What's next for the Higgs?
Martha - It's been an exciting year for the Large Hadron Collider, the LHC, CERN's high power particle accelerator in Switzerland. Recently, the facility announced that they have discovered evidence for the Higgs boson, the particle that gives things their mass. Liverpool University Physicist Tara Shears spends part of her time experimenting at the LHC and spoke at the [British Science Association] festival about what the discovery might mean.
Tara - Well, we've quite definitely found something completely new. We can be sure of that. And I know that the way that physicists are very reticent about claiming exactly what it is that's been discovered is something of a source of amusement for most people. But what's clear is that we've seen something absolutely new in our data and that something is doing the jobs that we think the Higgs is there to do. So, really, I'm pretty sure that it's the Higgs. This is the particle we've been looking for for the past 40 or 50 years since our subject started, and that's what makes it so amazingly exciting to us.
Chris - So, can we all go home now then, shut down CERN, Higgs is found, job done!
Tara - No, not at all! This is just the start of it and I'm not saying that because I enjoy doing my job.
Chris - Although you do have a vested interest! [Laughs...]
Tara - But really, this is the tip of the iceberg. We've seen this discovery. We've seen something new. We're still not sure though exactly what it is. I have to stress that. It could be the Higgs that we've been expecting to see in our current understanding of physics, but it could be something more exotic, and that's really exciting. It could be something that gives us the first clue to some deeper mysteries in the universe that we're also trying to answer.
Chris - So, what actually have you seen, when scientists from CERN are saying, "We have seen evidence of a Higgs-like particle." What actually does that mean?
Tara - What it means is we've combed through trillions, millions and trillions of proton-proton collisions from the collider, looking for specific experimental signatures that are characteristic of what we'd expect the Higgs particle to have. These signatures are rare, but clean and that's the key. So, if we see enough of them then we can be sure we're not looking at some random combination that is just nature being cruel and teasing us that we're seeing a Higgs. We're actually seeing the real deal. We have enough data now to really be confident that we're really seeing something that isn't random fluctuation. I mean, we're seeing something at level of 1 in 10 million, that sort of chance of being a background fluke. So, from that point of view, no. It's real. It's real, believe it.
Chris - People are saying this is definitely some kind of a boson. Is it the Higgs boson? And what do they mean when they make that fairly cautious statement?
Tara - So, the sort of particle we're looking for, a Higgs, is a type of particle called a boson and what that means is that it has a quantum property. It has what we call integer spin. That's what makes a boson a boson and not some other type of particle. But as to whether it's a Higgs boson, well, what we're looking at is to see if it behaves in the way that we expect the Higgs to behave. And what we mean by that is, we're looking to see how it interacts with the other particles, how often it joins up with them, how often it decays to them. What makes the Higgs special is that unlike the other bosons in nature that we know about that convey the forces of radioactivity or electromagnetism, this has in a sense a more fundamental role. It's responsible for giving the fundamental particles we know about mass, but that also has a knock-on effect of making the forces in the universe behave in the way they do. If you didn't have that Higgs there, then the Universe would be completely different. You wouldn't have atoms. You wouldn't have stars. You wouldn't have us. Everything would zip around at the speed of light and wouldn't even coalesce at all. So, it's that level of fundamentalness that we have interest in seeing this particular particle.
Chris - When people talk about you actually seeing the particle, and then, on the other hand, they're talking about a Higgs field - and the Higgs field is a bit like a gravity field, it's why things have mass - what's the difference between the particle and the actual field? How does one relate to the other?
Tara - In brief, because this field - this energy field that's the Higgs field - is invisible to us, the particle is the public face of the field. It's the only part that we can actually see; it accompanies it. What it means at a slightly deeper level is that if you think of space being filled with this sort of jelly-like, Higgs field-like substance, then a Higgs particle that we see corresponds to a ripple in this field, like a sound wave going through a room where the room was full of air. That's a good analogy to have in your head.
Chris - So, these Higgs particles are everywhere and they are creating the field, or giving rise to the field around them and matter interacts with that field, which is why matter has mass.
Tara - Pretty much. The Higgs particles are naturally associated - intimately associated - with this field. You don't get one without the other. But fundamental particles moving through this field get their mass by that interaction with the field. So, by discovering the Higgs particle, we know that the Higgs field is there, and because we know that the Higgs field is there, we know that that's how particles get their mass.
Chris - So, how does the collision actually give rise to a Higgs particle. Is it that the collision in some way changes the field and that means that we can see that signature sign of it being a Higgs particle there, or are we creating a Higgs particle when we do those enormous collisions.
Tara - If you like, when we have a proton-proton collision at the LHC, we're really shaking the field and giving it a sort of big knock on the side, and forcing a Higgs to come out. It's like going back to my analogy of having a sound wave propagating through a room. It's like you've got an enormous drum at one end that you're beating to make these things happen. So, our collisions make the Higgs visible for an instant of time and then we see the debris that the Higgs leaves behind once it decays down.
Chris - So, what are the next steps now that you'll be focusing on at CERN, and what are the big questions now you think you've got the Higgs? What's it going to take to firm this up, where are you going next?
Tara - The very first question we have to answer is what sort of Higgs are we looking at. That's very important and to answer that, we need to look in much greater detail of the way it behaves and compare that behaviour to our theories to see if it's matching up with the Higgs we expect or whether as I said, it can be a more exotic version. But that's just one thing we're trying to answer with the LHC. We're also trying to understand what the nature of dark matter is, what it's made of. We're trying to understand what the nature of anti-matter is and why we just don't have any in the universe anymore.
Chris - And since you mentioned it, just to finish off, do we think that anti-matter interacts with a Higgs particle or is the anti-matter equivalent of a Higgs particle?
Tara - That's an extremely interesting question. Anti-matter has mass; therefore, it must interact with the Higgs to get that mass. But as to whether the Higgs has its own anti-matter counterpart, well, that depends very much on the type of Higgs that we're looking at. It could well, or it could be its own anti-matter counterpart. I mean, it really gets very science fiction-y at this point since we know so little about it, but yes, it's one of the questions we want to know about...