How the Large Hadron Collider Works

The Large Hadron Collider has made significant strides in revealing the secrets of our universe, including the discovery of the Higgs boson particle.

The Quest for the Higgs Boson

In an effort to understand our universe, its workings, and structure, scientists proposed a theory called the Standard Model. This theory attempts to define and explain the fundamental particles that constitute the universe.

It marries concepts from Einstein's theory of relativity with quantum theory and addresses three of the four basic forces of the universe: the strong nuclear force, weak nuclear force, and electromagnetic force. However, it does not tackle the effects of gravity, the fourth fundamental force.

The Standard Model has made several predictions about the universe. Thanks to the LHC, one of its major predictions, the existence of the Higgs boson particle, was confirmed in 2012. The Higgs boson is crucial in explaining why some elementary particles have mass. While neutrinos and certain other particles lack mass, the Higgs mechanism theorizes a particle and a corresponding force that account for mass in other particles.

The discovery of the Higgs boson via the LHC was a monumental step in validating this theory. With this discovery, scientists continue to probe the LHC for further insights and possibly information not yet contemplated.

Mysteries of Antimatter and Dark Matter

A­nother question scientists have about matter deals with early conditions in the universe. During the earliest moments of the universe, matter and energy coupled. Just after matter and energy separated, particles of matter and antimatter annihilated each other.

If there had been an equal amount of matter and antimatter, the two kinds of particles would have canceled each other out. But fortunately for us, there was a bit more matter than antimatter in the universe.

Scientists hope that they'll be able to observe antimatter during LHC events. That might help us understand why there was a minuscule difference in the amount of matter versus antimatter when the universe began.

Dark matter is another focal area for LHC research. Current knowledge suggests that the observable matter makes up about 4 percent of the universe's total content.

The motion of galaxies indicates a significant amount of unseen matter, termed dark matter, accounting for about 25 percent of the universe. The remaining is attributed to dark energy, a force believed to drive the universe's expansion.

Scientists are optimistic that further LHC experiments will shed light on these enigmatic components of our universe.

Big Bang on a Small Scale

By smashing protons together hard and fast enough, the LHC causes protons to break apart into smaller atomic subparticles. These tiny subparticles are very unstable and only exist for a fraction of a second before decaying or recombining with other subparticles.

But according to the Big Bang theory, all matter in the early universe consisted of these tiny subparticles. As the universe expanded and cooled, these particles combined to form larger particles like protons and neutrons.

The Multidimensional Universe and String Theory

If theoretical particles, antimatter and dark energy aren't unusual enough, some scientists believe that the LHC could uncover evidence of other dimensions.

We're used to living in a world of four dimensions: three spatial dimensions and time. But some physicists theorize that there may be other dimensions we can't perceive. Some theories only make sense if there are several more dimensions in the universe. For example, one version of string theory requires the existence of no fewer than 11 dimensions.

String theorists hope the LHC will provide evidence to support their proposed model of the universe. String theory states that the fundamental building block of the universe isn't a particle, but a string.

Strings can either be open ended or closed. They also can vibrate, similar to the way the strings on a guitar vibrate when plucked. Different vibrations make the strings appear to be different things. A string vibrating one way would appear as an electron. A different string vibrating another way would be a neutrino.

Some scientists have criticized string theory, saying that there's no evidence to support the theory itself. String theory incorporates gravity into the standard model — something scientists can't do without an additional theory. It reconciles Einstein's theory of general relativity with the Quantum Field Theory.

But there's still no proof these strings exist. They are far too small to observe and currently there's no way to test for them. That has lead to some scientists to dismiss string theory as more of a philosophy than a science.

Supersymmetry and the Search for Superpartners

String theorists hope that the LHC will change critics' minds. They are looking for signs of supersymmetry. According to the standard model, every particle has an anti-particle. For example, the anti-particle for an electron (a particle with a negative charge) is a positron.

Supersymmetry proposes that particles also have superpartners, which in turn have their own counterparts. That means supersymmetric particles have three counter-particles.

Although we've not seen any indication of these superpartners in nature, theorists hope that the LHC will prove they actually exist. Potentially, superparticles c­ould explain dark matter or help fit gravity into the overall standard model.

