LHC TIMER // GLOSSARY

The Collider Glossary

Twenty six terms that unlock every LHC headline between now and the 2030 restart, written for humans rather than for other physicists.

Luminosity: The measure of a collider's collision producing intensity. Higher luminosity means more collisions per second and faster accumulation of data. The HL in HL-LHC.
Integrated luminosity: Luminosity summed over time; effectively the size of the dataset, measured in inverse femtobarns. The HL-LHC targets about 3,000 fb^-1, ten times the original LHC total.
Femtobarn: A unit of cross section equal to 10^-43 square centimetres. Its inverse (fb^-1) measures integrated luminosity; one fb^-1 corresponds to roughly 10¹⁴ proton collisions.
TeV: Tera electronvolt, a trillion electronvolts. The LHC collided protons at 13.6 TeV in Run 3 and targets 14 TeV in Run 4. Roughly the kinetic energy of a flying mosquito, concentrated into a single proton.
Higgs boson: The particle discovered at the LHC on 4 July 2012, the quantum of the field that gives elementary particles mass. Measuring it precisely is the centrepiece of the HL-LHC programme.
Higgs self coupling: The interaction of the Higgs field with itself, probed by producing pairs of Higgs bosons. Too rare for the original LHC; a flagship goal of the high luminosity era.
Long Shutdown (LS): A planned multi year stop for maintenance and upgrades. LS3, running from July 2026 to 2030, installs the High Luminosity upgrade.
Run: A multi year data taking period between shutdowns. Run 3 ended 27 June 2026; Run 4 begins after the 2030 restart.
Crab cavity: A superconducting radio frequency cavity that tilts proton bunches sideways just before collision so they overlap head on. Named for the sideways motion; first used on a hadron collider at the HL-LHC.
Inner triplet: The set of focusing quadrupole magnets on each side of a collision point that squeeze the beam to its smallest size. Replaced during LS3 with niobium tin magnets reaching about 12 tesla.
Niobium tin (Nb3Sn): A superconductor that sustains higher magnetic fields than the niobium titanium used in the original LHC, enabling the HL-LHC's stronger focusing magnets. Brittle and difficult to work with, which is partly why the upgrade took a decade to build.
Dipole magnet: One of the 1,232 fifteen metre superconducting magnets that bend the beams around the ring at fields up to 8.3 tesla.
Quadrupole magnet: A magnet that focuses the beam like a lens, squeezing it in one plane while spreading it in the other. Alternating quadrupoles keep the beam contained.
Cryogenics: The LHC's cooling infrastructure. Superfluid helium holds 36,000 tonnes of magnets at 1.9 kelvin, colder than the 2.7 K of outer space.
Interaction point (IP): One of the four locations where the counter rotating beams cross and collide, each surrounded by a detector: ATLAS, ALICE, CMS and LHCb.
ATLAS: The largest LHC detector, a general purpose experiment 46 metres long. Co discoverer of the Higgs boson; rebuilt its entire inner tracker during LS3.
CMS: The Compact Muon Solenoid, ATLAS's general purpose rival and cross check, built around the most powerful solenoid magnet ever made. Replaced its tracker and added a high granularity calorimeter during LS3.
ALICE: The detector specialised for heavy ion collisions, studying the quark gluon plasma that filled the universe in its first microseconds.
LHCb: The asymmetric detector studying beauty quarks and the differences between matter and antimatter.
Pileup: Multiple proton collisions occurring in the same bunch crossing. Around 60 in Run 3, up to 200 at the HL-LHC; the reason the detectors needed rebuilding.
Bunch: A packet of around 100 billion protons. Each beam carries up to about 2,800 bunches spaced 25 nanoseconds apart.
Injector chain: The sequence of smaller accelerators (Linac4, Booster, PS, SPS) that boost protons to 450 GeV before the LHC takes over. Restarts from mid 2028, ahead of the main ring.
Beam dump: The only object on Earth designed to absorb a full LHC beam: a graphite core block where beams are safely disposed of at the end of each fill.
Collimator: Adjustable jaws that shave off stray particles before they can hit magnets. Upgraded for the HL-LHC's roughly 700 megajoule beams.
Quench: The sudden loss of superconductivity in a magnet, dumping its stored energy as heat. Protection systems detect quenches in milliseconds and extract the energy safely.
Standard Model: The reigning theory of particle physics, spectacularly confirmed and visibly incomplete. The HL-LHC's precision programme is a systematic search for where it breaks.

Want the terms in context? Start with how the machine works or the luminosity explainer, then check the countdown to see how long until this vocabulary is live again.