TIME Talks to the Physicists Who Found the Higgs

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REIDAR HAHN / Fermilab

The Tevatron typically produces about 10 million proton-antiproton collisions per second.

It's not often that the world stops, cheers and generally goes nuts over a new discovery in particle physics. But that's what happened on July 4, when physicists from the European Organization for Nuclear Research (CERN) announced that they had at last confirmed the existence of the elusive Higgs boson, the particle that gives the universe mass. The Higgs suffuses an energy field that permeates space, and as particles move though it, they acquire a degree of mass that corresponds to their own energy level. Failing to find the Higgs would not only have meant that a new theory would have to be developed, but that the standard model of particle physics — one of the great pillars of the field for the past several decades — would fall apart.

But the Higgs was indeed run to ground, thanks to work conducted at the massive new Large Hadron Collider (LHC), which straddles the border of Switzerland and France (read more about it in the new issue of TIME, available to subscribers here). Thousands of physicists from dozens of countries contributed to the work, but there are three undisputed leaders: Joe Incandela and Fabiola Gianotti, who led the two research teams that made the discovery; and Rolf Heuer, CERN's Director General. TIME spoke to them all by phone in Melbourne, Australia, where just three days earlier they had presented their momentous findings to the International Conference on High Energy Physics.

TIME: So you did it. Almost 50 years after the Higgs was first theorized, you found it. How does that feel?

Gianotti: First of all, we are happy. To me personally this event is an arrival point and departure point. It's an arrival point because it's been the dream of all of us. But there's more. It brings more physics beyond the standard model. Among the questions we have in mind: dark matter, antimatter and matter symmetry. It's a very nice reward for the work.

Heuer: It does open as many questions as it answers. You always find an answer but this answer usually gets you to more questions.

Gianotti: provided you know the right question to ask.

Incandela: If you look at all the particles we've discovered before, they're either matter particles or copies of them. But the Higgs involves what makes up the universe. I give lectures to the public and say what we're searching for is the genetic code of the universe.

TIME: Of those other doors the Higgs could open, one of the most tantalizing involves dark matter, the as-yet unidentified force or particle that makes up 80% of the universe and holds the galaxies together gravitationally. How can the Higgs help?

Incandela: Dark matter enters in a funny way. Any particle at the subatomic level is constantly interacting with other particles in space time. Some of this is described through supersymmetry, in which sets of particles exactly parallel other particles but cancel out some of the mass. Dark matter enters because we believe that in supersymmetry the lightest supersymmetric particle doesn't decay. This is the dark matter. When you do the calculation it almost perfectly matches the mass or density for the amount of dark matter we think is in the universe.

TIME: And what about dark energy — the even less-understood force that contributes to the expansion of the universe?

Heuer: The Higgs would be the first fundamental scalar which we have in our hands. A scalar has zero spin — it has no preferred direction. If you are swimming in a river, the force exerted on you by the water is different depending on which way you're swimming. If you're in a swimming pool there's no preferred direction. The Higgs must be a scalar, or mass would depend on the direction a particle is moving. Dark energy must be a scalar too because dark energy moves in all directions. So now we have two scalars. We might with these be able to determine the nature of fundamental scalars.

TIME: What was it about the Higgs that made it such a consuming goal for physicists? After all, the field has looked for — and found — other particles before.

Heuer: It's not just another type of particle.

Gianotti: The top quark was discovered in 1995 and since then the Higgs has become our obsession because the standard model was incomplete with out it. We had to understand things like why the top quark was so heavy and the electron is so light. The Higgs is a big, important step.

Heuer: The difference between finding the top quark and the Higgs was that we knew the top quark had to be there but for the Higgs we were wishing it would be there but it didn't have to be. One thing that's important to say is that if we had excluded the Higgs in the energy range of the LHC we would have found its replacement. But it would have taken much longer because we wouldn't know its nature.

TIME: Had you begun to worry that you indeed might not find it?

Incandela: Only in the past few years did I begin to worry. Once we started in the LHC we eliminated a huge amount of space so quickly [in the particle weight spectrum.] We looked between 100 and 600 GeV [billion electron volts] and had only about a 15 GeV rage around 125. That's all that was left.

TIME: And that's right where you found it. What there a particular moment that you realized you'd succeeded?

Incandela: We were working so hard to put everything together, but when we unblinded the data and saw a big signal, I realized we had something. But I was reserved. The work was not done until I walked into the room [at the Melbourne meeting.] As I was giving the presentation and showed the distribution, it hit me. We really discovered this thing! It wasn't just that I had the moment, it was having the whole community and they believed it. If you get married by a judge in his office it's not like a church wedding.

Heuer: For me it's a little bit different. I'm not in the details. I have to be neutral. We had the agreement that they come to my office and show me their data and nothing leaks out. When I saw the first plot from Joe and the first plot from Fabiola, I thought 'OK, we have it.' They didn't know their own discovery. I had to spell it out to them. They were very resistant to use the world discovery, but I persuaded them, yes, it is a discovery. We can use discovery.