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McKay 1 Kathleen McKay Mrs. Awde AOIT 2 7 May 2017 The Large Hadron Collider The Large Hadron Collider, or LHC, is the most powerful particle accelerator in the world. A project that was first conceived in the 1980s, its construction was finally completed in 2008. It was built by the European Organization for Nuclear Research (CERN), and is a part of the CERN accelerator complex just outside of Geneva, Switzerland. The primary function of this huge (27 km circumference) synchrotron (a ring-shaped particle accelerator) is to accelerate particles of matter called hadrons and collide them at extremely high energies. It uses over 9,600 magnets to create two beams of the hadrons and move them at just under light speed around the circle. The beams will then meet at six different sites around the collider and crash into one another. The results of these collisions are what the thousands of scientists at CERN will be looking at. No one is quite sure what will be revealed by these tests but scientists hope to witness events akin to those at the beginning of the universe, finding proof for, among other things, String Theory, Higgs boson particles and dark matter. The potential for this machine is only just being realized, with the first experiment having occurred in this past year. Although no profitable insights have yet resulted from this machine, the accelerator itself is impressive enough that it is already been recognized as a success. Even while its predecessor, the Large Electron-Positron Collider (LEP), was being built, the LHC had begun to emerge. Designed to occupy the 27km tunnel that was the LEP, the Large Hadron Collider would replace the previous collider as the more powerful, more modern McKay 2 machine. “To reach the highest possible collision energies and intensities, it was proposed to use two beams of protons for the new machine.” (Group) The LEP operated between 1989 and 2000. In that time the design for the LHC had been perfected and presented to the CERN Council for approval. In December 1994 the new project was made a priority. In 1995 enough contributions had been made by countries such as Japan, the USA, India, Russia and Canada, that the project was now able to proceed in a single phase as opposed to the two-step plan that had been originally green lighted in 1994. Between 1996 and 2008 the project slowly came together. The experiments ALICE, ATLAS, CMS, and LHCb were the first to be approved. TOTEM and LHCf were added on later. In 2001 and 2004 the EDG (European Data Grid project) and the EGEE (Enabling Grids for E-sciencE) were launched. These would become a world computing grid for science, which would connect tens of thousands of computers all over the world to process data gathered by the LHC. Finally in 2008 construction was complete and it opened on April 5th. Several technical problems (magnetic failures and a helium leak) prevented any experiments from being done until 2010 when it successfully collided two beams of protons. (Group) Some think that the LHC will destroy all life on Earth, others have a more optimistic outlook, thinking that it could reveal more about the Big Bang Theory, String Theory and the Standard Model. The Big Bang Theory basically states that the universe began as a singularity (a zone of infinite density) and it expanded and continues to expand to this day. According to this model all matter in the early universe was made up of atomic subparticles. These particles are created when protons break apart. Unfortunately they are extremely unstable and only exist for a fraction of a second. Fortunately they can be created and observed by the Large Hadron Collider, in effect allowing the birth of the universe to be observed and studied. Another nearly McKay 3 instantaneous aspect of the creation of the universe is antimatter. In the beginning there was matter and antimatter. Almost immediately, though, they annihilated each other. But for some reason there was more matter than antimatter and that left over matter survived to create the cosmos. This and dark matter (undetectable material that exists in space) could be observable for the first time with the aid of the Large Hadron Collider. Another theory that needs some proving is the Standard Model. The Standard Model is a theory that “tries to define and explain the fundamental articles that make the universe what it is.” (Strickland) Most of the proposals it makes have already been proven, but some, like the Higgs boson particle, have yet to be confirmed. The Higgs boson particle is the only particle mentioned in the Standard Model that has never been observed. If the LHC were to affirm their existence than the origin of mass would finally be explained. A more dubious principle that the LHC will be studying is String Theory. String Theory claims that the building block of the universe is not the commonly accepted particle but a string. For this to be true the existence of “no fewer than 11 dimensions” (Strickland) would be required (there are only four yet discovered). The Large Hadron Collider, in the pursuit of String Theory, could very well uncover evidence of these other dimensions. But mainly what String Theorists, and