We need much larger particle accelerators. Or not. The debate is on the table

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The LHC and the detectors with which it works side by side are a real wonder. In fact, they are some of the most complex and advanced machines built by humans to date. However, despite its sophistication they are not immune to the passage of time. Scientists need to modify them with some frequency so that they are helpful in the new experiments that they are gradually devising.

At the end of 2018 the LHC ceased its activity with a purpose: should be modified, among other reasons, to increase the power of the injectors that introduce the particle beams into the collider. During the previous phase of activity, the proton beams acquired an energy of 6.5 TeV (teraelectron volts), but in the current phase this figure will increase to 6.8 TeV.

CERN’s strategy consists of alternating the cycles of activity and shutdown of the LHC successively to allow scientists to introduce the modifications they need in this accelerator. However, these improvements may pursue two different ends. One of them is to increase the brightness of the accelerator, and the other requires working with a higher energy level.

In any case, both options have something in common: they involve the development of new technology. During the next shutdown phase, which will arrive in 2024, CERN technicians will modify the LHC to increase its luminosity, a parameter that measures how many potential particle collisions produced per unit area and time. And, if all goes as planned, experiments at the high-luminosity LHC will begin in 2028.

CERN is designing a new circular accelerator with a circumference of 100 km

CERN scientists are clear: they need €21 billion to build your next big particle accelerator. The successor of the current LHC that has allowed us, among other achievements, to find the Higgs boson. On June 19, 2020, the management of this institution unanimously approved the construction project for a new circular particle accelerator that will have a circumference of no less than 100 km (that of the current LHC measures 27 km).

The successor to the LHC will be 100 km in circumference and will seek to help us go beyond the standard model on which current physics is built

This machine will pursue a very ambitious goal: to allow us to elaborate new physics. Go beyond the standard model on which current physics is built. And to make it possible, it will begin by colliding electrons and positrons, which are precisely the antiparticles of electrons. This experiment aims to shed light on the properties of the Higgs boson, but this is just the tip of the iceberg.

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This project is divided into two stages. The first will start, according to its initial plans, in 2038, and will require digging a circular tunnel with a circumference of 100 km very close to the location of the current LHC. Inside that tunnel they will build an electron and positron accelerator that will have the necessary energy to maximize the production of Higgs bosons at the instant in which the collision of these particles occurs.

The future electron-positron accelerator will have the necessary energy to maximize the production of Higgs bosons

In addition to the accelerator itself, the scientists involved in this project will have to build a detector to get all the information they need about the particles that will be generated in each collision. The complexity of this instrument is as high, or more if possible, than that of the particle accelerator itself, which allows us to form a fairly precise idea about the scope of this project.

CERN

During shutdown phases, CERN engineers and physicists make modifications to the LHC to make it possible to carry out new experiments that, with a bit of luck, could help us go beyond the standard model.

The first stage of the project will conclude in the middle of this century, and once that accelerator has fulfilled its purpose, it will be completely dismantled to build in its place another circular accelerator capable of working at nothing less than 100 TeV (teraelectronvolts). This level of energy is monstrous; in fact, the current LHC works with an energy of 16 TeV, which allows us to get an idea of ​​how ambitious this second stage of the project is, which would last until the end of this century.

This second accelerator will not collide electrons and positrons; intends to work with protons, particles that have a mass about 1836 times greater than that of electrons. No one knows what new discoveries physicists will be able to make using such a powerful tool, but no doubt an accelerator designed to work at such a high energy level will play a crucial role in the search for the long-awaited new physics. Who knows, maybe from there we can leave behind the current standard model. This is the real reason for a project as ambitious as this one.

Critics prefer many smaller experiments to one this large and expensive

The scientific community is large, and not all physicists row in the same direction. As we have just seen, many of them are committed to investing resources in a particle accelerator bigger and more ambitious than the current LHC that allows them to carry out new experiments, but others argue that it is preferable to allocate that investment to other smaller and much less expensive facilities.

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Kenneth Burch, researcher and professor of physics at Boston College, has repaired in that some teams, like the one he leads, have made great discoveries in recent years in the field of particle physics using relatively simple instruments and not particle accelerators. In a way, Burch and the researchers who share his line of thought advocate designing many clever little experiments instead of just a few much more complex and expensive ones.

There is no doubt that is one way of looking at it. It is difficult to predict which of these two strategies would allow us to obtain better results in the medium and long term, but what is not in dispute is that investing in science is worth it. On this all scientists (at least those with whom we have had the opportunity to speak) agree. And they are because the figures back them up. During the conversation we had with him, the physicist and disseminator Javier Santaolalla assured us that Spain recovers the money it invests in CERN with a 300% return. Investing in science is always a good idea. And works.

Images: CERN | CERN (Anna Pantelia)

The LHC and the detectors with which it works side by side are a real wonder. In fact, they are…

The LHC and the detectors with which it works side by side are a real wonder. In fact, they are…

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