The High-Luminosity Large Hadron Collider (HL-LHC) is an upgrade of the LHC which aims to achieve instantaneous luminosities a factor of five larger than the LHC nominal value, thereby enabling the experiments to enlarge their data sample by one order of magnitude compared with the LHC baseline programme. Following five years of design study and R&D, this project will require about ten years of developments, prototyping, testing and implementation with operation expected to start in the second half of this decade. The timeline is dictated by many critical components of the accelerator ending their lifetime and need to be replaced. The upgrade phase is therefore crucial not only for the full exploitation of the LHC physics potential, but also to enable operation of the collider beyond 2027.

The Large Hadron Collider (LHC) at CERN has been exploring the high-energy frontier since 2010 and attracts a global usercommunity of more than 7,000 scientists spanning more than 60 countries. In July 2012 the LHC experiments, ATLAS and CMS, announced the first major discovery: the long-sought Higgs boson, the cornerstone of the Standard Model (SM) of Particle Physics. After a two-year long shutdown, the LHC restarted delivering proton-proton collisions at a record of 13 TeV centre-of-mass energy in spring 2015. In order to further increase its discovery potential around the mid-2020s, LHC would eventually need an upgrade to increase the total number of collisions by a factor of 10. How this upgrade can be technically achieved is at the heart of the High Luminosity LHC project.