Boson

Transcription

So two guys walk into a bar. Really? No, seriously. Two guys walk into a bar, an ice cream bar: Dave, a physicist working on the Large Hadron Collider at CERN, the European laboratory for particle physics, and Steve, a blues singer. "Dave, how's it going?" "Steve, good to see you!" "Two scoops of chocolate almond for me." "Vanilla shake." "Hey, I just saw something about the LHC on TV. You guys found bozo in your detector?" "Well, not exactly. We found a boson, probably the Higgs boson." "What's that?" "It's a particle." "Don't you find particles all the time?" "Yes, but this one means that the Higgs field might really exist." "Field? What field?" "The Higgs field. It's named after Peter Higgs, although many others contributed to the idea. It isn't a field, like where you grow corn, but a hypothetical, invisible kind of force field that pervades the whole universe." "Hmmmm, okay. If it pervades the whole universe, how come I've never seen it? That's a bit strange." "Well, actually, it's not that strange. Think of the air around us. We can't see it or smell it. Well, perhaps in some places we can. But we can detect its presence with sophisticated equipment, like our own bodies. So the fact that we can't see something just makes it a bit harder to determine whether its really there or not." "Alright, go on." "So, we believe this Higgs field is all around us, everywhere in the universe. And what it does is rather special - it gives mass to elementary particles." "What's an elementary particle?" "An elementary particle is what we call particles that have no structure, they can't be divided, they're the basic building blocks of the universe." "I thought those were atoms." "Well, atoms are actually made of smaller components, protons, neutrons, and electrons. While electrons are fundamental particles, neutrons and protons are not. They are made up of other fundamental particles called quarks." "Sounds like Russian dolls. Does it ever end?" "Actually, we don't really know. But our current understanding is called the Standard Model. In it, there are two types of fundamental particles: the fermions, that make up matter, and the bosons, that carry forces. We often order these particles according to their properties, such as mass. We can measure the masses of the particles, but we never really knew where this mass came from or why they have the masses they do." "So how does this Higgs field thing explain mass?" "Well, when a particle passes through the Higgs field, it interacts and gets mass. The more it interacts, the more mass it has." "OK, I kind of get that, but is it really that important? I mean, what if there were no Higgs field?" "If there were no Higgs field, the world wouldn't exist at all. There would be no stars, no planets, no air, no anything, not even that spoon or the ice cream you're eating." "Oh, that would be bad. Okay, but where does this Higgs boson fit into things?" "Alright, now, you see the cherry in my shake?" "Can I have it?" "No, not yet. We have to use it as an analogy first." "Oh, right, the cherry's the Higgs boson." "No, not quite. The cherry is a particle moving through the Higgs field, the shake. The shake gives the cherry its mass." "I get it. Okay, so the molecules of the shake are the Higgs bosons!" "Well, you're getting closer. It takes an excitation of the Higgs field to produce the Higgs boson. So, for example, if I were to add energy by, say, dropping this cherry in the shake," "Ah, then the drops that spill on the bar are the Higgs bosons." "Almost! The splash itself is the Higgs boson." "Are you serious?" "Well, that's what quantum mechanics teaches us. In fact, all particles are excitations of fields." "Okay, right. Well, I kind of see why you like particle physics, it's quite cool, strange, but cool." "Yeah, you could call it a bit strange, it's not like everyday life. The Higgs boson is an excitation of the Higgs field. By finding the Higgs boson, we know that the Higgs field exists." "Right. So now you found it, we know this Higgs field exists. You must be done. Is there anything left of particle physics?" "Actually, we've just begun. It's a bit like, you know, when Columbus thought he had found a new route to India. He'd, indeed, found something new, but not quite what he was expecting. So, first, we need to make sure that the boson we found is actually the Higgs boson. It seems to fit, but we need to measure its properties to be sure." "How'd you do that?" "Take a lot more data. This new boson lives for only a very short time before it breaks down or decays into lighter, more stable particles. By measuring these particles, you learn about the properties of the boson." "And what exactly are you looking for?" "Well, the Standard Model predicts how often and in what ways the Higgs boson would decay to the various, lighter particles. So we want to see if the particle we have found is the one predicted by the Standard Model or if it fits into other possible theoretical models." "And if it fits a different model?" "That would be even more exciting! In fact, that's how science advances. We replace old models with new ones if they better explain our observations." "Right, so it seems like finding this Higgs boson gives a direction for exploration, a bit like that Columbus guy heading west." "Exactly! And this is really just the beginning."