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Why do you need high energy<br>to look at or observe quarks?

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How can you tell if a new type<br>of element has been created?

How did you make the detectors work in Halls A, B and C?

Well how did we get them to work? A lot of us worked in teams, really hard, and continue to work to make the detectors work. There are some people who have said that the detectors used in nuclear physics (done here at Jefferson Lab) and high energy physics (done at a sister lab of ours, Fermilab) are the most complicated devices ever devised by humans. Despite that, they operate on some rather simple principles. In a typical experiment there are two general classes of detectors. The first is called a tracking detector. These tell you the path that a particle has taken. The second type of detector is a calorimeter. These measure the energy that the particle has. It's the nature of these devices that make it very difficult to measure a particle's track and its energy at the same time. Therefore, the two detectors are often used in tandem.

There are two naturally occurring phenomena that we take advantage of to amplify our senses to the point where we can detect sub-atomic particles. These two phenomena make up the way most of the detectors work. The first is called scintillation. There is a property of some materials that when particles go through them, they give off a tiny flash of light. We can catch that flash with a very sensitive light sensor which tells us a particle just went through that material. The other technique is called ionization. This happens when a charged particle passes through a material and rips off electrons as it goes. We can collect those electrons or the ions left behind after the electrons are ripped off and they can tell something about the particle that went through our detector. Combinations of these two types of detectors are assembled in some clever ways to allow us to learn the most from our machine.

So you see, even though these devices are huge and seem enormously complex, they are actually based on fairly simple processes.

Author:

Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)