LHC Structure, Speed and Scale

The Large Hadron Collider is a massive and powerful machine. It consists of eight sectors. Each sector is an arc bounded on each end by a section called an insertion. The LHC's circumference measures 27 kilometers (16.8 miles) around. The accelerator tubes and collision chambers are 100 meters (328 feet) underground.

Scientists and engineers can access the service tunnel the machinery sits in by descending in elevators and stairways located at several points along the circumference of the LHC. CERN is building structures above ground where scientists can collect and analyze the data LHC generates.

The LHC uses superconducting magnets to steer beams of protons as they travel at 99.99 percent the speed of light. The magnets are very large, many weighing several tons. There are about 9,600 magnets in the LHC.

The magnets are cooled to a chilly 1.9 degrees Kelvin (minus 271.25 Celsius or minus 456.25 Fahrenheit). That's colder than the vacuum of outer space.

Speaking of vacuums, the proton beams inside the LHC travel through pipes in what CERN calls an "ultra-high vacuum." The reason for creating such a vacuum is to avoid introducing particles the protons could collide with before they reach the proper collision points. Even a single molecule of gas could cause an experiment to fail.

There are six areas along the circumference of the LHC where engineers will be able to perform experiments. Think of each area as if it were a microscope with a digital camera. Some of these microscopes are huge — the ATLAS experiment is a device that is 45 meters (147.6 feet) long, 25 meters (82 feet) tall and weighs 7,000 tons (5,443 metric tons) [source: ATLAS].

Data Collection and Energy Consumption

The LHC and the experiments connected to it contain about 150 million sensors. Those sensors will collect data and send it to various computing systems. According to CERN, the amount of data collected during experiments will be about 700 megabytes per second (MB/s).

On a yearly basis, this means the LHC will gather about 15 petabytes of data. A petabyte is a million gigabytes. That much data could fill 100,000 DVDs [source: CERN].

It takes a lot of energy to run the LHC. CERN estimates that the annual power consumption for the collider is about 600 gigawatt hours (MWh), "with a maximum of 650 GWh in 2012 when the LHC was running at 4 TeV."

What's Cooler Than Being Cool?

Why cool the magnets down to just above the temperature of absolute zero? At that temperature, the electromagnets can operate without any electrical resistance.

The LHC uses 10,800 tons (9,798 metric tons) of liquid nitrogen to cool the magnets down to 80 degrees Kelvin (-193.2 Celsius or -315.67 Fahrenheit). Then it uses about 60 tons (54 metric tons) of liquid helium to cool them the rest of the way [source: CERN].

The Journey of Protons in the LHC

The principle behind the LHC is pretty simple. First, you fire two beams of particles along two pathways, one going clockwise and the other going counterclockwise. You accelerate both beams to near the speed of light. Then, you direct both beams toward each other and watch what happens.

The equipment necessary to achieve that goal is far more complex. CERN's Large Hadron Collider is just one part of its overall particle accelerator facility. Before any protons or ions enter the LHC, they've already gone through a series of steps.

­Let's take a look at the life of a proton as it goes through the LHC process. First, scientists must strip electrons from hydrogen atoms to produce protons. Then, the protons enter the LINAC2, a machine that fires beams of protons into an accelerator called the PS Booster.

These machines use devices called radio frequency cavities to accelerate the protons. The cavities contain a radio-frequency electric field that pushes the proton beams to higher speeds. Giant magnets produce the magnetic fields necessary to keep the proton beams on track.

In car terms, think of the radio frequency cavities as an accelerator and the magnets as a steering wheel.

­Once a beam of protons reaches the right energy level, the PS Booster injects it into another accelerator called the Super Proton Synchotron (SPS). The beams continue to pick up speed.

By now, beams have divided into bunches. Each bunch contains 1.1 x 1011 protons, and there are 2,808 bunches per beam [source: CERN]. The SPS injects beams into the LHC, with one beam traveling clockwise and the other going counterclockwise.

Collisions, Discoveries, and Safety Measures

Inside the LHC, the beams continue to accelerate. This takes about 20 minutes. At top speed, the beams make 11,245 trips around the LHC every second.

The two beams converge at one of the six detector sites positioned along the LHC. At that position, there will be 600 million colliding protons per second [source: CERN].

