The LHC Experiments

Big questions require big answers, and occasionally, very big scientific facilities. Among the very largest of the scientific facilities ever built is the Large Hadron Collider or LHC. The LHC is a particle accelerator, fully 27 kilometers in circumference. It accelerates two beams of protons to nearly the speed of light and collides them together. I made a different video that tells about this incredible piece of technology. In 2012, my colleagues and I announced that we discovered the Higgs boson using the LHC. This particle, which was the last unconfirmed prediction of the Standard Model of particle physics and an accomplishment that took nearly half a century to achieve. If you’re watching this video, you’ve almost certainly heard reporters say things like “LHC scientists discover the Higgs boson.” However, even as amazing as the LHC is, it’s not the entire story. Being able to accelerate particles with the LHC is a crucial capability, but until you can record the outcome of the collisions, you really aren’t doing science the science that the accelerator was built to do. To capture these collisions, you need to use particle detectors. I made an earlier video about how particle detectors work, but in this video I want to talk about the specific detectors at the LHC. There are four main detectors at the LHC, each with unique capabilities. Each one is basically a huge camera that can study millions or billions of particle collisions per second. The four detectors are called ALICE, ATLAS, CMS and LHCb. ATLAS and CMS are the ones involved in the discovery of the Higgs boson, while the other two are specialty detectors. So let me tell you a little bit about each one in turn. ALICE (sometimes pronounced Alice) stands for A Large Ion Collider Experiment and is designed to study what happens when you collide two nuclei of lead together. It is 26 meters long and 16 meters high and weighs 10,000 tonnes. It takes about 1,500 physicists from 154 institutes and 37 countries to perform. Its purpose is to study a new state of matter, called a quark gluon plasma, in which matter is heated to 100,000 times hotter than the center of the sun- hot enough to literally melt protons and neutrons at the center of atoms. Conditions like these were last common in the universe about a millionth of a second after the Big Bang. The LHCb experiment is quite different. Its core purpose is to understand why the universe is made of 100% matter when our best understanding of the early moments of the universe say that matter and antimatter were made in equal quantities. It weighs about 4,500 tonnes. About 700 scientists, representing 69 universities and laboratories from 17 countries are involved. The name LHCb means LHC beauty, as beauty is an older name of a heavy and unstable quark. While that name is, well, beautiful, it is now more commonly called the bottom quark. It is thought that studying this ephemeral particle is the most promising way to shed light on this puzzling asymmetry between matter and antimatter. The ATLAS and CMS experiment are more similar in their fundamental goal. These two detectors are designed to record collisions between beams of protons at a collision energy of fourteen trillion electron volts. The energy densities in these collisions haven’t been common since the universe was less than a trillionth of a second old. Collisions occur at a rate of a billion times a second and these detectors inspect every single collision before recording only about a thousand select collisions each second. You may have heard that the LHC is colliding beams at 13 trillion electron volts, but that’s just to ensure that we can run the accelerator reliably. It also means that when we have more experience with the machine that we might still squeeze out another 7% or so more energy. The ATLAS experiment is physically the largest particle experiment ever built. Its name is an acronym for A Toroidal LHC ApparatuS. It is 45 meters long, more than 25 meters high and weighs about 7,000 tonnes. It’s about half as big as the Notre Dame Cathedral in Paris and it weighs the same as the Eiffel Tower. It involves over 3,000 scientists from about 180 universities and laboratories from 38 countries. More than a thousand Ph.D. students do their research using this detector. The Compact Muon Solenoid Experiment or CMS has some significant commonalities with ATLAS, but looks different in detail. For one thing, it is more massive, weighing 14,000 tonnes or about twice the weight of the Eiffel Tower. It is 22 meters long and about 15 meters in diameter. The detector consists of about 100 million individual elements. Like ATLAS, CMS requires 3,000 scientists to design, build and operate, from 182 institutions drawn from 42 countries all around the world. The solenoid from which the experiment draws its name is one of the biggest and strongest magnets in the world, at 6 meters wide and 13 meters long, with a field of 80,000 times that of the Earth and containing energy equivalent to about half a ton of TNT. These four experiments are crucial to the mission of the LHC. The Large Hadron Collider may provide collisions, but without these four experiments, there would be no LHC science. So you might be asking yourself which of the experiments is the best and most important. Unfortunately- or perhaps fortunately- there is no answer to that question. Each of the four detectors is exquisitely designed to answer difficult questions and each is truly a marvel of technology. It would be totally inappropriate of me to indicate that I have a favorite. Totally inappropriate. Not gonna do it. The research program at the LHC will fascinate science enthusiasts for the next couple of decades. The discovery of the Higgs boson was just the beginning of an ambitious research program, but the LHC experiments will make many more groundbreaking measurements. It may well be that these experiments will make discoveries that completely overturn what we think we know about matter and energy, teaching us something new and fundamental about the universe. As in all things, time will tell.

Channel: Fermilab

Views: 41,550

Keywords: physicist, proof, CMS, metaphor, scientist, Large Hadron Collider, Compact Muon Solenoid, example, Ian Krass, A Large Ion Collider Experiment, learn, Don Lincoln, educational, ALICE, CERN, particle, LHC, LHCb, particle detectors, Physics, discovery, A Toroidal LHC ApparatuS, explained, ATLAS, funny, Fermilab, physics, science, foam finger, higgs, boson, accelerator, detector, camera, huge, collisions, experiment, collide, amazing, technology, matter, quark, gluon, plasma, atoms, subatomic, big bang, universe, machines

Id: X3tvgyrb2X4

Length: 6min 54sec (414 seconds)

Published: Thu Mar 12 2015