Category: Science & Technology
Key figures: Rolf-Dieter Heuer (CERN Director-General), the ATLAS, CMS, ALICE and LHCb collaborations
Summary
On 30 March 2010, at 13:06 CEST, CERN’s Large Hadron Collider (LHC) achieved its first proton–proton collisions at a centre-of-mass energy of 7 teraelectronvolts (TeV) — 3.5 TeV per beam — marking the formal start of the LHC’s research programme. It was the highest-energy particle collision ever produced in a laboratory, roughly three and a half times the energy previously achieved at any accelerator, and it opened the physics run that would culminate two years later in the discovery of the Higgs boson.
The milestone came after a difficult commissioning period. The LHC, built in a 27-kilometre ring beneath the France–Switzerland border near Geneva, had first circulated beams on 10 September 2008 but was disabled nine days later on 19 September when a faulty soldered splice in a copper bus bar carrying 13,000 amperes of superconducting current between two dipole magnets in sector 3-4 caused an electrical arc. The arc punctured the insulating cryostat, releasing approximately 6 tonnes of liquid helium into the tunnel and damaging roughly 53 superconducting dipole and quadrupole magnets — a setback that required 14 months of repair and magnet consolidation work. Following those repairs, beams returned in November 2009, and on 30 November 2009 the LHC reached 1.18 TeV per beam, surpassing the previous world record for accelerator energy. The 7 TeV collisions of 30 March 2010 confirmed that the repaired machine could run reliably at high energy.
“It’s a great day to be a particle physicist,” CERN Director-General Rolf-Dieter Heuer said as the collisions were recorded. “A lot of people have waited a long time for this moment, but their patience and dedication is starting to pay dividends.”
The 2008 Quench Incident
The 19 September 2008 failure — known internally as the “quench incident” — was the most serious accident in the LHC’s history and became a reference case in superconducting magnet engineering. A “quench” in a superconducting magnet refers to the abrupt loss of the superconducting state, which causes the electrical resistance to rise from zero to a measurable value. The transition is self-reinforcing: resistance generates heat, which raises temperature, which raises resistance further, potentially releasing enormous energy very rapidly.
The sector 3-4 event was not a spontaneous quench but an electrically-driven one. A single poorly soldered splice between two bus bar segments — each nominally carrying 13,000 amps with zero resistance — had a measured resistance of approximately 200 nanoohms. At full current, this resistance dissipated enough heat to vaporize the surrounding copper and aluminium, producing an electrical arc. The arc burned through the cryostat’s insulating vacuum barrier in seconds, allowing superheated helium gas to expand explosively into the tunnel. The pressure wave displaced and damaged some 53 superconducting magnets in that sector — a mix of dipoles and quadrupoles — which had to be removed, transported to surface workshops, and cleaned or replaced with spare units.
The total repair and consolidation took 14 months. Engineers used the shutdown to also survey and reinforce all 10,000+ other bus bar splices around the ring, installing additional shunts and protection circuits to prevent recurrence. The fixes allowed the LHC to restart in November 2009 at reduced energies and to reach the 7 TeV operating point by March 2010.
The record and the machine
The 7 TeV figure represented the combined energy of two counter-rotating proton beams, each accelerated to 3.5 TeV, colliding head-on at four points around the ring where the LHC’s large detectors sit. The new record displaced the 0.98 TeV per beam (1.96 TeV combined) that the Tevatron collider at Fermilab in the United States had held for roughly eight years. CERN chose 3.5 TeV per beam — half the LHC’s 7 TeV per-beam design energy — as a cautious operating point while engineers continued to consolidate the magnet interconnections implicated in the 2008 fault.
Collisions were observed by the LHC’s four main experiments: ATLAS and CMS, two large general-purpose detectors designed to search for the Higgs boson and physics beyond the Standard Model; ALICE, optimized for the study of quark–gluon plasma in heavy-ion collisions; and LHCb, dedicated to the physics of particles containing the bottom quark. Each recorded its first 7 TeV events on 30 March, and the collaborations — comprising thousands of physicists worldwide — began analysing the data almost immediately.
CERN announced that the LHC would then run continuously at 7 TeV for a period of 18 to 24 months, long enough for ATLAS and CMS to accumulate the collision data needed to probe a wide range of possible Higgs boson masses.
