After smashing atoms together for 26 years, the Tevatron particle accelerator powered down on Friday. The 4-mile-long ring-shaped accelerator, located at the Fermi National Accelerator Laboratory in Batavia, Ill., was built to hurl tiny bits of matter at each other in the hopes that they would break apart into the basic building blocks of the universe. Though the Tevatron made major discoveries, it became essentially obsolete after the Large Hadron Collider in Geneva began conducting experiments in 2009.
University of Pisa physicist Giovanni Punzi has worked at the Tevatron since it generated its first collisions in 1985. He talked about the Tevatron on Wednesday, two days before it was shut down.
What made the Tevatron special?
The Tevatron was the highest-energy collider in operation for a very long time.
What does the Tevatron do?
It collides protons and antiprotons. We have particle detectors situated where we can analyze the products of these collisions and find what new particles are there.
Why would you want to do this?
When you get the highest possible energy in collisions of particles, you reproduce a level of energy that doesn't exist today. It only existed at a very early stage in the universe, after the big bang. Creating such energies lets you see new phenomena — including particles that are not found in ordinary matter. So you can study the very basic laws that underlie everything we see and are at the basis of the evolution of the universe.
It's a frontier of knowledge. You get to see things that have never been seen.
What did the Tevatron find that had never been seen?
A number of observations and precision measurements that have added to our understanding of high-energy physics. And the top quark was discovered here in 1995. That was a very big discovery.
Why was it important to find the top quark?
The top quark was crucial because without it, all of our theories of how subatomic particles behave wouldn't work. Quarks are the fundamental particles that combine to make protons and neutrons, and physicists knew there had to be a sixth quark. Everybody was puzzled by the fact that we couldn't find it. The reason we couldn't find it is because its mass was so large that scientists could not produce it until the Tevatron came along.
It was a very long search. If we had not found the top quark, understanding all of the rest of the physics would have been a problem.
How did physicists study basic particles before the Tevatron was built?
Before this machine they had proton-antiproton colliders at CERN [the European Organization for Nuclear Research] in Geneva, but they operated at lower energies.
I remember people saying it would be impossible to put together a thousand magnets and make them work at the same time. But the people here did it. People get used to the idea of doing something that yesterday was considered impossible. It pushes everybody to their best.
Now, of course, the record is going back to Geneva because CERN has built an even bigger machine — the Large Hadron Collider. It's 31/2 times more energetic than the Tevatron.
The Tevatron played a big role in the search for the elusive Higgs boson, the so-called "God particle" that gives rise to mass.
Yes — the Tevatron was able to restrict the possible mass of the Higgs boson to quite a small range.
And even though the collider will no longer operate, you'll continue that search?
Yes. We've used just a fraction of the data we have, and we've been improving analysis techniques over time. So now we want to give it our best possible shot and see what we can figure out about the Higgs boson.
The Large Hadron Collider is also looking for the Higgs. But we look for different modes of decay of the Higgs boson: two different faces of the same coin. Even if the Higgs is seen in Geneva, being able to see it here will be very important to confirm and to understand the nature of this particle, which up to now is completely mysterious. We will be certainly adding to the knowledge of this thing.
Who decided to shut down the Tevatron?
The Department of Energy (which operates Fermilab) and the lab directors decided it was time to go into new projects. We proposed last year to keep going and take some more data, but the decision was to begin exploring what's known as the "intensity frontier."
What does that mean?
Rather than going for the highest-possible energy of collisions, we will go for very intense beams with very large numbers of particles. Using these, Fermilab will produce a large number of collisions that will let scientists look for very rare processes. What they cannot make in terms of energy they try to make up in terms of intensity and frequency of the collisions.
There are a whole lot of things that have been developed here, especially on the side of neutrino physics, that require very intense beams.
Last week, physicists at CERN reported that they had measured neutrinos traveling faster than the speed of light. Scientists around the world are now trying to see if they can replicate that result — including a team at Fermilab, right?
Yes. This raised lots of discussion. Most of us were thinking this is too strange to be true. If it is really true it's a violation of the fundamental laws of physics. It's really beyond anything we've seen in the past.
What will happen during the shutdown on Friday?
We'll simply stop doing what we've been doing. People will turn off the accelerator and turn off our detectors. Then we will concentrate on trying to get the final results from the data we've already collected.
How long will that take?
It depends on how interesting the results are. In principle it can go on for several years without a problem, but I anticipate that most of the things will probably come within a couple of years, no more.
Are people at Fermilab emotional this week?
How can't you be emotional when it's been so long and such a successful program? As I said, we have a group of people who are still willing to do more. People never got bored, for all this time.
How many colliders remain in the world?
Well, we have this very big one in Geneva. Apart from that we have smaller machines for doing specialized kinds of physics.
What will become of the Tevatron itself?
It's my understanding that Fermilab will reuse some pieces for the next accelerator and put others on display in a museum.
This interview was edited for space and clarity.