Category: Science & Technology | Date: November 23, 2009 Key figures: Rolf-Dieter Heuer (CERN Director-General 2009–2015); Fabiola Gianotti (ATLAS spokesperson from 2009); Tejinder Virdee (CMS spokesperson 2007–2010); Steve Myers (CERN Director of Accelerators and Technology)
Summary
The Large Hadron Collider (LHC), the world’s most powerful particle accelerator, resumed operations on November 20, 2009, after a major quench incident in September 2008 had forced a 14-month shutdown. On November 23, 2009, the LHC achieved its first proton-proton collisions at 900 GeV (gigaelectronvolts) center-of-mass energy, marking the resumption of experimental physics at CERN near Geneva, Switzerland. The restart, accomplished on schedule after an unprecedented engineering repair campaign, set the stage for the machine’s eventual landmark achievement: the July 4, 2012, discovery of the Higgs boson.
Background: The 2008 Quench Incident
The LHC had been under construction and commissioning for years when, on September 10, 2008, it first successfully circulated beams of protons around its 27-kilometre circumference ring — an event celebrated globally. Just nine days later, on September 19, 2008, a catastrophic electrical fault in the interconnect between two superconducting dipole magnets triggered a “quench”: a sudden loss of the superconducting state in the magnets, causing a violent release of energy. The incident ruptured a helium-containment vessel, releasing approximately 6 tonnes of liquid helium into the machine tunnel and damaging 53 of the LHC’s superconducting dipole magnets, which had to be removed, repaired, or replaced at the surface.
The repair campaign lasted approximately 14 months and cost an estimated €40 million. CERN engineers also took the opportunity to install additional protection systems — specifically “quench protection” heaters on all magnet interconnects — to prevent recurrence. The incident and repair program became a case study in large-scale high-energy physics engineering.
Key Technical Details of the 2009 Restart
- November 20, 2009 — First proton beams re-injected and circulated around the LHC ring at injection energy (450 GeV per beam).
- November 23, 2009 — First proton-proton collisions recorded at 900 GeV center-of-mass energy (450 GeV × 2 beams), with all four main detectors (ATLAS, CMS, ALICE, LHCb) taking data.
- December 16, 2009 — LHC broke the world record for highest-energy particle collisions, achieving 1.18 TeV per beam (2.36 TeV center-of-mass), surpassing Fermilab’s Tevatron in the United States.
The LHC accelerates protons using 1,232 superconducting dipole magnets cooled to 1.9 kelvin (−271.25 °C, colder than outer space) using superfluid helium. At its designed operational energy of 7 TeV per beam (14 TeV center-of-mass), the protons travel at 99.9999991% of the speed of light, completing approximately 11,245 laps of the 27 km ring per second.
The machine is operated by CERN, which in 2009 comprised 20 European member states, with contributing institutions and physicists from over 100 countries — representing one of the largest international scientific collaborations in history.
The Four Main Experiments
Each of the four detectors had specific scientific goals in 2009 and beyond:
| Experiment | Size | Primary Goal |
|---|---|---|
| ATLAS | 46m long, 25m tall | General-purpose; Higgs boson and new physics searches |
| CMS | 21m long, 15m tall | General-purpose; Higgs discovery using different techniques |
| ALICE | 26m long, 16m tall | Quark-gluon plasma in heavy-ion collisions |
| LHCb | 21m long, 10m tall | Matter-antimatter asymmetry (CP violation) in B mesons |
The first 900 GeV collisions in November 2009 were low-energy “calibration” runs used by all four experiments to verify detector alignment, timing, and readiness for high-energy physics operations in 2010.
Significance
The 2009 restart resolved the most serious setback in the LHC’s construction history and validated the engineering resilience of the project. The successful re-commissioning demonstrated that complex superconducting accelerator systems can be recovered from catastrophic failures within a bounded time frame — an important precedent for future large-scale physics facilities.
More broadly, the November 2009 collisions marked the opening of a new experimental era. By March 30, 2010, the LHC achieved 7 TeV center-of-mass collisions — then the highest energy ever achieved in a particle accelerator — beginning the physics program that would lead to:
- The July 4, 2012 announcement by ATLAS and CMS of a new boson consistent with the Higgs boson, confirming the mechanism by which fundamental particles acquire mass (the Brout-Englert-Higgs field). Higgs and Englert were awarded the 2013 Nobel Prize in Physics.
- Precision measurements of the Standard Model of particle physics across multiple decay channels.
- New constraints on supersymmetry, dark matter, and extra dimensions.
The recovery and restart of 2009 thus served as the indispensable precondition for one of the most celebrated experimental physics results of the 21st century.
Sources
- Wikipedia: “Large Hadron Collider” — https://en.wikipedia.org/wiki/Large_Hadron_Collider
- Wikipedia: “2008 LHC quench incident” — https://en.wikipedia.org/wiki/2008_LHC_quench_incident
- CERN: “The First Proton-Proton Collisions at 900 GeV” — https://home.cern/news/news/physics/first-proton-proton-collisions-900-gev
- CERN: “LHC sets new world record” (December 2009 press release) — https://home.cern/
- Heuer, Rolf-Dieter (2009): CERN Director-General end-of-year address — archived at https://home.cern/