The Large Hadron Collider (LHC) -- world's most powerful particle accelerator -- has been stopped for about two years to enable major upgrades and renovations, CERN said.
Operators of the CERN Control Centre turned off LHC on December 3. The operations will resume in 2021.
During its second run (2015-2018), the LHC performed beyond expectations, achieving approximately 16 million billion proton-proton collisions at an energy of 13 TeV and large datasets for lead-lead collisions at an energy of 5.02 TeV, CERN said in a statement.
These collisions produced an enormous amount of data, with more than 300 million gigabytes now permanently archived in CERN's data centre tape libraries.
This is the equivalent of 1,000 years of 24/7 video streaming, researchers said.
By analysing these data, the LHC experiments have already produced a large amount of results, extending our knowledge of fundamental physics and of the universe.
"The second run of the LHC has been impressive, as we could deliver well beyond our objectives and expectations, producing five times more data than during the first run, at the unprecedented energy of 13 TeV," said Frederick Bordry, CERN Director for Accelerators and Technology.
"With this second long shutdown starting now, we will prepare the machine for even more collisions at the design energy of 14 TeV," Bordry said.
"Over the past few years the LHC experiments have made tremendous progress in the understanding of the properties of the Higgs boson," said Fabiola Gianotti, CERN Director-General.
"The Higgs boson is a special particle, very different from the other elementary particles observed so far; its properties may give us useful indications about physics beyond the Standard Model," Gianotti said.
A cornerstone of the Standard Model of particle physics -- the theory that best describes the elementary particles and the forces that bind them together -- the Higgs boson was discovered at CERN in 2012 and has been studied ever since.
In particular, physicists are analysing the way it decays or transforms into other particles, to check the Standard Model's predictions.
Over the last three years, the LHC experiments extended the measurements of rates of Higgs boson decays, including the most common, but hard-to-detect, decay into bottom quarks, and the rare production of a Higgs boson in association with top quarks.
During the two-year break, Long Shutdown 2 (LS2), the whole accelerator complex and detectors will be reinforced and upgraded for the next LHC run, starting in 2021, and the High-Luminosity LHC (HL-LHC) project, which will start operation after 2025.
Increasing the luminosity of the LHC means producing far more data.
"The rich harvest of the second run enables the researchers to look for very rare processes," said Eckhard Elsen, Director for Research and Computing at CERN.
"They will be busy throughout the shutdown examining the huge data sample for possible signatures of new physics that haven't had the chance to emerge from the dominant contribution of the Standard Model processes," Elsen said.
Several components of the accelerator chain (injectors) that feed the LHC with protons will be renewed to produce more intense beams.
Some improvements of the LHC are also planned during LS2. Civil engineering works for the HL-LHC that started in June this year will continue, new galleries will be connected to the LHC tunnel, and new powerful magnet and superconducting technologies will be tested for the first time.