Record Performance Marks Strong Start for Run 3
The Large Hadron Collider (LHC) has reached a significant operational milestone in its 2026 physics programme, delivering performance levels that have surpassed expectations. The achievement marks a strong start to the year’s experimental schedule, with scientists now progressing into specialised data collection phases aimed at high-precision measurements.
By the end of March, the LHC had successfully completed its intensity ramp-up phase, routinely operating at 1.8 × 10¹¹ protons per bunch in each beam — the nominal target for Run 3. This benchmark places the accelerator in a stable and highly productive regime, comparable to peak performance levels seen in previous years.
Stable Operations Exceed Expectations
Following the ramp-up, the collider entered a week-long period of stable physics production. During this time, performance exceeded projections, with high luminosity delivered to major experiments including ATLAS and CMS.
This early success has reinforced confidence in the LHC’s operational readiness for a demanding year of experiments, particularly those requiring both high data volumes and precision measurement conditions.
Specialised Low-Pile-Up Run Under Way
Cleaner Conditions for Precision Physics
The LHC has now transitioned into a dedicated three-week operational phase known as the “low-μ run”, designed to reduce the number of simultaneous proton–proton interactions per bunch crossing.
Under standard conditions, around 64 interactions occur at each crossing. During the low-μ run, this figure is significantly reduced, creating a much cleaner experimental environment. For researchers, this means improved detector accuracy and reduced background noise — essential for high-precision studies.
Because fewer collisions occur, these runs involve extended operating periods, with beam “fills” lasting up to 50 hours continuously.
Focus on W Boson Mass Measurement
A central objective of this phase is the precise measurement of the W boson mass, a key parameter in particle physics. Achieving the required level of accuracy depends on refined reconstruction of collision events, particularly measurements involving hadronic recoil and missing transverse energy.
Beyond this, the data collected will support a broader range of studies, including electroweak processes, heavy-flavour physics, and diffractive interactions — all areas critical to testing the Standard Model.
Calibration Plans Adjusted After Technical Issue
Van der Meer Calibration Run
A calibration exercise known as a Van der Meer (VdM) run had been scheduled during this period. This method involves sweeping particle beams across each other to precisely measure collision rates and establish an absolute luminosity scale — a crucial reference for all subsequent data analysis.
Preparing for such a run requires carefully configured beams across the entire accelerator chain, from the PS Booster through to the SPS, involving several days of dedicated setup.
Cryogenic Fault Forces Short Shutdown
However, operations were briefly interrupted due to a technical issue in the LHC’s cryogenic system. A warm screw compressor at Point 18 showed rapidly worsening vibration levels, signalling potential bearing failure.
To prevent further damage, engineers brought forward a planned replacement originally scheduled for May. The intervention required a three-day shutdown earlier this week.
Additional Challenges in the Injector Chain
At the same time, a separate issue affected the Proton Synchrotron (PS), where a fault in the main power supply system (POPS) disrupted operations. The problem involved communication and controller failures, necessitating component replacement and extensive diagnostics.
Although operations have since resumed, the incident highlights the ageing infrastructure within parts of the accelerator complex. It also underscores the importance of the upcoming POPS+ upgrade planned during the next long shutdown (LS3).
Strong Outlook Despite Interruptions
Despite these technical setbacks, the overall performance of the LHC remains robust. With nominal intensity achieved and specialised physics runs now in progress, the 2026 programme is fully under way.
Further milestones are expected in the coming weeks as researchers continue to exploit the collider’s capabilities, maintaining its position at the forefront of global particle physics research.
Conclusion
The LHC’s early success in 2026 demonstrates both the resilience of its operations and the scientific potential of its current run. While technical challenges remain, the accelerator is delivering the conditions required for some of the most precise measurements in modern physics, setting the stage for significant discoveries in the months ahead.
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