Beauty Quarks (Harry Cliff) | AI Podcast Clips
00:00:00.000 | So I work on a detector called LHCb, which is one of these four big detectors that are
00:00:05.640 | spaced around the ring. We do slightly different stuff to the big guys. There's two big experiments
00:00:11.360 | called ATLAS and CMS, 3,000 physicists and scientists and computer scientists on them
00:00:16.680 | each. They are the ones that discovered the Higgs and they look for supersymmetry in dark
00:00:20.200 | matter and so on. What we look at are standard model particles called bquarks, which depending
00:00:26.360 | on your preferences, either bottom or beauty. We tend to say beauty because it sounds sexier.
00:00:33.320 | But these particles are interesting because we can make lots of them. We make billions
00:00:39.360 | or hundreds of billions of these things. You can therefore measure their properties very
00:00:43.800 | precisely. So you can make these really lovely precision measurements. And what we are doing
00:00:49.060 | really is a sort of complementary thing to the other big experiments, which is, if you
00:00:54.840 | think of the analogy that I often use is, if you imagine you're in the jungle and you're
00:00:58.680 | looking for an elephant, say, and you are a hunter. Let's say the elephant is very rare,
00:01:06.280 | you don't know where in the jungle, the jungle is big. So there's two ways you go about this.
00:01:09.520 | Either you can go wandering around the jungle and try and find the elephant. The problem
00:01:13.200 | is if there's only one elephant and the jungle is big, the chances of running into it are
00:01:16.440 | very small. Or you could look on the ground and see if you see footprints left by the
00:01:21.840 | elephant. And if the elephant's moving around, you've got a chance, you've got a better chance
00:01:24.720 | maybe of seeing the elephant's footprints. If you see the footprints, you go, "Okay,
00:01:28.200 | there's an elephant. I maybe don't know what kind of elephant it is, but I got a sense
00:01:31.840 | there's something out there." So that's sort of what we do. We are the footprint people.
00:01:36.920 | We're looking for the footprints, the impressions that quantum fields that we haven't managed
00:01:42.520 | to directly create the particle of, the effects these quantum fields have on the ordinary
00:01:47.240 | standard model fields that we already know about. So these B particles, the way they
00:01:51.980 | behave can be influenced by the presence of say super fields or dark matter fields or
00:01:56.720 | whatever you like. And the way they decay and behave can be altered slightly from what
00:02:01.600 | our theory tells us they ought to behave.
00:02:04.280 | - Gotcha. And it's easier to collect huge amounts of data on B quarks.
00:02:09.280 | - We get billions and billions of these things. You can make very precise measurements. And
00:02:13.400 | the only place really at the LHC or in really in high energy physics at the moment where
00:02:18.080 | there's fairly compelling evidence that there might be something beyond the standard model
00:02:23.640 | is in these B, these beauty quarks decays.
00:02:28.200 | - Just to clarify, what is the difference between the four experiments, for example,
00:02:33.520 | that you mentioned? Is it the kind of particles that are being collided? Is it the energies
00:02:38.160 | at which they're collided? What's the fundamental difference between the different experiments?
00:02:43.220 | - The collisions are the same. What's different is the design of the detectors. So Atlas and
00:02:48.720 | CMS are called, they're called what are called general purpose detectors. And they are basically
00:02:53.160 | barrel shaped machines and the collisions happen in the middle of the barrel and the
00:02:57.400 | barrel captures all the particles that go flying out in every direction. So in a sphere
00:03:01.320 | effectively that can fly out and it can record all of those particles.
00:03:04.880 | - And what's the, sorry to be interrupting, but what's the mechanism of the recording?
00:03:09.800 | - Oh, so these detectors, if you've seen pictures of them, they're huge. Like Atlas is 25 meters
00:03:15.500 | high and 45 meters long. They're vast machines, instruments I guess you should call them really.
00:03:22.420 | They are, they're kind of like onions. So they have layers, concentric layers of detectors,
00:03:28.340 | different sorts of detectors. So close into the beam pipe, you have what are called usually
00:03:32.460 | made of silicon, they're tracking detectors. So they're little, made of strips of silicon
00:03:36.300 | or pixels of silicon. And when a particle goes through the silicon, it gives a little
00:03:39.940 | electrical signal and you get these dots, you know, electrical dots through your detector,
00:03:43.700 | which allows you to reconstruct the trajectory of the particle. So that's the middle. And
00:03:47.500 | then the outsides of these detectors, you have things called calorimeters, which measure
00:03:50.740 | the energies of the particles. And then very edge, you have things called muon chambers,
00:03:55.380 | which basically met these muon particles, which are the heavy version of the electron.
