CAMBRIDGE — A flexible blue tube snakes through labyrinthine hallways at Harvard University, traveling alongside rows of pipes before it ducks into a basement room filled with the bleating mechanical chirp of a laboratory refrigerator. Here, the tube feeds laser light to a table-top experiment that could help illuminate questions as profound as why the universe as we know it exists.
In an age where the best-known physics experiments involve big teams and bigger money, this setup is more home-grown apparatus than industrial-scale science. The plastic tube protects cables that channel laser light from an adjacent building and was strung by graduate students.
But the experiment — run by 11 Harvard and Yale university researchers on a budget in the low millions — is designed to probe some of the same unknown territory as the Large Hadron Collider in Europe, where scientists this summer apparently confirmed the existence of a long-sought particle called the Higgs boson. The local experiment cannot find the Higgs, but its leaders hope the modest experiment off Oxford Street could help guide or possibly even scoop the thousands of scientists working at the $10 billion collider, by detecting evidence of other new particles first.
The Cambridge team wants to find out whether the ordinary electron, the negatively charged particle that is a component of every atom, has got a “lumpy” charge — in essence, whether its charge is distributed evenly over a sphere, or is just a tad lopsided, like an egg.
Esoteric though it may seem, this basement experiment’s minuscule measurement could have a dramatic ripple effect for our understanding of nature. Most physicists believe the widely accepted “standard model” of physics is an incomplete explanation of the building blocks of the universe and how they interact. The Cambridge work could help reveal the existence of never-before seen particles, and it might throw doubt on or help confirm leading theories developed to explain what may lie beyond the standard model. It could also provide scientists a toehold into the fundamental mystery of why, after the Big Bang, there was a surplus of matter left over — the stuff that gave rise to the world and everything that we see in it.
“Any positive hint or an experimental result of this sort, first of all would be instantly, completely awesome. It would be completely transformative,” said Nima Arkani-Hamed, a theoretical physicist at the Institute for Advanced Study who is not involved in the experiment. “It would tell us there is new physics lying around not very far from where we’re looking around right now.”
It is a quirk of the way matter behaves at the smallest scales that trying to make a very precise and tiny measurement of a very ordinary particle — the electron — could reveal something about the existence of hypothesized but unseen heavy particles, which are still tiny but heavy for the realm of subatomic stuff.
John Doyle, a Harvard physicist and one of the three leaders of the experiment, explains it this way: The electron is like an antenna that can pick up the presence of those heavy particles. If those particles exist, they interact with the electron, creating a measurable lumpiness, called an electric dipole moment. If the scientists can measure a dipole, or rule one out at smaller and smaller scales, it will tell them something about the existence, or not, of such heavy particles.
They are not looking for much of a lump, said David DeMille, a Yale physicist and co-leader of the experiment. If you blew up an electron to the size of the earth, shaved a layer a tenth of the thickness of a human hair off one pole, and slapped it on the other side, it would be a larger deformation than the one the experiment is designed to detect.
To make such a sensitive and precise measurement, the team zaps a ceramic pellet with a powerful laser, creating a beam of molecules that is chilled with neon gas. The scientists expose the beam to electric and magnetic fields and, using other lasers — some channeled through the blue tube — they align the electrons and look for a tell-tale change in how one of the lasers interacts with the electrons.
The experiment is called ACME, which is part scientific acronym, part pop culture reference to the Looney Tunes cartoons in which Wile E. Coyote doggedly pursues the Road Runner, often brandishing tools that have an ACME brand.
The scientists are painstakingly tweaking the conditions of the experiment, often taking data for 10 to 15 hours a day, to ensure that they do not end up fooling themselves — that they measure what they intend to measure and are not thrown off by some imperfection in the experiment.
Detecting a lumpy electron — or not — could help determine the fate of one popular theory, which says all particles have heavy “supersymmetric” partners — a kind of particle twin. One type of these supersymmetric particles could help explain the mysterious dark matter that makes up nearly a quarter of the universe. But this supersymmetry theory predicts an electron dipole moment, so failing to detect any lumpiness in the electron at the range the ACME experiment hopes to measure would throw doubt on the theory of supersymmetry.
The scientists hope to get results by the end of the year, and have no idea what to expect.
“God decides and we measure,” said Gerald Gabrielse, a Harvard physicist. “Just because our theory is beautiful, doesn’t mean it works. Nature doesn’t have to respect a beautiful theory.”
Measuring a dipole moment could also help explain why, after the Big Bang, equal amounts of matter and antimatter did not just annihilate one another. Models that explain the surplus of matter that make up the world we live in predict a fundamental asymmetry beyond what has been observed so far.
Other experiments are trying to make similar measurements, including one at Imperial College London, creating a sense of urgency in the Cambridge lab. Although the ACME physicists are quick to point out the experiment at Harvard is complementary to the powerful Large Hadron Collider, there is a certain satisfaction that would come if they are able to pull back the curtain on physics’ next frontier first.
“I have to admit, I’d be very pleased for us to be the first experiment to see evidence of new physics beyond the standard model,” DeMille said. “I would like that, but the fun is in the chase in many ways.”