 |
 |
|
Scientists Provide the Answers by Kurt Riesselmann
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 seasons.
"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?"
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 interested in.
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?"
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 machine.
"What is antimatter? Can we use it as fuel for spaceships?"
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?"
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 the way.
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?"
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 of nature.
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 quarks.
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.
Cultural aspect:
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 gained today?
Technological spin-offs:
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 www.fnal.gov/pub/inquiring/matter/whysupport/ |
