CERN • GENEVA • RUN 4 INITIATING
Large Hadron
Collider
The countdown to the High-Luminosity LHC startup — the moment the most powerful machine humanity has ever built reawakens to begin CERN Run 4.
Target ignition — mid-June 2030 • 15 June 2030
Scroll Into The Beam
// The Machine
27 Kilometres Of Pure Physics
The Large Hadron Collider (LHC) is the world's largest and most powerful particle accelerator — a 27-kilometre ring of superconducting magnets buried 100 metres beneath the French-Swiss border at CERN near Geneva.
Inside its twin beam pipes, protons are accelerated to 99.9999991% of the speed of light and smashed together up to 40 million times every second. Those collisions recreate conditions a fraction of a second after the Big Bang, letting physicists probe the fundamental building blocks of reality. The LHC is where the Higgs boson was discovered in 2012 — and Run 4 is where the next discoveries are hiding.
27 km
Circumference of the underground ring
13.6 TeV
Peak proton-proton collision energy
-271.3°C
Magnet temperature — colder than deep space
x10
Luminosity boost from the HL-LHC upgrade
// The Upgrade
HL-LHC — The Dawn Of Run 4
After Long Shutdown 3, the collider returns transformed. The High-Luminosity Large Hadron Collider (HL-LHC) is a decade-long, multi-billion-franc upgrade that multiplies the machine's luminosity — the rate of useful collisions — by roughly a factor of ten.
More luminosity means more data, and more data means rarer events become visible. When the beams collide again in mid-2030, CERN calls it Run 4: the first physics run of the high-luminosity era, expected to gather more collision data than all previous LHC runs combined.
⚛10x Luminosity
New focusing magnets and crab cavities squeeze the proton beams tighter, packing in vastly more collisions per second.
✨Higgs Precision
Run 4 will measure the Higgs boson's properties with unprecedented accuracy — and hunt for cracks in the Standard Model.
🔭New Physics
Dark matter, supersymmetry, extra dimensions — the rare signatures of beyond-Standard-Model physics finally come within reach.
🧮3000 fb⁻¹
The HL-LHC aims to deliver ten times the integrated dataset of the original design over its lifetime.
// The Roadmap
Road To The Restart
Every LHC run is bracketed by long shutdowns for upgrades and maintenance. Here's the path that ends with the HL-LHC firing up for Run 4.
2012
The Higgs Discovery
The ATLAS and CMS experiments confirm the Higgs boson — the LHC's defining triumph.
2022 – 2026
Run 3
The LHC runs at a record 13.6 TeV, collecting data while the HL-LHC components are prepared.
2026 – 2030
Long Shutdown 3
The big rebuild. New triplet magnets, crab cavities and cryogenics are installed to enable high luminosity. You are here.
MID-2030
HL-LHC Startup — Run 4 Begins
The upgraded collider powers back on. Beams circulate, collisions resume, and the high-luminosity era officially starts.
2030s
The Discovery Decade
Years of high-luminosity running push the frontier of particle physics further than ever before.
// Frequently Asked
LHC & CERN Questions
When does the Large Hadron Collider restart for Run 4?
The HL-LHC is scheduled to start up and begin Run 4 in mid-2030, after Long Shutdown 3 wraps up. This live LHC countdown clock targets mid-June 2030 as the ignition moment.
What is the HL-LHC?
The High-Luminosity Large Hadron Collider is a major upgrade to the LHC that increases the number of particle collisions (its luminosity) by roughly a factor of ten beyond the original design — enabling far more precise Higgs measurements and deeper searches for new physics.
What is CERN Run 4?
Run 4 is the LHC's next major data-taking period, beginning when the High-Luminosity LHC comes online around 2030. It follows Run 3 and is the first run with the full HL-LHC upgrade operational.
How fast do protons travel in the LHC?
Protons in the LHC reach 99.9999991% of the speed of light, looping the 27-kilometre ring more than 11,000 times every second.
Where is the Large Hadron Collider located?
The LHC sits about 100 metres underground on the border between France and Switzerland, near Geneva, operated by CERN (the European Organization for Nuclear Research).
Is the LHC dangerous?
No. CERN safety reviews have repeatedly confirmed the LHC poses no danger — cosmic rays of far higher energy strike Earth's atmosphere constantly without harm. The collisions are tiny, controlled, and confined deep underground.
// Decode The Beam
Collider Glossary
The language of particle physics, decoded — every term you'll hear around the LHC, CERN, and Run 4.
- Luminosity
- A measure of how many collisions a collider produces. Higher luminosity = more data = more discovery potential.
- TeV
- Tera-electronvolt — a unit of energy. The LHC collides protons at up to 13.6 TeV.
- Higgs Boson
- The particle that gives mass to other particles, discovered at the LHC in 2012.
- Crab Cavity
- A radio-frequency device added for the HL-LHC that tilts proton bunches to maximise collisions.
- ATLAS & CMS
- The two giant general-purpose detectors that record LHC collisions.
- Long Shutdown
- A planned multi-year pause for upgrading and maintaining the accelerator complex.
// Don't Miss Ignition
The Universe's Biggest Machine Reboots
Time remaining until the HL-LHC startup and the beginning of CERN Run 4:
— — —
Set A Reminder