Technological Achievements of the Large Hadron Collider: Search for the Higgs Boson
Abstract: The Large Hadron Collider is a particle accelerator that produces gigantic amounts of energy in order to accelerate two beams of hydrogen protons until they are traveling at about
99% the speed of light. Once accelerated, the beams are injected into their respective tubes traveling in opposing directions until they collide at four distinct locations. After years of research and billions upon billions of these collisions, scientists have successfully discovered evidence of a particle that resembles the long sought-after Higgs boson, which is theorized to be the basic building block of everything in the universe. Its discovery and future implications are
discussed.
Introduction
Scientists all over the world have dedicated their lives to discovering how the universe was created. They are trying to answer life’s biggest riddles: How did life on Earth begin? What is dark matter? Are there more dimensions than the ones we can see? One question that has captured the wonder of scientists for years is from where did the universe originate? Today, the most widely accepted theory for the origins of the universe is described as the Standard Model of Particle Physics [1]. In the Standard Model, there are 12 elementary particles that interact with each other through four fundamental, unique forces: electromagnetic, strong, weak, and gravitational forces [1][2]. The first three forces are encompassed in the Standard Model. The last one, gravitational force, is important to us on a macroscopic level since larger masses feel the force of gravity more strongly. However, in the microscopic world where particle masses are miniscule, the force of gravity is negligible. Thus the Standard Model ignores this force [3].
Although gravity might be negligible, particle masses are not and figuring out how they gain mass is extremely important to building a more cohesive theory of the Standard Model. With the use of the Large Hadron Collider at CERN, the particle accelerator can help scientists explain why particles gain mass and how they engage each other.

Why We Need the Higgs
Since the Standard Model does not include the force of gravity in its explanation of how the atomic world is governed, scientists need an alternative force field to explain the way that particles interact. The Higgs boson serves as the solution to this dilemma. The Higgs boson is a neutral particle that comes with a corresponding Higgs field, both of which are the important part of the Standard Model [4]. Just as photons carry electromagnetic forces, the Higgs boson carries the Higgs field. The Higgs field is responsible for the addition of mass to particles with which it interacts. The more interactions a particle has with the Higgs field, the more massive it becomes [4]. This property of the Higgs field is important because even if no matter were present in the empty vacuum of space, the Higgs field would still be present, ready to impart mass to any particle accelerating through it [4][5].
Search for the Higgs Boson
Theoretically, the Higgs boson and field were the last missing piece of the cosmic puzzle that had the possibility to show us how everything from a beautiful, tiny hummingbird to the gas giant Jupiter came to existence. However, theories must be proved experimentally before scientists are able to offer answers to long debated physics questions. In order to conduct any experiment, the technological capabilities to do so must be available. In the case of the Higgs boson, particles must be collided with each other head-on. These collisions create debris in the form of other, smaller particles. Using advanced analytical machines, the Higgs boson could be discovered in the debris as a new particle. However, the challenge with finding the Higgs was the fact that it was not expected to exist for a long time after the collision due to its highly rapid

decaying nature [6]. In addition, debris from the resulting collisions also produces many other particles, making it even more difficult to identify the Higgs boson [2].
Although many challenges stood in the way of the scientists at the European Organization for
Nuclear Research, or CERN, they believed in the capabilities of the Large Hadron Collider. There were two ways that scientists could move forward with particle collisions: use a fixed target or use colliding beams. The former involves a beam of charged particles bombarding a target material made up of protons and neutrons. The latter involves accelerating proton beams of the same type and launching them towards each other on a sure fire collision course [2].To find the more efficient method, we must examine the energies involved, specifically the center-ofmass energy which is the total energy of both beams of particles “in a reference frame where they appear to approach each other with equal and opposite momenta.” [2]. The target fixed collider has center of mass energy of
𝐸 𝑐𝑚
= √2𝑀𝐸 while the beam accelerator has a center of mass energy of
𝐸 𝑐𝑚
= 2𝐸
[2]. Mathematically, it would be easier to increase the center of mass energy an order of magnitude higher using the beam accelerator. This was why a particle accelerator such as the
Large Hadron Collider was the best option for finding the Higgs boson.
How does the Large Hadron Collider work?

The Large Hadron Collider, or LHC, is a particle accelerator that collides two beams of protons at extremely high energies, operating at 7TeV [7]. On a macroscopic level, 1TeV is the energy it takes for a mosquito to fly around, so 7TeV is the amount of energy that a small swarm of mosquitoes expends. This may not seem like a great deal of energy, however, the LHC is able to contain all of this energy in a space that is less than the width of a human hair [10]. To keep the
LHC stable while squeezing this energy into such a small space, the machine itself must be huge. The circumference of the collider stands at 27 kilometers with the entire machine residing about 50-175 meters beneath Geneva near the Switzerland-France border [8]. Such giant chambers of the LHC are needed in order to accelerate the proton particles to high enough energies that collisions produce meaningful results. The luminosity of the LHC is also important, as it is basically the quantity that determines how many particle collisions occur per second. With a low luminosity, the possibility of a particle colliding with another particle is decreased and thus less debris is created through collisions. Higher luminosities increase the chances for particles to collide and therefore increase the creation of debris. For the LHC, the luminosity is approximately 10 34 𝑐𝑚 −2 𝑠 −1 , which roughly translates to almost a billion collisions per second [7]. With more collisions, the chance of the LHC particle detectors seeing the Higgs boson in existence before it decays into other lower energy particles increases, thus the chance of discovery is more likely.
In order to accelerate the proton beams to large enough energies, superconducting magnets are located throughout the 27 kilometer circumference of the LHC. The environment around the LHC must be near absolute zero such that outside gas particles do not interact with the

