universe is supersymmetric, then all begin to tug equally hard at precisely the same energy somewhere below the Planck scale. That should make it easier to roll them and gravity together in one grand unified theory, says Frank Wilczek, a theorist at the Massachusetts Institute of Technology in Cambridge.
SUSY might even provide the dark matter that glues the galaxies together. Physicists believe that dark matter must consist of some stable particle that barely interacts with normal matter, and the least massive superpartner might just fit the bill. With all this evidence supporting it, SUSY is almost too beautiful to be wrong, some theorists say. "All these clues could be misleading," Wilczek says, "but that would be a really cruel joke by Mother Nature--and in really bad taste on her part."
The LHC might also reveal far wilder phenomena, such as inner parts to electrons and other supposedly indivisible bits of matter, tiny black holes, or even new dimensions of space that open only at very high energies. The spare room could explain, for example, why gravity is so much weaker than the other forces. "Something like extra dimensions I give a very small probability," says Michael Tuts, a physicist at Columbia University. "But the potential is so big that it's very exciting."
A sure bet
None of these more exotic possibilities is guaranteed. And particle physicists say that just discovering the Higgs would be a triumph. "If the Higgs is anything like theorists predict, we will find it," says Peter Jenni, an experimenter at CERN. "We shouldn't be disappointed if we do."
Physicists also admit that, regardless of the intellectual foment it would cause, finding nothing would create problems, at least with the governments that paid for the LHC. "Just imagine if we go to the CERN Council and say, 'Thank you very much, we've just spent billions of Swiss francs, and there's nothing there,' " Ellis says. "I think they might be a tad disappointed."
However, finding only the Higgs may make life nearly as difficult for physicists trying to persuade governments to build the next great particle smasher, the proposed International Linear Collider (ILC). Costing between $10 billion and $15 billion, the ILC would map out the conceptual terrain opened by the LHC (Science, 9 February, p. 746). By colliding indivisible electrons and positrons, the ILC would generate cleaner collisions that should reveal details of new particles that will be obscured by the messy proton-on-proton collision at LHC.
But if the ILC has only the Higgs to study, then it becomes "a very hard sell both scientifically and politically," says David Cinabro, a particle-physicist-turned-astronomer at Wayne State University in Detroit, Michigan. "I think you'll have a really hard time arguing that's what you want $10 billion for," he says.
Others say such speculation is premature and pessimistic. "We are so used to discussing the new territory that we are going to enter that sometimes we think that we know what we are going to find," says Jos Engelen, chief scientist at CERN. "Well, we don't, and I think it will be much more exciting than we expect." That may be, but this much is certain already: Everyone hopes for more than just the Higgs.
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P.ს. პდფ თუ ვინმეს აინტერესებს ამ სტატიების ეგეც შემიძლია გავახერხო... აქ ვერ დავდებ რადგან 100კბზე მეტია...
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Absolute zero is cool...
Black hole sucks...
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ცერნის სინქროფაზოტრონი, ქართველების წვლილიც ყოფილა
თბილისის ფორუმი -> თემატური ფორუმი -> მეცნიერება და განათლება -> ტექნიკური და საბუნებისმეტყველო მეცნიერებები
