 The experiment I work on, Atlas, has just announced the observation of the direct interaction between the Higgs particle and the bottom quark. Let's explore a little bit about how this was accomplished and what the implications of this observation actually are. Let's begin by looking at the building blocks of all matter in the universe, including things like planets and stars, you and me, hamsters, etc. There are six building blocks called quarks. The lightest of these is the up quark, followed by the down quark. These two form the first generation of quark matter. The second generation is composed of the charm and the strange quark. And the third generation of matter is composed of the top and the bottom quark. We'll come back to the bottom quark in a little bit. The up and the down quark are all you need to build a universe that looks like ours today. Up and down quarks are found in the heart of every atom, the nucleus of the atom in its protons and neutrons. The charm, strange top and bottom seem to have played a more important role in the very early universe, although they play a background role in the universe today. The other six building blocks of matter are known as the leptons. There's the electron neutrino and its counterpart, the electron. That's the first generation of the leptons. Then there's the muon neutrino and its counterpart, the muon. And finally, the tau neutrino and its counterpart, the tau lepton. The lightest leptons, the electron and the neutrino, they also play a role in atomic matter. Electrons are found orbiting the nucleus of every atom in the known universe. Neutrinos play a role in the destabilization of the nucleus of the atom, known as nuclear decay. The other two generations, including the muon and the muon neutrino, play more of a role in extreme high-energy physics in the modern cosmos, such as cosmic rays that rain down on Earth all the time, or especially in the very early universe when the universe was very young. Now, in order to understand the problem that we're trying to come to grips with, let's start by using the proton as kind of our meter stick for mass in the cosmos. Protons can be found in every atom in the known universe. Let's consider the simple hydrogen atom, which has one proton at the center, orbited by one electron around the outside. This is a familiar lightest element in the periodic table of the elements. Now, if we focus in on the proton, let's use the proton's mass, whatever it is, as a fundamental unit of mass in the universe. We'll call it one. So when I say 25, I mean 25 times the mass of the proton. When I say 0.5, I mean 0.5 times the mass of the proton. The proton is our meter stick for mass in the universe. Now, let's compare the mass of the proton to the mass of one of the quarks, the bottom quark, which is a quark I've studied for a very long time in various experiments. Now, the bottom quark is interesting, because it has a mass that's about four and a half times that of the proton. And yet, unlike the proton, which is made of things like up and down quarks, the bottom quark doesn't appear to be made of anything. It seems to be a fundamental building block of nature. So where does it get its mass, and why does it have so much? Well, in modern particle physics, we think that one answer to this question is the Higgs boson, or the Higgs particle. This is a special particle that was discovered in 2012, 2013. And we think that it's responsible for the masses of things like bottom quarks and up quarks and electrons and so forth. Now, the Higgs itself is very heavy, about 125 times the mass of the proton. And because of the laws of physics, that means it doesn't stick around very long when it's made. So you have to make these things first. They're very heavy, so that takes a lot of energy. And then you have to wait for them to do things, like have their energy fall apart into other things that you can see. Because a Higgs doesn't stick around long enough for you to actually see it. And now, a prediction of the standard model of particle physics, which is the best mathematical description of nature that we have, is the following. That a Higgs boson will live for a very short period of time, and then its energy will fall apart into a pair of a bottom quark and its antimatter counterpart, the anti-bottom or B-bar quark in the parlance of our field. Now, this is expected to happen according to the standard model of particle physics. 60% of the time, if you make a Higgs, 60% of the time it's expected to fall apart in exactly this way. Well, that should be easy to spot, right? Eh, not so much. Here's the challenge. Here is a mathematician's concept of a particle detector, some kind of instrument that when particles pass through it, it responds in a way that it allows you to see those particles passing through material. So let's say we make a Higgs boson by smashing two protons together. And 60% of the time, the Higgs boson is expected to fall apart into bottom quarks, which manifests as sprays of particles in a particle detector called jets. The problem is, whenever you smash two protons together, assuming you even make a Higgs boson, you don't only get a Higgs boson. Protons are made of lots of stuff. And often, lots of protons in one interaction will actually smash together into one another. And this makes something like an average of 15 jet objects in a particle detector at one time. So even in one proton-proton interaction cycle, you have a mess to sift through. Which are the jets that came from the Higgs? Can you even tell anymore? But that's not even the biggest problem. Because the fact of the matter is, is that smashing one pair of protons together is not enough to make a Higgs. The possibility of making a Higgs boson at the energies that the Large Hadron Collider operates by doing just that process is maybe one in a billion or so. Let's visualize a whole bunch of pictures of proton-proton interactions making jets. That happens a lot of the time. In