HL-LHC Upgrade: New Detector Specs, 2030 Timeline, and the Physics Stakes

The HL-LHC Upgrade Will Collect 7x More Data by 2030

Estimated reading time: 10 minutes

Key Takeaways

• The HL-LHC upgrade is not about smashing particles harder. It is about doing it smarter, longer, and with far more precision than any particle collider has ever managed before.
• When they are done, the High-Luminosity LHC will be able to collect roughly seven times more collision data per year than the current machine.
• More data means rarer events become visible. Rarer events mean deeper tests of the Standard Model of particle physics.
• This article walks through every major part of the upgrade: the timeline, the new detectors, the engineering challenges, and what the physics community actually expects to learn.

The HL-LHC upgrade is not about smashing particles harder. It is about doing it smarter, longer, and with far more precision than any particle collider has ever managed before.

Right now, the Large Hadron Collider at CERN sits in a carefully planned pause. Engineers, physicists, and technologists from dozens of countries are tearing apart two of the world's most complex scientific instruments — the ATLAS and CMS detectors — and rebuilding them from scratch. When they are done, the High-Luminosity LHC will be able to collect roughly seven times more collision data per year than the current machine.

That matters enormously. More data means rarer events become visible. Rarer events mean deeper tests of the Standard Model of particle physics. And deeper tests mean we get closer to answering questions like: why does the Higgs boson behave the way it does, and is there physics hiding beyond what we currently understand?

This article walks through every major part of the upgrade: the timeline, the new detectors, the engineering challenges, and what the physics community actually expects to learn.

What the High-Luminosity LHC Actually Changes

The word "luminosity" is the key here. In particle physics, luminosity measures how many collisions a collider can produce per second per unit area. Higher luminosity means more collisions, more data, and more chances to spot rare processes.

The current LHC already delivered about 300 fb⁻¹ (femtobarns inverse — a unit of integrated collision data) across its first three runs. The High-Luminosity LHC is targeting a total of 3,000 fb⁻¹, with the hardware built to handle up to 4,000 fb⁻¹ if needed. That is a tenfold increase in total physics data over the life of the program.

To get there, CERN is upgrading the accelerator magnets, installing new superconducting crab cavities to squeeze the beams tighter at the collision points, and completely rebuilding the inner tracking and timing systems of both major detectors.

The result is a machine that does not collide beams at higher energy — the beam energy stays at 13.6 TeV — but collides them far more frequently and far more densely.

Key numbers to keep in mind:

• Up to 200 proton-proton interactions per beam crossing (called "pileup")
• Peak luminosity about 5–7.5 × 10³⁴ cm⁻² s⁻¹, leveled during operations
• Long Shutdown 3 (LS3) runs from 2026 to 2028
• First HL-LHC physics collisions expected around 2030
• Physics operations continue through the early 2040s

Source: report reveals full reach LHC programme

Long Shutdown 3 — What Is Happening Right Now

Long Shutdown 3, which started in 2026, is the single largest coordinated upgrade in CERN's history. It is not a simple maintenance stop. It is a full infrastructure overhaul running in parallel across the accelerator tunnel, both experimental caverns, and multiple surface facilities.

On the accelerator side

The LHC tunnel is receiving new niobium-tin (Nb₃Sn) superconducting magnets in the insertion regions near the ATLAS and CMS collision points. These magnets operate at higher field strengths than the current niobium-titanium magnets, which allows the beams to be focused more tightly and increases the collision rate.

Crab cavities — radio-frequency devices that tilt the beam bunches so they collide more head-on — are being installed. This alone can boost the effective luminosity significantly without changing anything else.

On the detector side

Both ATLAS and CMS are undergoing complete inner detector replacements. Their current silicon tracking systems cannot survive the radiation levels that 200 pileup interactions per crossing would produce. New all-silicon trackers are being installed that are both more radiation-hard and more granular.

A June 2026 LHCC machine report confirmed the LS3 schedule is progressing, with commissioning expected to begin after installation wraps in 2028 and peak pileup during early commissioning projected near 101 interactions per crossing, rising toward a leveled value of about 132 as operations mature.

Source: LHCC machine report

The ATLAS Timing Detector — Reading Collisions in Picoseconds

One of the biggest engineering challenges at 200 pileup is simple to describe but extraordinarily hard to solve: how do you tell which particles came from which collision?

When 200 interactions happen in the same beam crossing, they all occur at nearly the same point in space. Standard tracking — which measures where particles go — cannot separate them cleanly. The positions overlap too much.

The solution is time. If you can measure when each track was produced with enough precision, you can sort the 200 collisions in time even if they are piled up in space.

ATLAS is solving this with the High-Granularity Timing Detector (HGTD).

What the ATLAS HGTD does

The HGTD is installed in the forward region of the ATLAS detector (covering pseudorapidity 2.4 to 4.0 — the more angled tracks away from the beam axis). It uses Low-Gain Avalanche Detector (LGAD) silicon sensors, a technology specifically developed for this kind of ultra-fast timing work.

Key HGTD specifications:

• Per-track timing resolution: approximately 30–50 picoseconds
• Sensor technology: LGADs in the forward region
• Covers the high-pileup forward acceptance gap left by the inner tracker
• Designed to survive integrated radiation doses expected across the full HL-LHC run

To put 30–50 picoseconds in perspective: a picosecond is one trillionth of a second. Light travels about 9–15 millimeters in that time. The HGTD is measuring the arrival time of particles with enough precision to separate collision vertices that occurred fractions of a millimeter apart in time.