00:03:59.420 | They are, they're like high velocity bullets and they can get right to the edge of the
00:04:02.620 | detectors. If you see something at the edge, that's a muon. So that's broadly how they
00:04:06.580 | work.
00:04:07.580 | And all of that is being recorded.
00:04:08.580 | That's all being fed out to, you know, computers.
00:04:10.580 | That data must be awesome. Okay.
00:04:13.020 | So LHCb is different. So we, because we're looking for these be quarks, be quarks tend
00:04:18.140 | to be produced along the beam line. So in a collision, the be quarks tend to fly sort
00:04:23.540 | of close to the beam pipe. So we built a detector that sort of pyramid cone shaped basically,
00:04:29.220 | that just looks in one direction. So we ignore, if you have your collision stuff goes everywhere.
00:04:33.780 | We ignore all the stuff over here and going off sideways. We're just looking in this little
00:04:37.500 | region close to the beam pipe where most of these be quarks are made.
00:04:41.500 | So is there a different aspect of the sensors involved in the collection of the be quark?
00:04:49.300 | Yeah, there are some differences. So one of the differences is that one of the ways, you
00:04:54.180 | know, you've seen a be quark is that be quarks are actually quite long lived by particle
00:04:58.180 | standards. So they live for 1.5 trillionths of a second, which is if you're, if you're
00:05:02.420 | a fundamental particle is a very long time. Cause you know, the Higgs boson, I think lives
00:05:06.540 | for about a trillionth of a trillionth of a second, or maybe even less than that. So
00:05:11.460 | these are quite long lived things and they will actually fly a little distance before
00:05:15.540 | they decay. So they will fly, you know, a few centimeters, maybe if you're lucky, then
00:05:19.220 | they'll decay into other stuff. So what we need to do in the middle of the detector,
00:05:23.180 | you want to be able to see you have your place where the protons crash into each other and
00:05:27.420 | that produces loads of particles that come flying out. So you have loads of lines, loads
00:05:30.980 | of tracks that point back to that proton collision. And then you're looking for a couple of other
00:05:35.700 | tracks, maybe two or three that point back to a different place. That's maybe a few centimeters
00:05:39.740 | away from the proton collision. And that's the sign that a little be particle has flown
00:05:44.260 | a few centimeters and decayed somewhere else. So we need to be able to very accurately resolve
00:05:49.540 | the proton collision from the be particle decay. So we are, the middle of our detector
00:05:53.980 | is very sensitive and it gets very close to the collision. So you have this really beautiful,
00:05:58.780 | delicate silicon detector that sits, I think it's seven mil millimeters from the beam.
00:06:05.260 | And the LHC beam has as much energy as a jumbo jet at takeoff. So it's enough to melt a ton
00:06:09.180 | of copper. So you have this furiously powerful thing sitting next to this tiny, delicate,
00:06:13.660 | you know, silicon sensor. So those aspects of our detector that are specialized to measure
00:06:21.260 | these particular be quarks that we're interested in.
00:06:23.820 | - And is there, I mean, I remember seeing somewhere that there's some mention of matter
00:06:27.300 | and antimatter connected to the be, these beautiful quarks. Is that, what's the connection?
00:06:35.220 | Yeah, what's the connection there?
00:06:38.380 | - Yeah, so there is a connection, which is that when you produce these be particles,
00:06:44.980 | these particles, because you don't see the be quark, you see the thing that be quark
00:06:47.580 | is inside. So they're bound up inside what we call beauty particles, where the be quark
00:06:51.420 | is joined together with another quark or two, maybe two other quarks, depending on what
00:06:55.180 | it is. There are a particular set of these be particles that exhibit this property called
00:07:01.380 | oscillation. So if you make a, for the sake of argument, a matter version of one of these
00:07:06.820 | be particles, as it travels, because of the magic of quantum mechanics, it oscillates
00:07:12.820 | backwards and forwards between its matter and antimatter versions. So it does this weird
00:07:17.380 | flipping about backwards and forwards. And what we can use this for is a laboratory for
00:07:21.940 | testing the symmetry between matter and antimatter. So if the symmetry between antimatter is precise,
00:07:28.500 | it's exact, then we should see these be particles decaying as often as matter as they do as
00:07:33.980 | antimatter because this oscillation should be even. It should spend as much time in each
00:07:37.580 | state. But what we actually see is that one of the states it spends more time in, it's
00:07:43.060 | more likely to decay in one state than the other. So this gives us a way of testing this
00:07:47.820 | fundamental symmetry between matter and antimatter.
00:07:50.940 | [END]
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