When Sarah Demers gets a work-study job working on a particle detector, she has no idea what she's in for.
Sarah Demers is the Horace D. Taft Associate Professor of Physics at Yale University. She is a particle physicist and a member of the ATLAS and Mu2e Collaborations, studying fundamental particles and the forces with which they interact. Sarah graduated from Harvard University with an A.B. in physics in 1999. She received her Ph.D. from the University of Rochester as a member of the CDF Collaboration in 2005. She was a postdoc with Stanford's Linear Accelerator Center, based at CERN as a member of the ATLAS experiment before beginning her faculty position at Yale in 2009. She has been recognized for her research with an Early Career Award from the Department of Energy and has won awards for teaching and service at Yale. When she isn't doing physics she can be found spending time with her husband and two kids exploring in the woods behind their house, baking, reading and, recently, shoveling snow.
This story originally aired on May 5, 2017.
Story Transcript
I became a particle physicist because I needed a job. I was a work study student and had to work ten hours a week and needed it to pay tuition—a piece of my tuition—pay for books, phone bills. In those days—back in those days—for four college students, we had one phone. It was plugged in the wall and you had to hover over it if you wanted to talk into it—they made us pay for this indignity. There were a number of things that I had to pay for so I needed a job. When I started back at school, I wen t to work at the library. They’re always hiring at the library. But in my sophomore year it occurred to me, I could do something that’s tied to maybe a future career. Maybe I could try physics research. And I have to confess, I wasn’t too excited about the idea of it. I didn’t know what research was. When I pictured it, I pictured basements and white lab coats and safety glasses and people measuring with a paranoia and an amazing attention to detail. Everything that I do I must write down perfectly and catalog. And it just sounded kind of terrible. But I loved my physics classes and I wanted to give it a try.
So there was one physics professor who was hiring. Her name was Melissa Franklin. She was the first particle physicist—or the first woman to get tenure in the Harvard physics department doing particle physics. She had two openings in her lab, zero prerequisites, to upgrade a particle physics detector. She was looking for undergraduate grunt labor. So I contacted her and got an interview and I was very nervous. I remember walking into her office and she was over on the couch changing her infant son’s diaper. And she only briefly looked up at me and looked right back at her son and said, “She’s not wearing any socks. That’s weird.” I remember thinking, This is not going well. And then she asked me two questions. And the first question she asked me was, “Do you drop things?” And I thought, How does this non-sock-wearing person answer this? “I don’t know. I mean, I don’t drop things more than most people, but I can’t claim to drop things less than the average person so I think I’m an average dropper.” And then the second, and last, question she asked me was, “Are you nice?” And this one I hit out of the park. I’m a pastor’s daughter—I’m capable of great warmth and generosity. Yes! I am nice, and I may even be nicer than the average person.” And so I got the job.
I have to say that the basement—cavernous basement—of the Harvard high energy physics building was as I’d feared in terms of how it looked. It was full of electronics equipment. There were machines everywhere, cables everywhere, lots of epoxy and lead bricks. There was a clean room, and in this clean room you not only had to wear the white lab coat, but you had to wear booties and a hairnet. It was just incredibly intimidating.
But Melissa had a plan. She wanted us to make ten thousand gold Mylar field sheets to update a tracking detector. So this tracking detector you can think of like a big can on its side, ten feet long, six feet high, six feet in diameter, full of gas. It would surround the collisions that she wanted to study and when charged particles came plowing out of the collisions, they would knock free electrons as they went. The job of the tracking chamber was to just catch these electrons, in clumps, and follow where they went so you could figure out where the tracks in the detector went. And our gold Mylar field sheets, ten feet long, six inches wide, so thin you could see through them, they were supposed to basically mark the places and provide an electric field, a little push to the electrons, so we could grab them on our wires and see little blips as it went though. I loved it. Little engineering challenges—how are we going to glue this? How are we going to make this so it’s repeatable? It was amazing, and an incredible amount of fun.
I’ve heard people talk about particle detectors like the cathedrals of our day. It takes thousands of people to build them, years to put them together. And the resources, intellectual and financial, are immense. The detector that I work on, it’s six stories high, the length of a football field, hundred of millions of electronic channels, and it weighs as much as the Eiffel Tower. This thing is awesome.
I fell in love with particle physics through the detectors. And it’s a really good thing that I did. Because while I was doing this research, I was simultaneously taking physics classes. And they were getting harder. And they were getting a lot weirder too. A lot more abstract. I don’t know how much physics you’ve had, but it starts with mechanics. You’re pushing boxes around and watching how they move. Then you get to electricity and magnetism and all of the sudden the forces are invisible. And every once in a while, I would play with a refrigerator magnet just to feel magnetism and stay connected.
And then with quantum mechanics, you stop talking about where particles are and start talking about where they might probably be, with some probability. In special relativity, you get going really fast to slow down your clock compared to somebody else. And particle physics takes all the crazy and lumps it in together – just all of the craziest parts of physics all together
I remember calling my parents in college and telling them, “You are not going to believe what these particles are named. There are fermions and bosons. W boson, Z boson – the gluon. They even named the third quark that they discovered “the strange quark.” This is ridiculous. We used to laugh about all these different things.
By the time I got to graduate school, I had hung suspended from the ceiling cleaning detector pieces. I had glued and machined things. The detectors were so real for me. And I was just starting to make that transition to working with the computer code. The problem with these collisions is that you can’t see with your eyes what’s happening. You’re relying on your detector to do that translation for you. So we had to have a way to get these electronic signals into something we could interpret. And I was just starting to play with it.
But I had a concrete project. I was looking for pairs of top quarks that had tau leptons in their decays. I knew enough about taus to know that they were messy. Every time you make a tau, when it decays there’s a neutrino, and our detectors can’t see neutrinos. So you lose information. So any kind of nice description or plot that you try to make is going to be smeared out and it’s going to be messy. Which was why it was really terrible that one day I made a gorgeous plot, and I remember thinking, What have I done? Because every time I made a plot that had any interesting feature in it, it was a bug in my code.
I went back and I looked and I just couldn’t find a mistake. And I thought, What have I done?
So eventually I had to swallow my pride and take my plot to my adviser, say “What have I done?” And he laughed when he saw the plot and said, “Sarah, if you had made that plot twenty years ago, you would have won a Nobel Prize!” And so I laughed too because I thought this is probably a great joke, but I did not leave his office. I just stayed there. And he realized, Oh, she’s still confused. And he told me, “What’s happened is, you’ve discovered the Z boson. That code that you wrote to try to grab taus, it’s been faked by electrons. And so you’ve got a beautiful… it’s a mass peak—that bell-shaped curve is the mass of a z-boson.
And I said, Oh, thank you very much,” and walked out of his office. This is where you might start judging me. What I was thinking was, “Oh my – Z bosons are real?!” And you may wonder, how do you get to a point in your life when you’re starting graduate school in particle physics without confronting the possibility that these particles you’re studying are real? But in my defense, it started as a paycheck, it was a little paycheck. I fell in love with the detectors. And I maybe thought – and I would say that we were studying the universe – but this changed everything for me. These particles were real. And even on a day when I’m making a miniscule contribution to my field, I feel connected to human beings who for thousands of years have been asking this question: What is it that we’re made of? What is the universe? And that connection still brings me joy.