HiLumi LHC

The High-Luminosity Large Hadron Collider will increase the number of collisions to study fundamental components of matter in more detail.
Overview of the High-Luminosity LHC project. (Video: CERN)

The High-Luminosity Large Hadron Collider (HiLumi LHC) project aims to transform the LHC in order to increase the potential for discoveries after 2030. The objective is to maximise the performance of the LHC by increasing its integrated luminosity by a factor of 10 compared to its original design value.

Luminosity is an important indicator of the performance of an accelerator: it is proportional to the number of collisions that occur in a given amount of time. The higher the luminosity, the more data the experiments can gather to allow them to observe rare processes. 

The HiLumi LHC, which should be operational in mid-2030, will allow physicists to study known mechanisms in greater detail, such as the Higgs boson, and observe rare new phenomena that might reveal themselves. Over its lifetime, the HiLumi LHC could produce about 380 million Higgs bosons, compared with roughly 55 million Higgs bosons produced since the start of the LHC.

Its development requires replacing 1.2 kilometres of the LHC with completely innovative components. The first phase of the project began in 2011 and was partly financed by the European Commission’s seventh framework programme (FP7). The construction phase for the project then began at CERN, as well as in industry and at collaborating institutes in 2015. Civil engineering work began in 2018 and the installation in 2023. However, most of the installation will take place during a long shutdown period of the accelerators, beginning in mid-2026. This shutdown will also be used to upgrade CERN’s accelerator complex as well as to completely transform the two general-purpose experiments, ATLAS and CMS, to prepare them for the staggering number of collisions. 

The HiLumi LHC project is led by CERN with the support of an international collaboration of nearly 50 institutions in over 20 countries – the vast majority located in Europe. In addition to the funding provided by CERN Member States and Associate Member States, the project received special contributions from Italy, Spain, Sweden, the United Kingdom, Serbia and Pakistan, and from several non-Member States such as the United States, Japan, Canada and China.

Frequently Asked Questions

What is luminosity?
Instantaneous luminosity, which is the measure of the number of potential collisions per surface unit (or cross section) over a given period of time, is an essential indicator of an accelerator’s performance. Integrated luminosity is a measure of the collected data size and is measured in inverse femtobarns (fb-1). One inverse femtobarn of integrated luminosity equates to 100 million million collisions.

By the end of 2025, the LHC had produced 500 inverse femtobarns of data over its lifetime. The HiLumi LHC will produce more than 250 inverse femtobarns of data per year and will be capable of collecting up to 4000 inverse femtobarns during its operational period.
Why High-Luminosity?
The phenomena that physicists are looking for have a very low probability of occurring and this is why a very large amount of data is needed to detect them. Increasing luminosity produces more data, allowing physicists to study known mechanisms in greater detail and observe rare new phenomena that might reveal themselves. For example, the HiLumi LHC could produce about 380 million Higgs bosons over its lifetime, compared with the roughly 55 million Higgs bosons that the LHC has produced since it began operating.
How will the HiLumi LHC work?
Increasing the luminosity means increasing the number of collisions: 140–200 collisions will be produced each time two particle bunches meet at the heart of the ATLAS and CMS detectors, compared to around 60 collision events at present. To achieve this, the beam will need to be more intense and more focused than at present in the LHC. New equipment will need to be installed over about 1.2 of the LHC’s 27 kilometres.

Find out more about the high-luminosity technologies used in the LHC.
What is the work schedule?
The civil engineering work began in April 2018 at LHC Point 1 (in Meyrin, Switzerland), where the ATLAS experiment is located, and at LHC Point 5 (in Cessy, France), the site of the CMS experiment. A new shaft of around 80 metres, as well as underground caverns and a 300-metre-long service tunnel has been dug on each site.

This service tunnel is linked to the LHC tunnel by four connecting tunnels and 14 vertical cores for each of the two high luminosity experiments ATLAS and CMS. The four main connections between the new and old infrastructures were established in 2019 and five surface buildings have been built on each site to house the electrical, cryogenic, cooling and ventilation infrastructure of the new HiLumi LHC equipment.

All new components are now either fully in series production mode or have already completed the production cycle. The performance of the new magnets and their integration with associated equipment are tested on a test bench that replicates the underground installation.

The installation of most components will take place during a four-year shutdown of the accelerators starting in mid-2026.
Who is involved in the project?
CERN and its Member and Associate Member States are supported by an international collaboration of 50 institutes in more than 20 countries, mostly based in Europe.

In addition to funding from Member and Associate Member States, the project receives special contributions from Italy, Spain, Sweden, the United Kingdom, Serbia and Pakistan, as well as several non-member states, notably the United States, Japan, Canada and China.
How will society benefit from the HiLumi LHC?
The HiLumi LHC will further our fundamental knowledge, which is CERN’s primary mission. To develop this accelerator upgrade, CERN is pushing several technologies to new limits, such as electrical engineering, superconductors, vacuum technologies, computing, electronics and industrial processes. In the long term, these innovations will benefit daily life.

For example, superconducting magnets are used in medical imaging and cancer treatment with particle beams (hadron therapy). European industry is also studying magnesium di-boride cables to transport high electrical power over long distances sustainably.

The project also contributes to training new scientists – physicists, engineers and technicians. Several hundred bachelor’s and master’s students, doctoral students, post-doctoral researchers and fellows from dozens of nationalities are participating in the project.

Technologies