When two protons collide, they break apart into even smaller particles. That includes subatomic particles called quarks and a mitigating force called gluon. Quarks are very unstable and will decay in a fraction of a second.

The detectors collect information by tracking the path of subatomic particles. Then the detectors send data to a grid of computer systems.

Not every proton will collide with another proton. Even with a machine as advanced as the LHC, it's impossible to direct beams of particles as small as protons so that every particle will collide with another one.

Protons that fail to collide will continue in the beam to a beam dumping section. There, a section made of graphite will absorb the beam. The beam dumping sections are able to absorb beams if something goes wrong inside the LHC. To learn more about the mechanics behind particle accelerators, take a look at How Atom Smashers Work.

More Particles

The events inside the LHC will also produce photons (the particles of light), positrons (anti-particles to electrons) and heavy particles called muons (negatively charged particles that are heavier than electrons).

The six areas along the circumference of the LHC that will gather data and conduct experiments are simply known as detectors. Some of them will search for the same kind of information, though not in the same way. There are four major detector sites and two smaller ones.

ATLAS

The ­detector known as A Toroidal LHC ApparatuS (ATLAS) is the largest of the bunch. It measures 46 meters (150.9 feet) long by 25 meters (82 feet) tall and 25 meters wide. At its core is a device called the inner tracker. The inner tracker detects and analyzes the momentum of particles passing through the ATLAS detector.

Surrounding the inner tracker is a calorimeter. Calorimeters measure the energy of particles by absorbing them. Scientists can look at the path the particles took and extrapolate information about them.

The ATLAS detector also has a muon spectrometer. Muons are negatively charged particles 200 times heavier than electrons. Muons can travel through a calorimeter without stopping — it's the only kind of particle that can do that.

The spectrometer measures the momentum of each muon with charged particle sensors. These sensors can detect fluctuations in the ATLAS detector's magnetic field.

CMS

The Compact Muon Solenoid (CMS) is another large detector. Like the ATLAS detector, the CMS is a general-purpose detector that will detect and measure the subparticles released during collisions. The detector is inside in a giant solenoid magnet that can create a magnetic field nearly 100,000 times stronger than the Earth's magnetic field [source: CMS].

ALICE

Then there's ALICE, which stands for A Large Ion Collider Experiment. Engineers designed ALICE to study collisions between ions of iron. By colliding iron ions at high energy, scientists hope to recreate conditions similar to those just after the big bang. They expect to see the ions break apart into a quark and gluon mixture.

A main component of the ALICE experiment is the Time Projection Chamber (TPC), which will examine and reconstruct particle trajectories. Like the ATLAS and CMS detectors, ALICE also has a muon spectrometer.

LHCb

Next is the Large Hadron Collider beauty (LHCb) detector site. The purpose of the LHCb is to search for evidence of antimatter. It does this by searching for a particle called the beauty quark.

A series of sub-detectors surrounding the collision point stretch 20 meters (65.6 feet) in length. The detectors can move in tiny, precise ways to catch beauty quark particles, which are very unstable and rapidly decay.

TOTal

The TOTal Elastic and diffractive cross section Measurement (TOTEM) experiment is one of the two smaller detectors in the LHC. It will measure the size of protons and the LHC's luminosity. In particle physics, luminosity refers to how precisely a particle accelerator produces collisions.

LHCf

Finally, there's the Large Hadron Collider forward (LHCf) detector site. This experiment simulates cosmic rays within a controlled environment. The goal of the experiment is to help scientists come up with ways to devise wide-area experiments to study naturally occurring cosmic ray collisions.

Each detector site has a team of researchers ranging from a few dozen to more than a thousand scientists. In some cases, these scientists will be searching for the same information. For them, it's a race to make the next revolutionary discovery in physics.

Oops!

Scientists had hoped to bring the LHC online in 2007, but a major magnet failure slowed things down. An enormous magnet built by Fermilab suffered a critical failure during a stress test.

Engineers determined that the failure stemmed from a design flaw that didn't take into account the enormous asynchronous stresses the magnets could endure.

Fortunately for researchers, engineers fixed the flaw fairly quickly. But another one in the form of a helium leak popped up.

