CERN: Large Hadron Collider gets stronger, better, brighter | Science| In-depth reporting on science and technology | DW | 15.06.2018
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Science

CERN: Large Hadron Collider gets stronger, better, brighter

On June 15, workers at CERN start modernizing its largest Synchrotron — the LHC. They aim to generate many more particle collisions and collect considerably more data about Higgs- and other particles.

The European Center for Nuclear Research, CERN, is Europe's larges joint research facility. Here, particle physicists from 85 countries ranging from China to Latin America team up. The facility is located near Geneva. The physicists use huge particle accelerators to generate particle streams for all kinds of basic research projects.

The largest of the synchrotrons is the Large Hadron Collider (LHC) with a circumference of 27 kilometers (16.8 miles). Physicists deal with protons that eventually fall apart into the tiniest of elementary particles. It's here that the existence of the famous Higgs particle was demonstrated in 2012. And it's here where researchers want to find out what happened during the Big Bang, what our universe is made of and what the mysterious dark matter is.

The data center of CERN, which collects and processes all the data from those experiments is unique and connected to all the cooperating institutes and universities in the world. The worldwide web was invented here.

CERN is already a huge facility, and it is getting even bigger. Roughly €1 billion is the price tag on the next big modernization of the LHC over the coming years.

By 2020, the engineers want to upgrade the synchrotron in such a way that it produces considerably more particle collisions than before.

Read more about particle physics: The KATRIN Tritium Neutrino experiment: A giant scale for the tiniest particles starts

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Dark matter

It's all about luminosity

The project is dubbed "High Luminosity." Luminosity is a term from astronomy and means the total energy emitted by a star over a given time in the entire electromagnetic spectrum.

At the LHC, luminosity is roughly the same: It is emitted when particles collide and fall apart into smaller elementary particles. The energy that goes into the synchrotron only partly adds to that luminosity.

So far, the LHC reached collision energies of 13 tera electron volts (TeV). From 2020, the scientists hope to run the LHC with energies of 14 TeV. After modernization completes in 2025, the energy volumes may be even higher, probably reaching more than 16 TeV.

More important for luminosity than the sheer energy, however, is the number of collisions actually taking place, with proton rays crossing.

Engineers are thus implementing several technical improvements to increase the number of collisions, probably resulting in a tenfold increase in luminosity.

Zwei gegenläufige LHC-Rohre (DW/F.Schmidt)

Two pipes with proton beams running in opposite direction. The beams crash into each other inside the detectors

More precise rays and rotating particle packages

One of these improvements includes upgrading the precision of the particle rays. If they meet in a smaller area, you get more particle collisions. Currently the ray measures 16 micrometers in the collision point. In the future, half of that diameter will be reached.

The luminosity will also increase by changing the shape of the particle packages inside the particle beam just before the collision. So called "crab cavities" — specially built resonators — will make the particle packages rotate. This results in a larger surface of the packages and a higher likeliness of  protons actually colliding.

You could compare this to two thin arrows being shot at each other: As long as they face each other in a straight line, they are likely to miss each other. If both are turned sidewise they are likely to collide. And more collisions result in more generated elementary particles.

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Theory of everything

For example, the researchers expect that the Hi-Lumi LHC will be able to generate as many as 15 million Higgs particles per year. In 2012, when the existence of this particle was first verified, the synchrotron only produced about 1.2 million Higgs particles.

Trying to understand the fabric of our universe

But the physicists are also looking for many other particles that may help them understand the fabric of our universe. While everybody is talking about Higgs particles, those are actually rather rare.

Currently, the LHC produces roughly 1 billion particle collisions per second. With high luminosity in place, it's supposed to be five times higher

The LHC must be able to handle this amount, and that requires a lot of work in the coming months. The engineers are installing new, more powerful superconducting electric magnets. And they completely reconfigure the four huge detectors of the LHC. Those detectors work like digital cameras. In order to handle high luminosity, the sensors must be more robust and be able to process collected data more quickly.

That also goes for the huge CERN data center, in which all the pictures from the collisions get stored like on the memory stick of a digital photo camera. Then the data gets redistributed to other servers all over the world where physicists analyze and interpret it.

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