LHC dipole magnets in the tunnel
A chain of LHC dipole magnets inside the tunnel at point 1 (ATLAS) towards the end of Long Shutdown 2 (LS2).When the Large Hadron Collider (LHC) begins Run 3 next year, operators aim to increase the energy of the proton beams to an unprecedented 6.8 TeV. (Image: CERN)

Run 3 of the Large Hadron Collider

Run 3, a new period of data taking, begins in July 2022 for the experiments at the Large Hadron Collider (LHC), after more than three years of upgrade and maintenance work. Beams have already been circulating in CERN’s accelerator complex since April. The LHC will now run for close to four years at the record collision energy of 13.6 trillion electronvolts (TeV) – 6.8 TeV per beam.

In preparation for data taking, the four big LHC experiments performed major upgrades to their data readout and selection systems, with new detector systems and computing infrastructure. The changes will allow them to collect significantly larger data samples, of higher quality than previous runs. 

What is CERN going to do during Run 3? Fabiola Gianotti, CERN Director-General (Video: CERN)

The ATLAS and CMS detectors expect to record more collisions during Run 3 than in the two previous LHC physics runs combined. The LHCb experiment underwent a complete revamp and looks to increase its data-taking rate by a factor of ten, while ALICE is aiming at a staggering fifty-times increase in the number of recorded collisions.

With the increased data samples and higher collision energy, Run 3 will further expand the already diverse LHC physics programme.

What do we call a “run” at the LHC? Rende Steerenberg, Head of the Operations Group in the Beams Department (Video: CERN)

What is new about the Run 3 of the LHC? Mike Lamont, Director for Accelerators and Technology (Video: CERN)

Pourquoi le Run 3 est important pour le LHC ? Malika Meddahi, Deputy Director for Accelerators and Technology (Video: CERN)

Run 3 expectations

1. Probe the nature of the Higgs boson

Scientists at the ATLAS and CMS experiments will be probing the nature of the Higgs boson with unprecedented precision and in new channels in Run 3.

“We’ve scratched the surface,” said Peter Higgs in 2019. “But we have clearly much more to discover.”

By pushing the precision frontier, researchers will look at how strongly the Higgs boson interacts with matter and force particles. They will explore whether it decays to new particles, for example those that could make up dark matter. The Higgs-boson interaction with the heaviest known particle – the top quark – is of particular interest as it is one of the places to search for new physics.

What does ATLAS expect from Run 3? Andreas Hoecker, ATLAS experiment spokesperson (Video: CERN)

What does CMS expect from Run 3? Luca Malgeri, CMS experiment spokesperson (Video: CERN)

2. New precision measurements paving the way to new physics

With this third run, scientists at the LHC experiments will be able to improve the measurement precision of numerous known processes addressing fundamental questions, such as the origin of the matter-antimatter asymmetry in the universe.

They will also be searching for candidates for dark matter and for other new physics phenomena, either through direct searches or – indirectly – through precise measurements of properties of known particles.

What are your physics expectations for Run 3? Sophie Renner, theoretical physicist at CERN (Video: CERN)

Which physics results do you expect from Run 3? Michelangelo Mangano, theoretical physicist at CERN (Video: CERN)

3. Lepton flavour universality violation

The Standard Model of particle physics predicts that decays involving different flavours of leptons should occur with the same probability. This feature, known as lepton flavour universality, is usually measured by the ratio between the decay probabilities. In the Standard Model of particle physics, the ratio should be very close to one.

The LHCb experiment observed a possible difference in the behaviour of different types of lepton particles, with intriguing results indicating hints of a deviation from one.

If confirmed, as more data are collected and analysed, the results would signal a crack in the Standard Model.

What does LHCb expect from Run 3? Chris Parkes, LHCb experiment spokesperson (Video: CERN)

4. Heavy-ion collision programme

The upcoming heavy-ion collision programme will allow the experiments, in particular ALICE, to investigate quark-gluon plasma (QGP) – a state of matter that existed in the first 10 microseconds after the Big Bang – with unprecedented accuracy.

In addition to the main lead–lead runs, a short period with oxygen collisions will be included for the first time, with the goal of exploring the emergence of QGP-like effects in small colliding systems.

What does ALICE expect from Run 3? Luciano Musa, ALICE experiment spokesperson (Video: CERN)