Physicists Wait for ‘Surprises’ of LHC

Public fanfare greeted the activation last year of the Large Hadron Collider, the massive particle accelerator that physicists hope will herald a leap forward for the field.

But the initial excitement was short lived: a helium leak only nine days after the LHC was switched on led to an explosion that postponed data collection along with the careers of graduate students and postdoctoral fellows an ocean away—including several at Harvard. In the next few months, researchers plan to test the LHC a second time, in the hope that their years of hard work will finally help unravel some of the mysteries of the universe.

“Everybody in the physics community is looking forward to that with great anticipation and Harvard is no exception,” said Christopher W. Stubbs, chair of the Department of Physics.

The one-year delay has been an obstacle for graduate students whose dissertation research depends on data from the LHC, and on postdoctoral fellows and junior faculty hoping to secure appointments, said Stubbs.

“It’s an extra year of their life and it’s a terrible thing, but when you try and do anything for the first time you have to be prepared for something unexpected,” said Thomas J. LeCompte, the physics coordinator of a key LHC experiment. “This is why I personally don’t do space physics—if your satellite explodes on the launch pad you’re in even worse shape.”

Other professors echoed LeCompte’s sentiments and said they tried to find suitable topics for their graduate students to pursue while waiting for the LHC to be up and running. “There are certainly students that have had their careers substantially delayed by this—it’s a real worry for them and I’m extremely sympathetic,” said John Huth, a professor of physics and a member of the Harvard team associated with the LHC’s ATLAS experiment. “Everybody is just chewing their nails about it, but they’re the ones who are most strongly affected.”

Even when the LHC does regain function, the future is far from assured. Paradoxically, if all goes exactly according to plan, scientists could find themselves no better off than before. “Even if it does work, if they turn it on and find nothing new at all—if they don’t find [the hitherto unseen] Higgs Boson, for example, or if they find stuff they expect to discoverer and nothing else, it is unclear what the future of that field is,” said Stubbs.

“The thing that we hope for the most is something that is completely surprising and confusing,” said LeCompte. “In science you don’t learn anything by getting the answer you expect.”

The field, physicists say, is left hoping to witness something unforeseen.

‘SOMETHING HAS TO HAPPEN’

Located in a huge underground tunnel near Geneva, Switzerland, the LHC is overseen by the European Organization for Nuclear Research (CERN) in collaboration with scientists in over 100 countries. There are six main experiments that data collection at the LHC will service—each of which will address a different question about particle physics, Lecompte said.

Harvard has had a “nontrivial” role in building the detectors that will be used in the ALTAS project, said Stubbs.

The LHC itself consists of a 27-kilometer ring of superconducting magnets, inside of which two beams of high-energy particles are collided in a vacuum at very low temperature: -271 degrees Celsius, according to LeCompte.

When activated, the LHC will be used to examine a hole in what is known as the Standard Model of particle physics—a theoretical framework that is used to draw links between the four “fundamental forces” of the universe and the 12 elementary particles on which those forces act.

Thus far, the Standard Model has only been able to account for the behavior of three of the four fundamental forces—gravity has yet to be integrated, explained Huth.

“Gravity seems to be a missing piece [that] we can’t quite get to work with everything,” said Huth.

Huth added that physicists also do not know where mass comes from, but the most likely hypothesis is that it is bestowed by a particle called the Higgs Boson—which has never been observed.

When the particles in the LHC collide at high energies, “We’ll see huge numbers of particles coming out and every so often there will be a very rare collision that will produce some exotic form of matter,” said Huth.

It is through the analysis of this data that researchers hope to fill in the missing theoretical pieces. “This energy scale is so interesting because something has to happen,” added Huth. “At this energy scale, the theory basically breaks down unless something new happens and we don’t have a really good idea of what it is.”

The collisions may also produce or help explain the entity known as “dark matter,” which is believed to compose 96 percent of the universe, and “antimatter,” which has the same mass as matter but the opposite electric charge, explained Huth. “The Higgs Boson is the simplest model for explaining what happens in the theory and that’s what we’re designing for,” said Huth. “We aren’t under any illusions that that’s going to be the answer—a lot of us suspect nature will be more complicated than that.”

WAITING ON SURPRISES

Unfortunately for Huth, the mysteries of nature have had to be put on hold while the LHC is repaired.

When scientists were running currents through the device’s magnets in 2008, soon after its completion, a breakdown known as a “quench” occurred that caused overheating, said Joao Guimaraes da Costa, an assistant professor of physics and a member of the Harvard ATLAS team.

This failure allowed helium gas to leak into the vacuum and explode, moving the magnets and destroying a large area of the experiment, added da Costa.

The magnets are now in the midst of the long cooling process back towards absolute zero temperatures, and the LHC is slated to be turned on again late this year or in early 2010.

In the meantime, scientists are bracing themselves for the unknown.

“Nature is infinitely resourceful,” wrote James D. Wells, a member of the CERN theory group, in a recent e-mail from England, “and will keep us very busy no matter what surprises the LHC reveals.”

—Staff writer Alissa M. D’Gama can be reached at adgama@fas.harvard.edu.

—Staff writer Huma N. Shah can be reached at hshah@fas.harvard.edu.