Yale scientists began work Wednesday on the Large Hadron Collider (LHC), the largest and most expensive international particle physics experiment to be undertaken to date.
The Yale team, which will work on ATLAS, one of the six LHC experiments, will join nearly 7,000 scientists from 80 other countries that are expected to experiment with the LHC in the years to come. The scientists will search for particles that resemble the still-theoretical construct of “dark matter,” which scientists think — along with dark energy — makes up most of the universe, Yale researchers said in interviews.
But Yale researchers say their work will be far from done even if a dark matter particle is isolated. The investigation’s path-breaking nature — the LHC makes possible the most high-energy particle physics experiments in history — means that, along the course of discovery, entirely new concepts and questions could emerge. The machine may, in fact, be a “revolution for particle physics,” as physics professor Keith Baker put it.
A veritable behemoth at 27 kilometers in circumference, the LHC is the most advanced particle accelerator ever created, with the ability to collide opposing beams of protons into each other at a speed within one millionth of a percent of the speed of light. When the particles collide, scientists think they may recreate — just for a few fractions of a second — the material conditions following the Big Bang. In the debris that will result, they hope to find rare particles that may unlock the door to many of physics’ mysteries and perhaps even usher in a new era for the field.
“I would call this a singular moment in human history,” Baker said. “[Like] … crossing the Alps on elephants, the building of the pyramids — these are things that defined humanity. I think what we’ll do over the next decades or few decades to describe the universe could be another singular period in human evolution.”
This is no hyperbole when the LHC’s near-tetrascale parameters are considered. Each proton the LHC will collide carries 7 TeV of energy — seven times as much as any other machine of its kind. To put this into context, the circulating particles can collectively carry as much as the kinetic energy of about 900 cars each traveling at 100 kilometers per hour, according to Scientific American. Six giant detectors, located underground at intersection points along the chamber where collisions occur, will track and measure the spewed-out particles.
One of the collider’s primary values will be to validate — or disprove — the standard model of particle physics by attempting to find the Higgs boson, the last remaining undiscovered particle it predicts, said physics professor Paul Tipton.
The discovery of the particle will seal holes in the dominant theoretical approach to the particulate world. But if the particle is not found, it may signal a need for a complete overhaul of this framework, he said. Indeed, in a BBC interview Stephen Hawking said, “I think it’ll be much more exciting if we don’t find the Higgs. That’ll show that something is wrong and we need to think again.”
Scientists say the LHC will probe other unknowns too, such as exploring the existence of a single unifying force, the apparent violations of the symmetry between matter and antimatter, the complete nature of quarks and other particles, the existence of supersymmetry, the possibility of extra spatial dimensions — as inspired by string theory — and the nature of dark matter and dark energy.
The last of these aims is what concerns Baker and Tipton, a team also including Michael Zeller, Yale professor of physics, among others.
The group hopes that the colliding protons will emit a candidate for the enigmatic dark matter, Tipton said. Dark matter, though, cannot be described using the standard model, he said.
Currently, Baker said, matter understood by physicists that can be studied in the laboratory amounts to just 5 percent of that contained in the universe. Physicists estimate that dark matter accounts for nearly 25 percent, while dark energy accounts for the rest.
“None of the things in our particle lexicon can be dark matter,” Tipton said. “Within our particle zoo, there are particles like neutrinoes, quarks… but none of these are massive enough. We’re trying to find a new particle.”
Data indicate that dark matter must exist because there appears to be a stronger gravitational pull than can be accounted for by visible matter, he said. But, since it does not interact with the electromagnetic force, which includes light, scientists cannot observe it, he explained.
Earlier theories that the matter was composed of mini black holes have now been disproved, he added — leaving physicists without a candidate for the massive particle.
Whether the LHC will yield results is largely unclear, but there’s “good reason to believe that there’s something we should find there,” Tipton said.
“It’s like turning on the lights for the first time in a city and being able to take in new vistas,” he said of the LHC. “At the end of the day, it’s research, though. Whether it’ll be a complete barren wasteland with nothing new — that would be fascinating and interesting in itself … or whether we see a complex family of new particles, we can’t say.”
Zeller, who helped create the zero degree calorimeter back at Yale — a part of the ATLAS that will help detect the particular debris at zero degrees from the beam — echoed the unpredictability of the experiment’s outcome.
“What did they say in ‘Star Wars’? We’re going where no man has ever been? Well, that’s where we’re going,” he said.
Richard Wall GRD ’13, who works with Tipton, said the LHC may also have the potential to create black holes, at least based on mathematical models and theoretical predictions.
“So all you need to really do is get matter really very, very close together,” he said.
But he dismissed media-based hype suggesting that laboratory-generated dark holes would “swallow up the Earth,” since the holes would theoretically evaporate nearly as soon as they would be produced.
Tipton said it will be at least a few years before the Higgs experiment will be completed, but that many smaller experiments can be conducted in the meantime. The ATLAS will likely near completion before Higgs is in full swing, he said.
And so far, so good: The LHC passed its first test-run with flying colors. Yesterday — the inaugural day of the LHC’s operation — the first beam of protons was circulated through the collider both clockwise and counterclockwise, three kilometers at a time, Tipton said. The first high-energy collisions are scheduled for Oct. 21, when the LHC will be officially unveiled.