You have heard about Fermilab, accelerators, quarks and the Big
Bang. But how do all those things fit together?
If you only knew a scientist whom you could ask...
More than a year ago, physicist Peter Garbincius and some of his
colleagues recognized the problem. They had seen many people
visiting Fermilab, who-after seeing videos, reading posters and
exploring displays-still had questions. Clearly these visitors needed
to "Ask a Scientist," giving the new outreach program its name.
On Sunday, September 2, 2001 the Ask-a-Scientist program
celebrated its first anniversary. Since the beginning of the program
about 50 physicists have volunteered to spend two or more hours on
a Sunday afternoon at the lab. In teams of two they have greeted
visitors in Wilson Hall and answered questions ranging from particle
physics to the occasional homework problem.
Since September 11, the program has been on hold as public
access to the previously open Fermilab campus is severely
restricted. No visitors are allowed to enter the site on weekends.
Nevertheless, Garbincius and his colleagues are determined to keep
the program alive. They have investigated possible alternative
locations, and they plan to use the Web, a particle physics invention,
to reach out to people far away. At present, real-time
Ask-a-Scientist sessions on the Internet are under test.
To keep up with the expansion, Garbincius, who organizes the
program, is looking for additional manpower.
"We would be happy for more scientists, including students or
postdocs, to volunteer," he said. "If somebody hasn't done it before,
we team them up with our senior people."
In the past, the program has remained a steady draw throughout the
"We averaged more than 20 visitors each session," said Garbincius.
"Even on Super Bowl Sunday we didn't seem to have a significant
drop in attendance."
Some physics questions just can't wait for an answer.
"Why did you choose to become a particle physicist?"
Physicist Roger Dixon, Cryogenic
Dark Matter Search experiment:
The short answer is that I had an
intense interest in astrophysics
when I finished college, and I saw
particle physics as the most
attractive path to studying the topics
in astrophysics that I was most
I had always been interested in the
sky from the time I was a very small child. I spent most of my
summers with my Grandfather on his ranch in the mountains of New
Mexico. We looked at the sky together most every night and he
would tell me all about the constellations and the mysteries of life. I
was so enthralled just to be with him, I wanted to be like him in every
way. He only had a second grade education, but he had quite a few
patents including the first one for cruise control in an automobile. I
think the gene pool got watered down a bit by the time it got to me.
Anyway, the magic of those moments faded as the time approached
for me to go to college. I thought I would study something practical
like engineering, but once I began taking the physics and math that
was required, the magic came back. And here I am.
"What does a particle physicist do? Is the work dangerous?"
Physicist Jeff Appel, E791 and BTeV experiment:
As in other branches of science, there are two types of particle
physicists: experimental and theoretical. An experimental particle
physicist designs and builds experiments to answer specific
questions about the nature of the smallest components of matter and
their interactions, and analyses the data that is collected in the
experiments. This involves a host of disciplines and technologies,
and working with engineers, technical support groups, and industry.
We work together to design, build, and operate accelerators,
particle detectors, and computing systems. A theoretical physicist
helps interpret the results of a range of experiments, and helps
frame the questions that the experimenters attempt to answer. For
both experimentalists and theorists, the use of computers plays a
major role these days, and we work in collaborations that stretch
around the world.
At the moment, my own efforts as an experimentalist are focused on
developing a new kind of particle detector, called a hybrid pixel
detector, which will make certain kinds of experiments possible in
the future - including the experiment I want to do!
Working at Fermilab is similar to working in a university laboratory or
the research division of a high-tech company. We have no nuclear
energy or weapons research program. Our main instruments are
accelerators, much smaller versions of which you find at hospitals
and inside television sets. Hence our work is no more dangerous
than the work of an electrician or a nurse working with an x-ray
"What is antimatter? Can we use it as fuel for
Physicist Steve Holmes, Associate Director for Accelerators:
We and the world we see around us are made of matter. At the
atomic scale this means protons, neutrons, and electrons. We know
that for each of these matter particles there is a corresponding
antimatter particle (or antiparticle for short). Antiparticles have
exactly the same mass as their particle cousins, but exactly the
opposite 'quantum numbers.' For example, the proton has positive
charge, +1, and the antiproton has negative charge, -1.
If a particle and its antiparticle ever come into contact they annihilate
into a tiny flash of pure energy. Fortunately, antimatter does not
appear to occur naturally in any significant quantities-there are no
anti-trees on earth, and we don't think there are anti-solar systems
or anti-Milky Ways-so we don't have to spend a lot of time worrying
about going poof.
Perhaps we could use antimatter as fuel for spaceships, but our
resources wouldn't get us very far. NASA has calculated that it
would take about a ton of antiprotons to propel a spaceship to the
nearest star. This is about 1,000,000,000,000,000 times the amount
of antiprotons that we produce at Fermilab in a year. So we would
have to keep at it for an awful long time.
"How do you accelerate particles? Can they go faster than the
speed of light?"
