Particle physics experiments

CERN: organization, experiments and facts

CERN is the European particle physics laboratory located near Geneva in Switzerland. If you see a headline about new, exotic subatomic particles, chances are the discovery was made at CERN. A recent example occurred in January 2022, when scientists at CERN announced “evidence of X particles in the quark-gluon plasma produced in the Large Hadron Collider (LHC)”, according to MIT News.

Behind this techno chatter hides the startling fact that CERN has succeeded in recreating a situation that did not occur naturally for a few microseconds after the Big Bang. This particular study was based on pre-existing LHC data.

The Atom Breaker

The LHC is a particle accelerator, a device that propels subatomic particles to enormous energies in a controlled way, so scientists can study the resulting interactions, according to CERN.

The “large” that the L represents is an understatement; the LHC is by far the largest accelerator in the world, occupying a circular tunnel about 16.7 miles (27 kilometers) in circumference.

The middle letter, H, stands for “hadron” – the generic name for composite particles such as protons which are made up of smaller particles called quarks. Finally, the C stands for ‘collider’ – because the LHC accelerates two beams of particles in opposite directions, and all the action takes place when the beams collide.

Like all physics experiments, the goal of the LHC is to test theoretical predictions – in this case, the so-called Standard Model of particle physics – and see if there are any holes in them, as Live Science previously reported. Strange as it may sound, physicists are eager to find some holes in the Standard Model because there are some things, like dark matter and dark energy, that can’t be explained until they do. .

The LHC opened in 2009, but CERN’s history goes back much further than that. The first stone was laid in 1955, following a recommendation from the European Council for Nuclear Research – or “Conseil Européen pour la Recherche Nucléaire” in French, from which it takes its name, according to CERN.

Between its creation and the opening of the LHC, CERN has made a series of groundbreaking discoveries, including weak neutral currents, light neutrinos and W and Z bosons. , we can expect these discoveries to continue, according to CERN.

Inside the LHC

The Large Hadron Collider is currently closed for maintenance, which has created an opportunity to provide public access. (Image credit: Ronald Patrick/Stringer/Getty Images)

CERN experiments

One of the main mysteries of the universe is why it apparently contains so much more matter than antimatter. According to the Big Bang theory, the universe must have started with equal amounts of both.

Yet very early on, probably within the first second of the universe’s existence, virtually all antimatter was gone, and only the normal matter we see today remained. This asymmetry has been given the technical name of CP violation and its study is one of the main objectives of the LHCb experiment at the Large Hadron Collider.

All hadrons are made of quarks, but LHCb is designed to detect particles that include a particularly rare type of quark known as beauty. According to CERN, studying CP violation in particles containing beauty is one of the most promising ways to shed light on the emergence of matter-antimatter asymmetry in the early universe.

climate science

Apart from the LHC, other CERN facilities carry out important research. An experiment at CERN’s proton synchrotron links particle physics to climate science. It is a smaller and less sophisticated accelerator than the LHC, but it is still capable of doing useful work.

A CLOUD experiment scientist

One of the project scientists inside the CLOUD experiment chamber. (Image credit: CERN)

The climate experiment is called CLOUD, which stands for “Cosmics Leaving Outdoor Droplets”. It has been theorized that cosmic rays play a role in cloud formation by seeding tiny water droplets around the Earth.

It’s not an easy process to study in the real atmosphere, with real cosmic rays, which is why CERN uses the accelerator to create its own cosmic rays. These are then fired into an artificial atmosphere, where their effects can be studied much more closely.

Exotic Particle Hunt

Sharing the same underground cavern as LHCb is a smaller instrument called MoEDAL, which stands for Monopole and Exotics Detector at LHC. While most CERN experiments are designed to study known particles, this one aims to discover undiscovered particles that lie outside the current Standard Model.

A monopole, for example, would be a magnetized particle consisting of only a north pole with no south pole, or vice versa. Such particles have long been assumed, but never observed. The purpose of MoEDAL is to search for monopoles that could be created during collisions inside the LHC, according to CERN.

This experiment could also potentially detect some stable massive particles that are predicted by theories beyond the Standard Model. If it succeeds in finding one of these particles, MoEDAL could help answer fundamental questions such as the existence of other dimensions or the nature of dark matter.