proton beams inside LHC rings. Thus the LHC is cryogenically cooled using liquid nitrogen and then liquid helium to reach temperatures colder than that of the vacuum of outer space [8].
Once the length of the LHC has been sufficiently cooled, experiments are ready to be conducted.
Scientists first strip hydrogen molecules of their electrons leaving only protons and neutrons.
The proton bunches are then accelerated to their “first stage” using a linear particle accelerator, LINAC 2, until they reach 50 MeV. These are then injected to the “second stage” called Proton Synchrotron Booster (PSB) which further accelerates the protons to 1.4 GeV. The
“third stage” occurs as the Proton Synchrotron (PS) takes the protons from the PSB and accelerates them to 26 GeV. Before finally injecting the protons to the main LHC ring, they pass through their “fourth stage,” the Super Proton Synchrotron, to be accelerated to a whopping speed of 450 GeV. Once injected into the final “fifth stage,” the main rings, the protons are accelerated to a maximum energy of 7TeV and sent on their collision course [8]. Accelerating protons in this “staged” manner allows for incremental increases in energy that would be difficult and would also make the process longer without it.
Analyzing billions of collisions per second is not only difficult, it is near impossible. However the
LHC contains four separate chambers where the collisions occur that make data analysis easier.
The four detectors within the LHC analyze a small amount of the collisions searching for specific parameters. Two of these detectors, known as the ATLAS and CMS detectors, are the biggest and are the ones responsible for the discovery of the Higgs boson.

Discovery of the Higgs Boson
After years of collecting data and witnessing billions upon billions of collisions, the day that scientists had been waiting for had finally arrived. On July 4, 2012, data from the ATLAS and
CMS detectors found that a new particle was detected around the energy level of 125 GeV [4].
Before scientists could claim that this was indeed the Higgs boson, they had to guarantee that this was not the result of some experimental fluke. In order to do so, scientists needed to be within five standard deviations of their result, meaning that the error for the existence of the particle is less than a 1 in a million chance [4][8]. For years the LHC had been collecting data, doubling since December 2011 with analytical methods becoming more efficient [11]. Slowly, previous experimental data of the energy range where the Higgs boson could be found revealed the energy range where the Higgs boson could exist [9]. Further experiments and data analysis from the ATLAS and CMS detectors concluded that this particle was definitely a Higgs boson in the range of 125 GeV, roughly within 5.9 standard deviations [8]. This five standard deviation level is the level that elementary particle physics considers a discovery [11]. Therefore, scientists were able to declare the discovery of the Higgs boson on July 4, 2012.
Future Implications
The discovery of this Higgs boson led scientists to a more cohesive theory of the Standard
Model. Although the discovery of a Higgs boson is a massive step forward towards finding a universal theory, there are still many more components that must be worked out. The LHC experiments found a particle that has all the qualities to be the Standard Model Higgs boson.
However, there are still many more factors that must be defined for the true Standard Model

Higgs boson, such as spin properties and how the particle decays [4]. Further experiments at the LHC will be able to determine these properties and more. Still, the Higgs boson is just the beginning. Many more experiments are left to uncover the physics behind more mysterious concepts such as the origins of dark matter and the revelation of more dimensions. For these questions, the LHC has only just begun finding answers. In the coming years, the experiments at the LHC will possibly uncover the true Higgs boson or shed light on the mystery of dark energy.
Whichever the case, the importance of the LHC’s contributions to the physics community cannot be denied and has re-fueled the excitement of scientists and the public alike.

References
[1] Wickham, Chris. “Unraveling the Higgs Particle.” Reuters, July 5, 2012
[2] Choudhury, Debajyoti and Mukhopadhyaya, Biswarup. “The Large Hadron Collider: Overall
Motivation.” Department of Physics and Astrophysics, University of Delhi
[3] CERN, “The Standard Model.” [Online]. Available: home.web.cern.ch/about/physics/standard-model
[4] Brumfiel, Geoff. “What is the Higgs” Nature pp. 148, July 12, 2012.
[5] Greene, Brian. “Waiting for the Higgs Particle.” New York Times 2011
[6] Luntz, Stephen. “The Hunt for the Higgs Boson.” Australasian Science pp. 40. 2014
[7] Virdee, T.S. “Physics requirements for the design of the ATLAS and CMS experiments at the
Large Hadron Collider.” Philosophical Transactions of the Royal Society A, 2012.
[8] Rhodes, Christopher J. “Large Hadron Collider (LHC).” Science Progress pp. 95. Spring 2013
[9] Bruning, Oliver, Chohana, Vinod and Chattopadhyay, Swapan. “Accelerator Physics and
Technological Challenges of the Large Hadron Collider.” CERN, Geneva, Switzerland. Cockcroft
Institute, United Kingdom.
[10] “LHC Glossary” [Online]. Available: http://lhc-machine-outreach.web.cern.ch/lhc-machineoutreach/lhc_glossary.htm.
[11] Rubakov, V. “Large Hadron Collider’s Discovery of a New Particle with Higgs Boson
Properties.” Physics of our Days pp. 55. 2012