even those trying to fill the gaps in the Standard Model, are looking for is supersymmetry (basically that every particle has three counter-particles). All of these things, from the weird to the more reasonable, will be addressed by one or more of the LHC’s six different detectors. Around the circle that is the LHC there are six sites that will collect data and do experiments. The biggest of these is ATLAS, A Toroidal LHC ApparatuS. “It measures 46 meters long by 25 meters tall and 25 meters wide.” (Strickland) It is equipped with an inner tracker at its core, a calorimeter which surrounds the inner tracker and a moun spectrometer. The McKay 4 inner tracker can detect and analyze the momentum of the particles that pass by. The calorimeter measures the energy of the particles by absorbing them and will show the path that the particles take. The moun spectrometer will use charged particle sensors to measure the momentum of muons (particles that are too heavy to be caught by the calorimeter) by detecting fluctuations in the magnetic field. Similar to ATLAS there is CMS (Compact Moun Solenoid). They both are general purpose detectors for the subparticles released during collisions. This detector however is contained inside a solenoid magnet that creates a magnetic field almost 100,000 times stronger than the Earth’s. A Large Ion Collider Experiment (ALICE) is different in that it is meant to study the collisions of iron ions. ALICE has a moun spectrometer and additionally the Time Projection Chamber (TPC), which studies the particle trajectories. The LHCb (Large Hadron Collider beauty) is meant to search for antimatter or rather the beauty/bottom quark, which will provide evidence of the unseen antimatter. Around this collision site there are 20 meters of small detectors, which are able to move in precise ways to catch the elusive bottom quarks. Lastly there are the two significantly smaller sites, the TOTal Elastic and diffractive cross section Measurement (TOTEM) and the Large Hadron Collider forward (LHCf). TOTEM will measure the size of protons and how precisely the particle accelerator is producing collisions (its luminosity). LHCf will stimulate cosmic rays within a controlled environment in an attempt to devise experiments where scientists can observe naturally occurring ray collisions. The scientists who work at each of these stations will all be working on different projects and studying different data to try to find the answers to different problems. Although all working nearly independently, the thing that unifies them is accelerator itself, which is what makes each of their separate stations, run. (Strickland) McKay 5 100 meters below ground lies the Large Hadron Collider. This synchrotron (a ring-shaped particle accelerator) is 27km long and is designed to send two beams of particles in opposite directions around its circumference and collide them. Not exactly circular, the LHC is actually made up of eight arches and eight insertions. The insertions are long straight sections that control the coming and going of the particle beams. There are three kinds—injection, beam dumping and beam cleaning. These let beams in and out of the vacuum tube. “The LHC has the particularity of having not one but three vacuum systems.” (AB Department) The beam vacuum is the tube that the particles travel through. It is set up in order to prevent the beams from colliding prematurely with gases while they travel around the tube. There is also the insulation vacuum for cryomagnets and the insulation vacuum for the helium distribution line. Inside the vacuum tube are over 9,600 electromagnets of various types. The magnets serve as a guide for the particle beams into the collisions and through the insertions. Although there are an enormous variety of magnets the three main kinds are the dipole magnets, quadrupole magnets and accelerating cavities. The quadrupole magnets focus the beam to try to get the most particles into the smallest space possible to increase the chances of contact during the collision. The accelerating cavities use electromagnetic resonators to first accelerate the particles and then keep them at a constant speed, while compensating for energy losses. The most important magnets though are the dipole magnets. A feat that took incredible scientific reasoning, these magnets are the ones that keep the beams going in a circular motion. Made of niobium-titanium cables they are able to generate an incredible field of 8.33 T (Tesla, the unit for measuring the strength of magnets). Normally these magnets wouldn’t generate a strong enough field, at room temperature they only get to 6.38 T. So a cooling system had to be created to get the magnets cold enough to conduct electricity with zero resistance. Using 120 tons of super fluid helium, five cryogenic ‘islands’ pump the liquid to McKay 6 the 27 km of magnets, cooling them down to a record 1.9 K (-456.25º F). To get these magnets colder than outer space three steps must be taken over a few weeks. First the helium must be cooled to 80 K by using 10,000 tons of liquid nitrogen. Then it will be cooled down to 4.5 K by the refrigerator turbines, and injected into the magnets. Lastly, once the magnets are filled, the refrigeration