The LHC Computing Grid and Data Management

With 15 petabytes of data (that's 15,000,000 gigabytes) gathered by the LHC detectors every year, scientists have an enormous task ahead of them. How do you process that much information? How do you know you're looking at something significant within such a large data set?

Even using a supercomputer, processing that much information could take thousands of hours. Meanwhile, the LHC continues accumulating even more data.

CERN's solution to this problem is the LHC Computing Grid. The grid is a network of computers, each of which can analyze a chunk of data on its own. Once a computer completes its analysis, it can send the findings on to a centralized computer and accept a new chunk of data.

As long as scientists can divide the data up into chunks, the system works well. Within the computer industry this approach is called grid computing.

The scientists at CERN decided to focus on using relatively inexpensive equipment to perform their calculations. Instead of purchasing cutting-edge data servers and processors, CERN concentrates on off-the-shelf hardware that can work well in a network.

Their approach is very similar to the strategy Google employs. It's more cost efficient to purchase lots of average hardware than a few advanced pieces of equipment.

Tiered Structure and Data Security

Using a special kind of software called midware, the network of computers is able to store and analyze data for every experiment conducted at the LHC. The computers organize the structure for the system into tiers:

A­ny Tier 2 site can access any Tier 1 site. The reason for that is to allow research institutions and universities the chan­ce to focus on spe­cific information and research.­

One challenge with such a large network is data security. CERN determined that the network couldn't rely on firewalls because of the amount of data traffic on the system. Instead, the system relies on identification and authorization procedures to prevent unauthorized access to LHC data.

Some people say that worrying about data security is a moot point. That's because they think the LHC will end up destroying the entire world.

Concerns and Theories Surrounding the LHC

The LHC allows scientists to observe as particles collide at an energy level far higher than any previous experiment. Some people worry that such powerful reactions could cause serious trouble for the Earth. In fact, a few people were so concerned that they filed a lawsuit against CERN in an attempt to delay the LHC's activation.

In March 2008, former nuclear safety officer Walter Wagner and Luis Sancho spearheaded a lawsuit filed in Hawaii's U.S. District Court. They claimed the LHC could potentially destroy the world [source: MSNBC].

What is the basis for their concerns? Could the LHC create something that could end all life as we know it? What exactly might happen?

One fear is that the LHC could produce black holes. Black holes are regions in which matter collapses into a point of infinite density. C

ERN scientists admit that the LHC could produce black holes, but they also say those black holes would be on a subatomic scale and would collapse almost instantly. In contrast, the black holes astronomers study result from an entire star collapsing in on itself. There's a big difference between the mass of a star and that of a proton.

Another concern is that the LHC will produce exotic particles called strangelets. One possible trait of strangelets is particularly worrisome. Cosmologists theorize that strangelets could possess a powerful gravitational field that might allow them to convert the entire planet into a lifeless hulk.

Scientists at LHC dismiss this concern using multiple counterpoints.

Another theoretical particle the LHC might generate is a magnetic monopole. Theorized by P.A.M. Dirac, a monopole is a particle that holds a single magnetic charge (north or south) instead of two. The concern Wagner and Sancho cited is that such particles could pull matter apart with their lopsided magnetic charges.

CERN scientists disagree, saying that if monopoles exist, there's no reason to fear that such particles would cause such destruction. In fact, at least one team of researchers is actively looking for evidence of monopoles with the hopes that the LHC will produce some.

Safety Measures and the Natural Occurrence of Collisions

Other concerns about the LHC include fears of radiation and the fact that it will produce the highest energy collisions of particles on Earth. CERN states that the LHC is extremely safe, with thick shielding that includes 100 meters (328 feet) of earth on top of it. In addition, personnel are not allowed underground during experiments.

As for the concern about collisions, scientists point out that high-energy cosmic ray collisions happen all the time in nature. Rays collide with the sun, moon and other planets, all of which are still around with no sign of harm. With the LHC, those particle collisions will happen within a controlled environment. Otherwise, there's really no difference.

Will the LHC succeed in furthering our knowledge about the universe? Will the data collected raise more questions than it answers? If past experiments are any indication, it's probably a safe bet to assume the answer to both of these questions is yes.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.

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