by Jon Butterworth as told to Caitlin Schneider
How do you find something that’s not made of anything? That’s exactly what a team of physicists, including London-based professor Jon Butterworth, did when they pinpointed the Higgs boson particle in 2012. We asked Butterworth, author of the new book Most Wanted Particle, how he ended up involved in one of the most important discoveries in physics this century.
Even when I was a little kid, I knew that the human race was progressing. I had this moment where I realized scientists were still finding stuff. I wanted to be part of that: There were definite things you could learn, and it wasn’t a matter of opinion. Once you’ve got a certain amount of mathematics, physics starts getting more and more complicated. And then suddenly it becomes more and more simple. Somehow it all clicks into place.
After getting my PhD, I spent some time doing postdoc work at Penn State in Hamburg, and then I got a job at University College London. The Large Hadron Collider was being built by then. It was designed to prove or disprove the existence of the Higgs boson, a longstanding fixture of physics. It all comes down to what we think of as a fundamental particle—a particle that, as far as we know, is not made of anything else. Take an electron: No matter how hard you hit it, you can never smash it up. There’s nothing inside it. The same applies to a quark. It’s almost a childish problem: How can anything that’s not made of anything else be anything? That is what Peter Higgs and François Englert and Robert Brout were trying to solve back in the 1960s.
The answer, it turns out, is that you fill the whole universe with an energy field we call the Brout-Englert-Higgs field. The way things have substance and mass depends on how they stick to this field. The only way of really proving that it exists is to hit it really hard and make it wobble. This is what we did with the Large Hadron Collider. We hit that field really hard, and we saw the little wave. The wobble in the field is a quantum excitation, which is a particle—a Higgs boson. It’s proof that the field exists.
We knew, because of everything we know about fundamental particles, that the Large Hadron Collider would find the Higgs if it existed. To prove a negative is really quite rare and quite beautiful, so it had to go one way or the other. The first paper I wrote on Higgs physics took the most pessimistic view: Higgs is wrong, but let’s see what we can do with this machine anyway. Initially, the day-to-day involved writing lots of code and building electronics and trying to make sure everything fit together. But once the collider was running, a huge amount of data was coming through.
We started in 2008 in a blaze of glory. Nine days later, we had a massive helium leak failure. It set us back 18 months. Once the collider was running again, we had hundreds of meetings all week, often around the clock, because [scientists were working in] different time zones, trying to guide students and postdocs through understanding the detector, and writing our papers in a coherent way. It was just loads of meetings, but they were pretty exciting. It didn’t matter whether you were a new PhD student or an aged professor; if you had something important to contribute, you could say it.
The most significant high point was when we first saw this huge, complex machine working. Not only did we have particle collisions, but we had enough of them to measure some processes and see that they agreed with our expectations. We were looking for a bump in a distribution. That’s how you find the particle, when you show that a bump in the data is not just noise, but it’s actually a real bump that’s not going away. We’d had instances of them in 2011, and then we stopped at Christmas. We started again with a different beam energy and changed bits of the detector around. In April 2012, we saw the first data from the new run. This Higgs was still there. That was the moment I thought, “All right, that’s it!”
Obviously, a lot of this was about motivation. You have to really love what you’re doing. You’re seeing new things that no one has ever seen before. Once they get learned, they never get unlearned.