17.4 Quarks

Okay, we're gonna start our last topic for the course, and we're gonna look at what we call quirks. Where quirks come from is we think that leptons are pretty small, so we looked at things like electrons and things like that. We thought those are probably the fundamental particles. And hey, drones are really big, like protons and neutrons, so we thought that maybe those are just made up of other things. But in the 1960s, a couple of guys said that there's actually things that make up the hey drones and these particles. So, they're basically saying that there are particles within these particles that actually make these up, and they called them quarks. So, what happened there? They basically said that everything, all hey drones, could actually be made up with quarks. So they just, they basically came up with the idea of just three quarks were needed. And they said that the up quark had a positive two-thirds elementary charge, and they use the symbol for u‚ CN for up. They had a down quark that said it was a negative one-third charge, and there is a symbol for D. This whole idea seemed strange to most physicists, and they never thought it was possible to have a fraction of a charge. But in the later 60s, they were making a high-energy particle accelerator, and they were shooting electrons off protons. What they found is that the electrons actually deflected around the proton in weird patterns, and they weren't evenly spread out. They actually got things to change depending on this third model. So, they saw if an electron lives near the down quark, which was negative, they actually got a little bit of repulsion. The electron curved away. If it was near an up quark and it was really close, because those are positive, you can see there's lots of attraction. The electron curves closer and so on. They got some weird things. Going on in terms of the deflection, they actually thought that this quark model was true. So, the quark model has actually been built up to have six quarks and antiquarks. But, we've only narrowed down to just the first generation for the Diploma. So, we think of a proton as being made up of quarks, specifically two up quarks and a down quark. These three particles make up the one proton. What happens is that all of these particles can be built from two or three of these quarks, depending on the particle. The exception is the theta, which is actually built up of five quarks, which is kind of weird. But, most particles are typically made up of three quarks, and a few of them are made up of two. The second generation in their generation idea is sort of like having a proton. It's made up of these three quarks. Within each of those quarks, it's made up of three within. Inside of that, and then inside of those, there's also more of them. So that's how they get the first, second, third generation idea. So let's use up and down quarks to figure out what a proton and a neutron would be made out of. A proton has a charge of positive one, so we know that to get a positive one only using two-thirds and negative one-third. We do the math, we know we'd have to have two positive two-thirds and one negative one-third. So if we do the math on that, you can see we get positive 4/3 minus 1/3, which would end up being 3/3. This would be the same thing as positive one. So, our proton would basically be built up of two up quarks and the down quark. A neutron is another hadron and it's neutral, so we have to do the same thing to make it neutral. In this case, if we have two positive two-thirds and two negative one-thirds, that would give us zero, which is neutral. So, a neutron is an up quark and two down quarks. We can apply this same process to other hadrons, breaking them down into up and down quarks, and so on. We can use this logic because we know that when a proton or a neutron undergoes a positive-to-negative decay, it is simply changing into something else. So, we can use this sort of logic to describe this. We know that in a negative decay, we start with a... Neutron and it decays into a proton. Then, we get our electron shooting a little bit, plus or anti-neutrino. So, our beta particle is that electron. If we actually do this in terms of quarks, we see that our neutron, which started as an up and two downs, changes into a proton, which is two ups and one down. And if we actually do that, if we do the comparison, you can see we actually have we went from a down to enough, so went from negative one to positive two-thirds. We've actually made a difference of one whole charge. That's why the electron has to be generated to balance the charge. We have to get our net charge of zero. We got to get our net change. We started with a neutron; we still better end up with a zero. So, even though using the quark idea, we've changed one of the quarks to go from a proton to a neutron. That's why the electron also has to be created to balance things out and invade a positive. It's just the opposite; we start with a proton, and it converts into a neutron and a positron. So if we do this, you can see the same sort of thing works out the same. Our proton was two ups and one down. Our neutron is one up and two downs. So we'd have, in this case, we're going from a positive one charge to a zero. So we end up having to have that extra positive one charge to make up for it. So the same sort of idea, we do a Down quark of negative one-third, we subtract a positive two-thirds, that ends up giving us that net charge of one. So we still end up with an overall charge of 0, which works. And we still have our neutrino (I didn't put that on there, but that would also exist). So the idea is With quarks, it kind of helps explain how the conversions work and to make sure we're still following the conservation of charge. We are now done with Physics 30, so there's no more lessons, nothing to do. So, we're pretty much done, except just a small thing called the Diploma exam. And that's it.