I’m a research fellow in the department of physics at the University of Michigan and a member of a research group in particle physics. I live in Ann Arbor, a very nice university town, but we don’t do our experiments right here—a particle accelerator takes up so much space and is sufficiently expensive that very few universities, even big ones like Michigan, can have one on campus. Instead, my group does its research work at the Fermi National Accelerator Laboratory, a Department of Energy facility located 30 miles west of Chicago, and a four-and-a-half hour drive west of Ann Arbor. (I’ll be there later this week.) There, the Tevatron accelerator collides protons (the nuclei of hydrogen atoms) and antiprotons (the proton’s antimatter partner—yes, antimatter really exists) at extremely high energies. Einstein’s famous equation, E=mc2, says that energy can be converted into mass, and vice versa. We convert the energies of the protons and antiprotons into new, massive particles that are never seen in our day-to-day lives, but that were abundant in the high-energy environment of the early universe.
The experiment that I work on, the Collider Detector at Fermilab, seeks to discover and understand these massive particles. As I mentioned yesterday, there are 500 physicists from around the world working on CDF, and we all share the data and use it to explore our own particular physics interests, much as social-science researchers share data from the U.S. census to study their interests. I myself, (and most of my group at Michigan) am interested in the properties of the top quark, the most massive elementary particle yet discovered, 175 times more massive than a hydrogen atom. The top quark was first definitively observed at Fermilab in 1995, but we still don’t know too much about it, and its huge mass is quite a puzzle. And this is an exciting time for us—we’ve spent the last six years refurbishing CDF, putting in improved instrumentation and preparing to take 20 times the amount of data we had in 1995, maybe enough data to solve this and other puzzles.
The heartbeat of a university is the pounding of construction equipment building new research facilities, and today it pounded its way into my own office, taking over my computer. No real work for today, I guess. But there are other things to do anyway, such as our weekly group meeting. We’re lucky to have a relatively large research group; having more people means that we can work on more interesting problems. Our group is comprised of four professors, six postdoctoral researchers (including myself), seven graduate students, and a handful of undergrads. Three of our group members are women, and we represent four different countries. Most of us live in Ann Arbor, but right now one postdoc and five grad students are stationed at Fermilab, so they join our meeting through video conferencing.
People at different stages of their careers have different responsibilities in the group. The professors set the intellectual direction for the group and decide what major projects we will work on, but they teach classes and handle the management issues and don’t have a lot of time for hands-on work. (Management includes applying for research grants so that the postdocs and students can get paid; most of our grant money goes toward the education of the younger people in the group.) The postdocs run the hands-on part—we have the experience to know how to realize the plans of the professors and turn them into measurements that we can publish. The graduate students are learning their way around the field, and working on their Ph.D. theses, with assistance from the professors and postdocs. Despite this hierarchy, we all educate each other; everyone knows something that someone else can learn from. By the time a student has finished a thesis, he or she typically knows much more about the topic than the professors!
At our group meeting today, one of our students showed some of his recent work. Nate is trying to understand the characteristics of a particular subsample of our recent collision data. He doesn’t quite yet; he can’t get plots made from simulations of the data to match up to the plots from the real data. But that’s OK; we’re all just starting out with this, and we have a lot to learn, and by the time we’re done Nate will understand it better than the rest of us. The professors and postdocs offered suggestions of other plots to make to help understand the matter better, and all of us tried to understand what physical processes led to the data in this sample. We know that we have to explain these data before we can get on to our real goal, studying top quarks, which are produced much more rarely than Nate’s events. We spent some time talking about what we can do to get that going; we’ve been recording data at a slower rate than we had hoped, but we are starting to convince ourselves that soon we will have enough to learn about top-quark physics.
By the time we’re done with the meeting, my desk has been liberated. Now I can continue on the quest for knowledge.