The physicists at the European research center Cern near Geneva had to be patient for a long time.

After a three-year conversion and maintenance phase, the world's largest particle accelerator and storage ring has resumed routine operation.

This afternoon, two proton beams rotating in opposite directions will collide again in the "Large Hadron Collider" and the fragments will be analyzed with the large detectors.

Manfred Lindinger

Editor in the department "Nature and Science".

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For the first time, the hydrogen nuclei collide with a total energy of 13.6 trillion electron volts (teraelectron volts).

This corresponds to 6.8 TeV per proton beam.

The previous energy record was 13 TeV and dates from 2018. For comparison: the electrons in a traditional electron tube were accelerated to 20,000 electron volts.

In addition, one wants to increase the luminosity of the proton beams circulating in the LHC and thus the collision rate of the hydrogen nuclei.

During the particle collisions, conditions arise for a brief moment that existed trillionths of a second after the big bang 13.8 billion years ago.

Expectations are high.

With the upgraded machine and the four completely overhauled detectors Atlas, CMS, LHCb and Alice, the particle physicists hope to gain new insights into the Higgs particle, which was discovered ten years ago and whose discovery was officially announced on July 4, 2012 at CERN.

Information about many of its properties has already been elicited from this boson, which gives the other elementary particles mass.

In the meantime, many of the Higgs decay channels predicted by the Standard Model have been demonstrated extremely precisely - including the decay into two high-energy photons and the decay into four muons as well as into the heavy dew particle and into pairs of heavy bottom and top quarks.

However, the rare decays into electrons and into the light up and down quarks have not yet been observed.

We now hope to be able to do this again.

Due to the high luminosity of the surrounding proton beams, rare events should be more clearly visible in the measurement data.

The question of why the mass of the Higgs boson is around 125 GeV and no more is also a mystery to physicists.

Because if it were harder, it would hardly have been possible to prove it at CERN.

There may even be other heavier Higgs bosons.

That's not out of the question.

Chasing the Unknown

In addition, the particle physicists hope to encounter completely new particles and unknown physical phenomena.

Because there are still many unanswered questions to which particle physicists have not yet had satisfactory answers.

For example, it is still unclear why there is matter in the universe but no antimatter, even though both originally emerged in equal parts from the Big Bang.

Why are there four forces of nature?

And what is the dark matter made of, which makes up the majority of the matter in the cosmos, but has so far only been shown indirectly in the cosmos through its gravitational effect?

Preparations for today had already begun on April 22, when the first protons were fed into the 27-kilometer-long storage ring and chased through it in the opposite direction.

But it took ten weeks before the machine could run at full speed.

The LHC is now to be operated around the clock for almost four years.

While comparatively few particle collisions per second will take place today, the collision rate will gradually increase in the coming weeks and months.

The goal is trillions of proton-proton collisions per second.

In order to be able to process the resulting amount of data, all electronic systems for fast data acquisition and processing were upgraded accordingly.