fact, most of the time at the Large Hadron Collider, if I smash a pair of protons together, I'm gonna make jets. So let's imagine taking a whole bunch of images of protons smashing into each other and making lots and lots of jets. Okay, fine. So here I have about 100 such images. Which of these would contain a Higgs boson that came to a pair of bottom quark jets? Well, that's pretty hard to tell. And again, that's not even the worst of it. Because these roughly 100 pictures represent maybe one one hundred thousandth of a second of data taking at the Large Hadron Collider. And we collect data for roughly eight to nine months out of the year, usually in three-year bursts called runs. So you have a real problem on your hands. Sure, the Higgs boson falls apart into bottom quark jets 60% of the time, but most of what the Large Hadron Collider makes is jets. And so how are you going to find this needle in a haystack in all the haystacks in the Midwest of the United States? That's the problem that we face as physics analysts. So how do we actually look for this process? There are a couple of things we can do right off the bat. First of all, we can not look for just a Higgs boson being produced in proton-proton collisions. That Higgs boson would be produced all alone in a sea of jets. That's a pretty sad event. We're not going to see that very easily. So rather what we do is we look for the Higgs boson being produced along with some easy to detect friends. So spotting a friend alone in a big crowd is really hard. But if you know your friend is with another recognizable friend of yours, it'll be much easier to spot them in a big crowd. So we look for the Higgs boson being produced in partnership with other kinds of particles known as Zs or Ws, which have very distinctive fingerprints in particle detectors. And so this is much easier to spot, and that makes our game a lot easier to play. A second thing we can do is to focus on those jets that come from the bottom quarks themselves. It turns out that these jets actually have some very distinctive fingerprints in them that make them look quite different from other quark-initiated jets. And so we play this game of using computer algorithms and mathematical techniques to identify those bottom quarks. This is known as bottom quark tagging, or flavor tagging, comes in many little jargon terms. And the idea is that we use these distinctive characteristics of these jets to isolate them even in a sea of other jets in the same proton-proton collision event. And so now, if we do have an event that we think contains a Higgs and one of its friends, we can also look for evidence of those bottom quarks that it's decaying into. And finally, I think the most important thing that we can do is take advantage of the fact that we operate in large collaborations with a diversity of perspectives, people, talents, and abilities. And so one of the things that you can simply do is have a really talented and dedicated and hard-working team of physicists, graduate students, post-doctoral researchers, faculty, staff scientists, and so forth, who are willing to group together in teams of 5, 10, 15, 20, 30, 40 people and split up the work and come up with neat ideas to make this process a lot easier to spot. Now that can take years, and that's part of why it takes so long to do these measurements. But having that talented team with people focusing on advanced machine learning, people focusing on new and clever ways to identify bottom quarks or reduced backgrounds, that's the way that you can make real progress in this. And that's one of the things I'm very proud of in terms of the measurement that we've been able to make with this now. And so at the end of the day, after you've done all of your hard work, you basically do some counting. It's fancy counting, but you're counting. You look at events where you have identified bottom quark jets, you calculate the mass represented by a pair of bottom quark jets, and you expect that mass to accumulate at a value consistent with the Higgs mass, which is 125 times the proton mass. So you look for the number of candidate Higgs bosons decaying to be an anti-B quarks against the mass of that quark pair. And lo and behold, what we've observed is that there's a very distinctive bump or peak or rise at exactly the mass that the standard model would have predicted for this process to occur in this kind of event. And this is very exciting. And it's so distinctive now with the ability to reduce the background to this process and the amount of data that we've taken that we're very confident, better than 99.9994% confident or so, that we really have observed a direct interaction between the Higgs boson and the bottom quark. And this is very exciting because this is the biggest way that the Higgs falls apart in an experiment like ours at the Large Hadron Collider. And so it offers us a whole new potential window on the universe. It will give us some new insights into what happened just after the moment of the Big Bang that set the universe into motion in the first place. It will give us some idea about the structure and the details of the structure of matter in the very early universe, what laws were at play at that time. And if we look really closely at this process over the next decade or two, perhaps we'll even spot little deviations from what the standard model has predicted and we might spy new laws of nature lurking in the details of things that we expected to happen in the first place. So I invite you to stay tuned for more news from the Large Hadron Collider regarding the interaction and use of Higgs and bottom quarks. This is a very exciting time for Higgs physics at the Large Hadron Collider because not only have we discovered a new particle, we are beginning to really discover how much it interacts with its friends and the standard model and I think we can say with some confidence that the Higgs and the bottom quark are really besties forever in the universe.