HiLumi LHC Upgrade: Dismantling the Large Hadron Collider to Install HL-LHC Equipment and Unlock Precision Higgs Physics

Overview

As CERN prepares the High-Luminosity LHC upgrade, the LHC is temporarily quiet as teams dismantle sections of the accelerator to install HiLumi hardware. When the machine switches back on around 2030, it will become the HL-LHC and deliver roughly seven times more data than the collider that discovered the Higgs boson. The upgrade involves major system and detector enhancements, including particle-tracking detectors and precision timing systems, to cope with a densified collision environment and unlock new Higgs physics.

• Sevenfold data increase and extended physics reach for Higgs studies
• Atlas and CMS detector upgrades to tracking and timing systems
• Construction and integration coordinated across CERN and partner labs
• Aim to test Higgs properties and search for new physics beyond the standard model

HL-LHC Upgrade Overview

The Large Hadron Collider (LHC) has entered a long shutdown during which engineers are dismantling 1.2 kilometres of the machine to install the High-Luminosity upgrade, HiLumi LHC. This extensive upgrade is designed to dramatically increase the collider’s luminosity, enabling approximately seven times more proton-proton collisions over its lifetime. The goal is to extend the physics program beyond what was possible with the original LHC, particularly in precision Higgs boson studies, by collecting vastly larger data samples and by improving detector performance to cope with the resulting higher event rates.

In the United States and Europe, researchers have spent years planning the HL-LHC era, coordinating upgrades across the two flagship experiments at the LHC, Atlas and CMS. The upgrades are not limited to the accelerator itself; they require revolutionary improvements to the detectors, electronics, cooling, and data-processing systems to ensure that the experiments can exploit the increased data flow without being overwhelmed by pile-up, the simultaneous collisions that occur in each bunch crossing.

When the HL-LHC turns on again around 2030, it will deliver roughly seven times more data than the collider that discovered the Higgs boson. This boost is expected to transform Higgs physics by enabling precision tests of the Higgs couplings to other particles and, crucially, the self-coupling of the Higgs field, which governs the Higgs potential and the evolution of the early universe. The upgrade is a collaboration that spans continents, with key roles for major detectors and their upgrade programs, including silicon pixel detector modules for Atlas and for CMS, which will be housed in upgraded inner trackers and extra-fast timing detectors.

From the perspective of the scientists and engineers involved, the HL-LHC represents a watershed in experimental physics. The project is not just about building more powerful accelerators; it is about rethinking the detectors to capture and interpret data with unprecedented precision. The upgrade also aims to cross-check discoveries across two major experiments, ensuring that any observed anomalies are robust against systematic effects and independent verification.

Joao Batista Lopes of CERN captures the image of the dismantling and the ongoing installation work, while Steven Goldfarb of CERN provides a perspective on how the Atlas and CMS experiments will operate in this enhanced HL-LHC era, helping readers understand the scale and ambition of the upgrade. Daniela Bortoletto, involved with Atlas in Oxford, describes the first complete pixel ring and the beauty of the silicon detector assemblies as they become a reality after extensive design reviews and production efforts. The article highlights that thousands of components from around the world must come together to realize the HL-LHC’s detector upgrades and to enable deep measurements of the Higgs properties in the HL-LHC era.

Investigating the Higgs in the HL-LHC Era

One of the central motivations for the HL-LHC is to test the Higgs boson’s behavior with much higher precision than before. The standard model predicts how the Higgs interacts with lighter particles, and any deviation, even a small one, could signal new particles or forces. The HL-LHC aims to refine our understanding of these couplings, particularly in rarer Higgs decays such as to two muons or to charm quarks, which are challenging to observe with the current data volume. In addition, observing Higgs boson pairs would enable a direct measurement of the Higgs self-coupling and shed light on the shape of the Higgs potential, which has implications for the early universe following the Big Bang.

The increase in collisions is not just about higher energy; it is about higher statistics. The HL-LHC will enable physicists to perform more precise cross-checks of the standard model’s predictions and to look for subtle discrepancies that might hint at physics beyond the standard model, including the nature of dark matter and potential new forces. The upgrade thus supports a broader goal: to move from discovery-driven work to precision Higgs physics that could open windows to new phenomena in particle physics.

Detector Upgrades: Pixel Detectors and Precision Timing

Central to the HL-LHC’s physics goals are new silicon tracking detectors replacing the existing systems in Atlas and CMS. These detectors must endure extremely high radiation levels while maintaining exceptional spatial resolution to reconstruct particle trajectories with unprecedented accuracy. Among the most innovative features is the addition of precision timing detectors. The High Granularity Timing Detector planned for Atlas and a counterpart in CMS will measure particle arrival times with a precision on the order of tens of picoseconds. By adding time as a fourth dimension to tracking, physicists can disentangle multiple collisions occurring in the same crossing, enabling clearer reconstruction of rare Higgs events that would otherwise be obscured by overlapping interactions.

The projects behind these detector upgrades involve multi-disciplinary advances in silicon sensor technology, fast electronics, cooling, and lightweight mechanical structures. The upgraded detectors must work in harmony with the upgraded accelerator to handle the increased data rates while preserving the quality and integrity of the recorded events. The article notes the human dimension of this large-scale science effort, with students and early-career researchers participating in the assembly and testing of detector components, highlighting the long career trajectories involved in the HL-LHC program.

The Road Ahead: Timeline, Collaboration, and Expectations

The HL-LHC timeline envisions a switch-on around 2030, following a prolonged shutdown during which the LHC is dismantled and upgraded. The upgrade’s success depends on global collaboration, the reliability of enduring technologies, and the ability to manage vast volumes of data. The article emphasizes that the HL-LHC will not only extend the LHC’s scientific program but also inaugurate an era of precision Higgs physics, potentially revealing cracks in the standard model or confirming it with unprecedented precision. The HL-LHC’s data and detector capabilities are expected to influence particle physics research for decades, shaping strategies for future experiments and theoretical developments.

Overall, the piece depicts a moment of transition from a past era of Higgs discovery into a future era of precision measurement and exploration of the Higgs sector. It highlights the essential cooperation between accelerator scientists, detector engineers, theorists, and students, all contributing to a shared scientific mission. The article’s framing underscores that the HL-LHC is a leap forward not just in raw power but in the sophistication of the detectors and the analysis techniques that will unlock new physics from the collisions at the heart of the LHC complex.

In summary, the HL-LHC upgrade represents a concerted push to extend the physics program at CERN by delivering more collisions, upgrading the detectors for high-rate operation, and enabling precision studies of the Higgs boson. The project is a global effort with the potential to deepen our understanding of the fundamental forces and constituents of matter, and to guide future explorations in particle physics for years to come. The article is anchored by contributions from Joao Batista Lopes and Steven Goldfarb of CERN, with Atlas and CMS researchers involved in the detector upgrades, and it captures the excitement and scientific promise of the HL-LHC era.