It was the biggest experiment in the history of physics, a $10-billion project to find a subatomic particle called the Higgs boson.

An army of scientists and engineers spent nearly 30 years designing and building the Large Hadron Collider, a 17-mile underground track near Geneva where protons would accelerate to nearly the speed of light and collide in a shower of subatomic particles. If the Higgs turned out to be one of them, it would validate the so-called Standard Model of particle physics and help scientists understand why there was mass in the universe.

In the months before the collider switched on in 2008, a pair of physicists set out to document the excitement, anxiety and intellectual fervor at the machine’s home at at CERN, the European Organization for Nuclear Research. The result is “Particle Fever,” a surprisingly emotional film that takes viewers deep behind the scenes of a landmark achievement in science. Spoiler alert: The Higgs boson was found, and its discovery was recognized in 2013 with a Nobel Prize.

David Kaplan, a theoretical particle physicist at Johns Hopkins University, came up with the idea for the documentary. Mark Levinson, who earned a doctorate in theoretical physics at UC Berkeley before pursuing a career in film, signed on as director. “Particle Fever” is now playing in theaters in Los Angeles and Orange counties.

Kaplan and Levinson discussed the movie during a recent visit to The Times.

What made you think the search for the Higgs boson would make an entertaining movie?

David Kaplan: I knew that when the Large Hadron Collider turned on, it was going to change us in some very dramatic way. Most of us felt very confident we would discover the Higgs. But an entire generation of physicists had not seen any information about the theories we’d all been working on. We knew it could be a total erasure of all of our work.

I bought a camera and started filming in January 2007.

What was the most difficult concept to convey?

DK: We didn’t explain the Higgs in any real thorough way. But people came out of the movie and said, “My God, that was the best explanation I’ve ever heard!” If you go back, no it wasn’t. We tricked people into thinking they understood a lot more than they did because they digested it in an emotional context.

Mark Levinson: To me, it’s not a question of what was the hardest thing to explain. The hardest thing was deciding what we’re not going to explain.

DK: What to leave out.

What did you leave out?

ML: We left out string theory. That was a hard decision.

DK: For one of us.

How difficult was it to get people to talk to you and let you be there for the big moments?

DK: It was very easy.

ML: They couldn’t see how it could ever be a story. They only had two requests: “Please don’t make us look boring,” and “Can you introduce us to Nicole Kidman?”

DK: One out of two ain’t bad.

But a lot of people had a lot to lose, depending on how the experiments turned out and the mass the Higgs was found to have.