Download Harvard-Yale team on trail of electron`s mysteries

Harvard-Yale team on trail of electron’s mysteries
By Carolyn Y. Johnson
| Globe Staff
Matthew J. Lee/Globe Staff
Gerald Gabrielse (from left), John Doyle, and Dave DeMille with their equipment in Lyman Laboratory at
Harvard.
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.”
Carolyn Y. Johnson can be reached at [email protected]. Follow her on Twitter @carolynyjohnson.