MoEDAL illustration

The MoEDAL experiment is located in the same cavern as LHCb. (Image credit: CERN)

make antimatter

Antimatter often appears in CERN’s high-energy accelerators as one half of a particle-antiparticle pair. But in the usual course of events, antiparticles don’t last long before they are annihilated in collisions with ordinary particles. If you want to create antimatter that sticks around long enough for detailed study, you need more than just an accelerator.

This is where the CERN antimatter factory comes in.

It takes antiparticles created in the proton synchrotron and slows them down to manageable speeds in what is effectively the exact opposite of a particle accelerator: the antiproton decelerator, according to CERN.

The resulting anti-atoms can then be studied by a range of instruments such as AEGIS (Antihydrogen Experiment: Gravity, Interferometry and Spectroscopy). One question that AEGIS should be able to answer soon is the intriguing question of whether antimatter falls downwards in a gravitational field, like ordinary matter, or upwards in the opposite direction.

AEGIS Experience

AEGIS uses electromagnets to trap antimatter so that it does not annihilate upon contact with ordinary matter. (Image credit: CERN)

Is CERN dangerous?

Over the years, for various reasons, people have speculated that experiments at CERN could pose a danger to the public. Fortunately, such worries are unfounded. Take for example the N of CERN, which stands for nuclear, according to the public body UK Research and Innovation (UKRI).

It has nothing to do with the reactions that occur inside nuclear weapons, which involve the exchange of protons and neutrons inside nuclei. CERN’s research lies at an even lower level, in the constituents of protons and neutrons themselves. This is sometimes referred to as “high energy” physics, but energies are only “high” when viewed on a subatomic scale.

Particles inside the LHC, for example, usually only have the energy of a mosquito, according to the official CERN website. People also feared that the LHC might produce a mini black hole, but even if it did – which is unlikely – it would be incredibly small and so unstable that it would disappear in a fraction of a second, according to the The Guardian.

Interview with a CERN scientist

Portrait of Dr. Clara Nellist

Dr Clara Nellist standing next to the ATLAS detector at CERN. (Image credit: Clara Nellist)

We spoke to CERN scientist Clara Nellist about her work with the LHC’s ATLAS detector, one of the LHC’s two main general-purpose detectors.

How did you come to participate in the ATLAS experiment?

“I started on ATLAS for my doctoral research. I was developing new pixel sensors to improve the measurement of particles as they pass through our detector. It’s really important to make them resistant to radiation damage, which is a big concern when placing the sensors close to particle collisions.

Since then, I have had the opportunity to work on several different projects, such as understanding how the Higgs boson and the top quark interact. Now I apply machine learning algorithms to our data to search for dark matter clues. One of the biggest mysteries in physics right now is: what is 85% of the matter in our universe? We call it dark matter, but we don’t know much about it!”

How is it to work with such a unique and powerful machine?

“It’s really amazing to be able to work on this incredibly complicated machine with people from all over the world. No one can make everything work, so each team becomes an expert on their specific part. Then when we all work together, we can do discoveries about the smallest building blocks of our universe.”

Are there any exciting new developments that you are particularly looking forward to?

“We’re starting the Large Hadron Collider again this year, so I’m really excited to see what we might find with it. Part of our job is to understand the particles we already know in as much detail as possible to verify that our theories match what we’re measuring. But we’re also looking for brand new particles that we’ve never seen before. If we find anything new, it could be a candidate for dark matter, or it could be something completely unexpected !”

Additional Resources

For more information about CERN and the LHC, visit their website. See also “A Day at CERN: A Guided Tour at the Heart of Particle Physics”, by Gautier Depambour and “Large Hadron Collider Manual (Haynes Manuals)” by Gemma Lavender.

Bibliography

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  • Matthew Sparks, “Preview 2022: The Large Hadron Collider will reach the limits of physics”, New Scientist, December 2021.
  • Micho Kaku, “The end of the world as we know it?”, The Guardian, June 2008.
  • UK Research and Innovation, “Facilities and Resources”, January 2022.
  • CERN, “Where it all started?”, accessed April 2022.
  • CERN, “Facts and figures about the LHC”, accessed April 2022.
  • CERN, “LHC Safety”, accessed April 2022.
  • CERN, “LHCb”, accessed April 2022.
  • CERN, “MoEDAL-MAPP”, accessed April 2022.
  • CERN, “MoEDAL-MAPP Experiment”, accessed April 2022.
  • Ana Lopes, “LHCb sees a new form of matter-antimatter asymmetry in strange beauty particles”, CERN, October 2020.