units will continue to drop the temperature until it has reached a chilly 1.9 K. That is how the machine is set up and prepared. The particles still have a ways yet to go before they are ready to collide. The main function of the LHC is to send two beams of particles, one clockwise and one counterclockwise, around in a circle at 99% the speed of light and collide them. That sounds pretty simple, but to get those particles to the collision much must be done. Before you even begin to form any beams you must get the particles. Scientists do this by stripping electrons from hydrogen atoms to produce protons (or lead ions for some experiments). The protons then enter a machine called the LINAC 2 which will send them to another machine called the PS Booster. Using radio frequency cavities these machines accelerate the protons to form beams. At this point the radio-frequency electric fields from the cavities, give control over to the magnets. The beams are then directed to the Super Proton Synchotron (SPS) which continues to accelerate the beams but also divides them into bunches. There are 2808 bunches in a beam and 1.1 x 1011 protons in a bunch. Once the proper energy level has been reached the beams can finally be injected into the LHC. It takes about twenty minutes from there for the beams to reach a top speed of 11,245 trips around the LHC per second. Once that maximum is reached the beams will be positioned to collide at one of the six sites around the LHC where there will be 600 million collisions every second. What is produced from these collisions will vary. There could be quarks (subatomic particles), a gluon (mitigating force), photons (particles of light), positrons (the anti- McKay 7 particles to electrons) and muons (the negatively charged, heavier version of electrons). The particles that do not collide will continue on along the track and be directed into one of the beam dumping insertions. There are about 150 million sensors in the LHC. During the experiments there will be about 700 megabytes of data collected per second. It is estimated that a total of 15 petabytes will be collected yearly. The scientists realized that that much data would be too much for even the CERN Control Center to take on, so back when the construction of the LHC was underway another project was being set up. The LHC Computing Grid is a three tiered network of computers that divides the data gathered during experiments into chunks and sends it to tens of thousands of computers around the world to be separately, analyzed and then sent back to a centralized computer at CERN. To do this it uses a type of software called midware. “Tier 0 is CERN’s computing system, which will first process information and divide it into chunks for the other two tiers.” (Strickland) Tier 1 computers are at twelve sites in various countries. They receive the data over dedicated computer connections at a rate of 10 gigabytes per second and proceed to divide the information further before sending it off to the final tier. The job of Tier 2 is to process and analyze the small chunk of data it receives through a standard network connection from Tier 1. Once finished with that job, the computers, which are located at universities all over the world, will send the information back through the tiers so that it can arrive back at CERN to be properly studied. To keep all of this information safe CERN has decided to trust identification and authorization procedures rather than firewalls because of the sheer amount of data traffic that needs protecting. (Strickland) All in all the Large Hadron Collider is quite an amazing thing. Being the world’s first and best and biggest is not an easy feat. It took years of work and thousands of tons of materials to McKay 8 put it together. Going where no particle accelerator has gone before, the LHC is able to do experiments the likes of which hadn’t even been thought possible before its invention. The first collision, which happened in 2010, produced an astounding 7 trillion electronvolts (“One electronvolt is the energy needed to move an electron between two points with a potential difference of one volt.” (Cumalat)). In the coming years the LHC is expected to perform more such experiments and produce results that will help revolutionize physics. All around the world scientists are racing to make the next big discovery and it is to CERN that many turn to, looking for the evidence to change the world. McKay 9 Works Cited AB Department, AT Department, PH Department, SC. "CERN-Brochure-2009-003-Eng." February 2009. cdsmedia.cern.ch. 4 October 2010 <http://cdsmedia.cern.ch/img/CERNBrochure-2009-003-Eng.pdf>. Communications, Web. CERN- How the LHC Works. 2008. 4 October 2010 <http://public.web.cern.ch/public/en/LHC/HowLHC-en.html>. Cumalat, John P. Large Hadron Collider. 2010. 1 October 2010 <http://www.worldbookonline.com/student/article?id=ar750238&st=hadron+collider>. Group, Communication. LHC Milestones. 2008. 4 October 2010 <http://lhcmilestones.web.cern.ch/LHC-Milestones/LHCMilestones-en.html>. Strickland, Jonathan. How The Large Hadron Collider Works. 30 June 2008. 4 October 2010 <http://science.howstuffworks.com/science-vs-myth/everyday-myths/large-hadroncollider7.htm#>.