Download The Large Hadron Collider, or LHC, is the most powerful particle

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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
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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
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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
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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)
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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
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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-
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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
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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.
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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#>.