Q&A: Discovery of the Higgs boson

Scientists at the European Organisation for Nuclear Research (CERN) have discovered a new subatomic particle.

Two separate experiments run by CERN’s Large Hadron Collider, a particle accelerator, have found a particle believed to be the Higgs boson, also known as the “God particle”. The particle was first theorised almost 50 years ago by Peter Higgs, a physicist at Edinburgh University, but until now experiments had failed to confirm its existence.

The existence of the Higgs boson would provide strong evidence for the “Standard Model” of particle physics, which explains what the universe is made of and how subatomic particles interact with one another.

Brian Cole, a physics professor at Columbia University who specialises in experimental nuclear physics, spoke to Al Jazeera about the discovery of the particle and its broader significance.

Why has the Higgs boson been called the “God particle”?

I actually dislike that terminology. It was actually a physicist who invented it, but a lot of us think it’s maybe a bit overstated. It’s called the God particle because the Higgs is, as we understand it, the thing that essentially generates the masses of all the other fundamental particles that we know of in the universe. … In that respect it’s maybe one of the most important building blocks of nature.

Why has it taken so long to confirm the existence of the Higgs boson?

The real difficulty has been that the Higgs is actually quite heavy, and so only now have we had an accelerator that has enough energy in the collisions to produce the Higgs with a sufficient rate for us to be able to detect it. So the LHC [Large Hadron Collider] was really the breakthrough there.

The other thing is that measuring the Higgs is quite complicated. When you collide particles many things come out, and you have to sort through all of the debris, maybe hundreds of particles coming out of the collision, to find the signatures of the Higgs decay. And the detectors that are now running at the LHC are basically, I would say, the most sophisticated experimental detectors ever built by man. They can do measurements in a way that has never really been possible before in particle physics.

What are the broader ramifications for the field of physics?

This is one of the final puzzle pieces in what we call the standard model of particle physics. Basically, it … essentially provides the origin of mass.

I would say over the last decade in particular, people really started to question whether the Higgs existed – because there are other possible ways of essentially solving the problem that the Higgs was invented for, which is to understand where mass comes from. And people were starting to doubt that the original idea proposed by Higgs and others was correct.

But, in fact, now we have experimental evidence. Not only was the idea correct, but the Higgs is appearing in a place where people had predicted it would appear.

The Higgs could have played an important role in the early evolution of the universe. We know that very early in the universe, a period of what’s called inflation occurred, when the universe grew incredibly rapidly over billionths of a billionths of a second. And we don’t yet know quite how that happened, but it’s possible that had to do with the Higgs. So I think the understanding of the Higgs … will also drive better understanding of the early universe.

The Higgs boson only lasts for tiny fractions of a second, so how is it detected?

The easiest decay mode for us to see is the Higgs can decay to two photons. Photons are the fundamental quanta that are light: they’re essentially the particle analogues of electromagnetic waves. And our detector is actually very good at measuring photons. So a Higgs can decay to two photons and that’s a very easy decay mode for us to see.

There are many others that we can also see, so we try to look in various different modes that the Higgs could decay into, and potentially each of those modes we can reconstruct the mass of a hypothetical particle that decays to them.

Then you look at the distribution of masses. For the photons, we see there’s a smooth background that comes from other processes, and then there’s a small peak that sits on that background that is essentially the products of the Higgs decay.

Are the results of CERN’s findings statistically significant enough for it to be called a discovery?

Yes. Both experiments, I would say, are being relatively conservative. But each experiment has a very high significance, and if you take the two together I think it reaches a level of what any reasonable person would consider a discovery, because both experiments really are measuring independently … neither experiment knew what the results of this latest data would be.

Both experiments are essentially seeing the same phenomenon, same decay modes of the Higgs, with the same mass. So I would say at this point it’s really at the level of a discovery.