Source: ATLAS Prepares HLLHC

The CMS MIP Timing Detector — A Hermetic Timing Shell

CMS is taking a different but equally ambitious approach. Instead of focusing only on the forward region, CMS is building a hermetic timing layer that wraps around its entire Outer Tracker — both the barrel (central cylinder) and the endcaps (the disc-shaped end sections).

This system is called the MIP Timing Detector (MTD).

What the CMS MTD does

MIP stands for Minimum Ionizing Particle — a term for the low-energy charged particles that are most common in LHC collisions. The MTD is designed to time-stamp essentially every charged track that passes through the CMS detector.

Key MTD specifications:

• Timing resolution: approximately 35 picoseconds
• Barrel: Uses LYSO scintillating crystals read out by Silicon Photomultipliers (SiPMs) — an approach borrowed and scaled from medical imaging technology
• Endcaps (ETL): Uses LGAD silicon sensors, the same core technology as the ATLAS HGTD
• Hermetic coverage means almost no track escapes without a timestamp

The barrel and endcap split is a practical engineering choice. In the barrel, the radiation levels are lower and LYSO+SiPM provides excellent timing with a well-understood manufacturing path. In the endcaps, radiation levels are far higher, so the more radiation-hard LGAD sensors are used.

Together, the barrel and endcap layers give CMS the ability to perform 4D tracking — three spatial coordinates plus time — for the first time in a collider experiment operating at this scale.

Source: new precision timing detector

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Radiation-Hard Electronics — The Invisible Engineering Problem

Timing detectors get the headlines, but there is a quieter challenge underneath all of it: the electronics have to survive.

At 200 pileup interactions per crossing over a decade of running, the radiation doses inside ATLAS and CMS will be extreme. Silicon sensors in the innermost tracking layers will absorb radiation doses measured in hundreds of megarads. Standard commercial chips would fail within weeks.

CERN and its collaborators have developed a new generation of radiation-hard ASICs (Application-Specific Integrated Circuits) specifically for the HL-LHC. These chips are designed in specialized CMOS processes that remain functional after the projected lifetime dose.

For the LGAD sensors themselves, radiation hardness is a core design criterion. As LGADs absorb radiation, their internal gain — the property that makes them fast — gradually degrades. The sensors are designed with this degradation factored in, so even at end-of-life radiation doses, they still meet the timing resolution requirements.

The all-silicon inner trackers replacing the current mixed silicon/straw-tube systems at both ATLAS and CMS are similarly optimized: smaller pixels, more granular, and built from materials that degrade more predictably under radiation.

Source: arXiv analysis

The Physics Targets — Why This Level of Precision Matters

The HL-LHC is not being built to discover a specific new particle. That is an honest and important distinction. It is being built to measure things we already know exist with far higher precision, and to search for rare processes that the current LHC simply cannot accumulate enough data to see.

Higgs boson precision measurements

The Higgs boson was discovered in 2012. More than a decade later, we still do not know its properties well enough to fully test the Standard Model predictions. Several Higgs coupling measurements currently have uncertainties of 10–20%. The HL-LHC is designed to bring those uncertainties down to the few-percent level.

Specific targets include:

• Higgs self-coupling — does the Higgs interact with itself the way the Standard Model predicts? This requires observing di-Higgs production, an extremely rare process
• Higgs couplings to second-generation fermions — particularly the coupling to muons, which is tiny and has never been cleanly measured
• Rare Higgs decay modes that are invisible to the current dataset

Rare processes and searches beyond the Standard Model

With 3,000 fb⁻¹ of data, processes that occurred only a handful of times in Run 1, 2, and 3 combined will be produced thousands of times. This includes:

• Rare B-meson decays sensitive to new physics
• Direct production of new particles, if they exist near the TeV scale
• Precision electroweak measurements that test quantum corrections

A 2025 arXiv analysis of the full HL-LHC physics program confirmed that the combination of higher luminosity and improved detector resolution — particularly the 4D tracking capability from the new timing layers — significantly extends sensitivity to many of these processes compared to a simple extrapolation from current data.

Source: arXiv analysis and report reveals full reach LHC programme

The Economic and Industrial Case for the Upgrade

Large-scale science projects always face the question: is the cost justified?

CERN commissioned a formal social cost-benefit analysis of the HL-LHC program. The results are concrete:

• Benefit-cost ratio: approximately 1.7
• Probability of positive net present value: 94%
• Significant spillover effects in industrial training, advanced manufacturing, and high-technology procurement

The analysis counts not just the direct scientific output but the broader economic activity generated: contracts with European and international industry for superconducting magnets, cryogenics, precision mechanics, electronics, and software. Universities and research institutes gain trained engineers and physicists who carry those skills into commercial sectors.

This is consistent with the historical record of large physics infrastructure. Technologies originating from CERN particle detector work have found applications in medical imaging, radiation therapy, and semiconductor manufacturing.

Source: record 2319300

What Comes After HL-LHC

The HL-LHC program is formally planned to run through the early 2040s, accumulating up to 3,000 fb⁻¹ with hardware headroom to reach 4,000 fb⁻¹.

What comes after is still being debated. The European Strategy for Particle Physics — the field's long-range planning document — is currently under review. Leading candidates for a post-HL-LHC machine include a Future Circular Collider (FCC) at CERN, which would reach much higher energies in a new 91-kilometer tunnel, and a muon collider, which would offer a different physics approach at a smaller physical scale.

None of those decisions are finalized. What is certain is that the HL-LHC represents the definitive end of the current LHC era and the last major use of the existing accelerator infrastructure before something fundamentally new is required.

The data collected through the 2040s will define the questions that the next machine must answer.

Source: report reveals full reach LHC programme

FAQ — HL-LHC Upgrade Explained