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Explained: What is the Large Hadron Collider, now poised to seek answers to fundamental questions in particle physics?

The world’s most powerful particle accelerator, the Large Hadron Collider (LHC), will begin smashing protons into each other with unprecedented energy from July 5.

Scientists will record and analyze the data expected to provide evidence of “new physics” — or physics beyond the Standard Model of particle physics, which explains how the basic building blocks of matter governed by four fundamental forces interact .


The Large Hadron Collider is a vast, complex machine built to study particles, which are the smallest known building blocks of all things.

Structurally, it is a 27 km loop of track buried 100 meters underground on the Swiss-French border. In operation, it shoots two proton beams in opposite directions at almost the speed of light in a ring of superconducting electromagnets.

The magnetic field created by the superconducting electromagnets keeps the protons in a taut beam and guides them along the path as they travel through beam tubes and eventually collide.

“Immediately before the collision, a different type of magnet is used to push the particles closer together to increase the likelihood of collisions. The particles are so tiny that the task of making them collide is like firing two needles 10 km apart, so precisely that they meet halfway,” according to the European organization for Nuclear research (originally Conseil Européen pour la Recherche Nucléaire or CERN). in French), which operates the particle accelerator complex that houses the LHC.

Because the LHC’s powerful electromagnets carry almost as much current as lightning, they need to be cooled. The LHC uses a liquid helium distribution system to keep its critical components ultracold at minus 271.3 degrees Celsius, which is colder than interstellar space. Given these requirements, it is not easy to warm up or cool down the gigantic machine.

Last upgrade

Three years after it was shut down for maintenance and upgrades, the collider was turned back on this April. This is the third run of the LHC, and starting Tuesday, it will operate 24/7 for four years at unprecedented energy levels of 13 teraelectronvolts. (A TeV is 100 billion, or 10 to the power of 12 electron volts. An electron volt is the energy imparted to an electron by accelerating it through an electrical potential difference of 1 volt.)

“Our goal is to deliver 1.6 billion proton-proton collisions per second for the ATLAS and CMS experiments,” said CERN’s director of accelerators and technology, Mike Lamont, according to an AFP report. This time, the proton beams will be narrowed to less than 10 microns — a human hair is about 70 microns thick — to increase the collision rate, he said.

(ATLAS is the largest general-purpose particle detector experiment at the LHC; the Compact Muon Solenoid (CMS) experiment is one of the largest international scientific collaborations in history, with the same goals as ATLAS but with a different magnet system design. )

Previous Runs & Discovery of “God Particle”.

Ten years ago, on July 4, 2012, scientists at CERN announced to the world the discovery of the Higgs boson, or “God particle,” during the first run of the LHC. The discovery ended decades of searching for the “force-bearing” subatomic particle and proved the existence of the Higgs mechanism, a theory put forward in the mid-1960s.

This led to Peter Higgs and his collaborator François Englert being awarded the Nobel Prize in Physics in 2013. The Higgs boson and associated energy field are believed to have played a crucial role in the formation of the universe.

The second run of the LHC (Run 2) began in 2015 and lasted through 2018. The second season of data collection produced five times more data than Run 1.

In the third run there are 20 times more collisions compared to run 1.

“New Physics”

Following the discovery of the Higgs boson, scientists have begun using the data collected as a tool to look beyond the Standard Model, which is currently the best theory of the universe’s most elementary building blocks and their interactions.

Scientists at CERN say they don’t know what Run 3 will reveal; the collisions should be used to deepen the understanding of the so-called “dark matter”.

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This elusive, hoped-for particle is believed to make up most of the universe but is completely invisible as it does not absorb, reflect or emit light.

Luca Malgeri, a scientist at CERN, told Reuters: “CERN scientists hope it could be detected, albeit fleetingly, in the debris of billions of collisions, just like the Higgs boson.”