Physicist Jim MacLachlan,
We accelerate particles
that carry electric charge. A
proton, for example, has a
positive charge. To
accelerate the proton, you
place a negative charge
nearby: the proton will feel
the force of the electric
field and move toward the
charge, speeding up along
Particles that have low
energy we can accelerate
with a constant electric
field. The acceleration
occurs between electrodes
with a high voltage across
them. The Cockcroft-Walton accelerator at Fermilab is an example.
It operates at a voltage of 750,000 volts. A charged particle
traveling through this accelerator gains 750,000 electron volts (eV) in
energy. Our most powerful accelerator, the Tevatron, takes particles
to energies of nearly one trillion electron volts (1 TeV).
To achieve such a high energy, the economical way of supplying the
electric field changes drastically. Instead of charging electrodes with
a constant electric field, we use accelerators with an oscillating
electric field, which is produced by an alternating voltage. Sending
particles in bunches, synchronized with the oscillations of the field,
the particles always feel forces pulling them forward as they travel
through the accelerator.
Using larger and larger accelerators, the energy of a particle can be
increased more or less indefinitely. However, all charged particles
have mass. According to Einstein's theory of special relativity, their
maximum velocity is always below the speed of light in vacuum. At 1
TeV, a proton has a velocity of 99.99996 percent of the speed of
light. Though we can add more and more energy to such a proton, it
will never reach or exceed the velocity of light. The additional energy
effectively makes the proton "heavier," not faster.
"What happens when two particles collide at high energy?"
Physicist Herman White, KTeV
and CKM experiments:
Through a collision we break the
forces that bind together the
internal components of a particle.
Similar to cracking an egg, a
collision reveals the inner
structure of the particles involved.
By colliding beams of protons
with their antiparticles
(antiprotons), we are able to
reveal the smallest building
blocks of matter: quarks. At the very high collision energies reached
at Fermilab, the quarks inside a proton are interacting with the
quarks inside an antiproton. The violent collision not only annihilates
proton and antiproton, but it rearranges their quarks to produce
composed particles that do not usually exist. Unlike protons, these
new particles only exist for a short period of time and then decay.
Carefully analyzing these particles and their properties, we can
deduce the properties of matter at the smallest scale. Thus we learn
a great deal about how quarks behave and the fundamental forces
"How do you 'see' particle collisions?"
Physicist William Wester, CDF experiment and ASIC testing lab:
When particles collide, all sorts of particles can get created and can
fly out of the collision point. By detecting and making measurements
of this emerging "debris," we are able to "see" the particle collisions,
which would otherwise be invisible. Consider a collision at the center
of the CDF or DZero detector in which top quarks are produced.
Each top quark immediately decays into two other particles (a W
boson and a b quark), which lead to "jets of particles" and many
different particles flying out. The detectors, which we built, are like
huge microscopes that surround the collision area. They yield
electronic signals that allow us to determine position, path, energy,
and sometimes the type of the outgoing particles. Our computer
programs put this information together. By using the known laws of
physics, we are able to combine groups of the "debris" particles
back together to identify the original decay products of each top
quark. We are thus able to "see" when a collision produced top
"Why should I care about elementary particle physics? Will
I ever benefit from this research?"
Physicist Peter Garbincius, FOCUS experiment and future
I would like to address these questions on three levels: culture,
benefits and spin-offs. These are some of the reasons that I think
particle physics is both fun and important.
Mankind has always been driven to try to understand what the
universe is all about. Such drives to explore and to understand seem
to be at the core of what it is to be human. We want to know what
are the building blocks, how they are put together, and how the
more complex structures, such as atoms, molecules, cells,
organisms, planets, stars, galaxies, and the universe itself, come
about and work. In elementary particle physics, we focus on
investigating the smallest, most basic structures and the forces that
govern their interactions. This quest represents an extension of the
series of unending questions, "What's this made of? What's inside of
that?" questions asked by both little children and some of the
greatest thinkers throughout history.
Benefits from nature:
Basic science, driven by the curiosity of its investigators, has proven
its worth time and again by providing the understanding necessary to
use nature to benefit mankind. For example, nobody was able to
foresee the utility of early investigations of electricity,
electromagnetic waves, light, radioactivity, quantum physics,
relativity, atoms, or nuclei, but the fruits of those studies are a large
part of our standard of living.
Over 150 years ago, Michael Faraday, when asked by his patrons in
the British government as to the usefulness of his experiments on
electricity replied prophetically, "I do not know, but I am sure that
one day you will be able to tax it."
Due to the rapid progress of the physical sciences during the
Twentieth Century, we may have come to expect instant returns on
research investment. I'll grant that it may be more difficult to readily
apply elementary particle physics because of the higher energies
and larger machines involved, but who can imagine the possible
benefits to future generations from the scientific understanding being
Although not our main goal or mission, the tools and technologies
developed by the elementary particle physics community have had
some spectacularly beneficial applications. Among others, they have
led to computerized tomography (CAT scans), neutron (a Fermilab
specialty) and proton cancer therapy, superconducting magnets for
magnetic resonance imaging (MRI) and the world-wide-web
(originally a communication tool for high-energy physicists).
These are my personal thoughts about why we study elementary
particle physics. More aspects are given at
The Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.