The 7 TeV run ultimately extended through 2010 and 2011, during which the accelerator’s instantaneous luminosity — a measure of collision rate — climbed from an initial ~10²⁸ cm⁻² s⁻¹ to a peak of approximately 3.65 × 10³³ cm⁻² s⁻¹ by October 2011. Over the full 7 TeV campaign, ATLAS and CMS each recorded approximately 5 inverse femtobarns (fb⁻¹) of integrated collision data. To put the scale in context, a single inverse femtobarn at 7 TeV corresponds to roughly 60 trillion proton–proton collisions. In 2012 the beam energy was raised to 4 TeV per beam (8 TeV combined), and it was data from that 8 TeV run — combined with the 7 TeV dataset — that provided the statistical significance needed to announce the Higgs boson on 4 July 2012. A planned shutdown for magnet consolidation began in February 2013 (Long Shutdown 1, LS1) and lasted until April 2015, after which the LHC restarted at its near-design energy of 6.5 TeV per beam (13 TeV combined).
Early Physics Results from the 7 TeV Run
Within weeks of the first collisions, ATLAS, CMS, ALICE, and LHCb each published initial measurements from their first datasets:
- Charged particle multiplicity (March–May 2010): Both ATLAS and CMS measured the average number of charged particles produced per collision at 7 TeV, finding approximately 5.6–6.0 charged particles per pseudorapidity unit — slightly higher than Monte Carlo models had predicted, providing early constraints on models of QCD soft interactions.
- Inelastic cross-section: CMS measured the total inelastic proton–proton cross-section at 7 TeV as approximately 60–64 millibarns, consistent with the extrapolation of lower-energy data and validating the collider’s luminosity calibration.
- W and Z boson production: By mid-2010, both ATLAS and CMS reported observations of W bosons (decaying to lepton + neutrino) and Z bosons (decaying to lepton pairs) at the expected rates, confirming that the Standard Model’s electroweak sector was performing correctly at 7 TeV.
Physics Beyond the Standard Model
The 7 TeV energy frontier opened the door to searches for phenomena predicted by theories beyond the Standard Model. Supersymmetry (SUSY) — a hypothetical symmetry linking fermions and bosons — predicted partner particles (squarks, gluinos, neutralinos) that would decay into Standard Model particles and missing transverse energy. Using only the first few hundred inverse picobarns of 7 TeV data, ATLAS and CMS excluded squarks and gluinos with masses below roughly 500–900 GeV in several simplified SUSY models — extending the limits well beyond the reach of the Tevatron, which had probed only a few hundred GeV. Similarly, theories of extra spatial dimensions (ADD model, Randall–Sundrum) predicted Kaluza–Klein graviton resonances accessible at TeV energies; early ATLAS and CMS searches using di-lepton and di-photon events excluded graviton resonances below approximately 1 TeV. While neither supersymmetry nor extra dimensions were discovered in the 7 TeV run, the null results placed the tightest direct experimental constraints yet on these models across a significant portion of their predicted parameter space, steering theoretical work toward compressed-spectrum and split-SUSY frameworks.
Significance
The 7 TeV collisions launched the experimental campaign that particle physicists had anticipated for decades. Operating at an energy frontier no earlier machine had reached, the LHC could produce and study particles too heavy to create elsewhere, allowing direct tests of the Standard Model and searches for supersymmetry, extra dimensions, and — above all — the Higgs boson, the last unconfirmed particle predicted by the Standard Model’s mechanism for giving mass to elementary particles.
That search succeeded: on 4 July 2012, drawing on data taken during the 7 TeV run (later raised to 8 TeV) that began in March 2010, the ATLAS and CMS collaborations jointly announced the discovery of a new particle consistent with the Higgs boson. The finding validated theoretical work by François Englert and Peter Higgs, who shared the 2013 Nobel Prize in Physics. The 30 March 2010 milestone thus stands as the practical beginning of the LHC’s scientific output and one of the defining moments in early twenty-first-century experimental physics.
Related
- /2010/news/science-technology/graphene-nobel-prize-physics-2010/ — the October 2010 Nobel Prize in Physics honoring two-dimensional materials.
- /2010/news/science-technology/kepler-9-exoplanet-discovery/ — the August 31 confirmation of the first multi-planet transiting system.
- /2010/news/science-technology/gliese-581g-exoplanet/ — the September 29 announcement of a contested habitable-zone candidate.
Sources
- First LHC collisions at 7 TeV — CERN Timeline — CERN’s official record of the 30 March 2010 milestone.
- Large Hadron Collider — Wikipedia — encyclopedic overview of the collider, its energy records, and its four main experiments.
- LHC research programme launched with 7 TeV collisions — Symmetry magazine — contemporaneous specialist reporting, including the CERN Director-General’s remarks and the planned run length.
- CERN sets date for first attempt at 7 TeV collisions in the LHC — CERN press release — official announcement of the collision attempt and its physics goals.